When the pn junction on the surface of the solar cell is irradiated by sunlight, if the energy of the incident photon is higher than the forbidden band width of the silicon material, electron holes will be generated in the n region, p region and junction region due to the absorption of photons , The minority carriers generated in the n region near the junction will diffuse because of the concentration gradient. If the distance of minority carriers from the pn junction is less than its diffusion length, there will be a chance of diffusion to the junction interface.