Tingkai Li, Gongchuang Photovoltaic Co., Ltd.
Michael Mastro, U.S. Naval Research Laboratory
Meng Tao, Arizona State University
Qi Wang, National Renewable Energy Laboratory
E2: Cross-Cutting Issues I
Tuesday PM, April 07, 2015
Moscone West, Level 3, Room 3006
2:30 AM - *E2.01
An Overview of the Australian Centre for Advanced Photovoltaics and the Australia-US Institute for Advanced Photovoltaics
Richard Corkish 1 Martin A. Green 1 Andrew W. Blakers 2 Paul L. Burn 4 Yi-Bing Cheng 3 Renate Egan 1 Kenneth P. Ghiggino 5 Paul Meredith 6 Fiona H. Scholes 7 Gerry Wilson 8
1University of New South Wales Sydney Australia2Australian National University Canberra Australia3Monash University Clayton Australia4University of Queensland Brisbane St Lucia Australia5University of Melbourne Melbourne Australia6University of Queensland Brisbane St Lucia Australia7CSIRO Clayton Australia8CSIRO Clayton AustraliaShow Abstract
The Australian Centre for Advanced Photovoltaics (ACAP) co-ordinates the activities of the Australian partners in the Australia-US Institute for Advanced Photovoltaics (AUSIAPV), supported by the Australian Renewable Energy Agency, to develop the next generations of photovoltaic technology and to provide a pipeline of opportunities for performance increase and cost reduction. The Australian partners in ACAP are UNSW, ANU, University of Melbourne, Monash University, University of Queensland and the Commonwealth Scientific and Industrial Research Organisation (CSIRO) with industrial partners Suntech R&D Australia (now Wuxi Suntech), Trina Solar, Bluescope Steel and BT Imaging.
AUSIAPV links ACAP with US-based partners, specifically the NSF/DOE Energy Research Center for Quantum Energy and Sustainable Technologies (QESST), the National Renewable Energy Laboratory, Sandia National Laboratories, Lawrence Berkeley National Laboratories, Stanford University, Georgia Institute of Technology and University of California Santa Barbara. These national and international research collaborations provide a pathway for highly visible, structured photovoltaic research collaboration between Australian and US researchers, institutes and agencies with significant joint programs based on the clear synergies between the participating organizations.
The research program is organised under five collaborative Program Packages (PP1-PP5). PP1 deals with silicon wafer-based cells, focussing on three main areas: cells made from solar grade silicon, rear contact and silicon-based tandem cells. Program Package 2 (PP2) involves research into a range of organic solar cells, organic/inorganic hybrid cells, "earth abundant" thin-film materials, including Si and CZTS, and more futuristic "third generation" approaches, with the overall goal of demonstrating efficiency above 15% during the program for cells of above 1cm2 area and of demonstrating the feasibility of costs below the US SunShot targets. PP3, concerned with optics and characterisation, targets experimental demonstration that theoretical conversion limits can be increased by the use of structures that have a high local density of optical states, with particular emphasis on thin film organic and inorganic solar cells. PP4, manufacturing issues, will deliver a substantiated methodology for assessing manufacturing costs of the different technologies under investigation by the ACAP/AUSIAPV partnership. The overall cost target is to exceed the SunShot targets, for one or more of the technologies, in at least one major SunShot targeted application, as deduced by a substantiated costing methodology. PP5 involves education, training and outreach.
ACAP/AUSIAPV began in February 2013 and will have an eight-year life. National and international partnerships have been and are being formed and significant results have been generated already. The main research topics, results and plans for the future will be presented.
3:00 AM - E2.02
Comparison of Hybrid Tandem Module Technologies Based on c-Si and Wide Band Gap Thin Film Photovoltaics
Dong Zhang 1 Wim Soppe 1 Ruud E.I. Schropp 1 2
1ECN - Solliance Eindhoven Netherlands2Eindhoven University of Technology Eindhoven NetherlandsShow Abstract
By placing a wide band gap semitransparent thin film solar cell in front of a high-efficiency crystalline silicon (c-Si) cell, the practical c-Si single junction conversion efficiency limit of about 26% can be surpassed, which is attractive for further reduction of systems costs provided that the thin film cell is inexpensive and does not have too much parasitic optical absorption or shadow losses. We have investigated by computer simulation (using thin film optics and ray-tracing models) the optical behavior of several hybrid junction stacks and have evaluated their relative potential. As the module concept we adopted the 4-terminal approach, as this avoids constraints regarding band gap values and absorber thicknesses, while in later production also constraints regarding processing temperatures and chemicals used can be avoided in this way. The cost of substrates and encapsulants is eliminated by the concept of depositing the thin film solar cell on the inside of the c-Si module cover glass. We considered three types of thin film PV cells: 1. Enlarged-bandgap oxygenated amorphous silicon (a-SiO:H) cells, 2. Wide band gap chalcopyrite (CuGaSe2) cells, and 3. Perovskite (CH3NH3PbI3) cells. In our model we also included the change in electrical output parameters by the color-filtering effect of the top cells.
Our modelling showed a few interesting results. Starting with an interdigitated back contact (IBC) c-Si cell with a conversion efficiency of 20%, and adding the top cell while minimizing the reflection and parasitic absorption losses by choosing proper thicknesses of absorber and contacting layers and implementing light scattering by texturing the glass, we find that +2.0% (absolute) conversion efficiency can be gained using state-of-the-art a#8209;SiO:H (band gap of 2.0 eV) and CuGaSe2 (1.8 eV) top cells and +4.75% can be gained using perovskite cells (1.55 eV). The perovskite cell type appears to be particularly suitable as the overall reflection loss is small due to the low refractive index of the absorber layer. Moreover, in the case of a perovskite top cell, light trapping by texturization of surfaces is not needed which helps avoiding parasitic absorption losses.
3:15 AM - E2.03
Light Emitting Diodes in the Experimental Practice for the Characterization of Novel Photovoltaics
Mauro Pravettoni 1 2 Loris Manni 1 Sebastian Dittmann 1
1University Appl. Sciences and Arts of Southern Switzerland Canobbio Switzerland2University of Pavia Pavia ItalyShow Abstract
Light Emitting Diodes (LEDs) have recently gained importance in the experimental practice of novel photovoltaic (PV) devices. Tunability of peak wavelengths and the high efficiency of light emission have finally shown LEDs full potential in a variety of techniques. In this work, the following applications in the indoor characterization of PV cells and modules are presented, some of which are consolidated, while some others are totally novel.
LEDs have recently been introduced as an alternative to conventional xenon or halogen based solar simulators. High intensity LEDs are now on the market and the authors show preliminary results and related challenges in the indoor characterization with a LED-based, steady state solar simulator for cells and commercial size modules. The continuous source is of fundamental importance in testing novel devices (e.g. organic PV, dye sensitized solar cells, capacitive and high-efficiency c-Si modules) where few millisecond pulsed simulators are no-longer reliable. Most importantly, the standard IEC 60904-9 Class A spectral irradiance requirement can be reached with a set of different LEDs and can be improved, for example via overlapping commercial halogen bulbs.
The dependence of the electrical parameters on the Average Photon Energy (APE) is a new insight that emerged in the last years, giving interesting information for energy rating: the combination of powerful LED lamps with a conventional Class AAA large area solar simulator is also presented in this work, showing that a wide range of target APE values can be easily obtained. Comparison with the results from the outdoor field is shown.
Multi-junction PV structures take also advantage of the use of coloured LEDs in experimental tools. Indeed, the standard IEC 60904-9 Class A spectral irradiance requirement can be really poor for such devices, which easily exhibit current limitation under artificial spectra and the consequent measurement artifacts that are widely studied in the literature. This work shows how the use of powerful LEDs can transform a conventional, single source pulsed solar simulator in a tunable simulator for spectral characterization of multi-junction modules, thus enhancing the spectral mismatch correction when measuring such devices.
From the same point of view, the importance of LEDs as additional bias light (superimposed over a pulsed solar simulator) is also shown for a number of applications, such as spectral responsivity of multi-junction modules and the investigation of the dependence of the electrical parameters on the angle of incidence.
With the revision and introduction of all the experimental challenges above, this paper represents a useful tool for any research centre dealing with the characterization of PV devices, with special interest in pre-normative techniques of measurements where standard procedure are still under discussion.
3:30 AM - E2.04
Solar Powered Infotainment Spot: Design, Feasibility Study and Fabrication of an Autonomous PV System
Vincent Weeda 1 Olindo Isabella 1 Miroslav Zeman 1
1Delft Univ of Technology Delft NetherlandsShow Abstract
Information technology has recently eased the access to all kinds of information. For example, the Photovoltaic Materials and Devices (PVMD) group at Delft University of Technology, via its website (pvmd.ewi.tudelft.nl), shares information on its research and education. However, one could argue that not everybody in the university campus knows the latest developments in the PV industry or the activities of the PVMD group. This has driven the desire for an infotainment spot (information + entertainment) in the campus of the university that we report in this contribution. Our demonstrator provides information to people on campus via a rugged touchscreen that is powered by solar energy. In such an autonomous system characterized by a minimal loss of load probability, a flexible CIGS module is deployed as market alternative to rigid c-Si modules.
