Doping regulation of highly conductive PBTTT films

Abstract

Doping is a key strategy for enhancing the charge mobility and thermoelectric properties of polymers. While advancements utilizing the anion exchange technique have notably enhanced doping efficiency, there is a need for further optimization of the doping process. This study introduces a two-step doping approach combining solid-state diffusion with anion exchange, applied to poly[2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene] (PBTTTC14) films. Initial 2,3,5,6-tetrafluoro-7,7,8,8-tetracyano-quinodimethane (F4TCNQ) diffusion doping followed by anion exchange with F4TCNQ/ionic liquid achieved higher conductivity than one-step anion exchange doping. Spectral and structural analyses elucidated the enhanced doping mechanism. Additionally, adjusting the molecular weight (MW) of PBTTTC14 from 11,867 to 175,199 improved doping levels and conductivity, reaching 1,103.8 S cm⁻¹. A medium MW (MW = 99,407) optimized thermoelectric performance by balancing conductivity and Seebeck coefficients. These findings provide insights into controlling doping and performance of conductive semiconductor polymers through a two-step doping process and MW engineering.