A Thiazole-Based Polymer Donor for Efficient Organic Solar Cells

The development of new materials plays a critical role in improving the efficiency of organic solar cells (OSCs). At present, the relatively high-lying highest occupied molecular orbital (HOMO) level of the high-efficiency polymer donor is regarded as one of the main reasons for the low open-circuit voltage (V-oc). In this work, we introduced the strong electron-withdrawing thiazole unit into the construction of a polymer donor. We designed and prepared an alternating donor-acceptor material, namely PSZ, by copolymerizing 4-methyl thiazole with an electron-donating benzodithiophene unit and studied its application in high-efficiency OSCs. The optical and electrical properties of the new material were characterized by UV-Vis absorption spectroscopy and electrochemical cyclic voltammetry. Results show that PSZ is a typical wide-bandgap material with a high optical bandgap of 2.0 eV and a deep HOMO level of - 5.70 eV. When a non-fullerene BTP-eC9 was selected as the acceptor material, V-oc reached 0.88 V in the resulting device, and the corresponding power conversion efficiency (PCE) was 8.15%. In addition, when PSZ was added as the third component to the binary photoactive combination with PBDB-TF as the donor and BTP-eC9 as the acceptor, V-oc of the cell device could be increased, thereby obtaining a high PCE of 17.4%. These results indicated that introducing thiazole units into polymer donors can remarkably reduce the HOMO levels and improve V-oc and PCE in OSCs.