Order of decay of mobile charge carriers in P3HT:PCBM solar cells

The charge carrier dynamics of organic solar cells are strongly influenced by trapping and allow to draw conclusions on the loss mechanisms limiting the photovoltaic performance. In this study, we derive the recombination order Δ of mobile charge carriers. For annealed P3HT:PCBM solar cells, it allows us to pinpoint the dominant recombination of mobile with trapped charge carriers in tail states. While the characteristic tail state energy of about 40 meV rises to about 100 meV for 30 h oxygen exposure under illumination, Δ decreases only weakly from 1.70 to 1.62. This corresponds to a slight shift towards trap-assisted recombination.