Synthesis of Highly Soluble Copolymer based on Bisbenzothiadiazole and 2,7-Carbazole units for Optoelectronic Application

Abstract

On the mechanistic concept of intramolecular charge transfer (ICT), bisbenzothiadiazole-based donor-acceptor copolymers had previouly been synthesized and used as p-type materials in bulk-heterojunction (BHJ) solar cells. Taking the HOMO and LUMO levels of the polymers, the theoretical efficiencies using the Konarka efficiency map for single layer of BHJ solar cells showed very high (＜8.0% ). However, the device performance was low due to the lack of solubility as well as low molecular weights of the polymers. To solve these problems, we introduced alkyl substituted thiophenes onto carbazole-core unit, resulting in significantly enhanced solubility and high molecular weight of the bisbenzothiadiazole-based copolymer.