Enhanced efficiency of CsPbIBr₂ perovskite solar cells through dual-layer ETL engineering

By incorporating 4% Nb doping and using bilayer electron transport layers (ETLs) consisting of titanium dioxide (TiO₂), pure tungsten trioxide (WO₃), and Nb-WO₃, significant enhancements were achieved in the structural, optoelectronic, and photovoltaic properties of CsPbIBr₂ perovskite films. The perovskite film was analyzed using X-ray diffraction (XRD), revealing an increase in crystal size from 26.6 nm to 71.8 nm and a decrease in lattice constant from 6.010 Å to 5.982 Å after the addition of Nb doping. These data indicate an improvement in the degree of crystalline structure of the film. The light absorption efficiency increased when the energy band gap of pure and Nb-CsPbIBr₂ fell from 2.021 eV to 1.955 eV, respectively. The refractive index of pure and Nb-CsPbIBr₂ increased from 2.618 to 2.640, respectively, leading to improved light trapping and absorption. The XRD analysis of the WO₃ ETLs revealed a monoclinic crystal structure with a higher lattice constant, which enhances the transport of charge carriers. Raman spectroscopy verifies the structural soundness of Nb-WO₃. The UV-Vis absorption spectra show that Nb-WO₃ has more absorption in the visible region and a larger bandgap compared to Nb-doped CsPbIBr₂. Photoluminescence spectroscopy reveals emission peaks that are indicative of flaws, which are essential for enhancing the efficiency of Nb-WO₃. The J-V tests demonstrated a significant enhancement in the efficiency of perovskite solar cells when double ETLs were included. This gain was evident in the increased fill factor (FF) range of 0.839–0.865 and open-circuit voltage (V_oc) range of 1.064–1.073. Consequently, the overall efficiency rose from 9.81% to 10.85%.