Mechanism of Charge Transport in Hybrid Organic-Inorganic PEDOT:PSS/Silicon Heterojunctions

We study the temperature and voltage dependence of current density in hybrid poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS)/Si heterojunctions. It is shown that charge transport follows distinct mechanisms at reverse and forward bias. The current is found to be injection limited at reverse bias owing to the quasi-Schottky-barrier at the organic-inorganic interface. At forward bias, the carrier transport is governed by space-charge-limited current in PEDOT:PSS. Trap-limited current at low forward bias is associated with trap states in the organic layer. The total density and the characteristic energy of localized states of PEDOT:PSS are estimated as Nt≃5.6×1015cm-3 and Ech≃0.107eV, respectively. The commonly observed double-logarithmic character at forward bias is interpreted as the signature of transition from the Mark-Helfrich regime to the Mott-Gurney regime.