Transport and spectroscopic studies of the effects of fullerene structure on the efficiency and lifetime of polythiophene-based solar cells

Time-dependent measurements of both power conversion efficiency and ultraviolet-visible absorption spectroscopy have been observed for solar cell blends containing the polymer poly(3-hexylthiophene-2,5-diyl) (P3HT) with two different functionalized C60 electron acceptor molecules: commercially available [6,6]-phenyl C61 butyric acid methyl ester (PCBM) or [6,6]-phenyl C61 butyric acid octadecyl ester (PCBOD) produced in this laboratory. Efficiency was found to decay with an exponential time dependence, while spectroscopic features show saturating exponential behavior. Time constants extracted from both types of measurements showed reasonable agreement for samples produced from the same blend. In comparison to the PCBM samples, the stability of the PCBOD blends was significantly enhanced, while both absorption and power conversion efficiency were decreased. ► We study P3HT-based solar cells with two different fullerenes. ► We made time-dependent measurements of both efficiency and UV–vis absorption. ► Modified PCBM devices are more stable but less efficient. ► Absorption and efficiency are seen to correlate.