Photoexcitation-Assisted\nMolecular Doping for High-Performance\nPolymeric Thermoelectric Materials

Molecular doping plays a crucial role in modulating the\nperformance\nof polymeric semiconductor (PSC) materials and devices. Despite the\ndevelopment of numerous molecular dopants and doping methods over\nthe past few decades, achieving highly efficient doping of PSCs remains\nchallenging, primarily because of the inadequate matching of frontier\nenergy levels between the host polymers and the dopants, which is\ncritical for facilitating charge transfer. In this work, we introduce\na novel doping method termed photoexcitation-assisted molecular doping\n(PE-MD), capable of transcending limitations imposed by energy level\ndisparities through the mediation of efficient photoinduced electron\ntransfer between polymers and dopants. This approach significantly\namplifies the electrical conductivity of the PDPP4T polymer, increasing\nit by more than 4 orders of magnitude to a maximum value of 349.67\nS cm<sup>–1</sup>. Given that only the irradiated region experiences\na substantial increase in doping level, the PE-MD process facilitates\nthe photoresist-free and precise patterning of doped polymers at a\nresolution down to 1 μm. Furthermore, the enhanced electrical\nconductivity of the photoexcitation-assisted molecularly doped PDPP4T\nfilm promotes efficient thermoelectric conversion, yielding an impressive\ninitial power factor of 226.1 μW m<sup>–1</sup> K<sup>–2</sup> and a figure-of-merit (<i>ZT</i>) of 0.18,\naccompanied by improved thermal and ambient stability. The PE-MD strategy\nnot only remarkably elevates the doping level of PSCs toward efficient\nthermoelectric conversion but also preserves the easy processability\nof flexible and integrated devices.