Temperature dependent charge transport in electrostatically doped poly [benzimidazobenzophenanthroline] thin films

Charge transport in electrostatically doped poly[benzimidazobenzophenanthroline]-BBL thin films in a field-effect transistor geometry were investigated in the temperature range 150 K < T < 370 K. At low temperatures activation and hopping transport mechanisms dominated, while phonon scattering dominated at high temperatures. The activation energies (E-A) were found to lie in the range 140 meV < E-A < 400 meV implying the existence of deep traps within the polymer bandgap of 1.8 eV. Two quasi-linear dependencies of E-A on the gate voltage (V-g) were observed with E-A decreasing as V-g increased. An unexpected "metallic-like " transport characteristic appeared for T > 335 K which depended on V-g. Enhanced electron delocalization combined with increased carrier density could be responsible for this "metallic-like " behavior. Our results show that the existence of deep traps with multiple energy distributions, combined with increased carrier density led to the unusual temperature dependence of charge transport observed in BBL.