Partitioning the Tin-Lead Perovskite Solar Cells to Control the Oxidation and Ion Migration leads to Improved Efficiency and Stability

Shahrir Razey Sahamir1, Gaurav Kapil1, Takeru Bessho2, Hiroshi Segawa2, Qing Shen1, Shuzi Hayase1 1The University of Electrocommunications, Chofu, --, Japan /2The University of Tokyo, Meguro, --, Japan

The efficiencies of the tin-lead (SnPb) perovskite solar cells (PSCs) with equimolar ratio (1:1) of tin (Sn) and lead (Pb) have reached over 23%. However, their stabilities are still being questioned which left these solar cells still behind in term of commercialization. There are several approaches such as doping, interfacial and interlayer engineering that has been introduced in order to enhance the efficiency and the stability of the SnPb PSCs. However, there is still a large gap between their achievement compared to their Pb based PSCs counterpart. In this work, we will demonstrate a structural partitioning technique which was achieved in-situ and can be applied in order to enhance the efficiency and the stability of the SnPb based PSCs. We introduced germanium (Ge) as a dopant that interestingly only formed on the surface of the SnPb film as evident from depth-profiling XPS experiment. The self-assembled monolayer (SAM) was used as the hole extraction layer instead of the conventional PEDOT:PSS hole transport layer (HTL). With this achievement, we are able to partition the SnPb PSCs by creating a physical boundary between the bottom and the top interfaces of the SnPb perovskite film. This physical boundary hindered the ion migration towards the electron transport layer (ETL) and also mitigated the formation of oxidized Sn4+ species. The SAM improved the stability as less corrosive and unreacted layer was used as the replacement unlike the PEDOT:PSS. Further, SnOx layer was coated via atomic layer deposition (ALD) near the ETL side. We also found that, the Ge layer helps to prevent the damage due to ALD process and ultimately improved the overall efficiency and the stability of the SnPb PSCs. Efficiency over 21% and retainment of more than 94% after 1000 hours of thermal test at 85 °C has been achieved.