Effects of neat C₆₀ doping on the performance of bulk-heterojunction solar cells based on P3HT:PCBM

ABSTRACT

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 (J_sc). 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 J_sc found in C₆₀-doped BHJ OPVs.

KEYWORDS:

• Fullerene
• organic
• photovoltaic
• polymer