Solution-processed bulk-heterojunction organic solar cells employing Ir complexes as electron donors

To explore enhancing photocurrent in organic solar cells (OSCs) via harvesting triplet excitons, two novel bicycloiridium complexes (R1 and R2) are designed and synthesized. Conventional bulk-heterojunction triplet OSCs are solution processed using R1 or R2 as sole electron donors and phenyl-C71-butyric acid methyl ester (PC71BM) as the electron acceptor. A decent short circuit current (Jsc) of 6.5 mA cm−2 is achieved though the overlap between the absorption spectrum (with ∼550 nm absorption onset) of R2 and the solar flux is relatively small. With an open circuit voltage of 0.74 V and a fill factor of 0.42, an encouraging power conversion efficiency of 2.0% is achieved in the OSCs based on R2 and PC71BM without any processing additives and post-treatments. Our preliminary result demonstrates the possibility of utilizing Ir complexes as sole electron donors in OSCs, which extends available soluble small molecules for OSCs.