The impact of anchoring groups on the efficiency of dye-sensitized solar cells: 2-Cyanoacrylic acid vs. ethyl 2-cyanoacrylate

Abstract

Due to their promising performance, coumarin-based dyes have been widely used in third-generation dye-sensitized solar cells (DSSCs) and as nonlinear optical (NLO) materials. In this study, we have designed and synthesized coumarin-based sensitizers in conjugation with common phenyl as a π-linker and ethyl-2-cyanoacrylate (SPDSSC 7) and 2-cyanoacrylic acid (SPDSSC 8) as an anchor and determined their DSSC performance. Photovoltaic results showed that 2-cyanoacrylic acid-based sensitizer (SPDSSC 8) performed better than ethyl-2-cyanoacrylate-based sensitizer (SPDSSC 7) which improves with a thicker coating of TiO2. Density functional theory (DFT) results showed an inverse relationship between band-gap (BG) and chemical potential and electrophilicity index but a direct relationship between BG and hardness and hyperhardness. Time dependent-DFT (TD-DFT) showed a similar trend as observed in the experiment. It was also found that first-order hyperpolarizability (β0) and second-order hyperpolarizability (γ) and PCE is related directly through CT properties. Furthermore, calculations of sensitizers@TiO2 revealed that sensitizer with ethyl-2-cyanoacrylate was linked as unidentate and 2-cyanoacrylic acid linked bidentatly to TiO2 clusters. Furthermore, quantitative analysis of the HOMO-LUMO and MEP plots revealed that SPDSSC 8 showed more efficient electron transfer from the sensitizer to the TiO2 cluster than SPDSSC 7. These results were consistent with the calculated Eadsorption for both sensitizers. The monodentate binding of SPDSSC 7 to TiO2 results in inferior charge transfer in the semiconductor’s conduction band, ultimately negatively impacting DSSC performance.