Data from a weather station of the Royal Dutch Meteorological Institute was used to accurately estimate the amount of solar energy available in the Netherlands. The influence of the surroundings of the infotainment spot on the amount of all irradiance components was then accordingly investigated. Furthermore, a methodology was developed to make an accurate estimate of the solar irradiance on a curved surface, since the key component in the design of our infotainment spot was the flexibility of our PV panel. In particular, the curved surface was approximated by a limited number of linear segments. Knowing the irradiance on the PV module, its power output was estimated by a PV model taking temperature, wind and irradiance effects into account. Consequently, the system topology was designed to have the smallest possible losses and highest yield of PV power. A load profile was developed in combination with the measurements of actual power consumption to simulate the system performance throughout the year.
Our study indicated that the meteorological data guarantees an average annual minimal horizontal irradiation of 1000 kWh/m2 in the Netherlands. The methodology to estimate the solar irradiance on a curved plane showed that a quarter of a circle can be accurately described by four linear segments. An extensive analysis of the surroundings was performed with a 3-D modelling resulting in a sky view factor for each part of the PV module and a shading coefficient as function of time. With the temperature and irradiance effects taken into account, the energy production of the 90-W rated CIGS module is 62 kWh/year. The load profile combined with performed power measurements claims an energy consumption of 19.3 kWh/year. The 12-V DC system is completely autonomous with zero loss of load probability with a battery of 120 Ah, regulated by a charge controller. The system can be adjusted in terms of rated power of the PV module and the battery size if the infotainment spot were to be installed in a different location. Pictures of the fabricated infotainment spot and its performance will be presented at the conference.
4:15 AM - *E2.05
Reliability Modelling of CdTe Photovoltaics
Dragica Vasileska 1 Da Guo 1
1Arizona State University Tempe United StatesShow Abstract
Thin-film modules of all technologies often suffer from performance degradation over time. Some of the performance changes are reversible and some are not, which makes deployment, testing, and energy-yield prediction more challenging. Manufacturers devote significant empirical efforts to study these phenomena and to improve semiconductor device stability. Still, understanding the underlying reasons of instabilities remains clouded due to the lack of ability to characterize materials at the atomistic levels and lack of the interpretation from the most fundamental material science. The most commonly alleged causes of metastability in CdTe device, such as “migration of Cu,” have been interrogated rigorously over the past fifteen years. Still, the discussions often ended prematurely by stating observed correlations between stress conditions and changes in atomic profiles of impurities or CV doping concentrate-on. Multiple hypotheses suggesting degradation of CdTe solar cell devices due to interaction and evolution of point defects and complexes were proposed, and none of them received strong theoretical or experimental confirmation.
The novelty of the work that will be presented at the workshop is that the Unified 1D Solver, developed as part of the DOE PREDICTS project, enables improved prediction of long-term solar-cell performance as well as the separation of reversible and irreversible changes. Overall, the confidence in the prediction of thin-film module reliability with this tool has the opportunity to move away from empirical observation to scientific understanding. Based on the detailed understanding, approaches are proposed to overcome the long-term instability of the CdTe solar cell under stress.
This research is supported by the Department of Energy DE-EE0006344 PREDICTS project entitled “Uni-fied Numerical Solver for Device Metastabilities in CdTe Thin-Film PV”.
1. D. Guo, R. Akis, D. Brinkman, I. Sankin, T. Fang, D. Vasileska and C. Ringhofer, “One-Dimensional Reaction-Diffusion Simulation of Cu Migration in Polycrystalline CdTe Solar Cells”, 40th IEEE Photovoltaic Specialists Conference, June 8-13, 2014, Denver, CO.
2. R. Akis, D. Brinkman, I. Sankin, T. Fang, D. Guo, D. Vasileska, and C. Ringhofer, “Extracting Cu Diffusion Parameters in Polycrystalline CdTe”, 40th IEEE Photovoltaic Specialists Conference, June 8-13, 2014, Denver, CO.
3. D. Guo, R. Akis, D. Brinkman, I. Sankin, T. Fang, D. Vasileska and C. Ringhofer, “CdTe Solar Cells: The Role of Copper”, IWCE 2014, June 6-9th, 2014, Paris, France.
4:45 AM - E2.06
Applications of Antireflection Coatings for Enhancing Power Output of Solar Panels
Gopal G Pethuraja 1 2 Roger E Welser 1 John W Zeller 1 Yash R Puri 1 Ashok K Sood 1 Harry Efstathiadis 2 Pradeep Haldar 2 Jennifer L Harvey 3
1Magnolia Solar Inc. Albany United States2SUNY Polytechnic Institute Albany United States3NYSERDA Albany United StatesShow Abstract
Nanostructured antireflection (AR) layers on the front sheet of a solar panel can significantly increase the power output of the solar panel, and thereby lower the cost of solar electricity production. Sunlight incident on the front surface of conventional panels undergoes Fresnel reflection due to the mismatch between the refractive indices of air and of the front sheet of the panel. This reflection loss is around 4% at noon and can be greater than 40% at dawn or dusk. An optical interface layer with intermediate refractive indices at the air/front sheet interface can eliminate or greatly reduce the unwanted reflection. Designing the optical interface layer, i.e., antireflection structure is challenging due to the unavailability of material with the required intermediate refractive indices.
Recent developments in nanostructured coatings have overcome this limitation and provide new avenues for novel antireflection structures. The need for broadband and wider angle AR structures has been significantly amplified due to recent development of novel PV technologies, such as tandem cells that harvest the entire spectrum of sunlight with greater efficiencies. However, most of the approaches previously developed to create broadband high-performance nanostructured AR coatings have experienced difficulties due to limitations in tuning the refractive index of the coating materials and lack of controllability in achieving the desired thickness of the ultra-low refractive index material. We have developed a scalable self-assembled nanostructure process that overcomes these limitations. Our process has the ability to create ultra-low refractive index (down to 1.08) material with controllability in both layer thickness and refractive index.
Our nanostructured AR layers have demonstrated ultra-high, omnidirectional transmittance over the entire accessible portion of the solar spectrum and a wide range of optical incidence angles. In this paper, we review our latest work on high performance nanostructure-based AR coatings, including recent efforts to deposit such AR coatings on large area substrates. The high performance of these coatings has been demonstrated on a variety of front surfaces employed in the production of solar panels, including polyester (PET), polycarbonate, fluorinated ethylene propylene (FEP), and ethylene tetrafluoroethylene (ETFE) films, as well as ridged glass sheets. AR coated front sheets integrated on solar panels demonstrate 3% higher short-circuit current at normal incidence and 22% higher short-circuit current for light incident 80° from the normal. Furthermore, NREL&’s System Advisor Model (SAM) predicts based on experimental results that Magnolia&’s AR coatings can yield 5.4% and 6.4% greater annual power output for flat installations of solar panels at Tucson, AZ and Albany, NY locations, respectively, and 8.8% and 12.4% higher annual power output for vertical installations in Albany, NY and Honolulu, HI, respectively.
5:00 AM - E2.07
Angular-Resilient and Bright-Colour Filters for Built-Integrated Photovoltaic Applications
Juan Camilo Ortiz Lizcano 1 Andrea Ingenito 1 Rudi Santbergen 1 Olindo Isabella 1 Miroslav Zeman 1
1Delft Univ of Technology Delft NetherlandsShow Abstract
Urban areas are among the greatest contributor to CO2 emissions. As by 2035 nearly 60% of the urban areas worldwide will be either new or renovated, several programs around the world are underway with the purpose of reducing the carbon footprint of urban areas. Their goal is to achieve carbon-neutral buildings by next 15-20 years. Implementation of technical solutions that allow the production of part of the energy required by a building within the building itself is considered instrumental. Built Integrated Photovoltaic (BIPV) systems can fulfil this demand. Despite their potential to supply more than 20% of the energy demands of the building sector, BIPV systems remain a niche technology with only 1% of market share. This is because architects are often reluctant to use BIPV systems based on aesthetic grounds. By deploying so-called optic filters, the appearance of standard crystalline silicon (c-Si) modules and solar cells can be tuned in order to provide aesthetic flexibility with little impact on performance. In this contribution, multi-layer stack formed by pairs of dielectric materials in the role of optic filters are designed and implemented on glass substrate or on fabricated c-Si solar cells.
A computational model describing human perception of colours was created to design and tune the colour of optic filters for application in both PV c-Si modules and solar cells. Materials like SiO2 and Si3N4 were selected for their non-absorptive nature, availability, applicability at industrial level and adequate refractive index values over the entire visible spectrum. Both the colour model and the optic filter design were validated by matching accurately simulated to experimental reflectance spectra. By arranging the layers in such a way that the outermost layer is the one with a refractive index closest to that of glass (i.e. SiO2) the filter can be deposited on glass or on the solar cell prior encapsulation. This provides protection to the optic filter from environmental hazards such as hails or dusty winds, and also scratches due to accidents during installation or maintenance procedures. Colour matrices of the designed optic filters as function of SiO2 and Si3N4 thicknesses provided a rich amount of different colours. These were characterized by variable brightness and hue and angular resilience higher than 40°. Three optic filters were selected and fabricated for performance assessment: green, bright yellow, and red. Results show a reduction of the conversion efficiency at module level by 2.8%, 3.5% and almost 4%, respectively. When deposited on flat solar cells, the filters reduce the efficiency by 2.6%, 3% and 3.4%, respectively. Finally, when these filters are installed on a textured cell, reflectance patterns present low peaks that on the one hand reduce the efficiency of the cell by less than 2% but on the other produce slightly less bright colours.
