  We investigated the influence of oxygen on the performance of P3HT:PCBM
(poly(3-hexylthiophene):[6,6]-phenyl C61 butyric acid methyl ester) solar cells
by current--voltage, thermally stimulated current (TSC) and charge extraction
by linearly increasing voltage (CELIV) measurement techniques. The exposure to
oxygen leads to an enhanced charge carrier concentration and a decreased charge
carrier mobility. Further, an enhanced formation of deeper traps was observed,
although the overall density of traps was found to be unaffected upon oxygen
exposure. With the aid of macroscopic simulations, based on solving the
differential equation system of Poisson, continuity and drift-diffusion
equations in one dimension, we demonstrate the influence of a reduced charge
carrier mobility and an increased charge carrier density on the main solar cell
parameters, consistent with experimental findings.
