Charge separation at metal-oxide/organic hybrid photovoltaic devices is studied with prototypical model systems comprised of a planar interface between a metal-oxide and the polymer poly(3-hexylthiophene) (P3HT). The comparison of ZnO, SnO2, and (Zn,Mg)O alloys as electron acceptor allows us to get insight into the underlying processes of charge separation and recombination at the heterointerfaces.
It is established that prior to the generation of free charges, a hybrid charge transfer state (HCTS) between an electron in the oxide’s conduction band and a hole in the P3HT HOMO is formed. The dissociated HCTS yields the free carriers of the photocurrent .
The competing processes of dissociation and recombination at the hybrid interface are investigated by complementary temperature-dependent photovoltaic measurements and electroluminescence spectroscopy in the near IR spectral range where radiative recombination of the HCTS is observed .
HCTS recombination can be identified as the fundamental energy loss mechanism reducing the VOC and thus limiting the device performance. Based on this finding, a strategy is proposed to reduce these losses in order to fully exploit the potential of hybrid interfaces in solar energy conversion.
 M. Eyer et. al. Appl. Phys. Lett. 107, 221602 (2015).  M. Eyer et. al. (2017), submitted.