A next-generation Cd-free CIGS solar cell enabled by ZnMgO window engineering and Al2O3 interface passivation

This paper proposes a next-generation Cd-free CIGS solar cell architecture, including a wide-bandgap ZnMgO window layer and a 10-nm Al2O3passivation layer, combined with an S-rich Zn (O, S) buffer engineered to optimize band alignment and suppress interface recombination. A complete ZnMgO/Al2O3/Zn (O, S)/CIGS stack was simulated and optoelectronically analyzed using TCAD and optical TMM approaches. The proposed device demonstrates a significantly enhanced short-circuit current density (JSC) of 46.39 mA/cm², exceeding the experimental benchmark of 40.59 mA/cm². The open-circuit voltage (VOC) increases from 0.50 V to 0.71 V, attributed to reduced interface trap density at the CIGS/buffer junction. The optimized window/passivation stack also boosts maximum output power (Pmax) from 14 mW/cm² to 16.2 mW/cm², resulting in a marked efficiency rise from 18% to 23%. The fill factor (FF) improves from 0.65 to 0.75, reflecting lower series resistance and improved diode quality. Optical analysis reveals a substantial enhancement in photon absorption, with peak photon flux increasing from 64 mW to 92 mW and peak spectral irradiance rising from 1.4 to 2.8 W/m2/nm, accompanied by a blue-shift in peak absorption wavelength from 600 nm to 485 nm due to the wider ZnMgO bandgap. Depth-dependent absorption shows an increase in F(X) from 1.32 to 1.55 W/m²/nm, confirming superior light penetration and reduced surface reflection. The proposed design surpasses traditional structures in both electrical and optical performance, offering a scalable pathway toward next-generation, eco-friendly, and high-efficiency CIGS photovoltaic.