Effect of absorbing layer thickness on efficiency solar cells multijunctions vertical based CIGS Using SILVACO TCAD

In this study, we performed numerical simulations using SILVACO-TICAD to analyse microelectronic and photonic structures and identify the optimal device configuration between multi-junction tandem and vertical multi-junction solar cells. We focused on thin-film CIGS (Copper Indium Gallium Selenide) solar cells under normalized conditions (AM1.5G, 0.1 spectral irradiance, and 300 K). The vertical tandem structure analysed consists of three junctions. Multi-junction solar cells offer higher efficiencies than single-junction cells. By combining CGS (Copper Gallium Selenide) with CIGS, about a 10% efficiency improvement is achieved over a vertical multi-junction (Gover A,1974) CIGS-only solar cell. The optimized vertical multi-junction structure showed the following photovoltaic parameters: **short-circuit current density (Jsc) = 32.42 mA/cm², open-circuit voltage (Voc) = 2.52 V, and a conversion efficiency of 34.68%**. This study highlights the potential of multi-junction solar cells, especially when combining different materials, to achieve significant performance improvements over traditional single-junction configurations.