Enhancement of the hole injection into regioregular poly(3-hexylthiophene) by molecular doping

The hole injection in Schottky barriers formed between p-type doped regioregular poly(3-hexylthiophene-2,5-diyl) (rr-P3HT) and silver (Ag) is investigated. The rr-P3HT is controllably doped using the acceptor 2,3,5,6-Tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ). We demonstrate that only one order of magnitude increase in the background hole density p(0), from 2x10(16) to 2x10(17) cm(-3), enhances the hole injection with two orders of magnitude. The hole injection barrier is lowered by 0.5 eV and exhibits a linear dependence on p(0), which can be explained by doping induced surface charges. (C) 2010 American Institute of Physics. [doi:10.1063/1.3464560]