Improving Charge Separation across a Hybrid Oxide/Polymer Interface by Cs Doping of the Metal Oxide

The process of photoinduced charge carrier separation in hybrid optoelectronics remains only partially understood, with the mechanism behind creation and dissociation of bound charge pairs (BCPs) being open questions. To investigate these processes, we employ the model hybrid ZnO/P3HT system and show that Cs doping of ZnO results in a decrease in the density of gap states at the metal oxide surface and in turn, a reduction in the yield of BCPs. This provides direct experimental evidence for a previously proposed model of BCP creation by electron trapping at the metal oxide surface states. Furthermore, Cs doping is found to substantially increase open circuit voltage in these devices without the negative effects on short circuit current that were observed in studies with other dopants. This offers new possibilities for hybrid photovoltaic devices with increased power conversion efficiencies and provides valuable insights on the charge separation processes in hybrid organic-inorganic photovoltaics.We kindly thank Prof. Annemarie Pucci and Prof. Uwe Bunz for providing access to the AFM and the device fabrication facilities, respectively. A. A. B. is a Royal Society University Research Fellow. P. E. H. and Y. V. thank the Excellence Initiative for funding.This is the author accepted manuscript. The final version is available from Wiley via http://dx.doi.org/10.1002/admi.20150061