Dependence of the mobility and trap concentration in evaporated copper phthalocyanine thin films on background pressure and evaporation rate

Abstract

Current density-temperature measurements performed at constant applied voltage have been made on evaporated copper phthalocyanine thin films, with chamber pressure to deposition rate ratio P/R varying in the range 2.6*10⁴-1.3*10⁹ Pa m^-1s. In common with previous measurements these results were interpreted in terms of a space-charge limited mechanism dominated by an exponential distribution of trapping levels. There was a systematic decrease in mobility from 10^-6 to 10^-8 m² V^-1 s^-1 and an increase in trapping concentration from 5*10²² to 6*10²⁴ m^-3 as P/R was increased in the stated range, but the temperature parameter characterising the trapping distribution remained constant at approximately 750K. The variations in mobility and in trapping concentration were ascribed to the scattering and trapping effects of incorporated ambient gas molecules, thus indicating that these parameters are particularly sensitive to deposition conditions.