High-Efficient Cs₂AgBiBr₆ Perovskite Solar Cells with Rare-Earth-Doped Absorber and Front Contact: A Numerical...

This work proposes a simplified HTL-free PSC structure based on Cs₂AgBiBr₆ doped with praseodymium (Pr³⁺). By reducing interfacial layers, this design reduces defect-induced recombination and increases the resistance of the device under environmental stresses (such as temperature, oxygen, and humidity). The performance of the Pr³⁺-doped PSC (Cs₂Ag_0.95Pr_0.05BiBr₆) with both FTO and Tb-FTO as front contacts were investigated using solar capacitance simulation software (SCAPS-1D) version 3.3.10. The FTO-based reference device showed photovoltaic parameters of V_oc = 0.86 V, J_sc = 12.52 mA/cm², FF = 70.13%, and PCE = 7.51%, while the Tb-doped FTO device showed V_oc = 0.86 V, J_sc = 12.67 mA/cm², FF = 72.98%, and PCE = 7.91%. The performance of the device was analyzed based on variation in absorber thickness and defect density, ETL thickness and dopant concentration, band gap, and ETL/absorber interface defect density in the Tb-FTO/TiO₂/Cs₂Ag_0.95Pr_0.05BiBr₆/C to obtain optimal values of 1.0 μm, 10¹³ cm^-2, 0.09 μm, 10²¹ cm^-2, 1.5 eV, and 10⁸ cm^-3. Utilizing these optimized values, the final device predicted a PCE of 19.93%, FF of 84.51%, J_sc of 27.73 mA/cm², and V_oc of 0.85 V. The device was also found to be sensitive to variations in the back-contact work function, ambient temperature, series and shunt resistances. A PCE of ~27.65% was achieved at higher metal work function (e.g., W_F = 5.9 eV for Se), with a corresponding FF of ~82.69%, J_sc of ~27.78 mA/cm², and V_oc of 1.20 V. Therefore, while direct experimental validation for the proposed HTL-free structure is not yet available, the comparison with experimentally demonstrated HTL-containing counterparts provides confidence in the predictive capability of our model. We expect that the present work will serve as a theoretical foundation and motivation for future experimental fabrication and characterization of HTL-free devices.