Simple (thienylmethylene)oxindole‐based polymer materials as donors for efficient non‐fullerene polymer solar cells

Abstract Although the significant progress in the power conversion efficiencies (PCEs) of non‐fullerene polymer solar cells (PSCs) has proved their commercial potential, the development of efficient photovoltaic materials from easily available raw materials and simple chemical synthesis is still lagging. In this work, three copolymers donors (PTEI‐H, PTEI‐F, and PTEI‐Cl) based on easily synthesized (Z)‐3‐(thiophen‐2‐yl‐methylene)‐indolin‐2‐one (TEI) as electron‐deficient unit were synthesized and characterized. As compared to the polymer PTEI‐H, the fluorinated and chlorinated polymers (PTEI‐F and PTEI‐Cl) show broader band gaps and deeper HOMO energy levels. However, after blending with small molecule acceptor Y6, the as‐cast PTEI‐H devices exhibit a PCE of 8.27%, outperforming those of the PTEI‐F devices (7.22%) and PTEI‐Cl devices (6.50%). The relatively high photovoltaic performance of the PTEI‐H devices are associated with their increased short‐circuit current density and fill factor values, resulting from the efficient exciton dissociation and charge generation, balanced charge transport properties, and reduced recombination loss. In consideration of the merits of the structural simplicity and synthetic accessibility of TEI unit, we believe it is a potential electron‐deficient moiety in developing high‐performance polymer donors for possible mass‐production of non‐fullerene PSCs