Dye-sensitized solar cell performance improvement by dye-solvent polarity and redox mediator potential alignment

Abstract

Maximizing dye-adsorption onto semiconductor surface is critical to improve dye@ZnTiO3 n-type dye-sensitized solar cell (n-DSSC) performance. Polarity of solvent, used in loading merocyanine dye (MC-540) onto ZnTiO3 film electrode, is investigated here for the first time. With higher dye-adsorption energy (-37.1792 eV), the highly-polar water solvent yields an MC-540@ZnTiO3-based DSSC with higher cell performance, compared to organic solvents ethyl alcohol, acetone and diethyl ether, using iodide/iodine redox couple. This is evidenced by Time-Dependent Density-Functional Theory (TD-DFT). The least polar diethyl ether solvent shows a turbulent behavior at the MC-540@ZnTiO3 interface, with low absorbance (0.072 at 540 nm), and low adsorption energy −0.7952 eV (-18.3390 kcal/mol). The simulations are confirmed by experimental spectral results and photo-current density vs. potential (J-V) characteristics, where diethyl ether exhibits immeasurably low photo-current, let alone other technical difficulties due to high volatility. Among the various solvents, water exhibits highest short-circuit photocurrent density (0.075 mA/cm−2), open circuit potential (0.150 V), fill factor (0.363) and conversion efficiency (0.04%). Potential diagrams for the MC-540@ZnTiO3 interface in dark and under illumination are described. Simulation and experimental results combined dictate using the environmentally friendly highly polar water solvent over organic dyes in manufacturing MC-540@ZnTiO3-based DSSCs.