Bifacial dye-sensitized solar cells utilizing green-colored NIR sensitive unsymmetrical squaraine dye

Abstract

Dye-sensitized solar cells (DSSCs) with the capability of photon harvesting from both front and rear sides, consisting of newly developed NIR dye (SQ-140), iodine-based redox electrolyte, and transparent counter electrode with high bifaciality factor (BFF) and good cumulated photoconversion efficiency (PCE), are successfully fabricated and characterized. The use of transparent TiO2-based photoanode leads to improved BFF as compared to its opaque TiO2 counterparts: from 74% to 86% under similar experimental conditions and device parameters. The high molar extinction coefficient of the NIR dye SQ-140, needing a thinner TiO2 layer, was found to be advantageous to maintaining the high BFF even in thicker TiO2 films without serious compromise in the PCE. The lower efficiency of the bifacial DSSC under rear illumination was attributed to the hampered optical penetration as well as absorption of light by the intense colored iodine-based redox electrolyte.