"3,4-Disubstituted Polyalkylthiophenes for High-Performance Thin-Film Transistors and Photovoltaics"

Sangwon Ko: Eric Verploegen, Sanghyun Hong, Rajib Mondal, Eric T. Hoke, Michael F. Toney, Michael D. McGehee, and Zhenan Bao; Journal of the American Chemical Society , 10/5/11.

Additional Authors: Eric Verploegen, Sanghyun Hong, Rajib Mondal, Eric T. Hoke, Michael F. Toney, Michael D. McGehee, and Zhenan Bao

Abstract:

We demonstrate that poly(3,4-dialkylterthiophenes) (P34ATs) have comparable transistor mobilities (0.17 cm2 V–1 s–1) and greater environmental stability (less degradation of on/off ratio) than regioregular poly(3-alkylthiophenes) (P3ATs). Unlike poly(3-hexylthiophene) (P3HT), P34ATs do not show a strong and distinct π–π stacking in X-ray diffraction. This suggests that a strong π–π stacking is not always necessary for high charge-carrier mobility and that other potential polymer packing motifs in addition to the edge-on structure (π–π stacking direction parallel to the substrate) can lead to a high carrier mobility. The high charge-carrier mobilities of the hexyl and octyl-substituted P34AT produce power conversion efficiencies of 4.2% in polymer:fullerene bulk heterojunction photovoltaic devices. An enhanced open-circuit voltage (0.716–0.771 eV) in P34AT solar cells relative to P3HT due to increased ionization potentials was observed.