Nonfullerene Acceptor−Iridium Coordination Polymer as a Triplet Sensitizer for Efficient Organic Photovoltaics

ABSTRACT

Utilizing triplet excitons has been recognized as a promising method to boost performances of organic solar cells (OSCs). Although long lifetime and diffusion length of triplet excitons have been observed in some systems, efficiencies of triplet‐sensitized OSCs are still moderate because of the lack of an efficient way to generate and transfer triplet excitons. In this study, we report a nonfullerene acceptor–iridium coordination polymer (BTP‐N‐Ir) as a triplet sensitizer in ternary OSCs for utilizing triplet excitons to improve photocurrents. The triplet polymer sensitizer shows a small singlet‐triplet energy gap, facilitating the generation of long‐lived triplet excitons, which transfer to an intra‐moiety excited (i‐EX) state of the acceptor in ternary films, dissociating into free charges to contribute photocurrents. Such a new triplet‐exciton transfer pathway with the i‐EX as an intermediate state is more effective than those in previous systems, leading to the highest efficiency of 20.37% for OSCs with a triplet sensitizer.