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

Abstract

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 (J_sc) 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.