A comparative investigation of trap-limited hole transport properties in organic bulk heterojunctions

We have investigated the bulk hole transport properties of copper phthalocyanine (CuPc): fullerene (C-60) and zinc phthalocyanine (ZnPc):C-60 bulk heterojunctions by analyzing thickness-and temperature-dependent current density-voltage (J-V) characteristics in hole-only device configurations, i.e. indium-tin-oxide (ITO)/poly(ethylene-dioxythiophene): polystyrenesulphonate (PEDOT:PSS)/CuPc: C-60 or ZnPc:C-60/molybdenum oxide (MoO3)/Al. It has been found that the hole transport is governed by a space-charge-limited current (SCLC) model in the presence of exponentially distributed traps within the bandgap. The hole mobility of CuPc: C60 mixture (1 x 10(-5) cm(2) V-1 s(-1)) is higher than that of ZnPc:C-60 mixture (6.2 x 10(-6) cm(2) V-1 s(-1)), which can be ascribed to the differences of the characteristic trap energy and the total density of traps in both bulk heterojunctions. These results indicate that the SCLC method is applicable for studying the transport properties in organic bulk heterojunction.