Charge transport and recombination in organic solar cells

Measurements of transient photoconductivity and the cell spectral response provide information about the carrier mobility, recombination mechanisms and the electronic structure in bulk heterojunction solar cells. The presence of band tail states is deduced from the dispersive transport and from the low energy spectral response, which give a consistent values for the slope of the band tail. An approximate density of states distribution is developed by combining data for the band tails, the band edges and the deep states, based on these results along with other information. Measurements show that geminate recombination is not a dominant recombination process in P3HT:PCBM or PCDTBT:PCBM cells. Instead, it is argued that there is good evidence that recombination through interface traps is important.