A1‐A2 Type Wide Bandgap Polymers for High‐Performance Polymer Solar Cells: Energy Loss and Morphology

Abstract

Introducing electron‐withdrawing groups onto donor‐acceptor (D‐A) type conjugated materials is a commonly used method for lowering their highest occupied molecular orbital (HOMO) energy level to achieve higher open circuit voltage (Voc) in polymer solar cells (PSCs). However, this method is rather costly due to the tedious synthesis and low yield involved in preparing the target monomers. Here, a novel design concept of using two different acceptor units to construct acceptor1‐acceptor2 (A1‐A2) type polymers with a deep HOMO level is proposed. Two A1‐A2 type wide bandgap (WBG) polymers, PB24‐3TDC and PB68‐3TDC, were designed for PSCs. The developed polymers possess proper energy levels and complementary absorption with an efficient electron acceptor ITIC‐Th. More importantly, by slightly regulating the alkyl side‐chains, molecular stacking and photoluminescence (PL) emission energy loss of polymers can be alternated significantly. As a result, tuned Voc from 0.9 to 1.0 V and short‐circuit current (Jsc) from 9.4 to 17.0 mA cm−2 can be achieved. The device based on PB24‐3TDC:ITIC‐Th exhibits a higher power conversion efficiency (PCE) of 10.3% compared to PB68‐3TDC:ITIC‐Th based device with a PCE of 7.88%. These results show that the design concept of A1‐A2 type polymer donors have great potential for blending with non‐fullerene acceptors for achieving high performance PSCs.