Doping levels and deep levels in In0.65Ga0.35N single junction solar cells are studied theoretically, and simulation of cell properties is performed. Effective-mass approximation (EMA) is used to calculate the ionization energies and the radius of ground-state orbit for donors and acceptors in wurtzite In0.65Ga0.35N. The ionization energies of donors and acceptors are estimated to be about 15.5 and 92.9 meV, respectively. The validity of EMA to wurtzite InGaN alloy has also been discussed. AMPS-1D software is used to simulate the doping levels and deep levels in In0.65Ga0.35N single junction solar cells with assumption that the deep level is located at the middle of In0.65Ga0.35N band gap where the recombination is maximum. Band structure and concentration distributions of equilibrium carriers are obtained. The influence of deep level recombination on efficiency is estimated to be about 9.6% while recombination center concentration is 5 x 10(15) cm(-3), and capture cross section is 10(-13) cm(2). The simulated results show that the increase of reverse saturation current and the decrease of open-circuit voltages (V-oc) and fill factor (FF) are mainly responsible for the decrease of the efficiency. Short-circuit current density (J(sc)) is found to be not sensitive to deep level concentrations and capture cross sections. As the crystal quality of InGaN and p-type doping of In-rich InGaN may be the most important challenges for InGaN solar cells, this study is useful for the study of InGaN-based super-high efficiency solar cells.