Unleashing the Potential of All-Perovskite Tandem Solar Cell Structures: A Hybrid DFT and Numerical Simulation Insights

The widespread use of lead-based perovskites in photovoltaic (PV) applications is hindered by their toxicity, instability, and environmental concerns, creating a critical need for sustainable alternatives. In this study, we explore the structural and optoelectronic properties of the lead-free, all-inorganic <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\mathrm{Sr}}_{3}{\mathrm{NX}}_{3}$</tex-math></inline-formula> (X = I, Br, Cl, F) perovskite family using density functional theory (DFT) and many-body perturbation theory (GW-BSE). These materials exhibit direct bandgaps tunable from 1.04 eV to 2.65 eV and high absorption coefficients ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$10^{5} {\mathrm{cm}}^{-1}$</tex-math></inline-formula>), demonstrating their potential as efficient absorber layers in photovoltaic devices. Numerical simulations using SCAPS- 1D are performed to evaluate device performance in both unijunction and tandem solar cell (TSC) architectures. Among the uni-junction configurations, the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\mathrm{Sr}}_{3}{\mathrm{NBr}}_{3}$</tex-math></inline-formula>-based device achieved the highest power conversion efficiency (PCE) of 23.06%. A monolithic TSC composed of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\mathrm{Sr}}_{3}{\mathrm{NBr}}_{3}$</tex-math></inline-formula> (top) and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\mathrm{Sr}}_{3}{\mathrm{NI}}_{3}$</tex-math></inline-formula> (bottom) absorbers attained a PCE of 30.22%, with a open circuit voltage (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$V_{o}c$</tex-math></inline-formula>) of 1.75 V and short circuit current density (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$J_{s}c$</tex-math></inline-formula>) of 20.8 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\mathrm{mA/cm}}^{2}$</tex-math></inline-formula>. This work demonstrates the practical viability of leadfree Sr-based perovskites and offers a promising pathway toward high-efficiency, stable, and environmentally friendly solar energy technologies.