Recent development of n-type thermoelectric materials based on conjugated polymers

Thermoelectric (TE) materials based on conjugated polymers have received much attention due to their great advantages of solution processibility, light weight, flexibility, and low thermal conductivity. These advantages make them potential candidates for large-area, low-cost and low-power TE applications. Both efficient p-type and n-type conjugated polymers with high and comparable thermoelectric performance are required for practical TE applications. However, due to the inefficient n-doping efficiency and unstable electron transport of most n-type conjugated polymers, the TE performance of n-type polymers is much poorer than that of their p-type counterparts, impeding the development of polymer TE materials. Great efforts have been made to address the low n-doping efficiency and TE performance of n-type polymers, including the chemical modification of traditional n-type polymers, the design of new n-type conjugated polymers, and the development of more efficient n-dopants, as well as doping engineering. Nowadays, the TE performance of n-type polymers has been greatly improved, indicating a bright future for polymer TE materials. In this review, we summarize the recent progress made on n-type polymer TE materials, mainly focusing on the structure-performance relationships based on promising n-type polymers for TE applications. This review aims to provide some guidelines for future material design.