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 V-oc 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. V-oc was found to be the most sensitive photoelectric parameter to surface recombination. The relative effect of surface recombination on V-oc increases with the increase of trap density as well as V-oc becomes more sensitive to the presence of deep traps due to surface recombination. In the presence of surface recombination slope V-oc 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 V-oc vs. light intensity dependences in the presence of trap assisted and surface recombination was outlined. (C) 2015 Elsevier B.V. All rights reserved.