A photon confinement theoretical model is proposed, and a solar cell structure model is designed based on the theoretical model, thereby providing a photonically-confined solar cell and optoelectronic device to effectively reduce the probability of photons escaping from the cell. The theoretical model is established by the following steps: obtaining a relationship between a photocurrent density and an incident photon energy; obtaining a relationship between a radiative recombination photocurrent density and the incident photon energy; determining a relationship between the radiative recombination photocurrent density and a total recombination photocurrent density; obtaining a relationship between the photocurrent density generated by the standard spectral irradiance, the total recombination photocurrent density and an external current density of the solar cell; obtaining an output open-circuit voltage of the cell; obtaining an output short-circuit current density of the cell; obtaining a fill factor (FF); and obtaining a maximum power conversion efficiency (PCE).