Triad-type, multi-functional compatibilizers for enhancing efficiency, stability and mechanical robustness of polymer solar cells

Abstract

The operation stability of polymer solar cells (PSCs) is one of the most important prerequisites for their practical use. In this work, we report a new acceptor-donor-acceptor (A-D-A) triad-type small molecule,5TRh-PCBM, as a compatibilizer for enhancing the thermal stabilities and mechanical properties of efficient PSCs while increasing their power conversion efficiencies (PCEs). This multifunctional5TRh-PCBMmolecule, consisting of an oligothiophene segment as the central core and fullerene derivatives as the end groups, is designed to enable strong interactions between the 5TRh-core with various types of efficient polymer donors containing thiophene or fused-thiophene units, while the end fullerene groups preferentially interact withPCBMacceptors. To examine the effectiveness of this molecular compatibilizer, PSCs with different donors (PTB7-Th,PBDB-T, andP3HT) have been fabricated and tested, with addition of various amounts of5TRh-PCBM. The addition of 5 and 10 wt% of5TRh-PCBMsignificantly enhances the thermal and mechanical stabilities of all tested PSCs. Importantly, unlike typical compatibilizers, the addition of5TRh-PCBMcan increase the PCEs of the PSCs due to its light harvesting capability. In particular, the PCE ofPTB7-Th:PCBM-based PSCs is increased from 9.37% to 10.09% with the 5 wt% addition of5TRh-PCBM. Our comprehensive investigations have revealed the effects of5TRh-PCBMon the optical, morphological, photovoltaic, and mechanical properties of molecularly engineered PSCs.