Benzothiadiazole-based Conjugated Polymers for Organic Solar Cells

Benzothiadiazole (BT) is an electron-deficient unit with fused aromatic core, which can be used to construct conjugated polymers for application in organic solar cells (OSCs). In the past twenty years, huge numbers of conjugated polymers based on BT unit have been developed, focusing on the backbone engineering (such as by using different copolymerized building blocks), side chain engineering (such as by using linear or branch side units), using heteroatoms (such as F, O and S atoms, and CN group), etc. These modifications enable BT-polymers to exhibit distinct absorption spectra (with onset varied from 600 nm to 1000 nm), different frontier energy levels and crystallinities. As a consequence, BT-polymers have gained much attention in recent years, and can be simultaneously used as electron donor and electron acceptor in OSCs, providing the power conversion efficiencies (PCEs) over 18% and 14% in non-fullerene and all-polymer OSCs. In this article, we provide an overview of BT-polymers for OSCs, from donor to acceptor, via selecting some typical BT-polymers in different periods. We hope that the summary in this article can invoke the interest to study the BT-polymers toward high performance OSCs, especially with thick active layers that can be potentially used in large-area devices.