Extension of π-conjugation and enhancement of electron-withdrawing ability at terminal indenedione for A-π-D-π-A small molecules for application in organic solar cells

Abstract

A class of A-π-D-π-A type organic small-molecule (SM) donor materials used in heterojunction solar cell has been designed and investigated by means of quantum chemical calculations. The structural modification of the end-capped 1,3-indenedione (IND) by expanding the π-conjugation and enhancing the electron-withdrawing ability are expected to improve the photovoltaic performance. To gain a better understanding of the effects of such structural modulation of IND on the electronic and photophysical properties of SM donor materials, the geometrical and electronic structures, absorption spectra, energy loss, intramolecular charge transfer (ICT), and exciton dissociation and charge recombination rates at the interface have been analyzed in detail to establish structure-property relationships for the investigated A-π-D-π-A molecules. This work demonstrates that why such terminal structural modification could increase open circuit voltages, enhance light-absorption ability and ICT properties, reduce energy loss, facilitate exciton dissociation, and suppress charge recombination, thus leading to improved photovoltaic performance as predicted by Scharber diagram. This study could give the theoretical guidelines for molecular design and shed a light on the exploration of high-performance A-π-D-π-A type SM donor materials.