High‐Efficiency and UV‐Stable Planar Perovskite Solar Cells Using a Low‐Temperature, Solution‐Processed Electron‐Transport Layer

Efficient metal‐halide perovskite solar cells (PSCs) with a regular structure typically use high‐temperature‐processed TiO 2 electron‐transport layers (ETLs), which suffer from high electron recombination and inherent UV instability. Herein, we present low‐temperature solution‐processed lithium bis(trifluoromethanesulfonyl)imide (Li‐TFSI)‐doped C 60 (Li‐C 60 ) ETLs for high‐efficiency and UV‐stable planar PSCs with an n‐i‐p architecture. We found that simple Li‐TFSI doping ensured a better energy match between the active layer and the cathode, considerably enhanced the electron mobility of the ETL, and even improved CH 3 NH 3 PbI 3 crystallization finally to increase the power conversion efficiency (PCE) from 15.3 to 17.8 % with a minor hysteresis effect. Moreover, it was demonstrated that replacing TiO 2 with Li‐C 60 resulted in PSCs that were much more stable under UV light under an air atmosphere with almost no degradation after 3000 h under a nitrogen atmosphere.