Hole mobility in optimized organic photovoltaic blend films obtained using extraction current transients

The advantage of Charge Extraction by Linearly Increasing Voltage (CELIV) to evaluate bulk conductivity and drift mobility (not influenced by contact barriers of sandwich sample) of equilibrium carriers bypasses problems associated with conventional techniques. Ambipolar CELIV transients however do present problems because it is hard to distinguish holes from electrons. In this letter, a blocking electrode is used to extract mobility of only holes in optimized ambipolar alkylthiophene: [6,6]-phenyl-C61-butyric acid methyl ester [PCBM] bulk heterojunction based solar cells which has proved to be difficult in the past. Universality of this method has been demonstrated by using different p-type polymer:PCBM systems for the study. Necessity of balance of mobility of electron and hole has been demonstrated for high fill factors and consequently higher efficiency devices.