10.20% Efficiency polymer solar cells via employing bilaterally hole-cascade diazaphenanthrobisthiadiazole polymer donors and electron-cascade indene-C70 bisadduct acceptor

A series of crystalline copolymers, PBDTSA-DAPT, PBDTTA-DAPT and PBDTTS-DAPT, have been designed towards the application of multi-blend polymer solar cells (PSCs). These copolymers exhibit low-lying HOMO levels by incorporating benzodithiophene (BDT) donor and 9,10-diazaphenanthro[3,4-c;5,6-c]bis[1,2,5]thiadiazole (DAPT) acceptor in the main chains. They were added as the hole-cascade polymer donors into the PTB7: PC71BM blend. When adding 10 wt% of the resulting copolymers, the PCEs of 8.59%, 9.03% and 8.91% were achieved for PBDTSA-DAPT-, PBDTTA-DAPT- and PBDTTS-DAPT-based ternary devices, respectively. In order to further elevate the performance of PBDTTA-DAPT devices, indene-C70 bisadduct (IC70BA) was also incorporated into the PBDTTA-DAPT-based ternary blend. This cascade band structure would give steadier energy level alignment and afford more charge transfer channels, which could promote simultaneously both the hole and electron transfer. When adding 5 wt% of IC70BA, the quaternary PSC device showed a top PCE of 10.20%. This PCE value is the best efficiency for PTB7 based PSCs reported so far. Our work not only demonstrates a design strategy for high performance hole-cascade polymer donors in multi-blend PSCs, but also provides a first quaternary strategy with bilateral cascade energy band structures to increase the Voc, Jsc and FF simultaneously for high efficient organic solar cell applications.