This paper presents the effect of emitter thickness and post-annealing process on the conversion efficiency of crystalline silicon (c-Si) solar cells. Diffusion parameters like pre-deposition temperature, drive-in temperature, and process duration assist to control the emitter thickness and inturn improves the conversion efficiency of the solar cells. It is observed that shallower emitter cells have higher conversion efficiency of 10.81% than deeper emitter cells of 7.62%. Post-annealing process at 700 °C for 60 minutes boosts the efficiency of shallower emitter cell from 10.81% to 12.06%. Dark current-voltage characteristics authenticate the formation of p-n junction and also elucidate the presence of recombination saturation current along with diffusion saturation current. Illuminated and dark current-voltage characteristics further provide the evidence that post-annealing process during phosphorus diffusion reduces the trap density and thus the recombination saturation current, which helps to improve the efficiency. The combination of a shallower emitter with post-annealing process provides an excellent approach to enhance the solar cell efficiency.