Photoelectron spectroscopic study of band alignment of polymer/ZnO photovoltaic device structure

Using x-ray photoelectron spectroscopy, we investigated the band alignment of a Ag/poly (3-hexylthiophene-2,5-diyl) (P3HT)/ZnO photovoltaic structure. At the P3HT/ZnO interface, a band bending of P3HT and a short surface depletion layer of ZnO were observed. The offset between the highest occupied molecular orbital of P3HT and the conduction band minimum of ZnO at the interface contributed to the open circuit voltage (Voc) was estimated to be approximately 1.5 +/- 0.1 eV, which was bigger than that of the electrically measured effective Voc of P3HT/ZnO photovoltaic devices, meaning that the P3HT/ZnO photovoltaic structure has the potential to provide improved photovoltaic properties. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4790298]