In this paper, an intermediate-band solar cell (IBSC) with only one IB was designed, where the three-dimensional InxGa1−xN/InN quantum dot supracrystals were regularly arrayed in the i layer of the p-i-n type structural cell. IB characteristics such as position and width derived from discrete quantized energy levels in quantum dots were determined via solving the Schrödinger equation with the Kronig-Penny model. The principle of detailed balance was used to deal with the photoelectric conversion process in the IBSC. Characteristic parameters of the cell such as open circuit voltage, short circuit current density, and photoelectric conversion efficiency were numerically calculated. The influence of In content, average size of QDs, and interdot spacing on the cell performance was further analyzed.