5:15 AM - E2.08
Reliability and Degradation of Optical Interfaces in Concentrator Photovoltaic Modules
Can Cai 2 David C. Miller 1 Reinhold H. Dauskardt 2
1National Renewable Energy Laboratory Golden United States2Stanford University Stanford United StatesShow Abstract
High efficiency multijunction solar cells in concentrator photovoltaic (CPV) modules are becoming an increasingly cost effective and viable option in utility scale power generation. In order to compete with tradition silicon-based installations, CPV modules need to guarantee similar operational lifetimes of greater than 25 years. The reliability of optical elements in CPV modules poses a unique materials challenge due to increased UV irradiance and enhanced temperature cycling associated with concentrated solar flux. The polymeric and thin film materials used in the optical elements are especially susceptible to UV damage, diurnal temperature cycling and active chemical species from the environment. Understanding the underlying mechanisms of defect evolution and materials degradation is critical for commercialization of CPV technology. In addition, understanding degradation of materials under concentrated solar flux can offer unique insights into degradation modes in similar materials used in traditional PV. In this work, we have surveyed leading CPV industry module and optics manufacturers to develop a pareto of critical adhesive interfaces for investigation. We have developed fracture mechanics based metrologies to characterize degradation of materials and interfaces associated with CPV optics. Industry feedback identified that the most critical interface to study is the attachment of the secondary optical elements to the multijunction cell, which typically uses a silicone based adhesive. We characterized the degradation of adhesion energy and found that during broad band UV-B exposure, delamination mode changes from adhesive to cohesive, where the adhesion energy decays as the silicone is UV-B aged. We found changes in chemical structure at silicon and carbon sites as a result of heat, environmental species and solar irradiation. With these studies, we can model the fundamental connection between mechanical strength and defect evolution in silicone adhesives.
E3: Poster Session
Tuesday PM, April 07, 2015
Marriott Marquis, Yerba Buena Level, Salon 7/8/9
9:00 AM - E3.01
Highly Flexible Woven Dye Sensitized Solar Cells Internal Frame of Textile Produced by Weaving Technology
Minju Yun 1 Seung I. Cha 1 Seon Hee Seo 1 Dong Y. Lee 1
1Korea Electrotechnology Research Institute Changwon Korea (the Republic of)Show Abstract
The wearable electronic device requires appropriate portable electric sources that can be integrated into the devices. Flexible dye-sensitized solar cells (DSSCs) have considerable attraction due to their characteristic properties including low cost, high efficiency at low light intensity. It can be a trigger for enlarging application field into smart and wearable electronics as a energy source.
Textile is final form that is combined the advantages of textiles such as flexibility and mechanical robustness for wearable electronics. Therefore, the solar cell connected to textile form is required and important. However, the development of a textile based solar cell is currently at the initial stage and there requires much advance to achieve applicable forms of textile solar cells. Therefore, to develop textile based solar cells there required new approaches which is suitable for the actual weaving process as well as easy to combine to the wearable devices.
We have shown that woven DSSCs internal frame of textile can be implemented by weaving the stainless steel ribbon with the TiO2 layer and carbon fiber filaments are playing a role as photoanode and counter electrode respective into some part of woven textile for wearable electronics. The woven DSSCs have the core integrated DSSCs structures by using the weaving process, it has the characteristics of the textile so can be highly flexibility, have a potential application field including the wearable devices and BIPV fields.
The edge part of the textile is holding and fixing the photoanode and counter electrode as a frame. As warps of internal textile frame, the transparent monofilaments are used in order to make the light to be transmitted to the counter electrode. For the frame of the textile, the glass fiber was used as warps and wefts at edge of the textile. Before the weaving the woven DSSCs internal frame of textile, both electrodes are prepared with heat treatment after the deposition of the TiO2 layer on the stainless steel ribbon and Pt deposition on the carbon fiber filaments, electrodes were completed the treatment were woven as weft into the part of the textile during the weaving process then followed the dye loading process. Gone through the heat treatment before the weaving process, the monofilaments do not need to have heat resistance characteristic at high temperature, which is an important factor of the producing the woven DSSCs internal frame of textile.
These woven dye sensitized solar cells internal frame of textile exhibited high energy-conversion efficiency about 2.63%. The woven DSSCs internal frame of textile have highly flexible characteristic and maintain the structure and form under curvature of 1cm radius. The presented work provides the development of textile form DSSCs fabrication for combining into the wearable devices and flexible solar cells.
9:00 AM - E3.02
Zn(II)-Porphyrin Sensitizers for Highly Efficient Dye-Sensitized Solar Cells
SungHo Kang 1 Hwan Kyu Kim 1
1Korea University Sejong Korea (the Republic of)Show Abstract
Dye-sensitised solar cells (DSSCs) have been widely regarded as next-generation photovoltaics for providing electricity at lower expense and with more versatility. Porphyrins are one of the most widely studied sensitisers for DSSCs because of their strongly absorbing Soret bands (400-450 nm) and moderately absorbing Q bands (550-600 nm).[1-6] In fact, the push-pull porphyrin sensitizer (SM315) with co-adsorbent (CDCA) using a cobalt-based electrolyte attained a power conversion efficiency of 13.1%. Despite the high efficiency of porphyrin dyes in DSCs, further improvements to light harvesting through the use of stronger acceptors remains relatively unexplored. Studies unrelated to the DSC have demonstrated that integration of pro-quinoidal units into the porphyrin structure causes strong perturbations to the electronic structure of the macrocycle. These perturbations in benzothiadiazole-porphyrin analogues result in improved light harvesting by broadening and red-shifting absorbance of the Soret and Q-bands. In this presentation, two kinds of push-pull structured (D-π-A) Zn(II)-porphyrin sensitizers based on the structural modification of SM315 containing bulky alkoxy group substituted diphenyl amine and fluorene-derived electron donor moieties for efficient retardation of charge recombination were newly designed and synthesized. The device with new porphyrin sensitizers exhibited the highest photovoltaic conversion efficiency (PCE) with comparable to or better than the PCE of the device with SM315.
 M. S. Kang, S. H. Kang and H. K. Kim, et.al., Chem. Comm, 48 (2012) 9349.
 B. J. Song, H. and H. K. Kim, et.al., Chemistry-A European Journal, 17 (2011) 1115.
 S. H. Kang, I. T. Choi and H. K. Kim, et.al., J. Mater. Chem. A, 1 (2013) 3977.
 M. S. Kang, Y. W. Kim and H. K. Kim, et.al., J. Mater. Chem. A, 1 (2013) 9848.
 I. T. Choi, M. J. Ju and H. K. Kim, etal., Chemistry-A European Journal, 19 (2013) 15545.
S. H. Kang and H. K. Kim, et. al., ChemElectroChem, 1 (2014) 637.
[7\] Simon Mathew and Michael Grätzel, et.al., Nature Chemistry, 6 (2014) 242.
9:00 AM - E3.03
Edge-Fluorinated Graphene Nanoplatelets as High Performance Electrodes for Dye-Sensitized Solar Cells and Lithium Ion Batteries
Myung Jong Ju 1 Jong-Beom Baek 2 In Taek Choi 1 Hwan Kyu Kim 1
1Korea University Sejong Korea (the Republic of)2Ulsan National Institute of Science and Technology (UNIST) Ulsan Korea (the Republic of)Show Abstract
Edge-selectively fluorinated graphene nanoplatelets (FGnPs) were prepared by mechanochemically driven reaction between fluorine gas (20 vol.% in argon) and activated carbon species from graphitic C-C bonds unzipped by high-speed stainless steel balls with a high kinetic energy. The fluorination at edges of the unzipped GnPs was confirmed by various analytical techniques while the content of fluorine in FGnPs was determined to be 3.0 and 3.4 at.% by X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDS), respectively. Because of the large difference in electronegativity between carbon (chi; = 2.55) and fluorine (chi; = 3.98) and the strong C-F bond, the edge-fluorination of GnPs can provide the maximized charge polarization with an enhanced chemical stability. Thus, electrodes based on the resultant FGnPs demonstrated superb electrochemical performance with excellent stability/cycle life in dye-sensitized solar cells (DSSCs) (FF: 71.5 %; Jsc: 14.44 mA cm-2; Voc: 970 mV; PCE: 10.01 %) and lithium ion batteries (LIBs) (650.3 mAh g-1 at 0.5 C, charge retention of 76.6 % after 500 cycles).
9:00 AM - E3.04
Organic Sensitizers Based on Benzothieno[3,2-b]thiophene as New Chromophore for Highly Efficient Dye-Sensitized Solar Cells
Yu Kyung Eom 1 Hwan Kyu Kim 1
1Korea University Sejong Korea (the Republic of)Show Abstract
Dye-sensitized solar cells (DSSCs) have recently been extensively studied as a promising candidate for low-cost, lightweight, and applicable solar cells. A typical DSSC consists of a transparent conducting oxide (TCO) substrate, a mesoporous semiconductor (predominately TiO2) film adsorbed with sensitizers, an electrolyte layer containing a redox couple, and a counter electrode. Among them, organic sensitizers have proven to be extremely important in improving the performance of DSSCs. The key component in a DSSC device is organic sensitizer which consists of an electron donor and acceptor connected by a π-conjugated bridge in D-π-A structured organic sensitizers. Many kinds of organic sensitizers with such configuration have been explored for DSSCs, including sensitizers based on coumarin dyes, triarylamine dyes, hemicyanine dyes, thiophene-based dyes, indoline dyes, porphyrin dyes, and phthalocyanine dyes. A huge number of modification of the π-conjugation has been carried out, thus indicating that the π-conjugated bridge plays a key role in the final performance of the dye. Here, we present organic sensitizers having a novel benzothieno[3,2-b]thiophene as a new π-conjugated chromophore between the bulky alkoxy biphenylamine as an electron donor and a cyanoacrlyic acid as an electron acceptor. With the introduction of various π-linkers between the π-conjugated bridge and acceptor, the HOMO and LUMO levels of the sensitizers have been tuned, extending the major absorption peak of the sensitizers and exhibition of excellent charge-transport properties. At present, a solar cell based on benzothieno[3,2-b]thiophene-based sensitizers exhibited superior photovoltaic performance with a JSC of 16.79 mA cm-2, a VOC of 841 mV, and an FF of 0.73, corresponding to an overall conversion efficiency eta; of 10.38%. Their chemical structures, absorption spectra, electrochemical, photovoltaic properties and DFT calculation have been extensively investigated.
