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 Z of 30 samples = 16.59 +/- 1.13%, best = 18.4%) compared with PCBM film (average eta 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 Z of 20 samples = 13.91 +/- 0.84%, best = 15.4%) compared with PCBM (average eta 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.