Rare-earth-doped TiO₂ photoanode DSSCs for indoor photovoltaics: a comparative study

This work focuses on using rare-earth (RE) elements to titanium dioxide (TiO₂) to fabricate effective photoanodes for dye-sensitized solar cells (DSSC) designed for indoor applications. Using a straightforward solid-state hand-grinding technique, different RE elements, including Nd⁺³, Sm⁺⁴, Er⁺³, and Yb⁺³ were used as dopants in TiO₂. The impact of RE-doping on TiO₂ bandgap engineering and device performance was thoroughly investigated. Enhanced photophysical properties of RE-doped TiO₂ were unveiled through several characterization methods such as ultraviolet photoelectron spectroscopy (UPS), photoluminescence (PL) analysis, X-ray diffraction (XRD), and UV–visible absorption. These results led to the construction of DSSCs with RE-doped TiO₂ that showed better photoconversion efficiency (PCE) than pristine TiO₂ under household light sources such as white LED and CFL lamps with 1000 lux and 300 lux illuminance levels, respectively. Among them, Er⁺³-doped TiO₂ exhibited the highest PCE. The PCE values were 6.7% under A.M1.5G light, 11.6% under LED light, and 7.9% under CFL light. External quantum efficiency (EQE) spectrum responses were in favor of enhanced PCE with RE-doped TiO₂. Rapid electron injection from dye molecules to the conduction band (CB) of Er-doped TiO₂ was observed by time-resolved photoluminescence (TRPL) analysis. Moreover, Er-doped TiO₂-based DSSCs have reduced interfacial resistances, according to electrochemical impedance spectroscopy (EIS) tests. When the doped TiO₂ photoanode was compared to other doped photoanodes, the optimal stoichiometry of Er (0.4%) showed greater PCE with enhanced current density (J_sc). The outcomes highlight the possibility of using rare-earth-doped TiO₂ as a material to improve the efficiency of DSSCs that rely on indoor light.