Mitigating Intrinsic Interfacial Degradation in Semi-Transparent Perovskite Solar Cells for High Efficiency and Long-Term Stability

Conventional semi-transparent perovskite solar cells (ST-PSCs) generally exhibit inferior performance and stability relative to opaque PSCs. However, a comprehensive understanding of the origins of inferior performance and stability of ST-PSCs and a practical solution to these challenges are both lacking. Here, it is shown for the first time that lithium ions from a lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)-doped 2,2 ',7,7 '-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9 '-spirobifluorene (Spiro-MeOTAD) hole-transport layer (HTL) can diffuse into the molybdenum trioxide buffer layer at their interface, yielding ST-PSCs with lower efficiency and accelerated degradation. It is also demonstrated that this undesired Li-ion diffusion can be avoided by HTL surface modification with stable lithium oxides. Using this approach, the constructed ST-PSC exhibits a new record power conversion efficiency (PCE) of 22.02% (21.68% certified) and a fill factor of >80%, with >99% shelf-stability after 400 h and >99% operational stability for 240 h, which clears away this longstanding limitation of the performance and stability of ST-PSCs. This strategy is also applied to fabricate four- and two-terminal perovskite/silicon tandem solar cells with bifacial equivalent efficiencies of 31.5% and 26.34%, respectively, at 20% albedo.