A dithieno[3,2-a:3′,2′-j][5,6,11,12]chrysene diimide based polymer as an electron transport layer for efficient inverted perovskite solar cells

The electron transport layer (ETL) plays an important role in promoting both photovoltaic performance and stability of perovskite solar cells (PSCs). n-Type conjugated polymers have been developed to replace the widely explored phenyl-C61-butyric acid methyl ester (PCBM) as an ETL, especially in p-i-n inverted planar PSCs, owing to their high-quality film features and excellent electron transport ability. Herein, a series of electron-deficient conjugated polymers (P(DTCDI-T), P(DTCDI-2T) and P(DTCDI-3T)) consisting of dithieno[3,2-a:3′,2′-j][5,6,11,12]chrysene diimides (DTCDI) and different thiophene based units (thiophene (T), 2,2′-bithiophene (2T) and 2,2′:5′,2′′-terthiophene (3T)) are reported as effective ETLs for inverted PSCs. Compared to control devices based on the PCBM ETL, these polymer-based devices display better photovoltaic performance, which is mainly due to the optimized electron extraction and transport properties of these DTCDI-based polymers, resulting in a champion power conversion efficiency (PCE) of 17.88% for P(DTCDI-2T) ETL based devices. Moreover, thanks to better film features, more effective interfacial passivation, lower trap-state density and hydrophobicity, these polymeric ETL based devices exhibit considerably improved stability.