Alkyloxime Side Chain Enabled Polythiophene Donors for Efficient Organic Solar Cells

Electron-withdrawing alkyloxime was, for the first time, used as a novel side chain for conjugated polymers. Two polythiophenes, PTOBT-Z with the Z-isomer alkyloxime side chains and PTOBT-Z/E with a mixture of Z- and E-isomer alkyloxime side chains, were synthesized. They possess deep highest occupied molecular orbital energies (EHOMO's) down to −5.44 eV and wide band gaps of up to 1.94 eV, which are desirable donor characteristics for matching the non-fullerene acceptors for organic solar cells (OSCs). In addition, they exhibited excellent field effect hole mobilities of ∼10–2 cm2 V–1 s–1. OSCs using PTOBT-Z as the donor and ITIC as the acceptor achieved a high power conversion efficiency of up to 9.04%. Importantly, PTOBT-Z has a very low synthetic complexity of 23.4%. The results strongly demonstrate that alkyloxime groups are a new type of functional solubilizing side chains for developing polymer donors with both high performance and low cost.