Design, Synthesis and Application of Imidazole-Based Organic Dyes in Dye Sensitized Solar Cells
Metal-free D–D–π–A type dyes (i.e., Car-Cy, Car-Rh, Dpa-Cy, and Dpa-Rh ) were designed and synthesized for dye-sensitized solar cells (DSSCs). In the structure of the sensitized dyes, an imidazole ring is connected to a carbazole or diphenylamine moiety as a donor while cyanoacetic acid or rhodanine-3-acetic acid was introduced as an acceptor/anchor. The molecular structures of D–D–π–A type dyes were characterized using IR, NMR and MS spectral data. The optical, electrochemical, theoretical, light harvesting property, HOMO/LUMO levels, redox behavior, and photovoltaic properties of the synthesized dyes were evaluated. Among the fabricated photovoltaic devices based on the prepared dye, Dpa-Cy dye containing diphenylamine as a donor and cyanoacetic acid as an acceptor exhibited a high-power conversion efficiency of 1.70% with a short-circuit current density ( J SC ) of 4.48 mA cm −2 , an open-circuit photovoltage ( V OC ) of 0.53 V and a fill factor of 72% under AM1.5 illumination (85 mW cm −2 ) in comparison with other dyes. Plane-wave calculations indicate that the dye binds reasonably strongly to the TiO 2 surface, and the generated DOS picture shows an overlap of the molecular orbitals of the dye and the TiO 2 bands. We conclude that the dyes have a promising role as sensitizers in DSSCs.