Inverted CH₃NH₃PbI₃ perovskite hybrid solar cells with improved flexibility by introducing a polymeric electron conductor

Inverted-type CH₃NH₃PbI₃ flexible perovskite solar cells (FPeSCs) with improved flexibility were prepared by incorporating a polymeric electron conductor, poly([N,N′-bis(2-octyldodecyl)-1,4,5,8-naphthalene bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)) (PNDI-2T), into small-molecule electron conductor phenyl-C₆₁-butyric acid methyl ester (PCBM). PCBM : PNDI-2T electron conductor films with different compositions (100 : 0, 75 : 25, 50 : 50, 25 : 75 and 0 : 100) were employed in PeSCs. The 75 : 25 PCBM : PNDI-2T film showed slightly improved power conversion efficiency (average η of 30 samples = 16.59 ± 1.13%, best = 18.4%) compared with PCBM film (average η of 30 samples = 16.49 ± 1.15%, best = 17.8%), as well as similar electrical conductivity and electron mobility, and lower absorption loss. Similarly, inverted planar FPeSCs of 75 : 25 PCBM : PNDI-2T films showed improved performance (average η of 20 samples = 13.91 ± 0.84%, best = 15.4%) compared with PCBM (average η of 20 samples = 13.04 ± 0.97%, best = 15.0%). Furthermore, the 75 : 25 PCBM : PNDI-2T inverted planar FPeSC films showed significantly improved flexibility compared with PCBM-based devices, due to the entangled polymeric PNDI-2T matrix relieving stress on the PCBM domains.