Learning from Polymeric π‐Backbone to Film Sequences Unravels that a Coexistence of Bilayered and Mixed Morphologies Optimally Strengthens Thermoelectrics

Abstract π‐Conjugated polymers can be manipulated at the molecular and thin‐film levels to strengthen thermoelectric performance. Herein, two distinctive polymers—PBDP‐T and PBDB‐T with respective outstanding Seebeck coefficient ( S ) and electrical conductivity (σ) are selected and their functional units are integrated to synthesize random terpolymers via the ′backbone sequence′ strategy. The resulting disordered π‐backbones of terpolymers however lead to an unsuccessful acquisition of high power factor (PF). Alternately, the ′film sequence′ strategy is utilized and representative high‐σ P2F and high‐ S PTB7‐Th polymers are blended. Note that 3D conductive paths are generated in the blend films when the PTB7‐Th content falls between 35–80 wt%, which favors charge transportation and yields high σ . At an optimal 65 wt% PTB7‐Th, a maximum PF of 145.5 µW m −1 K −2 is obtained, far surpassing that of each parent polymer, which marks a breakthrough of the ′two‐phase combination′ rule. The peak PF achieved in medium PTB7‐Th content is attributed to the coexistence of bilayered and mixed morphologies, the former of which delivers slowly declining σ while the latter results in greatly elevated S with increasing PTB7‐Th. Given the notably lower thermal conductivity acquired in blend than neat polymers, the room‐temperature thermoelectric figure‐of‐merit as high as 0.15 is achieved.