The appearance of Ti~(3+) states in solution-processed TiO_x buffer layers in inverted organic photovoltaics

摘要

We study the low-temperature solution processed TiO_x films and device structures using core level and valence X-ray photoelectron spectroscopy (XPS) and electronic structure calculations. We are able to correlate the fraction of Ti~(3+) present as obtained from Ti 2p core level XPS with the intensity of the defect states that appear within the band gap as observed with our valence XPS. Constructing an operating inverted organic photovoltaic (OPV) using the TiO_x film as an electron selective contact may increase the fraction of Ti~(3+) present. We provide evidence that the number of charge carriers in TiO_x can be significantly varied and this might influence the performance of inverted OPVs.