Thenoyl-functionalized polythiophenes with deep HOMO levels as polymer donors for organic solar cells

Abstract

Polythiophene derivatives are promising donor materials for organic solar cells (OSCs) due to their simple synthesis process and low production cost. However, their photovoltaic performance is often undesirable due to their rather shallow highest occupied molecular orbital (HOMO) energy levels. Herein, we report three polythiophene derivatives (P2T-TCl, P3T-TCl and P4T-TCl) by attaching a novel chloro-substituted thenoyl side chain to the backbone fully composed of purely thiophene units with low synthetic complexity values of 22–26%. These polythiophene derivatives exhibited not only deep HOMO energy levels down to −5.37 eV, but also enhanced stretchability with a crack onset strain of up to 53%, due to the introduction of thenoyl side chains with both electron-deficient properties and steric hindrance effects. As the number of unsubstituted thiophenes in each repeat unit increased, more ordered molecular packing and higher crystallinity were observed in both neat films and blend films with the non-fullerene acceptor Y6-BO. Therefore, OSCs using P4T-TCl as the donor and Y6-BO as the acceptor achieved a higher power conversion efficiency of 9.15% than P2T-TCl:Y6-BO (5.25%) and P3T-TCl:Y6-BO (5.62%) based OSCs. This research demonstrates the promising potential of thenoyl-functionalized thiophene units in constructing cost-effective donor materials for high-performance OSCs.