Résumé
Nowadays, most photovoltaic (PV) technologies absorb the visible domain of the light spectrum. As a consequence, these devices are not transparent or at least semi-transparent. In this contest, far-red/near infra-red (NIR) light is indubitably interesting to widen solar harvesting corresponding to 25% of overall solar light available on earth’s surface. The photoconversion efficiency expected by the exploitation of these frequencies (700-1000 nm) is lower with respect to the visible region, but, far red-NIR sensitizers allow to tune the colors of final devices from blue to green, or even to colorless. Transparent cells without any coloration would allow the visible light to pass through unhampered reaching a fully integration of PV devices in building-integrated applications (BIPV).The photosensitizer has a crucial role in a NIR-DSSC system. Different families of NIR chromophores have been investigated for applications in DSSCs with relatively low success in terms of transparency and power conversion efficiency. At present, NIR-based DSSCs exhibited at best 2.3% PCE with very thick electrodes sensitized with a cyanine dye absorbing at 805 nm. [2]. Our research group developed several squaraine dyes for DSSC absorbing in the NIR region.Recently a few series of new efficient all organic polymethine sensitizers based on squaraine [5], cyanine and croconine moieties with a shifted absorption as high as 830 nm have been synthesized and fully characterized. DSSCs based on these new efficient sensitizers are able to convert up to 36% IPCE until 850 nm. Their light-to-electricity performances have been optimized by using highly diluted dye solution to promote the formation of a free self-assembled monolayer.