High-performance four-terminal perovskite/Si tandem devices

Perovskite solar cell (PSC) attracts much attention in laboratory due to its tunable bandgap, from 1.4 to 2.3 eV. According to Shockley-Queisser limit, under the global solar spectra, AM 1.5, the single-junction solar cell could reach 33.16% at 1.34 eV. In order to approach the SQ limit, many research groups turned their attention to perovskite/Si tandem solar cells (PSTSC). But instability of perovskite stops the practical application of monolithic PSTSC. Hence, I recommend mechanically stack four terminal (4T) PSTSC, where perovskite is the top cell and Si solar cell is the bottom cell, which are working separately, and preparation of four terminal tandem devices have high processing capability. Surface passivation plays an important role in photovoltaic, and as for perovskite, the defects are mainly formed at the surface of perovskite layer. The interface of hole transport layer (HTL) and perovskite layer is optimized by the use of 2PACz, so we concentrate on the interface of electron transport layer (ETL) and perovskite layer. 2D passivation is seemed as the most popular way for passivation. Here, we study the passivation mechanism of quaternary ammonium halide salts and rise the idea of a potential new mechanism. Optical loss is another obstruct to stop the development of 4T-PSTSC. It includes two parts. Firstly, the transparency and conductivity of the top electrode for the top cells play an important role to increase the power conversion efficiency (PCE) of the 4T (four-terminal) solar cells. Hence, we introduced indium zinc oxide (IZO) and indium zirconia oxide (IZrO) as two transparent conductive films (TCFs). Secondly, due to multi-air device interfaces, reflection loss need to be minimized. Hence, we used MgF$_2$ ARC (anti-reflective) layer to reduce reflection loss. Compared HIT and IBC, we select the better bottom cells for four terminal perovskite/Si tandem devices and reach highest efficiency, compared with all related published papers. In this case, the top cells are single-junction perovskite solar cells, whose champion PCEs are 18.12% and 18.47%, on IZO and IZrO based substrates, respectively. And the champion PCEs of 4T-PSTSCs are 28.99% and 29.44%, respectively.