9:30 AM - EN06.01/EN07.01.04
Effect of the HTM/TCO Interface on the Electrical Properties of Semi-Transparent Perovskite Solar Cells for Tandem Applications
Emilie Raoult1,2,3,Marion Provost2,Romain Bodeux1,2,Sébastien Jutteau1,2,Marie Legrand1,2,Samuel Rives1,2,Armelle Yaiche1,2,Damien Coutancier2,4,Jean Rousset1,2,Stéphane Collin2,3
Electricité De France (EDF)1,Institut Photovoltaïque d'Ile-de-France (IPVF)2,Centre for Nanoscience and Nanotechnology (C2N)3,CNRS4
Spiro-OMeTAD, CuSCN and PTAA are attractive hole transport materials (HTM) in conventional n-i-p architectures for perovskite cells1. In this work, we combine these three HTMs on semi-transparent (ST) solar cells with different sputtered electrodes made of In2O3-SnO2 (ITO) or In2O3-ZnO (IZO) to study their impact on the optical and electrical properties of the cells.
First, thanks to an optical model based on the Transfer Matrix Method and careful material characterizations2,3, a good agreement has been obtained between the transmission, reflection and absorption spectra of the complete structure of the ST cell with Spiro and ITO. This model allows to simulate the efficiency of a tandem cell with a silicon bottom cell, to identify optical losses and to optimize the thickness and properties of the each layer. It is shown that the Spiro and ITO layers have a non-negligible parasitic infrared absorption in the IR, resulting in a lower efficiency for the filtered silicon cell. The gain in efficiency enabled by the use of PTAA, CuSCN and IZO, which are almost transparent in the IR region, is assessed.
Second, triple cation perovskite solar cells with these three HTMs are synthetized and characterized in detail using scanning electron microscopy, ellipsometry spectroscopy, glow discharge emission optical spectroscopy, X-ray diffraction and transmission spectroscopy. Regarding the electrical properties, the Spiro is a layer known for its sensitivity, and the poor reproducibility obtained on ST cells is often associated with degradation due to energetic sputtering4. Investigations using CuSCN as HTM showed a slightly better reproducibility than Spiro but strong light soaking effects also appeared, and the resulting efficiencies are low. The replacement of the Spiro by PTAA has improved the reproducibility of cells, while maintaining good performances. A 17.4% efficiency perovskite semi-transparent cell with PTAA was obtained and which is significantly above our previous results with Spiro (16.4%)5.
After electrode sputtering deposition, a characteristic S-shape appears in IV characteristics. By regularly following the cells over time while keeping them under vacuum atmosphere and in the dark, IV curves recovered until the S-shape disappeared completely. For example, a cell with Spiro and ITO have 8.7% efficiency and 43% Fill Factor (FF) the first day and reach 16.8% with FF=70% after 66 days. When the Spiro is replaced by PTAA, the S-shape is less pronounced and the recovery time markedly reduced to 15 days. These effects are not visible on cells with CuSCN.
Lee et al.6 obtained a similar S-shaped curve on perovskite cell with a Spiro/silver electrode, with a short recovery time of about one day. A local reaction between the dopant Li-SIF and the silver could cause the deoxygenation of the Spiro at the surface, which would create a temporary electrical barrier. It is interesting to note that this dopant is common to PTAA and Spiro but not to CuSCN. Preliminary results obtained by time resolved photoluminescence (TRPL) shows a decrease of the PL signal over time. Experiments are underway to determine if the cause of this decrease is due to improved extraction at the HTM/TCO barrier as suggested by Lee et al.6, or if it comes from a reduction in radiative recombination related to defect healing. We will discuss the reaction mechanisms for these three HTM.
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 E. Raoult et al., 36th Eur. Photovolt. Sol. Energy Conf. Exhib. 757, 2019
 E. Raoult et al., SPIE: Physics, Simulation, and Photonic Engineering of Photovoltaic Devices IX, 2020
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 F. J. Ramos et al., Sci. Rep., 8, 1, 2018
 D. G. Lee et al.,, ACS Appl. Mater. Interfaces, 11, 51, 48497, 2019