Squaraine dyes for organic photovoltaic cells

Recently, squaraine (SQ) dyes used as donor materials in organic photovoltaic (OPV) cells have received increasing attention because of their simple synthetic routes, high absorption coefficients with tunable bandgaps and bandwidths in the visible-near infrared region, as well as high photochemical and thermal stabilities. Using fullerenes or their derivatives as electron accepting materials, SQ: fullerene-based OPV devices have shown power conversion efficiencies as high as over 8%, which indicates the potential of SQ dyes for future solar cell applications. In this review, we briefly introduce the history of this group of materials, and present recent advances in SQ dye materials and their applications to OPV cells, including the major methodologies employed to exploit the full potential of these molecules as light harvesting materials in OPV devices. From the perspective of the current status of this field, we provide an overview of the primary issues affecting future development of OPV, as well as possible solutions.