SYNTHESIS AND CHARACTERIZATION OF NEAR INFRARED DYES FOR COLORLESS DYE SENSITIZED SOLAR CELLS

Transparent photovoltaics (TPV) is an emerging and disruptive technology in which the solar cells selectively transmit the visible light to human eyes harvesting UV and/or NIR photons. TPV is attractive as it widens the deployment of PV into new sectors, like building integrated photovoltaics (BIPV), greenhouses, car windows and sunglasses, thus providing an immense potential to generate solar electricity beyond the conventional rooftops and solar power plants. One possible approach to TPV is based on wavelength-selective absorbers where the dye requires an absorption far from the photopic response of the human eye. Limited classes of dyes possess energetic levels that can ensure an efficient injection while having a bandgap sufficiently narrow to selectively absorb the NIR region. Among these classes, cyanine dyes are promising for their high molar extinction coefficient and easily tunable properties through modification of central core or lateral units and have already been investigated for dye sensitized solar cell (DSSC) devices with promising results in terms of transparency and performance. Fully transparent and colorless DSSC were built reaching 80% transmittance in complete devices.3 The aim of the present work was the development of a library of NIR dyes in order to increase the device’s efficiency and stability without losing transparency. The synthesis of new series of NIR cyanines dyes have been performed in a one or two-step reaction. A simple crystallization of the crude products yielded very low cost and industrially scalable products. These new sensitizers have been deeply characterized in terms of their optical, photophysical and electrochemical properties, showing interesting structure/property relationships. Finally, photovoltaic performances have been evaluated in lab-scale DSSCs and optimized by different anode modifications and electrolyte formulations.