Structure-activity relationship in NIR photosensitizers for transparent Dye-Sensitized Solar Cells

Dye-Sensitized Solar Cells (DSSCs) offer an interesting and sustainable choice for the development of transparent, and even colorless, photovoltaic devices, thanks to their ability to exploit diffuse and low intensity light as well as their wide versatility in dyes, electrolytes and redox couples. Among them, the photosensitizer plays a crucial role in obtaining transparent wavelength-selective NIR-DSSC system [1]. Until now, different families of NIR chromophores have been investigated with relatively low success in terms of transparency to visible light and power conversion efficiency. In this work, thanks to the joint efforts of different research groups within the European IMPRESSIVE project (https://impressive-h2020.eu/), we proposed fully transparent DSSCs based on organic polymethine dyes (e.g. squaraine and cyanine) that can display intense absorption in NIR region close to 900 nm, while negligible in visible region (Figure 1). Power conversion efficiency up to 3% and average visible transmittance (AVT) up to 76%, while reaching a color rendering index (CRI) of 92 [2]. Starting from these results and their structure-activity relationship, innovative strategies on synthesis approach and device optimization should be applied to outperform the obtained values and to design stable and low-cost materials for the implementation in real devices [3].