Temperature Dependence of Trap Density Distribution in Poly(3-hexylthiophene) and 1-(3-Methoxycarbonyl)-propyl-1-phenyl-(6,6)C61 Based Blending Films under Illumination

Measurements of the current density--voltage ($J$--$V$) characteristics of a poly(3-hexylthiophene) (P3HT) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61 (PCBM)-based electron-dominated device as functions of temperature were carried out. A transport transition from three-dimensional variable range hopping (VRH) to space-charge-limited current (SCLC) with an exponential distribution of traps (filled and unfilled) was observed. The bulk trap density, about $10^{18}$ cm -3 , of the P3HT:PCBM blend film was evaluated by the differential method. A shift to the lowest unoccupied molecular orbital (LUMO) state of PCBM for trap density distribution was observed owing to the temperature dependence of the Fermi level of PCBM materials. It is supposed that the Fermi level of PCBM materials is strongly temperature-dependent similarly to that of amorphous silicon semiconductors.