9:00 AM - E3.05
Superior Performance of Copolymer-Templated Nitrogen-Enriched Nanocarbons as Metal-Free Cathodes for High-Efficiency Dye-Sensitized Solar Cells
In Taek Choi 1 Myung Jong Ju 1 Krzysztof Matyjaszewski 2 Hwan Kyu Kim 1
1Korea University Sejong Korea (the Republic of)2Carnegie Mellon University Pittsburgh United StatesShow Abstract
We demonstrate the superior performance of dye-sensitized solar cells (DSSCs) with novel, metal-free counter electrodes (CEs) comprised of copolymer-templated nitrogen-enriched such as, nitrogen-heteroatom enrichment including pyrrolic, pyridonic, pyridonic N-oxide, and quaternary configurations, nanocarbons (CTNCs) with well-controlled morphology and nanoporosity. This superior performance is due to the high catalytic activity of CTNCs toward the reduction of Co(bpy)32+/3+, as evidenced by unusually low charge transfer resistance (RCT) at the CE/electrolyte interface. The observed activity is attributed to the combination of CTNCs&’ high surface area afforded by a three-dimensional, hierarchical pore structure, and to their unique electronic properties stemming from the presence of nitrogen heteroatoms located on the edges of nanographitic domains. Altogether, use of CTNC CEs enhanced the efficiency and fill factor (FF) of JK-306 dye, Co(bpy)32+/3+ redox couple based DSSCs at one sun illumination up to, respectively, 10.54% and 73.5%, pointing to the considerable promise of these materials as an attractive alternative to costly Pt-based CEs. Interestingly, use of CTNCs did not lead to the analogous beneficial lowering of the RCT in I-/I3- redox couple based N719-sensitized DSSCs, limiting their FF and short circuit current density (JSC). This chemical specificity indicates that the type of nitrogen bonding configurations, rather than the total N-content, is the key factor determining the catalytic activity.
9:00 AM - E3.06
3D-Printed External Light Trap for Solar Cells
Lourens van Dijk 2 Ulrich Wilhelm Paetzold 1 E.A. Pepijn Marcus 2 A. Jolt Oostra 4 Gerhard A. Blab 5 Ruud E.I. Schropp 3 6 Marcel Di Vece 2
1Forschungszentrum Julich GmbH Julich Germany2Physics of Devices, Debye Institute for Nanomaterials Science, Utrecht University Utrecht Netherlands3ECN - Solliance Eindhoven Netherlands4University of Groningen Groningen Netherlands5Molecular Biophysics, Debye Institute for Nanomaterials Science, Utrecht University Utrecht Netherlands6Eindhoven University of Technology (TU/e), Department of Applied Physics, Plasma and Materials Processing Eindhoven NetherlandsShow Abstract
A key factor limiting the solar cell efficiency is the incomplete absorption of sunlight due to unwanted reflection at the front interfaces, the reflection at the metal front contacts and the poor absorption in the long wavelength regime. Conventional light trapping approaches rely on surface texturing to improve the absorptance in a solar cell. However, the associated increase in surface area degrades the electrical cell properties due to an increase in surface recombination, in particular in thin film solar cells. Here we demonstrate the first successful prototype of a universally applicable 3D-printed external light trap that does not modify the cell architecture, and resolves the tradeoff between optical absorption and cell material quality. The trap enables enhanced absorption in flat solar cells of which the charge carrier collection efficiency surpasses that of textured solar cells. Thermodynamic considerations show that such an external light trap enables higher energy conversion efficiency limits due to the angular restriction compared to a cell without a light trap.
Our 3D-printed macroscopic external light trap is made of polished, silver coated plastic. The trap consists of a reflective parabolic concentrator on top of a cage. The trap is placed at the sun-facing surface of the solar cell. By concentration, light is funneled through a small aperture in the cage and is trapped. The trap directs the light that is reflected upwards by the solar cell back towards the solar cell. The external light trap thereby recycles both the unwanted reflection from the front side of the cell and the poor absorbed light in the long wavelength regime. Due to this retro-reflection the light traverses the solar cell many times. This enables a significant broadband absorption enhancement. We experimentally demonstrate an enhanced total power conversion efficiency of both a micro#8208;crystalline silicon (µc-Si:H) solar cell and an organic solar (OPV) cell. We also show the results of an array of concentrators for potential large area commercial application.
External light trapping thus leaves the solar cell properties intact as it does not internally modify the cell. While internal light trapping (by texturing the cell contacting surface) reduces the carrier collection efficiency, external light trapping benefits from the unaltered internal collection efficiency of the cell. We present a model that predicts the absorption enhancement by the trap based on the internal collection efficiency and the reflection data of the solar cell. The corresponding calculated path length enhancement by the light trap shows good agreement with the empirically derived value from the electro-optical data of the solar cell. The external light trap enables decoupling of the optical and electric optimization which yields interesting perspectives for the design of future solar cells.
9:00 AM - E3.07
One-Step Patterning of Light-Trapping Structure on Nanostructured TiO2 Photoelectrode for Dye-Sensitized Solar Cells via Femtosecond Laser Ablation
Xi Zhang 1
1University of Wisconsin-Madison Madison United StatesShow Abstract
We constructed light-trapping patterns at the surface of nanostructured TiO2 photoelectrodes for dye-sensitized solar cells (DSSCs) by a one-step femtosecond laser structuring method that utilized ablation to create the designed patterns. As a result, much more light was trapped in the photoelectrodes. A grating pattern and a orthogonal pattern were performed, and the light trapping performance was optimized through the adjustment of their grid spacing, which was easily realized in the laser ablation process. With a 5-µm-spacing orthogonal grid pattern, DSSCs showed a highest photon-to-electron conversion efficiency of 9.32% under AM 1.5G, a 13.5% improvement compared to the same cell without laser ablation. This simple and universal laser ablation method could be used to process many kinds of nanomaterials, and could be applied for various devices with nanostructures.
9:00 AM - E3.08
Thin Film Silicon Solar Module Encapsulation Technology Research
Huayi Hu 1 Yu Cheng 1 Tingkai Li 2
1Hunan Gongchuang Photovoltaic Science and Technology Co. Hunan China2gongchuang PV Hengyang ChinaShow Abstract
With the development of the solar module research, as well as the related application, more and more problems about the reliability and service life of the module also gradually exposed, so the encapsulation material and related technology research and development become more and more important. This article mainly discusses some different encapsulation technology of the thin film silicon solar module. Different encapsulation materials, equipments and the encapsulation process are compared and their impact on the manufacturing cost and module performance are discussed.
9:00 AM - E3.09
The Development and Application of High-Efficiency Low-Cost Silicon Thin Film Solar Cell
Xueshi Tan 2 Bingxue Mao 2 Feng Zhang 2 Jingjing Yang 2 Tingkai Li 1
1gongchuang PV Hengyang China2Hunan Gongchuang Photovoltaic Science and Technology Co Hunan ChinaShow Abstract
For the industrial application of silicon thin film solar cells, the current focus is on how to realize high-efficiency low-cost production process and minimize light-induced degradation effect, thus effectively reducing BOS costs of system integration. In this paper, a brief introduction based on our development and application in this area will be presented, highlighting in the achievement of some layers in a-Si:H/uc-Si:H tandem solar cell by optimizing the property of single layers, such as amorphous intrinsic layer, intermediate reflective layer and microcrystalline intrinsic layer. After transferring the process achievement to the industrial production line, we obtained the low-cost thin-film silicon solar cells with high photoelectric conversion efficiency of 10.2%.
9:00 AM - E3.10
A New Method of Fabrication for Multicolor Transparent Thin-Film Solar Cell Module
Meiying Han 2 Tingkai Li 1
1gongchuang PV Hengyang China2Hunan Gongchuang Photovoltaic Science and Technology Co Hunan ChinaShow Abstract
Recently using green or infrared laser to wipe off the silicon and back contact layer in perpendicular direction of cell is popular in transparent Si based PV module fabrication. But this method would result in more power loss than calculation value due to some badly side effect during the process such as constructional damage of module and shunt effect. A new method is proposed here which focus on wiping off more silicon layer by employing green pulsed laser(532 nm wavelength) during Pattern2 procedure, and it shows higher efficiency and more attractive appearance.
9:00 AM - E3.11
The Application of Infrared Thermo-Camera in Testing of Silicon-Based Thin-Film Solar Cells
Meiying Han 2 Tingkai Li 1
1gongchuang PV Hengyang China2Hunan Gongchuang Photovoltaic Science and Technology Co. Hunan ChinaShow Abstract
Thermo-camera is employed here to analysis kinds of quality abnormal and improve production process during manufacture procedure of silicon-based thin-film solar modules. It shows that thermo-camera device can help engineers to solve problem of production line quickly and accurately, and save the manpower and financial resources at the same time.
