In this groundbreaking study, we unveil the remarkable structural, electronic, and optical Properties of the newly discovered double perovskite material, K₂AgBiI₆, presenting a paradigm shift in materials science. The unique crystal structure and diverse atomic interactions inherent in this double perovskite make it an up-and-coming candidate for various technological applications, particularly in photovoltaics; owing to its stability and resistance to heat and humidity, we aim to shed light on the extraordinary potential of K₂AgBiI₆. Our study provides valuable insights for researchers engaged in tailored material design. We anticipate that the exceptional electronic properties of K₂AgBiI₆ will not only redefine the boundaries of materials engineering but also catalyze unprecedented advances in sustainable technology. Employing the powerful computational tool CASTEP, we conducted detailed electronic structure calculations within the framework of Density Functional Theory (DFT) to unravel the electronic properties of the double perovskite K₂AgBiI₆. Our investigation thoroughly explored structural properties, band structure, total density of states (DOS), and partial density of states (PDOS). Furthermore, we systematically examined the influence of different exchange-correlation functionals, including LDA, GGA, and m-GGA, on the electronic and optical features of the material by presenting a comparative analysis of these approximations.

Tandem solar cells have a wider photon absorption range, allowing them to provide better efficiency than single-junction SC. The upper cell absorbs high-energy photons, while the lower cell absorbs low-energy filtered photons. However, in order to obtain affordable, efficient, and long-lasting SC, the absorber layers of the top and bottom cells must be integrated with an adequate bandgap. This research suggests tandem perovskite solar cells as upper band active materials in this setting. The Si homojunction solar cell's performance was improved by investigating the thicknesses of the p−type and n−type layers, doping concentrations, and defect densities. The thickness variation of the perovskite solar cell (100−400nm) is then optimized. To precisely replicate the tandem devices, the estimated spectra of the perovskite SC are optically filtered onto the lower cells. Current matching was achieved by adjusting the thickness of the perovskite sub-cell with different bottom layer thicknesses, and the optimized efficiency of 36.26% for the perovskite/Si tandem device was shown. The discoveries will open the door for the upcoming creation of high−efficiency, low-energy solar cells.