3,4- Disubstituted polythiophenes for high-performance thin-film transistors and photovoltaics

초록

Poly(3-hexylthiophene) (P3HT) has been the most commonly used organic semiconductor for organic solar cells due to a high absorption and good charge transport. The high charge carrier mobility of P3HT has permitted the solar cells to be made thicker (~220nm) than most other polymer-fullerene devices. Conjugated polymers with (mostly) planar backbones are often considered as optimal for organic-based electronic devices. We systematically impose synthetically-tailored twists within the conjugated backbones of a family of poly(hexyl)thiophenes and examine their influence on charge carrier mobilities and bulk heterojunction (BHJ) solar cells. We demonstrate that poly(3,4-dialkyl-terthiophenes) (P34ATs) have comparable transistor mobilities and greater environmental stability (less degradation of on/off ratio) than regioregular poly(3-alkylthiophenes) (P3ATs). This suggests that a strong ？？-？？ stacking is not always necessary for high charge carrier mobility and that other potential polymer packing motifs in addition to the edge-on structure (？？-？？ stacking direction parallel to the substrate) can lead to a respectable electronic performance. The high charge carrier mobilities of the hexyl and octyl-substituted P34AT have enabled a high power conversion efficiency in a polymer:fullerene bulk heterojunction photovoltaic devices.