Optimization Study of Single Junction Structures Utilizing 1.12 eV Cs<sub>2</sub>AuBiCl<sub>6</sub> Double Perovskite: A Lead-Free Inorganic Absorber for Single and Tandem Solar Cell Applications

This study investigates the modeling and optimization of a single solar cell structure, utilizing the inorganic double perovskite Cs₂AuBiCl₆. This material features an A₂BB'X₆ composition and possesses a bandgap energy of 1.12 eV. The fundamental structure of the solar cell has been described, and the physical parameters of its primary layers have been outlined. A simulation model was developed to calculate the current-voltage characteristics and photovoltaic parameters, taking into account recombination rates due to defects within the absorber and at the interfaces with the electron transport layer (ETL) and hole transport layer (HTL). The influence of various parameters was analyzed, including bulk and interface density of defects, layer thicknesses, back contact work function and operating temperature. Additionally, the performance of structures with alternative transport materials for the ETL and HTL layers was evaluated. The impact of energy bandgap offsets with the absorbing perovskite layer was considered to identify materials that enhance the collection of photogenerated carriers and ultimately improve efficiency. The simulations revealed an optimized structure that demonstrated enhanced performance compared to the initial design. The optimized solar cell achieved a yield of 18.4 %, representing an increase of 5.4 % over the basic structure, with key performance metrics including, short-circuit current density Jsc = 36.75 mA/cm², fill factor FF = 76.76 %, open-circuit voltage V oc = 0.5879 V. Given its narrow bandgap value, the optimized structure was further examined in a tandem cell configuration, showcasing its potential for high-efficiency devices with a yield reaching 33 %. This work significantly contributes to the development of efficient, stable, and non-toxic perovskite solar cells for photovoltaic applications, paving the way for advancements in sustainable energy technologies.