9:00 AM - E3.12
Periodic DLC Nanomesh Mold for the Fabrication of Large-Scaled Sub-Wavelength Antireflective Nanostructures
Kai-Yu Peng 2 Sih-Sian Guu 5 Bo-Hong Jhuo 2 Yu-Hsuan Ho 3 Ming-Chih Tsai 1 Wei-Cheng Tian 3 Da-Hua Wei 2 Pei-Kuen Wei 4
1Graduate Institute of Biomedical Electronics and Bioinformatics Taipei Taiwan2National Taipei University of Technology Taipei Taiwan3National Taiwan University Taipei Taiwan4Research Center for Applied Sciences, Academia Sinica Taipei Taiwan5National Taiwan Ocean University Keelung TaiwanShow Abstract
We demonstrated a convenient method for the fabrication of sub-wavelength antireflective nanostructures by using periodic diamond-like carbon (DLC) nanomesh mold. Owing to significant fraction of 85% or more sp3 type C bonds, DLC films possess a lot of attractive physical and mechanical properties such as extreme mechanical hardness, high elastic modulus, good thermal and chemical stability, and low value of friction coefficient. In this work, we used 400 nm polystyrene nanospheres with proper etching and deposition processes to create hexagonal DLC nanostructures on the Si substrates for the fabrication of the DLC nanomesh mold. The 120-nm DLC thin films were deposited by a home-made 2-inch pure diamond powder target. Then we utilized the DLC nanomesh mold to make the sub-wavelength nanopillars on the polycarbonate (PC) substrate by thermal nanoimprint method. The average transmittance of PC films with antireflective nanopillar arrays was ~96%, which higher than the bare PC films (~87%). The contact angle (CA) of the antireflective PC films is ~120#8728; that possessed better hydrophobic property than bare PC films (CA = ~70#8728;). Using the as-prepared DLC nanomesh mold combined with thermal nanoimprint method performed potential for the fabrication antireflective nanostructures with large area, high throughput, and low cost.
9:00 AM - E3.13
Observation of Charge Extraction by Graphene Using Time-Resolved Surface Photoresponse Measurements
Lushuai Zhang 1 Susmit Singha Roy 1 Robert J. Hamers 2 Michael Scott Arnold 1 Trisha L Andrew 2
1UW-Madison Madison United States2UW-Madison Madison United StatesShow Abstract
Graphene is considered as a next-generation electrode for indium tin oxide (ITO)-free organic photovoltaic devices (OPVs). However, to date, limited numbers of OPVs containing surface-modified graphene electrodes perform as well as ITO based counterparts, and no devices containing a bare graphene electrode have been reported to yield satisfactory rectification characteristics. Exciton quenching by graphene has been indicated by fluorescence studies. But fluorescence does not reveal electronic properties since it depends on impurities and defects. Here we provide experimental data to learn tuning of electronic properties of organic semiconductors by monolayer graphene. Time-resolved surface photorespone measurements on pentacene-on-graphene films directly reveal that p-doped monolayer graphene efficiently extracts electrons, not holes, from photoexcited pentacene. Accordingly, a pentacene/MoO3 heterojunction on graphene displays a large surface photoresponse and, by inference, efficient dissociation of photogenerated excitons, with graphene serving as an electron extraction layer and MoO3 as hole extraction layer. In contrast, a pentacene/C60 heterojunction on graphene yields a comparatively insignificant surface photoresponse because both graphene and C60 act as competing electron extraction layers. The data presented herein provide empirical insight for future endeavors involving bare graphene as an electrode for organic photovoltaic devices (OPVs) and strongly suggest that p-doped graphene is best considered a cathode for OPVs.
E1: Silicon Solar Cells
Tuesday AM, April 07, 2015
Moscone West, Level 3, Room 3006
10:00 AM - *E1.01
Advanced Functional Materials: Intrinsic and Doped Silicon Oxide
Xiaodan Zhang 1
1Inst of Optoelectronics TFD amp; Tech Tian Jin ChinaShow Abstract
In comparison to other silicon materials, the particular two-phase structure of silicon oxide materials, in which hydrogenated microcrystalline silicon crystallites are surrounded by an oxygen-rich hydrogenated amorphous silicon phase, causes them present excellent photoelectrical material properties, such as a low-parasitic absorption in broadband spectral range, independent controllability of longitudinal and lateral conductivity, refractive indices (3.5-2.0), band gap (2.0-2.6 eV) and conductivity tenability (with orders of 1-10-9 S/cm) with oxygen doping, and so on. Various types of silicon oxide materials, including intrinsic, p- or n- type, applied in thin film solar cells have also played significant roles in improving the efficiency of various types of single-, dual-, and triple-junction thin-film solar cells from both the optical and electrical points of view. In this paper, we present our latest progress in studying the performance improvement role of intrinsic or doped silicon oxide materials in pin-type a-Si:H, a-SiGe:H, and mu;c-Si:H single-junction solar cells. By effectively tuning the band gap values of intrinsic a-SiOx:H materials with oxygen doping and adopting the layers with a suitable band gap (1.86 eV) as the P/I buffer layers of a-Si:H solar cells fabricated on metal organic chemical vapor deposition boron-doped zinc oxide substrates, a significant Voc increase up to 909 mV and an excellent external quantum efficiency response of 75% at 400 nm typical wavelength can be achieved by matching the band gap discontinuity between the p-type a-SiOx:H window and a-Si:H intrinsic layers. The high leakage current characteristics of pin-type narrow-gap (Eg<1.5 eV) a-SiGe:H single-junction solar cells can also be finely tuned by integrating a n-type mu;c-SiOx:H layer with a small oxygen content in addition to improving the long-wavelength response, an effective approach giving rise to the highest FF of 70.62% for pin-type a-SiGe:H single-junction solar cells with an average band gap of 1.48 eV. In addition, our studies proved that the application of p-type mu;c-SiOx:H window layers in mu;c-Si:H single-junction solar cells can effectively improve the short-wavelength light coupling by suppressing the parasitic absorption and promoting the anti-reflectivity with a graded refractive index profile. On the basis of the optimum single-junction solar cells with omnipotent silicon oxide materials, an initial efficiency of 16.07% has been achieved for pin-type a-Si:H/a-SiGe:H/mu;c-Si:H triple-junction solar cells. The omnipotent properties of silicon oxide layers in TFSCs, including effective optical coupling and trapping, suitability in compensating for the band gap discontinuity, the shunt-quenching capacity, and so on, make them likely to be extended to other types of solar cells such as polycrystalline chalcopyrite Cu(In,Ga)Se2 and perovskite-sensitized solar cells, opening up new opportunities for acquiring solar cells with higher performance.
10:30 AM - E1.02
Comprehensive Modelling and Sizing of PV Systems from Location to Load
Olindo Isabella 1 Arianna Tozzi 1 Gireesh Ganesan Nair 1 Jessica Hernandez Castro Barreto 1 Gautham Ram Chandra Mouli 2 Frank Lantsheer 3 Stephan van Berkel 4 Miroslav Zeman 1
1Delft Univ of Technology Delft Netherlands2Delft University of Technology Delft Netherlands3KNMI De Bit Netherlands4SolarNRG Poeldijk NetherlandsShow Abstract
Next to photovoltaic (PV) modules, several other devices constitute the so-called Balance of System (BoS) of a PV system. The BoS can be connected to the solar modules and to the load(s) in many different ways to form grid-connected, stand-alone or hybrid PV systems. Whatever is the topology of interest, the ratio between the power generated by PV modules and the input power is the DC-side yield, quantity always bigger than the overall yield of the PV system. This is because all BoS components, which are between the DC-side and the load, exhibit less than ideal performance because of thermal dissipation or other internal inefficiencies. However, the power delivered to the load is the benchmark value for assessing the performance of the entire PV system and for matching the load profile when sizing the PV system. Therefore a comprehensive modelling of the parts forming the PV system should be used to finally calculate the energy yield of the PV system. In this contribution we show our modelling results for (a) predicting the behaviour of PV systems based on location and real-time meteorological data, (b) sizing opportunely the DC-to-AC inverters depending on PV panels tilt and orientation and (c) applying mutual shading and environmental shading analysis on the overall yield calculation.
About topic (a), a web-application, the Dutch PV Portal (dutchpvportal.tudelft.nl), is available. Such website has several objectives: (i) to reveal the photovoltaic potential in the Netherlands by quantifying the real-time solar electricity production in the territory, (ii) to calculate realistic performances of small to very large PV systems in the Netherlands by means of interactive design tools and fluid-dynamic physical model for taking wind turbulence into account, (iii) offer latest information on developments in PV technologies and systems to a wide audience. About topic (b), a tool for users, installers and energy distributors is given to optimally size the inverter to be connected to an array of PV modules. Depending on their orientation and inclination angles, the model will calculate how much solar energy the array receives daily and how much power is delivered by the modules. Therefore, by considering all power levels that would be seen throughout an entire year, designers will make a proper choice for sizing the inverter. About topic (c), a location analysis is done to estimate the available energy and the amount that can be harnessed from it by a PV panel. Location specific parameters such as the weather and results from the shading analysis are incorporated to accurately predict this energy. Later an optimisation model is used to find the optimum module tilt and azimuth angles for a PV system in the Netherlands. In case of autonomous, hybrid or autonomous-hybrid PV systems, the system performance can be analysed under a load profile and performance indicators such as the loss of load probability of the system and energy autarky can be estimated.
