Layer-by-Layer Assembled Multilayer Tiox for Efficient Electron Acceptor in Polymer Hybrid Solar Cells

We demonstrate that TiOx nanocomposite films fabricated using electrostatic layer-by-layer (LbL) assembly improve the power conversion efficiency of photovoltaic cells compared to conventional TiOx films fabricated via the sal-gel process. For this study, titanium precursor/poly(allylamine hydrochloride) (PAH) multilayer films were rirst deposited onto indium tin oxide-coated glass to produce TiOx nanocomposites (TiOx NC). The specific effect a the LbL., processed TiOx on photovoltaic performance was investigated using the planar bilayer TiOxNC and highly regioregular poly(3-hexylthiophene) (P3HT) solar cells, and the P3HT/LbL TiOx NC solar cells showed a dramatic increase in power efficiency, particularly in terms of the short current density and fill factor. The improved efficiency of this device is mainly due to the difference in the chemical composition of the LbL TiOxNC films, including the much higher Ti3+/Ti4+ ratio and the highly reactive facets of crystals as demonstrated by XPS and XRD measurement, thus enhancing the electron transfer between electron donors and acceptors. In addition, the grazing incidence wide-angle X-ray scattering (GIWAXS) study revealed the presence of more highly oriented P3HT stacks parallel to the substrate on the LbL. Tio(x)NC film compared to those on the sal-gel TiOx films, possibly influencing the hole mobility of P3HT and the energy transfer near and at the interface between the P3HT and TiOx layers. The results of this study demonstrate that this approach is it promising one for the design of hybrid solar cells with improved efficiency.