<p>The development of efficient microcrystalline silicon (<i>µ</i>c-Si) thin-film solar cells offers a promising route to reduce photovoltaic costs. This work presents, for the first time, a comprehensive numerical model to optimize ZnMgO/µc-Si-based solar cells by analyzing its performance metrics. The model incorporates horizontal and vertical grain boundaries (GBs) in the absorber with Gaussian-distributed donor- and acceptor-like trap states. Key parameters studied are Mg concentration, thickness, and doping in the ZnMgO emitter, as well as GB-induced recombination in the <i>µ</i>c-Si absorber. Results show that increasing Mg concentration up to 20% significantly enhances performance, while higher concentrations yield negligible improvement. GB recombination critically affects performance: smaller grain size, which increases GB density, causes exponential degradation, and GB trap densities above 10¹¹ cm^− 2 lead to a sharp decline in metrics. The ZnMgO emitter exhibits optimal performance at ~ 100&#xa0;nm thickness and ~ 5 × 10¹⁶ cm^− 3 doping. A maximum efficiency of ~ 14.3% is achieved with 20% Mg, 100&#xa0;nm thickness, 5 × 10¹⁶ cm^− 3 doping in ZnMgO, and an absorber containing 10 GBs with trap density of 10¹¹ cm^− 2. The model is validated against previously reported results.</p>