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: PC 71 BM 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 (IC 70 BA) 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 IC 70 BA, 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 V oc , J sc and FF simultaneously for high efficient organic solar cell applications.