Delving into the Role of a Conjugated Rhodanine Acceptor in D–D′–A Dyes for Photovoltaic Applications

Dye-sensitized solar cells have arisen as economical substitutes for traditional photovoltaics with dye design being crucial in enhancing device efficiency. In this context, novel D–D′–A dyes were developed and characterized by using conventional methods. These dyes feature an N-aryl-substituted imidazole as the primary donor, an alkylated phenothiazine as the auxiliary donor, and rhodanine derivatives as the acceptor. Spectroscopic studies demonstrated that the rhodanine acceptors facilitate intramolecular charge transfer transitions, leading to strong visible-light absorption associated with a high-molar-absorption coefficient. Time-resolved fluorescence decay measurements demonstrated that the dyes display excited-state lifetimes within the nanosecond time scale, allowing sufficient time for effective electron injection into the conduction band of TiO2. Moreover, computational and electrochemical studies demonstrated that the energy levels of rhodanine-based dyes were well aligned for efficient electron injection as well as effective dye regeneration. Notably, the dye tethered with a conjugated rhodanine acceptor achieved a power conversion efficiency of 6.96 ± 0.26%, comparable to the benchmark N719 dye, due to its high short-circuit current density (JSC) and open-circuit voltage (VOC). In contrast, a dye bearing a rhodanine-3-acetic acid relying on through-space charge transfer experienced a significant recombination loss, resulting in a much lower power conversion efficiency of 0.26 ± 0.06%. The enhanced power conversion efficiency of conjugated rhodanine is attributed to its excellent charge transport properties and resistance to recombination. These findings highlight the role of the conjugated rhodanine acceptor in improving DSSC efficiency and interfacial charge dynamics, marking it as a promising candidate for photovoltaic applications.