This work studies and simulates a thin film solar cell based on the InGaN material. The single-junction n/p $In_{0.622}Ga_{0.378}N$ ($E_g = 1.39 \text{ eV}$) solar cell is the optimal structure found under normalized conditions (AM1.5G, 300K), we exhibit a comparison between three types of cells, with Lambertinne reflectors, textured reflectors, and flat reflectors to study optimum efficiency. The conversion efficiency increased from 16.46% with flat reflectors to 18.67% with textured reflectors, the solar cell exhibits a maximum efficiency of around 19.80% with Lambertinne reflectors. The investigation results show that the $In_{0.622}Ga_{0.378}N$ with Lambertinne reflectors solar cell was inversely proportional to the temperature. The optimum concentration for doping for the donor is $5 \times 10^{17} \text{ cm}^{-3}$ and for the acceptor is $5 \times 10^{17} \text{ cm}^{-3}$.