  Transient photovoltage (TPV) and voltage dependent charge extraction (CE)
measurements were applied to poly(3-hexylthiophene)(P3HT):[6,6]-phenyl-C61
butyric acid methyl ester (PCBM) bulk heterojunction solar cells to analyze the
limitations of solar cell performance in pristine and annealed devices. From
the determined charge carrier decay rate under open circuit conditions and the
voltage dependent charge carrier densities n(V) the nongeminate loss current
jloss of the device is accessible. We found that jloss alone is sufficient to
describe the j-V characteristics across the whole operational range, for
annealed and, not yet shown before, also for the lower performing pristine
solar cells. Even in a temperature range from 300 K to 200 K nongeminate
recombination is found to be the dominant and, therefore, performance limiting
loss process. Consequently, charge photogeneration is voltage independent in
the voltage range studied.
