Thermally Stable High-Performance Polymer Solar Cells Enabled by Interfacial Engineering.

Interfacial engineering plays an important role in determining the performance and stability of polymer solar cells (PSCs). In this study, thermally stable highly efficient PSCs are fabricated by incorporating a solution-processed cathode interfacial layer (CIL), including 4,4'-({[methyl(4-sulfonatobutyl)ammonio]bis(propane-3,1-diyl)}bis(dimethylammoniumdiyl))bis(butane-1-sulfonate) (MSAPBS) and polyethylenimine (PEI). For PSCs based on blends of poly{4,8-bis[5-(2-ethylhexyl)thiophen-2-yl]benzo[1,2-b;4,5-b']dithiophene-2,6-diyl-alt-[4-(2-ethylhexyl)-3fluorothieno[3,4-b]thiophene-2-carboxylate-2,6-diyl]} (PBDTTT-EFT) and [6,6]-phenyl C71 -butyric acid methyl ester (PC71 BM), the maximum power conversion efficiency (PCE) of inverted PSCs reaches 8.1 % and 7.2 % for MSAPBS and PEI CILs, respectively. The inverted PEI devices exhibit remarkable stability (lifetime >6000 h) under accelerated thermal aging (at 80 °C in ambient environment), which is much superior to that of the device with commonly used LiF CIL (lifetime≈33 h). This stability represents the best result reported for PSCs. The promising results based on this strategy can stimulate further work on the development of novel CILs for PSCs and pave the way towards the realization of commercially viable PSCs with high performance and long-term stability.