A Strategy To Boost the Efficiency of Rhodanine Electron Acceptor for Organic Dye: From Nonconjugation to Conjugation

Rhodanine-3-acetic acid is a very important and common electron acceptor of organic dye for dye-sensitized solar cells (DSSCs). However, the photovoltaic performances of organic dyes with rhodanine-3-acetic acid are relatively poor in the great majority of cases due to its nonconjugated structure between rhodanine ring and carboxyl anchoring group. Herein, a rhodanine derivative with conjugated structure between rhodanine ring and anchoring group is first employed as electron acceptor for TiO₂-based DSSCs. Organic dye with this conjugated electron acceptor can not only maintain wide absorption spectrum but also greatly improve the electronic structure and adsorption geometry on TiO₂, which significantly enhances the electron injection and slows the charge recombination. So the power conversion efficiency of DSSC based on organic dye CRD-I with this conjugated electron acceptor is increased by 2 times as compared with DSSC based on organic dye RD-I with nonconjugated rhodanine-3-acetic acid. Moreover, it is also found that CRD-I is superior to RD-I with respect to DSSC stability and binding ability to TiO₂. This work unambiguously demonstrates that the conjugated rhodanine derivative is a highly promising electron acceptor and provides a new strategy for high-efficiency rhodanine-based organic dyes in DSSCs.