Cosensitization in Dye-Sensitized Solar Cells

Dye-sensitized solar cells (DSCs) are a next-generation photovoltaic technology, whose natural transparency and good photovoltaic output under ambient light conditions afford them niche applications in solar-powered windows and interior design for energy-sustainable buildings. Their ability to be fabricated on flexible substrates, or as fibers, also makes them attractive as passive energy harvesters in wearable devices and textiles. Cosensitization has emerged as a method that affords efficiency gains in DSCs, being most celebrated via its role in nudging power conversion efficiencies of DSCs to reach world-record values; yet, cosensitization has a much wider potential for applications, as this review will show. Cosensitization is a chemical fabrication method that produces DSC working electrodes that contain two or more different dyes with complementary optical absorption characteristics. Dye combinations that collectively afford a panchromatic absorption spectrum emulating that of the solar emission spectrum are ideal, given that such combinations use all available sunlight. This review classifies existing cosensitization efforts into seven distinct ways that dyes have been combined in order to generate panchromatic DSCs. Seven cognate molecular-engineering strategies for cosensitization are thereby developed, which tailor optical absorption toward optimal DSC-device function.