<p>Kesterite solar cell (Cu₂ZnSnS₄) is gradually gaining the attention of scientists and innovators owing to its tremendous optical band gaps that range between 1.0 and 1.5&#xa0;eV and high optical absorption coefficient &gt; 10⁴&#xa0;cm⁻¹, which makes it a good absorber layer in photovoltaics technology. Its maximum power conversion efficiency (PCE) of 12.6% was the best result that could be achieved before the introduction of CZTS nanoparticles. To date, the uniqueness of the internal mechanism of CZTS nanoparticles in the nanoscale has not been fully known, with minimal successes recorded. This research is aimed at investigating the internal mechanism of CZTS nanoparticles using first principles. The Poisson and continuity equations were expanded to capture the mechanism of the Cu₂ZnSnS₄ solar cell, and the Hermite polynomial was used to improve on the formulated mechanism. Computational and numerical analyses were used to determine salient parameters. The CZTS nanoparticles were used in a normal solar cell architectural design using the solar simulator SCAPS-1D. It was observed that the main issue with the internal mechanism of CZTS nanoparticles is its susceptibility to reverse bias conditions that affect the quasi-Fermi current, open circuit voltage, and PCE. Another shortcoming of the CZTS nanoparticles' internal mechanism is its bandgap misalignment that leads to energy losses and reduced open-circuit voltage (Voc). This inherent shortcoming has a significant reduction of the PCE in an ordinary solar cell setup. The maximum PCE of the experiment, first principles, and the solar simulator was given as 18.3%, 31.45%, and 32.81%, respectively. It was recommended that the best transport layer that could reduce the shortcoming of CZTS is the intrinsic heterojunction thin layer (HIT).</p>