Isoindigo as a Building Block for Semiconducting Conjugated Polymers for High Performance Organic Photovoltaics

Abstract

One of the most important issues for enhancing the power conversion efficiency (PCE) of polymer solar cells (PSCs) is the development of conjugated polymers which exhibit broad light absorption with strong absorptivity, high charge carrier mobility, suitable energy level matching with the electron acceptor (fullerene derivatives), and appropriate molecular orientation to form an optimum pathway of charge carriers to the corresponding electrodes. In past few years, remarkable progress in the PCE surpassing 8% have been achieved with the configuration of bulk-heterojunction network structure consisting of high performance conjugated polymer as an electron donor and fullerene derivative as an acceptor. Isoindigo is a dye molecule with two lactam rings pertaining strong electron-withdrawing characteristic and planar ∏-conjugated structure. Particularly, the planar molecular structure is expected to afford high charge carrier mobility. Moreover, isoindigo-based organic compounds show broad optical absorption, high extinction coefficient, and deep HOMO energy level. Therefore, isoindigo is a promising building block for constructing low bandgap conjugated polymers to achieve high performance PSCs.