Lawrence Berkeley National Laboratory
Electronic Excitations and Metal-Insulator Transition in Poly(3-hexylthiophene) Organic
- Author(s): Sai, N.
- Li, Z.Q.
- Martin, M.C.
- Basov, D.N.
- Di Ventra, M.
- et al.
We carry out a comprehensive theoretical and experimental study of charge injection in poly(3-hexylthiophene) (P3HT) to determine the most likely scenario for metal-insulator transition in this system. Wecalculate the optical-absorption frequencies corresponding to a polaron and a bipolaron lattice in P3HT. We also analyze the electronic excitations for three possible scenarios under which a first- or a second-order metal-insulator transition can occur in doped P3HT. These theoretical scenarios are compared with data from infrared absorption spectroscopy on P3HT thin-film field-effect transistors (FETs). Our measurements and theoretical predictions suggest that charge-induced localized states in P3HT FETs are bipolarons and that the highest doping level achieved in our experiments approaches that required for a first-order metal-insulator transition.