Investigations of the effects of tempering and composition dependence on charge carrier field effect mobilities in polymer and fullerene films and blends

In this study we report on field effect mobilities of charge carriers in materials used in polymer photovoltaics. The field effect mobilities of charge carriers in polymer and fullerene films and in various blend compositions were investigated for the effects of tempering. Contact resistances were considered for more accurate mobility estimations. The field effect mobilities of holes in films of the conjugated polymer poly(3-hexylthiophene) (P3HT) were found to be in the 10−3cm2/Vs range and the field effect mobilities of electrons in films of the methanofullerene [6,6]-phenyl C61-butyric acid methyl ester (PCBM) were found to be in the order of 10−2cm2/Vs. The concentration of PCBM was then varied in P3HT:PCBM blends, and blend compositions with PCBM contents of 0%, 33%, 40%, 50%, 60%, 67%, and 100% weight percents were measured before and after tempering. Electron mobilities were not detected in untempered blend compositions with PCBM content lower than 67% PCBM. Tempering led to a large increase in the electron mobility in the blends, and electron mobilities were detected in all tempered blends with PCBM content above 40%. Electron and hole field effect mobilities were found to be roughly balanced in the 10−3cm2/Vs range for the tempered blend with 67% PCBM content.