Influence of nanostructure on the device performance and charge recombination dynamics of P3HT:PCBM solar cells

Abstract

In this paper, we investigated the recombination dynamics of photogenerated charge carriers in a poly(3-hexylthiophene) (P3HT):[6,6]-phenyl-C 61-butyric acid methyl ester (PC 61BM) blend system with donor-acceptor ratio of 1:1 before and after solvent annealing treatment. The technique of transient photocurrent and photovoltage measurements were used, and charge carriers were photogenerated by a 7 ns laser pulse at room temperature (298 K). In transient photocurrent measurement, we observed some differences in the saturation extracted charge in P3HT:PCBM solar cells with different power efficiencies. In addition, the bimolecular recombination coefficient β is found to be 3. 5×10 -13 cm 3 s -1 for annealed devices, while 9. 5×10 -12 cm 3 s -1 for as-cast devices. In the transient photovoltage measurement, we found that the photovoltage decay can be fitted by power-law equation at long time scale. The exponent parameter α is 2. 6 for annealed devices, which can be described as trap-free bimolecular recombination; α is 1. 76 for as-cast device due to the trap-limited bimolecular recombination. These experimental results indicate that the nanomorphology of active layer indeed have influence on charge carriers dynamics in P3HT:PCBM blend systems. © 2012 The Author(s).