Bandgap Engineering and Thickness Tuning to Enhance the Performance of Multi-Junction Elpasolite Solar Cell (MJ-ESC) for Flexible Photovoltaic Devices

Multi-Junction Elpasolite Solar Cell (MJ-ESC) achieves excellent efficiency by using customizable bandgaps and adjusted layer thicknesses. Bandgap engineering in multi-junction/tandem solar cell (TSC) is a vital step in improving their performance. TSCs combine two or more sub-cells with different bandgaps to catch a wider range of sunlight more efficiently than single-junction solar cells. The top cell usually has a wider bandgap (WBG) to efficiently absorb high-energy (short-wavelength) photons while allowing lower-energy photons to pass through the bottom cell. The bottom cell has a narrower bandgap (NBG), which allows it to absorb lower-energy (longer-wavelength) photons sent by the top cell. This study explores a novel tandem structure with a lead-free double perovskite/ elpasolite based top cell and a copper indium gallium selenide (CIGS) based bottom cell, using SCAPS 1-D modelling. The study found that the top and bottom cell absorber layers have optimal bandgaps of 1.4 eV and 1 eV, respectively. Thickness adjustment in TSCs is an important method for improving optical and electrical performance. Researchers can increase light absorption, reduce losses, and balance current between sub-cells by varying the thicknesses of specific layers in the top and bottom cells. The optimal thickness of the elpasolite and CIGS layers in the MJ-ESC device at 900 nm and 800 nm is found to be 2.389V, 35.39mA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>, 77.93% and 65.91% for open circuit voltage (Voc), short circuit current density (Jsc), fill factor (FF), and power conversion efficiency (PCE) respectively.