In CdS/CdTe solar cells, the dependence on the frequency of the applied voltage is essential to improve theoretical results. Our model is based on the conservation of energy and charge and considering a ternary layer and the existence of plasmons in the interface. In this work, the capacitance dependence as a function of the frequency of the induced field in the heterojunction is observed; furthermore, a plasmon was formed in the interface in the surface semiconductor. The results provided with the theoretical model were compared with the experimental data, and a better adjustment was obtained.