10:45 AM - E1.03
The Research and Applications of the Si Base Thin Film Photovoltaic Modules
Tingkai Li 1 Xueshi Tan 1 Jingjing Yang 1
1Hunan Gongchuang Photovoltaic Science and Technology Co Hunan ChinaShow Abstract
The high efficiency and stabilized properties of solar cell modules are very important for solar farm applications. In order to make high efficiency a-Si:H/uc-Si:H tandem solar cell modules, we optimized the property of each single layer such as amorphous intrinsic layer, intermediate reflective layer and microcrystalline intrinsic layer, n doped amorphous layer between microcrystalline i/n layer and employed the two-step growth method of low pressure chemical vapor deposition(LPCVD) process to fabricate the ZnO:B-TCO film etc. After optimization of the Si base solar module processes, the conversion efficiency of 11.87% can be achieved. The degradations of Si Base solar modules have been also investigated under light soaking and other various measurement conditions. The lower degradations of 5 - 7% drop in conversion efficiency have been obtained. On other hand, the Si base thin film modules for building integrated with photovoltaics (BIPV) applications have been developed. Such as the photovoltaic curtain wall, fence, sunroof, street lamps, pumps have been fabricated, and the solar farm with remote monitoring systems of solar farms have also been installed.
11:30 AM - *E1.04
Fundamentals and Technology of Silicon Heterojunction Solar Cells
Ruud Schropp 1 2
1ECN-Solliance Eindhoven Netherlands2Eindhoven University of Technology Eindhoven NetherlandsShow Abstract
Although the price of solar panels has recently decreased considerably, the production cost of solar cells is still too high for the generated electricity to compete with bulk electricity prices. The Dutch STW program FLASH aims at reducing the production costs of photovoltaic (PV) modules by improving the solar cell conversion efficiency, reducing materials consumption and using abundant materials only, and by applying low-cost and low-temperature processing methods, which lowers the energy costs in manufacturing as well. We focus on silicon heterojunction (SHJ) solar cells, because they combine the high efficiency of crystalline silicon (c-Si) wafer technology with the high throughput, low-cost production technologies for amorphous silicon thin-film solar cells. Thin film technology provides excellent methods for surface passivation and junction formation at low processing temperatures. Surface passivation, a method to electronically de-activate defects at the interface, is crucial for reducing losses in SHJ solar cells and leads to very high efficiencies. At present the world record efficiency of 25.6% by Panasonic for SHJ cells is even higher and is obtained on larger area than that of wafer-based technologies using conventional diffusion processes for junction formation.
SHJ devices have lower mechanical stress, which facilitates the use of thinner wafer material. This in turn facilitates a major contribution to cost reduction and improves the environmental profile of solar electricity significantly. We aim to further develop this by (i) smart defect engineering. In this approach new TCO&’s deposited by Atomic Layer Deposition are implemented; and (ii) the development of new silicon heterojunction cell structures and their production technology.
12:00 PM - E1.05
Influence of Lamination Process and Materials on the Residual Stress in the Silicon Solar Cells as Revealed by Synchrotron X-Ray Microdiffraction
Karthic Narayanan Rengarajan 1 Arief Budiman 1 Nobumichi Tamura 2 Martin Kunz 2 Caldwell W.A 3
1SUTD Singapore Singapore2Advanced Light Source Berkeley United States3SUNPOWER San Jose United StatesShow Abstract
In this study, we investigate the effect of two polymer encapsulation with different material properties such as Young&’s modulus (E), yield strength etc...on the residual stress gradients of silicon. We observe through synchrotron X-ray microdiffraction that, solar photovoltaic (PV) module laminated with encapsulants A and B which have Young&’s modulus of 6.34 and 28.32MPa respectively, reveals distinct variations in residual stress of silicon. The residual stress of silicon near the solder (stress concentration region), showed a maximum quantitative value of ~300 MPa with encapsulant A whereas for the solar PV with encapsulant B, it showed a much higher value of ~450 MPa. Further, this residual mechanical stress and its relation to fracture/crack initiation events of silicon were understood using three point bending tests. The result shows that with encapsulant A, crack initiation of silicon at force of 37KN is observed whereas for the PV with encapsulant B, silicon cracked at much lower force of 10KN. These studies confirm that encapsulant materials have a significant effect on the residual stress of silicon which directly affects the working efficiency and reliability of the solar PV.
12:15 PM - *E1.06
Effect of n Doped Amorphous Layer between Microcrystalline i/n Layer on the Performance of Micromorph Tandem Solar Cells
Jingjing Yang 1 Tingkai Li 1 Xueshi Tan 1 Feng Zhang 1 Bingxue Mao 1
1Hunan Gongchuang Photovoltaic Science and Technology Co Hunan ChinaShow Abstract
Pin/pin “micromorph” tandem solar cells were manufactured by the industrial production line of Hunan Gongchuang PV Science & Technology Co., Ltd. Based on this solar cells, a n-doped amorphous silicon layer deposited by plasma enhanced chemical vapor deposition(PECVD) was inserted between the microcrystalline silicon intrinsic layer and n-doped layer. The result shown that the introduced n-type amorphous silicon layer well improved the bad effect caused by microcrystalline silicon growth defects. Compared with the reference solar cells without inserting the n-doped amorphous silicon layer, the open voltage and conversion effeciency increased clearly. When the thickness of n-doped amorphous silicon layer was 8nm, the open voltage increased from 72.9V to 73.6V and conversion efficiency increased from 10.63% to 10.74%.
Tingkai Li, Gongchuang Photovoltaic Co., Ltd.
Michael Mastro, U.S. Naval Research Laboratory
Meng Tao, Arizona State University
Qi Wang, National Renewable Energy Laboratory
E6: Futuristic Solar Cells
Wednesday PM, April 08, 2015
Moscone West, Level 3, Room 3006
2:30 AM - E6.01
Nanotubular Structured Extremely Thin Absorber Solar Cells with All-Solid-State p-NiO/i-Sb2(SxSe1-x)3/n-TiO2 Synthesized by Atomic Layer Deposition
Seongrok Seo 1 Changdeuck Bae 1 Hyunjun Yoo 1 Myungjun Kim 1 Sunhee Lee 1 Hyunjung Shin 1
1Sungkyunkwan Univ Suwon Korea (the Republic of)Show Abstract
Extremely thin absorber (ETA) solar cells aim to combine the advantages of using very thin inorganic absorbing layer on nanostructured substrates with stable all-solid-state solar cells having potentials to provide low-cost alternatives to traditional thin film solar cell technologies. The best efficiency reported to date, however, is under 6%, mainly due to high rate of internal recombination and imperfect infiltration of inorganic absorbing film through whole nanostructured complexes. Herein, we report the nanotubular ETA solar cells with p-NiO/i-Sb2(Sx/Se1-x)3/n-TiO2 structures. All synthesized by Atomic layer deposition (ALD) based on negative Anodic Aluminum Oxide (AAO) templates, and are found the advantages of nanotubular structure and conformal ALD coatings: (a) Vertically aligned nanotube arrays can provide an optimal materials' architecture because of their large internal surface area, lower recombination losses, and vectorial charge transport along the nanotube axis, which is good for charge separation and transport in solar cells. (b) The homogeneous films through the whole structure can be deposited by ALD, which is also easily possible for ultra-precise control of film thickness. Furthermore, band gap engineering of absorbing layer from 1.2 to 1.7 eV was conducted for getting optimum energy level alignments of each interface by controlling compositional mixing of absorbing film (Sb2(Sx/Se1-x)3 (0le;xle;1). This work suggests that nanotubular structured all-solid-state ETA solar cells synthesized by ALD are very promising for highly efficient next-generation photovoltaics.
2:45 AM - E6.02
Highly Stable Supramolecular Hemicage Cobalt Mediators for Dye Sensitized Solar Cells
Marina Freitag 1 Wenxing Yang 1 Gerrit Boschloo 1 Anders Hagfeldt 2
1Uppsala University Uppsala Sweden2EPFL Lausanne SwitzerlandShow Abstract
In the pursuit of high stability redox mediators, we have developed novel hemicage cobalt complexes for dye sensitised solar cells. Cobalt complexes have a negligible extinction coefficient, and their redox properties can be tuned by synthetic modifications of the ligand. This approach offers an attractive alternative to the traditional I3minus;/Iminus; redox shuttle used as dye solar cells with cobalt, which have demonstrated the highest efficiencies with liquid electrolytes.1,2
An innovative synthetic approach for controlling the electronic and structural properties of the mediator couple systems was used. We combined all six nitrogen-donors in one multi-dentate ligand. This chelating ligand reduces the entropy losses during metal binding and suppresses dissociation of the Ligands as reported for [Co(bpy)3]2+/3+, leading to a high binding constant.3,4 The well-known 1,3,5-tri-ethylphenyl-platform was the base for attachment of three bipyridine-ligands in the 2, 4, and 6-position.5 The proposed rigid and symmetric bipyridine ligand system of the hemicaged complex can effectively shield the cobalt(II)-core, and provide an unprecedented control of the geometrical preorganization and binding geometry for exploring the electrochemical processes.
