Transient measurements of carrier relaxation time and density in the P3HT:PCBM organic photovoltaic cell

Abstract

The authors have used transient photovoltage measurements to evaluate carrier relaxation times (τ) in P3HT:PCBM based photocells over a wide range of open circuit voltages. Satisfactory agreement is found with data obtained by low frequency impedance measurements. The authors find the differential capacitance measurements yield data consistent with the theoretical value expected based on Langevin recombination. The Langevin coefficient is three orders of magnitude smaller than the theoretical one. For the low light levels, the relaxation time variation is determined by the RC time constant behavior of the photodiode.