Preferential Location of Dopants in the Amorphous Phase of Oriented Regioregular Poly(3-hexylthiophene-2,5-diyl) Films Helps Reach Charge Conductivities of 3000 S cm?1

Abstract

Doping polymer semiconductors is a central topic in plastic electronics and especially in the design of novel thermoelectric materials. In this contribution, we demonstrate that doping of oriented semi-crystalline P3HT films with the dopant tris(4-bromophenyl)ammoniumyl hexachloroantimonate), also known as magic blue (MB), helps reach charge conductivities of up to 3000 S/cm and thermoelectric power factors (PF) of the order of 170±30 mW/mK2 along the polymer chain direction. A combination of transmission electron microscopy (TEM), polarized optical absorption spectroscopy and thermoelectric property measurements helps clarify the conditions necessary to achieve such high charge conductivities. The mechanism of doping is intimately related to the semi-crystalline structure of the polymer and whether crystalline, amorphous or both phases are doped. In the case of MB, mainly amorphous P3HT domains are doped while the structure of crystalline P3HT domains is almost unaltered by doping. A comparison with other dopants such as FeCl3, F4TCNQ, F6TCNNQ and Mo(tdf-COF3)3 indicates that the highest charge conductivities are obtained when the only amorphous phase of P3HT is preferentially doped. Charge transport improves in the sequence: i) doping of the only crystalline phase (F6TCNNQ and F4TCNQ), ii) doping of both crystalline and amorphous phases (FeCl3, Mo(tdf-COF3)3) and iii) doping of the only amorphous phase (Magic blue).