The cobalt complex using a hemicage ligand [Co(ttb)]2+/3+ TFSI3/2 and [Co(teb)]2+/3+ TFSI3/2 as redox mediators in combination with a cyclopentadithiophene-bridged donor-acceptor dye (LEG 4), adsorbed on TiO2, yielded a power conversion efficiency of over 6% at 100 mW cmminus;2. This result indicates that the molecularly engineered cobalt redox shuttle is also a legitimate alternative to the commonly used cobalt redox mediators.
(1) Feldt, S. M.; Gibson, E. A.; Gabrielsson, E.; Sun, L.; Boschloo, G.; Hagfeldt, A. Journal of the American Chemical Society 2010, 132, 16714.
(2) Yella, A.; Lee, H.-W.; Tsao, H. N.; Yi, C.; Chandiran, A. K.; Nazeeruddin, M. K.; Diau, E W.-G.; Yeh, C.-Y.; Zakeeruddin, S. M.; Grätzel, M. Science 2011, 334, 629.
(3) Karunadasa, H. I.; Montalvo, E.; Sun, Y.; Majda, M.; Long, J. R.; Chang, C. J. Science 2012, 335, 698.
(4) Kashif, M. K.; Nippe, M.; Duffy, N. W.; Forsyth, C. M.; Chang, C. J.; Long, J. R.; Spiccia, L.; Bach, U. Angewandte Chemie International Edition 2013, 52, 5527.
(5) Wang, J.; Oyler, K. D.; Bernhard, S. Inorganic Chemistry 2007, 46, 5700.
3:00 AM - E6.03
A Layer-by-Layer Nanoassembly Platform for Large Interfacial Contact: New Avenue toward Higher Efficiency Energy Conversion
Mohamed Samir Eita 1 Abdulrahman El Labban 1 Federico Cruciani 1 Anwar Usman 1 Pierre Beaujuge 1 Omar F. Mohammed 1
1King Abdullah University of Science and Technology (KAUST) Jeddah Saudi ArabiaShow Abstract
To achieve sufficient electron transfer and subsequently high conversion efficiency in the solar cells, however, energy-level alignment and interfacial contact between the donor and the acceptor units are needed. Several techniques have been used to fabricate the acceptor layer or electron transport layer (ETL) in solar cells. These techniques vary from solid state techniques requiring ultrahigh vacuum equipments, e.g. sputtering, to solution-processed techniques, e.g. sol-gel synthesis. Despite major advances in these techniques which resulted in higher solar device efficiencies by the time, none of these techniques has resulted in adequate interfacial contact at the donor-acceptor interface to achieve the highest solar efficiency possible. Here, we introduce a layer-by-layer (LbL) protocol as a facile, room-temperature, solution-processed method to prepare the electron transport layer (ETL) from commercial ZnO nanoparticles and polyacrylic acid (PAA) with a controlled and tunable porous structure, which provides large interfacial contact with the active layer. Applying our LbL approach to bulk heterojunction (BHJ) polymer solar cells with an optimized ZnO layer thickness of ca. 25 nm yields solar cell power-conversion efficiencies (PCEs) of ca. 6%, exceeding the efficiency of amorphous ZnO interlayers formed by conventional sputtering methods. Interestingly, annealing the ZnO/PAA interlayers in nitrogen and air environments in the range of 100-300 °C reduces the device PCEs by almost 20 to 50%, indicating the importance of conformational changes of the PAA polymer in the LbL-deposited films on solar cell performance. Our developments pave the path to the fabrication of all solution-processed polymer solar cell devices that can be produced without the need for post-processing thermal annealing treatments, and in a process that is applicable to flexible devices printed on plastic substrates (e.g. PET, Etc.). Finally, due to the unprecedentedly interfacial contact in these thin films and the versatility of the method, the current platform could be employed in a variety of solar cells architectures and may extend to other fields that principally rely on the interfacial contact such as photocatalysis and fuel cells.
3:15 AM - E6.04
Efficient Spectral Downshifting in Planar Concentrators for Solar Conversion
James Banal 1 Kenneth P. Ghiggino 2 Wallace W.H. Wong 2
1The University of Melbourne Parkville Australia2The University of Melbourne Melbourne AustraliaShow Abstract
The efficiencies of luminescent solar concentrators (LSCs) based on organic dyes have been limited by the photophysical properties of the embedded organic chromophores, particularly a small Stokes shift leading to reabsorption losses and concentration quenching that limits the concentration of chromophores that can be embedded in the LSC. Recently, chromophores that exhibit aggregation-induced emission (AIE) have been shown as promising alternatives to traditional laser dyes due to their large Stokes shift and high quantum yield even at large concentrations in solid films.1 Experiments and simulations, including studies of LSC/solar cell couples, have shown that LSCs that utilize fluorophores exhibiting AIE can match, and exceed, the performance of state-of-the-art LSCs based on organic dyes.
1 Banal, J. L., White, J. M., Ghiggino, K. P. & Wong, W. W. H. Concentrating aggregation-induced fluorescence in planar waveguides: a proof-of-principle. Sci. Rep.4, 4635, (2014).
3:30 AM - E6.05
Transforming the Cost of Solar-to-Electrical Energy Conversion: Integrating Thin-Film GaAs Solar Cells with Non-Tracking Mini-Concentrators
Kyusang Lee 1 Jaesang Lee 1 Bryan A Mazor 1 Stephen Forrest 1
1University of Michigan Ann Arbor United StatesShow Abstract
A major hurdle of photovoltaic technology that has yet to be fully overcome is to achieve cost-efficient solar-to-electrical energy harvesting. Here we demonstrate the integration of integrating ultrathin, flexible GaAs solar cells with plastic, thermoformed truncated mini-compound parabolic concentrators (CPCs) that can achieve solar energy conversion that costs only 3% of that needed to fabricate substrate-based GaAs solar cells. In addition, using a modified, high throughput, non-destructive epitaxial lift-off (ND-ELO) cell fabrication process, our integrated solar cell+CPC costs only 11% that of conventional ELO-processed GaAs solar cells. The low-profile, 2 dimensional concentrators are designed to be truncated by 90%. While providing approximately 3 times concentration (and hence 3 times less solar cell material per area), the truncation eliminates the need for daily solar tracking, thereby replacing high concentration factor optics that demand expensive solar tracking paraphernalia. Moreover, the concentrators provide efficient light collection both in direct as well as in diffuse light. We find that the concentrated, thin film cells operate near room temperature by directly bonding the thin-film GaAs solar cells onto a heat-sinking metal layer. This represents a reduction in temperature of over 40oC when compared to substrate-based GaAs solar cells. Overall, these results represent a cost-effective plastic-based low-concentration solar module that enables light-weight, high efficiency GaAs-based solar cells to reduce the module and balance of systems costs compared with heavy, rigid modules that are also subject to wind loading damage and high installation costs. Our cost estimates suggest that this integration approach leads to power generation costs of only $0.30/Wp.
 Kyusang Lee, Jeramy D. Zimmerman, Tyler W. Hughes, S.R. Forrest, “Non-Destructve Wafer Recycling for Low-Cost Thin-Film Flexible Optoelectronics” Advanced Functional Materials (2014) Vol 24, Issue 27, 4284-4291
E4: Cross-Cutting Issues II
Wednesday AM, April 08, 2015
Moscone West, Level 3, Room 3006
9:30 AM - *E4.01
ZnO:B Thin Films Made by Two-Step Growth Method
Zhang Hengsheng 1
1Hunan Gongchuang Photovoltaic Science and Technology Co Hunan ChinaShow Abstract
Two-step growth method of low pressure chemical vapor deposition(LPCVD) process was employed to fabricate the ZnO:B-TCO film; For the first layer, the seed layer with a heavy doping concentration was deposited on the glass substrate, the film having higher deposition rate were then grown on the top of the first layer; It shows that the doping situations of the seed layer play an important role in electrical and optical performance of the whole ZnO:B-TCO layer, and the combination of this two properties is optimal when the doping ratio(B2H6/DEZ) was 0.4;
10:00 AM - E4.02
Organic-Acid Texturing of Transparent Electrodes toward Broadband Light Trapping in Thin-Film Solar Cells
Woojin Lee 1 Taehyun Hwang 1 Seung-Yoon Lee 1 Joonhyeon Kang 1 Taeho Moon 2 Byungwoo Park 1
1Seoul National University Seoul Korea (the Republic of)2Dankook University Cheonan Korea (the Republic of)Show Abstract
Regardless of the great importance of light trapping toward the breakthrough in saturated photoconversion efficiencies of Si thin-film solar cells, much research on the surface texturing of transparent conducting oxides (TCOs) has been focused just on the nanostructural control during thin film growth. Herein, an organic acid for the surface texturing of ZnO:Al is introduced as an alternative to conventional HCl, making highly scatterable surface morphology via the control of etching anisotropy. The texturing behavior by oxalic acid is investigated in terms of vertical roughness, lateral correlation length, and thickness change according to the crater evolution. Etching with oxalic acid results in superior light-scattering performance (by ~8% increase at lambda; = 1000 nm) with maintaining transparency and resistance, compared to the etching with HCl. This fascinating behavior is understood by easy crater formation with less amount of overall vertical etching. Significantly, this simple and reproducible texturing tactic extends tunability for desirable TCO morphology, enabling efficient light trapping, and therefore appears potentially applicable for large-scale photovoltaic devices in industry.  G. Li, H. Li, J. Y. Ho, M. Wong, and H. S. Kwok, Nano Lett.14, 2563 (2014).  Y. Kim, W. Lee, D.-R. Jung, J. Kim, S. Nam, H. Kim, and B. Park, Appl. Phys. Lett.96, 171902 (2010). Corresponding Author: Byungwoo Park: email@example.com
10:15 AM - E4.03
Efficiency Enhancement in ZnO:Al-Based Dye-Sensitized Solar Cells Structured with Sputtered TiO2 Blocking Layers
Alessandra Alberti 1 Giovanna Pellegrino 1 Guglielmo Guido Condorelli 2 4 Corrado Bongiorno 1 Saori Morita 3 Antonino La Magna 1 Tsutomu Miyasaka 3
1CNR-IMM Catania Italy2Universitagrave; Degli Studi di Catania Catania Italy3Graduate School of Engineering, Toin University of Yokohama Yokohama Japan4INSTM UdR Catania Catania ItalyShow Abstract
We explored new strategies for efficiency enhancement in dye-sensitized solar cells (DSSCs) by combining dehydrationminus;condensation reactions with sputtering deposition methods. The photoanodes were realized by means of low-temperature preparation of mesoporous TiO2 films on thin undoped TiO2 compact (blocking) layers on ZnO:Al (AZO) substrates and sensitization with ruthenium dye, N719. For photoanodes fabrication, an 8 mu;m thick mesoporous film of TiO2 and an under critical thermal budget, applied before dye loading (le;200 °C: i.e., 150 °C for the TiO2 mesoscopic layer and 200 °C for the TiO2 blocking/AZO bilayer), were employed, which renders the overall process competitive for the applications. The structural properties of the sputtered TiO2/AZO bilayer were optimized, and a cell efficiency as high as the 4.6%, above the current literature limit for AZO-based DSSC (3.8% for 10 mu;m thick mesoporous layers sintered at 450 °C and sensitized with N719), was achieved at T le; 200 °C. With the proposed scheme for the photoanode structure and using, instead, a conventional thermal treatment at 500 °C (30 s), the cell efficiencies were further raised up to 4.9%. It was thus evidenced that the use of optimized materials for the cell architecture makes the AZO-based DSSC nowadays rising devices.
