Blend composition study of poly(3,3‴-didodecylquaterthiophene)/[6,6]-phenyl C61 butyric acid methyl ester solution processed organic solar cells

Photovoltaic devices made from blends of poly(3,3‴-didodecylquaterthiophene) (PQT-12) and [6,6]-phenyl C61 butyric acid methyl ester have been fabricated and characterized. By varying the polymer loading in the blend, an optimal power conversion efficiency (PCE) of 0.70% has been achieved for a blend consisting of 15 wt % PQT-12, which is an order of magnitude higher than the PCE for a 50 wt % blend. The apparent reason for the large difference is the fact that blends with higher PQT-12 loading are transport limited, with much larger hole-to-electron mobility ratios.