Flexible ITO-Free Polymer Solar Cells

Indium tin oxide (ITO) is the material-of-choice for transparent conductors in any optoelectronic application. However, scarce resources of indium and high market demand of ITO have created large price fluctuations and future supply concerns. In polymer solar cells (PSCs), ITO is the single-most cost driving factor due to expensive raw materials and processing. Given the limited lifetime and stability of PSCs as compared with other mature technologies such as silicon-based solar cells, the technological future of PSCs beyond that of academic interests rests in reducing cost of production. In this regard, replacing ITO has the potential to dramatically reduce material and processing cost and the energy payback time of PSCs. Several alternatives to ITO are present but not all of them bring competitive advantage over ITO for application in PSCs. This review explores some potentially low-cost alternatives to ITO suitable for use in PSCs. These alternatives belong to four material groups: polymers; metal and polymer composites; metal nanowires and ultra-thin metal films; and carbon nanotubes and graphene. We further present the progress of employing these alternatives in PSCs and identify future challenges. (C) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 129: 1-14, 2013