Revealing the Molar Mass Dependence on Thermal, Microstructural, and Electrical Properties of Direct Arylation Polycondensation Prepared Poly(3-hexylthiophene)

Poly(3-hexylthiophene) (P3HT) is a "fruit fly" conjugated polymer in the field of organic electronics due to its simple chemical structure, decent photoelectric properties, and low cost. To date, the design of nonfullerene acceptors matching P3HT and the synthesis of high-quality P3HT via sustainable methods hold tremendous promises for advancing the P3HT solar cells. The use of P3HT via direct arylation polycondensation (DArP) has recently proven to be an efficient means for constructing efficient polythiophene solar cells, while the intrinsic properties of DArP prepared P3HT remain poorly understood, thus impeding further performance enhancements. Herein, six batches of P3HTs with weight-average molecular weights from 8.5 to 73.9 kg/mol were successfully synthesized via DArP, and multitechnique characterizations were employed to investigate the molecular weight effect of P3HT on its optical properties, crystallization behaviors, morphology, and electrical properties. P-52k with relatively high crystallinity and hole mobility was applied in photovoltaic devices matching a variant of the popular nonfullerene acceptor Y6. This photovoltaic combination afforded a good power conversion efficiency of over 7% in P3HT/nonfullerene solar cells. Importantly, this research not only provides insights into the physical properties of DArP prepared P3HT as a function of molecular weight but reveals the correlation between the key structure parameter and the electrical performance of P3HT for optoelectronic applications as well.