Abstract
As the world's population and industrial sector rapidly expand, the demand for energy is rising. Solar cells can address both global energy and environmental needs. With the aim to enhance dye-sensitized solar cell (DSSC) efficiency, we designed four metal-free biphenylamine- and triphenylamine-based dyes (RK2-RK5) based on the reference dye RK1, increasing the donor strength (substituting different groups such as biphenylamine and triphenylamine into the donor side of the dye) as such dyes improved DSSC power conversion efficiency. Density functional theory (DFT) was applied at the B3LYP/6-31G** level to calculate the ground-state (S(0)) optimized geometries of RK1-RK5. Time-dependent DFT was used to compute the absorption spectra, utilizing four functionals (B3LYP, CAM-B3LYP, PBE1PBE and BHandHLYP), in the gas phase and in solvents such as dichloromethane and ethanol. Comprehensive analysis of RK1-RK5 as well as dyes@TiO(2) was performed, and light was shed on the optoelectronic properties. Frontier molecular orbitals' charge density distribution revealed the sensitizers' intramolecular charge transfer from the donor to the acceptor unit. After adsorption of the dyes on TiO(2), charge transfer was seen from sensitizer to the TiO(2) semiconductor's surface in dyes@TiO(2). Adsorption of the dyes on the TiO(2) cluster would be stable, as revealed by the dyes@TiO(2) cluster's negative binding energy. Additionally, it was found that the presence of two donor groups raises the electronic coupling and electron injection constants in RK4 and RK5, indicating that the charge injection in these newly designed dyes would be superior. As a result, the DSSC efficiency in the newly designed derivatives has been improved to 8.05% for RK5 by substituting the triphenylamine unit at the R1 and R2 positions in the parent compound. These well established correlations between structure-property relationships and performance provide profound insight into how improving the donor moiety strength in organic sensitizers affects device performance. It boosted photovoltaic performance through enhanced short-circuit current density and light-harvesting efficiency. For high efficiency in DSSCs, this can provide a useful rational molecular design strategy for D-π-A organic sensitizers.