Thiazolo[5,4-d]thiazole-based organic sensitizers with strong visible light absorption for transparent, efficient and stable dye-sensitized solar cells

A small set of thiazolo[5,4-d]thiazole-based D-π-A organic dyes, endowed with bis-pentylpropylenedioxythiophene (ProDOT) moieties in the π-spacer, was designed with the aid of computational analysis, synthesized and characterized. The presence of bulky and electronrich ProDOT groups beside the electronpoor thiazolothiazole unit induced optimal physico-chemical properties, including broad and intense visible light absorption. As a consequence, the dyes resulted particularly suitable for application in thin layer dye-sensitized solar cells (TiO2 thickness: 3.0-6.5 µm). Small-scale (0.25 cm2) devices prepared using standard materials and fabrication techniques gave power conversion efficiencies up to 7.71%, surpassing those obtained with two different reference dyes. Transparent larger area cells (3.6 cm2) also showed good η values up to 6.35%, not requiring the use of a co-adsorbent, and retained their initial efficiency over a period of 1000 h storage at 85°C. These results make this new family of organic sensitizers promising candidates for successful application in the production of efficient and stable transparent DSSCs for building-integrated photovoltaics.