Preparation and Characterization of Squaraine Dyes containing Mono- and Bis-Anchoring Groups as the Light Absorber in Dye Sensitized Solar Cells

Abstract

Enhancing the charge transfer rate in dye sensitized solar cells (DSSCs) is one of the most important criteria determining the cell efficiency. This paper reports a novel strategy for enhancing charge transfer between squaraine dyes and TiO2 by increasing the anchoring number. Symmetrical (SSQ) and unsymmetrical squaraine (USQ) sensitizers with different numbers of anchoring groups in their chromophores are synthesized. SSQ dye containing a bis-anchoring group shows better electronic coupling with TiO2 than the USQ dye with a mono-bridge. This enhanced electronic coupling leads SSQ to exhibit better photovoltaic performance, though smaller amounts of SSQ dye is loaded on the TiO2 than the USQ dye. Under standard global AM 1.5 solar conditions, the optimized SSQ-sensitized solar cells show 7.76mAcm−2 of short-circuit photocurrent density, 0.62V of open-circuit voltage, and 0.65 of fill factor (FF), to give overall conversion efficiency of 3.20%, which is approximately 25% higher than the USQ-sensitized solar cells.