Enhancing Lead-Free Perovskite/Kesterite Solar Cells: Boosting Efficiency Through Dual Absorber (Cs₂ AgBiBr₆/CZTSSe) Layers

While lead-based perovskite solar cells have achieved impressive efficiencies, with some models surpassing $30 \%$, their future use is increasingly limited due to the significant environmental and health risks associated with lead toxicity. This growing concern is driving a transition toward safer and more sustainable alternatives. In response to this challenge, the current study presents an in-depth numerical simulation of a novel lead-free double absorber solar cell, utilizing Cs<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> AgBiBr<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</inf> (an inorganic perovskite material) and CZTSSe (a kesterite material) as absorber materials in the active layer. The research systematically explored the impact of various key parameters, such as the thickness and defect density of the absorber layers, and the reflectivity and work function of the back metal electrode, aiming to optimize the cell’s structure for peak efficiency. Through this detailed analysis, the study identified an optimal cell configuration: ITO/Cd<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</inf>Zn<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</inf>S/C<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</inf>2AgBiBr<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</inf>/CZTSSe/MoO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf>/Ni. This configuration demonstrated exceptional performance, achieving $V_{O C}$ of $1.0471 \mathrm{~V}, J_{S C}$ of $41.804 \mathrm{~mA} / \mathrm{cm}^{2}$, FF of $86.98 \%$, and an outstanding PCE of $38.07 \%$. This study is a huge step forward in the development of high-efficiency, Pb -free solar cells, demonstrating the promise of alternative materials for building environmentally acceptable and highly efficient photovoltaic technology.