Self-healing of defects in uniaxially aligned semiconducting polymer crystals via molecular doping: insights into crystallization from transient vs. settled amorphous phases

Abstract

We present the self-healing of defects and enhanced crystallinity in uniaxially aligned poly(3-hexylthiophene) (P3HT) crystals via molecular doping with F4TCNQ. Using eutectic friction transfer (EFT), highly aligned P3HT films (P3HT_EFT) were fabricated, exhibiting superior alignment and planarity compared to spin-cast P3HT (P3HT_SC). Upon doping, the self-healing of defects in P3HT_EFT films led to a significant increase in the charged-ordered phase from 5.4% to 80.3%, transforming transient amorphous phases into well-ordered crystalline domains. In contrast, the conventional P3HT_SC films formed settled amorphous phases, and exhibited no self-healing behavior. Structural analysis using polarized UV-VIS, FT-IR, Raman spectroscopy, and GIWAXS confirmed significant improvements in crystalline order and charge carrier mobility. This led to a dramatic increase in electrical conductivity, with doped P3HT_EFT (d-P3HT_EFT) films exhibiting four orders of magnitude higher conductivity compared to their spin-cast counterparts (d-P3HT_SC). These findings highlight the distinct crystallization behaviors of transient versus settled amorphous phases, emphasizing the critical role of uniaxial alignment in realizing highly crystalline semiconducting polymers for organic electronic applications.