A deep-purple-grey thiophene–benzothiadiazole–thiophene BODIPY dye for solution-processed solar cells

Abstract

In this work we explore the synthesis of an extended 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene dye (BODIPY) engineered from thiophene–benzothiadiazole–thiophene modules linked in the 3,5-substitution positions. We found that this highly soluble dye absorbs up to 800 nm in solution and up to 900 nm in thin films. An effective charge transfer absorption band was found at around 479 nm. The hybrid dye emits at 778 nm with a quantum yield of about 6%. Similar electrochemical and optical gaps were determined about 1.36 eV. When deposited in thin films the dye exhibits an ambipolar nature with well-balanced hole and electron mobilities. Bulk heterojunction solar cells based upon this dye blended with [6,6]phenylC_61or71butyricacid methylester (PC₆₁BM or PC₇₁BM) provide a power conversion efficiency of about 1.26% upon a mild thermal annealing.