Transparent Conducting Oxides: Selected Materials for Thin Film Solar Cells

Current photovoltaic technologies, as well as next-generation approaches to PVs, will place specific demands on the transparent contact layers beyond transparency and low resistivity. The mainstay of the transparent conducting oxides used today is based on indium tin oxide because, at present, no other TCO delivers the same performance and versatility. The high cost of In as a raw material and process restraints, however, make this oxide system less attractive for low-cost, high-volume PV applications. Alternative TCO materials, such as ZnO, appear to be promising for some of these applications, but processing and performance issues remain. In many of the novel PV technologies currently under development, such as organic photovoltaics, control of the morphology and surface chemistry of the TCOs used is critical to device per formance. Examination of current and future PV-TCO materials performance leads to the conclusion that new efforts to develop application-specific TCO materials and processes are needed. As new device structures evolve, it will be necessary to expand the toolkit of TCO materials available to take advantage of very different film properties and surface chemistries.