Most photovoltaic (PV) technologies are opaque to maximize visible light absorption. However, see-through solar cells open additional perspectives for PV integration. Looking beyond maximizing visible light harvesting, this work considers the human eye photopic response to optimize a selective near-infrared sensitizer based on a polymethine cyanine structure (VG20-C x ) to render dye-sensitized solar cells (DSSCs) fully transparent and colorless. This peculiarity was achieved by conferring to the dye the ability to strongly and sharply absorb beyond 800 nm (S 0 –S 1 transition) while rejecting the upper S 0 –S n contributions far in the blue where the human retina is poorly sensitive. When associated with an aggregation-free anatase TiO 2 photoanode, the selective NIR-DSSC can display 3.1% power conversion efficiency, up to 76% average visible transmittance (AVT), a value approaching the 78% AVT value of a standard double glazing window while reaching a color rendering index (CRI) of 92.1%. The ultrafast and fast charge transfer processes are herein discussed, clarifying the different relaxation channels from the dye monomer excited states and highlighting the limiting steps to provide future directions to enhance the performances of this nonintrusive NIR-DSSC technology.

Dye-sensitized solar cell (DSSC) is one of the promising photovoltaic (PV) technologies for applications requiring high aesthetic features combined with energy production such as building integration PV (BIPV). In this context, DSSCs have the ability to be wavelength selective, thanks to the development of new sensitizers by molecular engineering. The long history of dye research has afforded is technology different colorations for reaching panchromatic light absorption. However, nearly 45% of radiation from sunlight lies in the near-infrared (NIR) region, where human cones are not sensitive. This review provides the reader with key information on how to selectively exploit this region to develop colorless and transparent PV based on DSSC technology. Besides selective NIR absorbers, the triptych photoanode, counter-electrode, and redox mediator are together contributing to reach high aesthetic features. Details of all the components, interplay, and an opinion on the technological limitations to reach colorless and transparent NIR-DSSC are herein discussed in relationship with BIPV applications.