Steric‐Hindrance Modulation toward High‐Performance 1,3‐Bis(thieno[3,4‐b]thiophen‐6‐yl)‐4H‐thieno[3,4‐c]pyrrole‐4,6(5H)‐dione‐Based Polymer Solar Cells with Enhanced Open‐Circuit Voltage

Abstract

AbstractSolution‐processed bulk‐heterojunction polymer solar cells (PSCs) are indispensable in photovoltaics. π‐Conjugated donor–acceptor copolymers as electron donors have become the cornerstone as the most intensively studied topic in this field. Thieno[3,4‐c]pyrrole‐4,6‐dione (TPD) is one of the most commonly used electron‐withdrawing moieties. Based on TPD, a new building block, 1,3‐bis(thieno[3,4‐b]thiophen‐6‐yl)‐4H‐thieno[3,4‐c]pyrrole‐4,6(5H)‐dione (TBTT), is designed and a novel low‐bandgap TPD‐copolymer is developed with a power conversion efficiency (PCE) up to 7.5% with a low open‐circuit voltage (Voc) of 0.633 V when utilizing PC71BM as electron acceptor. To promote the performance of TBTT‐based polymers, four conjugated copolymers are designed and synthesized based on TBTT and benzodithiophene (BDT) building blocks by regulating their steric hindrance with side alkyl chains on BDT moiety. PSCs based on polymer P4 with an additional n‐hexyl side chain blended with PC71BM deliver a high PCE of 9.1% with a Voc of 0.78 V increased by 24%, which is among the highest in TPD‐based polymers. The study provides new insights into the molecular design and synthesis of high‐performance photovoltaic materials.