Dye-sensitized solar cells (DSSCs), environmentally sustainable devices of cost-effective and added functionality - such as flexibility, aesthetics, and lightweight- have attracted the attention of scientists as an alternative to traditional solar cells. The critical component of DSSC is the sensitizer, which is vital to achieving high photovoltaic performance and has now demonstrated 14.3% efficiency. Herein, in search of novel efficient metal-free organic sensitizers, two series of dyes have been designed based on the experimentally tested Ws-9 dye (fill factor (FF) of 0.71, open-cerciut voltage (V_OC) of 702 mV, short-circuit current (J_SC) of 18.15 mA/cm², and power conversion efficiency (PCE) of 9.02%). Each series has a distinct configuration D-A*-π-A and D-D*-π-A with a wide range of composite donors (D) and fixed π-A units. Hence, a large variety of novel dyes (25 dyes) has been designed to modify/reinforce the electron-donating ability of the donor unit. The geometrical, optical, and electronic properties, besides reorganization energies, vertical/adiabatic ionization/electron affinity energies, non-linear optical properties, and electrochemical properties have been studied using density functional theory (DFT) applying B3LYP/6-31+G(d,p) and time-dependent DFT method applying CAM/ B3LYP/6-31+G(d,p) along with the Conductor-like Polarizable Continuum Model (CPCM) to mimic the solvent effect (dichloromethane). The study extended to investigate the adsorbed dyes on the TiO₂ clusters by calculating adsorption energies and analyzing UV/vis spectra. In addition, the study was concluded by drawing a quantitative relationship between the electron-donating power- represented by the ionization energies of each donating unit- and different calculated parameters. The properties of the parent dye have been improved significantly, and the designed dyes are expected to be more promising sensitizers in DSSC applications.

Nuha Wazzan

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