Thiazolyl-Substituted Isomeric Benzodithiophenes Boost\nthe Photovoltaic Performance of Polymer Donors

The\ntwo-dimensional side groups on benzodithiophene, especially\nthiophene derivatives, play a critical role in tailoring the bandgap,\ninterchain packing, and photovoltaic outcomes of the most successful\npolymer donors. In light of the highly similar five-membered ring\nbut vastly different electron-deficient properties, thiazole is expected\nto not only inherit the ability of the thiophene side group in conformation\ncontrol but also be beneficial for constructing wide-bandgap polymer\ndonors with deeper highest occupied molecular orbitals (HOMOs). Herein,\ntwo isomeric polymers (PBDT-oTz and PBDT-iTz) with different thiazolyl\norientations on benzodithiophene are explored. A systematic investigation\nreveals that PBDT-oTz, featuring thiazolyl nitrogen far from benzodithiophene,\nachieves a deeper HOMO and appropriate molecular aggregation compared\nwith its PBDT-iTz counterpart. Consequently, the PBDT-oTz-based device\naffords an excellent power conversion efficiency of 15.02%, much better\nthan the 6.39% for PBDT-iTz. These results manifest the great effectiveness\nof thiazole in constructing high-performance wide-bandgap polymer\ndonors.