Effects of neat C60 doping on the performance of bulk-heterojunction solar cells based on P3HT:PCBM
We explored the effect of neat C60 doping on the performance of bulk heterojunction (BHJ) organic photovoltaic cells (OPVs) based on poly(3-hexylthiophene) (P3HT) and (6,6)-phenyl C61 butyric acid methyl ester (PCBM). The power conversion efficiencies (PCEs) were found to gradually decrease as the relative concentration of C60 increased. This PCE decrease is mainly due to the reduction in short-circuit current density (Jsc). Atomic force microscopy images revealed that C60-doped BHJ films consisted of unformed large P3HT crystals and many small PCBM aggregates. This morphology leads to a decrease in the effective P3HT conjugation length and an enhancement of absorption bleaching in neutral P3HT chains. These results explain well the blue-shift absorption spectra, the decrease of absorption coefficients, and the reduction in Jsc found in C60-doped BHJ OPVs.