Enhanced Photovoltaic Performance of CdSe Quantum Dot-Sensitized Solar Cells Utilizing Sm–Eu Co-Doped TiO2 Photoanodes

In this study, titanium dioxide (TiO ${}_{{2}}\text {)}$ nanoparticles co-doped with varying ratios of Eu and Sm were synthesized using a hydrothermal method. The energy bandgap ( ${E}_{\text {g}}\text {)}$ and conduction band minimum (CBM) of TiO₂ nanoparticles doped with 0.45 at% Sm@0.1 at% Eu were adjusted from 3.43 and −3.95 eV to 3.30 and −3.53 eV, respectively, determined from ultraviolet–visible (UV–Vis) absorption spectroscopy and ultraviolet photoelectron spectroscopy (UPS) measurements compared to undoped TiO₂. CdSe quantum dot-sensitized solar cells (QDSCs) based on TiO₂ doped with 0.45 at% Sm@0.1 at% Eu achieved an optimal power conversion efficiency (PCE) of 4.37%. Electrochemical impedance spectroscopy (EIS) revealed that the decrease in chemical capacitance ( ${\textit C}_{\mu }\text {)}$ and the increase in recombination resistance ( ${\textit R}_{\text {rec}}\text {)}$ of QDSCs based on 0.45 at% Sm@0.1 at% Eu-doped TiO₂ photoanodes facilitate charge extraction and suppress charge recombination at the TiO₂/electrolyte (EL) interface compared to undoped one.