Light dependent open-circuit voltage of organic bulk heterojunction solar cells in the presence of surface recombination

An analytical model for the light intensity dependence of open circuit voltage Voc in the presence of bimolecular, trap assisted and surface recombination mechanisms was proposed. The model quantitatively explains reported experimental deviations from the bimolecular and bimolecular/trap assisted recombination models.Voc was found to be the most sensitive photoelectric parameter to surface recombination. The relative effect of surface recombination on Voc increases with the increase of trap density as well as Voc becomes more sensitive to the presence of deep traps due to surface recombination. In the presence of surface recombination slope Voc vs. light intensity A does not reach value of 2.0 kT/q even at very high density of traps.Also a possible misinterpretation of the experimental Voc vs. light intensity dependences in the presence of trap assisted and surface recombination was outlined.