Thieno[3,4-c]pyrrole-4,6-dione Based Small Molecules for High VOC Organic Photovoltaics

Abstract

The optoelectronic properties of organic semiconductors are primarily governed by the type of conjugated unit in the molecular backbone. Especially, in utilization of the push-pull concept for designing low bandgap organic materials, selection of electron deficient unit requires special attention because the frontier orbital energy level, planarity and dipole moment in organic molecules may be determined by the properties of the unit. Herein we report the synthesis and characterization of new organic small molecule (SM) composed of thienopyrroledione (TPD) as electron-deficient unit and dithienosilole as electron-rich unit. Since TPD has strong electron-accepting properties, it is expected for TPD to lower the HOMO energy level of the SM, resulting in high VOC of OPV cell. The SM exhibits a deep HOMO level of ?5.50 as measured by cyclic voltammetry. As a result, the solar cell device fabricated from the new donor material shows a PCE of 5.5% with a high VOC of 0.95 V, which is, to the best of our knowledge, the best PCE value reported to date in TPD-based SM solar cells.