Optical Bandgap Tuning and Solar Cell Efficiency Enhancement in Green‐Synthesized Transition Metal‐Doped TiO ₂ Solar Cells

The present study investigates the optical bandgap tuning and solar cell performance of pollution‐free, green‐synthesized titanium dioxide (TiO 2 ) nanoparticles. Transition metal doping with copper, silver, gold, and platinum is explored to enhance TiO 2 ‐based solar cells. Plant extracts of coriander, spearmint, and fenugreek are used for synthesizing the doped TiO 2 nanopowders. X‐ray diffraction confirms successful incorporation of transition metals into the TiO 2 lattice, while scanning electron microscopy shows uniform particle distribution. The optical bandgap decreases upon metal doping, with Cu‐doped TiO 2 showing the maximum reduction to 2.21 eV. Solar cell performance is evaluated through J – V measurements. Among all dopants, Au‐doped TiO 2 exhibits the best results, with a short‐circuit current density ( J sc ) of 18.47 mA cm −2 and an efficiency of 13.65%. In comparison, Cu‐, Ag‐, and Pt‐doped TiO 2 samples showed efficiencies of 6.87%, 8.42%, and 12.23%, respectively. The enhanced performance is attributed to improved charge carrier separation due to doping, and in the case of Au‐doped TiO 2 , plasmonic effects that boost light absorption and charge transport. This study highlights the importance of selecting appropriate transition metal dopants to optimize TiO 2 for next‐generation photovoltaic applications.