10:45 AM - E4.04
Debonding Mechanisms of Photovoltaic Encapsulation Materials
Fernando Daniel Novoa 1 David C. Miller 2 Reinhold H. Dauskardt 1
1Stanford University Stanford United States2National Renewable Energy Laboratory Golden United StatesShow Abstract
Avoiding photovoltaic (PV) encapsulation debonding in PV modules has proven difficult and costly, particularly in non-conventional PV applications such as buildings integrated photovoltaics (BIPV). For example, once encapsulation debonding occurs, the PV module is often subject to corrosion and subsequent loss of performance or functionality. The damage caused by solar environments on PV encapsulation materials has traditionally been studied by exposing materials to the “qualification test” protocols, defined by specific elevated temperatures, moist environments and small doses of UV light. However, the mechanical stress and its importance in determining the kinetic mechanisms of interface adhesive and cohesive failure within a PV module has rarely been investigated. A quantitative understanding of the mechanisms that determine encapsulation debonding (which include molecular bond rupture processes), may be used to determine the longevity and reliability of PV encapsulation materials exposed to terrestrial environments.
Using a recently developed quantitative adhesion technique, we measured the energy required to debond industry-relevant encapsulation materials from glass, silicon cells, and other relevant substrates. The encapsulation materials included poly(ethylene-co-vinyl acetate) (EVA), polyvinyl-butyral (PVB), ionomers, and polyolefins. We report on the effect of indoor aging and demonstrate that encapsulant/glass debond energy decreases dramatically from 2000 J/m2 at 20 °C to less than 500 J/m2 at 60 °C. The mechanisms leading to encapsulation debonding, including viscoelastic deformation and debond-tip cavitation, are reported. Employing a debonding characterization method with in-situ UV, we measured debond growth rates (as low as 1 nm/s) for encapsulation films subject to applied mechanical loads in an environment of controlled temperature and relative humidity. The debond growth rate increased up to 1000-fold with small changes of temperature (10 °C). The effects of moisture, temperature and UV exposure on debond growth acceleration are then related to the rupture of molecular bonds at the debonding tip.
To elucidate the degradation processes leading to envrionmental debonding, the kinetics of the debond growth process are interpreted using a recently developed viscoelastic fracture-mechanics model, which accounts for the effects of moisture, temperature and UV light. We finally show how the model can be exploited to acquire, not only a fundamental understanding of damage formation and progression, but also to develop accelerated testing techniques, to make long term reliability predictions, and to design durable solar modules for industrial implementation.
E5: Tandem Cells
Wednesday AM, April 08, 2015
Moscone West, Level 3, Room 3006
11:30 AM - E5.01
European Metrology Project for III-V Materials Based High Efficiency Multi-Junction Solar Cells
Alexandre Cuenat 1
1National Physical Laboratory - NPL Middlesex United KingdomShow Abstract
Since July 2014, thirteen European metrology organizations are collaborating to address some of the main metrological challenges faced by the developments of high-efficiency III-V Multi-Junction Solar Cells (MJSC).
III-V MJSC structures are made of a high number of layers, which makes a pure experimental optimization difficult and expensive; this also limits the uncertainty of cell calibration due to the complexity of their spectral response.
The project is structured in three distinct parts:
1) improved accuracy in materials and transport characterization for existing MJSC;
2) improved accuracy and repeatability in traceable efficiency characterization for MJSC cells with three or more junctions and finally,
3) metrology for advance concept such as coupling with thermoelectric, dilute nitride, quantum dots or growth on Silicon.
Each part of the project will be presented, but our contribution will be centered on our initial results for the first part that is developing accurate and spatially resolved metrology to determine traceable and complete III -V material data sets.
In particular, the accuracy of existing and emerging methods to measure electrical transport properties of III -V complex heterostructures will be presented in details with an emphasis on experimental determination of band-gap alignment, dopant distribution, carrier density, and series -resistances.
11:45 AM - E5.02
Adhesion and Reliability of Complex Multijunction Photovoltaic Structures
Ryan Brock 1 Peter Hebert 2 Hector Cotal 2 James Ermer 2 Reinhold Dauskardt 1
1Stanford University Stanford United States2Spectrolab, Inc. Sylmar United StatesShow Abstract
Concentrating photovoltaics (CPV) incorporating high efficiency multijunction photovoltaic cells are a leading candidate for large-scale ground-based solar energy installations. As in other solar technologies, reliability over extended operating lifetimes is an important metric for success. Despite the successful application of multijunction cells in space based systems, the application of multijunction cells with their complex layered structures in terrestrial applications requires an improved understanding of thermomechanical reliability and testing metrologies as a basis for improved lifetime predictions. Of particular concern is the adhesion of the many internal interfaces including those involving backside metal contacts, substrates, active layers, antireflective coatings, and frontside metal gridlines. The effects of stressing parameters that include mechanical stress, temperature, and UV exposure in the presence of humidity from terrestrial environments are also of significant interest.
We discuss modified thin-film adhesion testing metrologies together with the first quantitative measurement of adhesion of selected interfaces within state-of-the-art multijunction cells. In particular, we address the adhesion of several 2- and 3-layer antireflective coating systems on multijunction cells along with frontside gridlines and backside metal contacts. Special modifications to previously established techniques were necessitated by the fragility of germanium and gallium arsenide substrates ubiquitously used in these devices. By varying interface chemistry and morphology through processing, we initially demonstrate the marked effects on adhesion and help to develop an understanding of how high adhesion can be achieved, as adhesion values ranging from 2 J/m2 to 12 J/m2 were measured. Furthermore, long-term temperature cycling and high-humidity exposures demonstrate environmental degradation modes and begin to build the basis for physics-based degradation models.
12:00 PM - E5.03
The Construction of Tandem Dye-Sensitized Solar Cells from Chemically-Derived Nanoporous Photoelectrodes
Hongsik Choi 1 Sangheon Lee 1 Taehyun Hwang 1 Seunghoon Nam 1 Joonhyeon Kang 1 Byungho Lee 1 Byungwoo Park 1
1Seoul National University Seoul Korea (the Republic of)Show Abstract
A tandem dye-sensitized solar cell (tandem-DSSC) was synthesized on the basis of thin-film semiconductor electrodes. The nanoporous p-type NiO films were successfully obtained by simultaneous deposition of Al and Ni, followed by selective etching of Al and oxidation. Likewise, the n-type photoanode was made where Ag was etched in nitric acid after the initial formation of Ag/TiO2 nanocomposites. Such dye-sensitized photoelectrodes were combined to construct a tandem solar cell which exhibited an enhanced open-circuit voltage. Also, the tandem devices were subjected to various light fluxes to correlate the experimental cell parameters (open-circuit voltage, short-circuit current, fill factor, recombination shunt resistance, etc.) with the ideal one-diode model. Interestingly, impedance spectra of the tandem cell was well matched with the parameters from each of the n-type or p-type DSSC, indicative of successfully-designed tandem structure.  C. Nahm, H. Choi, J. Kim, S. Byun, S. Kang, T. Hwang, H. H. Park, J. Ko, and B. Park, Nanotechnology24, 365604 (2013).  A. Nattestad, A. J. Mozer, M. K. R. Fischer, Y.-B. Cheng, A. Mishra, P. Bäuerle, and U. Bach, Nat. Mater.9, 31 (2010). Corresponding Author: Byungwoo Park: firstname.lastname@example.org