Optimizing solution-processed C60 electron transport layer in planar perovskite solar cells by interfacial modification with solid-state ionic-liquids

Low temperature solution-processed C-60 exhibits favorable electron mobility and band alignment, thus it is widely used to modify the interfaces between perovskite film and electron transport layer (ETL) in n-i-p planar heterojunction perovskite solar cells (PSCs). However, when C-60 was used as an independent ETL, PSCs exhibit poor performance. Herein, We have modified solution-processed C-60-based ETL with a solid-state ionic-liquid (1-ethyl-3-methylimidazolium iodide ([EMIM]I)). Using this interfacial modification method, we fabricated n-i-p planar heterojunction PSCs with optimized power conversion efficiency (PCE) of 15.09%, which was superior to that of PSCs based on unmodified C-60 ETL layer (12.11%). This work describes a novel method for low-temperature processing of efficient n-i-p PSCs.