Advanced Characterization of Three-Terminal Perovskite/Silicon Tandem Solar Cells

Perovskite solar cells have been shown to be ideal partners to silicon (Si) in tandem devices due to their flexibility in band-gap engineering by means of compositional variation, and potentially cost-effective fabrication [1,2]. Combining a perovskite top with a silicon heterojunction (SHJ) bottom cell has recently led to a new record power conversion efficiency (PCE) of close to 30% for perovskite/silicon (Si) tandem devices [3]. Most commonly, either a two- (2T) or four-terminal (4T) arrangement of the subcells are studied [1]. In a two-terminal (2T) arrangement, both sub-cells are connected in series in a monolithic device, sharing a common electron and hole contact. In this relatively straightforward device architecture, both sub-cells must, however, provide the same current for optimal operation. Opposed to that, four-terminal (4T) tandems feature electrically decoupled sub-cells with relaxed requirements regarding their respective electrical performance. On the downside, more complex subcell interconnection and potentially intricate module integration are major drawbacks of this concept. As an alternative, here we focus on a third approach that has gained attention only recently for perovskite/Si tandems, namely three-terminal (3T) tandems [4]. In 3T tandems, which are usually realized by using a bottom cell with interdigitated back-contacts (IBC), both subcells feature their own electron contact while sharing a common hole contact (or vice versa) [5]. This arrangement leads to a monolithic architecture that does not require current-matched sub-cells, and therefore combines the main advantages of the more commonly used 2T and 4T tandems. It has been shown that different sub-cell configurations, and especially the type of interconnection scheme, can lead to different electrical behaviors, even if the same materials are used in each case [6,7].<br/>In this contribution, we will report on our recent progress in 3T perovskite/IBC SHJ tandem solar cells with a PCE &gt; 25%. We will focus on different aspects regarding the measurement setup for such devices, the characterization of perovskite and silicon subcells and the visualization of advantages over 2T tandems through measurements and simulations. We will report on the design of a dedicated measurement setup featuring a dual-source source measure unit to accurately characterize the optoelectronic performance of 3T tandems. This is required since the solar cell characteristics of a 3T device cannot be retrieved from a single j-V scan but require simultaneous scanning of two voltages. This measurement setup and a tunable LED-based solar simulator are then used to study the response of 2T and 3T tandems to different illumination conditions. Further, we demonstrate how the individual measurement of the perovskite and Si subcell can be used to understand the behavior of not only 3T but also 2T. In addition to the experimental characterization of 3T, we use energy yield calculations to study the advantageous properties of 3T over 2T tandems. Lastly, we will point out pathways to achieving 3T PCEs in the range of state-of-the-art 2T and 4T tandems.<br/><br/><b>REFERENCES </b><br/>[1] T. Leijtens et al., Nat. Energy 3 (10), 828-838 (2018).<br/>[2] M. Jošt et al., Adv. Energy Mater. 10 (26), 1904102 (2020).<br/>[3] NREL, Best Research-Cell Efficiencies, https://www.nrel.gov/pv/cell-efficiency.html, 2022-06-16<br/>[4] P. Tockhorn et al., ACS Appl. Energy Mater. 2020, 3 (2), 1381-1392 (2020).<br/>[5] T. Nagashima et al., Conference Record of the 28th IEEE Photovoltaic Specialists Conference, Anchorage, Alaska, USA, 2000, pp 1193−1196.<br/>[6] E. L. Warren et al., ACS Energy Lett. 2020, 5 (4), 1233–1242 (2020).<br/>[7] P. Wagner et al., Presented at the 11th International Conference on Silicon Photovoltaics, Hamelin, Germany, 2021.<br/>.