In traditional III-nitride solar cells, the polarization-induced charges and potential barrier in the hetero-interfaces are demonstrated to be harmful for carrier collection. To solve these challenges, the elimination or mitigation of the abrupt hetero-interfaces should be efficient. In this study, various kinds of solar cell structures are investigated numerically. The structures under various situations of indium composition and degree of polarization are systematically explored. Specifically, the photovoltaic performance, energy band diagrams, electrostatic fields, and recombination rates are analyzed. Then, according to the simulation results, the appropriate solar cell structure which possesses high conversion efficiency is proposed.