Morphology controls the thermoelectric power factor of a doped semiconducting polymer.

ABSTRACT: The electrical performance of doped semiconducting polymers is strongly governed by processing methods and underlying thin-film microstructure. We report on the influence of different doping methods (solution versus vapor) on the thermoelectric power factor (PF) of PBTTT molecularly p-doped with F _n TCNQ (n = 2 or 4). The vapor-doped films have more than two orders of magnitude higher electronic conductivity (?) relative to solution-doped films. On the basis of resonant soft x-ray scattering, vapor-doped samples are shown to have a large orientational correlation length (OCL) (that is, length scale of aligned backbones) that correlates to a high apparent charge carrier mobility (?). The Seebeck coefficient (?) is largely independent of OCL. This reveals that, unlike ?, leveraging strategies to improve ? have a smaller impact on ?. Our best-performing sample with the largest OCL, vapor-doped PBTTT:F₄TCNQ thin film, has a ? of 670 S/cm and an ? of 42 ?V/K, which translates to a large PF of 120 ?W m^-1 K^-2. In addition, despite the unfavorable offset for charge transfer, doping by F₂TCNQ also leads to a large PF of 70 ?W m^-1 K^-2, which reveals the potential utility of weak molecular dopants. Overall, our work introduces important general processing guidelines for the continued development of doped semiconducting polymers for thermoelectrics.

SUBMITTER: Patel SN 

PROVIDER: S-EPMC5473677 | biostudies-literature | 2017 Jun

REPOSITORIES: biostudies-literature