Defect engineered (Er3+/Nd3+) codoped TiO2 photoanodes for enhanced photoelectrochemical and photovoltaic applications

Abstract

Herein, we describe an efficient way to engineer the electronic energy defects and achieve the defect passivation of codoping of two rare-earth (RE) ions, namely, neodymium (Nd³⁺) and erbium (Er³⁺), into the TiO₂ lattice. It is shown that the PEC performance is significantly improved using the RE-coated TiO₂ photoanode. X-Ray diffraction (XRD), transmission electron microscopy (TEM), and Raman study have confirmed the doping concentration's upper limit without modifying the single-phase structure of the TiO₂ lattice. The Brunauer–Emmett–Teller (BET) study established the optimal codoping composition of “Er_0.003Nd_0.001Ti_0.996O₂” with enriched surface properties. Photoluminescence (PL) investigations indicated defect passivation, which enabled a favourable energy landscape via intermediate trap-sites, improving charge transport characteristics. The photoelectrochemical (PEC) device with the optimized codoped TiO₂ photoanode has a higher increased photocurrent density (J_ph) of 16 μA cm⁻² in comparison to the device with pristine TiO₂ (J_ph: 7 μA cm⁻²). As a proof of concept, a simple sensitization of these engineered TiO₂ photoanodes with the cadmium sulfide (CdS) quantum dots resulted in a J_ph of 2.8 mA cm⁻², and with N719 ruthenium dye, a J_ph of 0.8 mA cm⁻² was obtained, indicating the improved performance of sensitized codoped TiO₂ photoanodes for PEC devices. As a proof of concept, N719 dye-based dye-sensitized solar cells with doped TiO₂ photoanodes demonstrated an enhanced power conversion efficiency.