This research provides a comprehensive density functional theory (DFT) analysis of alkali metal-based cerium nitrates A2CeN2 (A = Li, Na, K) with respect to their electronic structure, particularly their band gaps and exceptional optical properties, for optoelectronics and photovoltaic applications. To investigate the effects of varying alkali metals (from lithium to sodium and potassium) on the compound's properties, it is crucial to examine their structure, stability, electronic configuration, optical, mechanical, and thermal characteristics. The investigation demonstrates that all of the analyzed compounds are mechanically, dynamically, and thermally stable and thus all are viable for practical applications. The obtained band gap values with hybrid functional are 1.355 eV for Li2CeN2, 1.481 eV for Na2CeN2, and 1.138 eV for K2CeN2, which are in the visible range, rendering these materials suitable for various optoelectronic and photovoltaic applications. High absorption coefficients at approximately 106 cm−1 with low optical reflectivity has been demonstrated in all compounds, ensuring that they are excellent absorbers for photovoltaic devices. Among the A2CeN2 (A = Li, Na, K) compounds, the band gap of Na2CeN2 is within the visible spectrum and close to the Shockley-Queisser limit of 1.43 eV for optimal solar cell efficiency. In addition, Li2CeN2, with its suitable band gap, notable high unit cell density, elevated absorption coefficient, and significant reflectivity, emerges as a promising candidate for solar cell as well as electromagnetic radiation shielding applications. Conversely, K2CeN2 displayed relatively lower hardness, melting point, and thermal conductivity. Notably, all compounds exhibit anisotropic behavior, with the variations in bonding nature significantly influencing their overall properties. The results demonstrate that the alkali metal-based compounds studied exhibit outstanding optoelectronic performance. Their band gaps, which are near the Shockley-Queisser limit for peak efficiency, making them particularly promising for photovoltaic applications. These findings highlight their potential for use in next-generation optoelectronic devices.