Gives a detailed theoretical analysis of the response to monochromatic and to composite light (solar AM0 spectrum) at high intensities, when the usual Shockley theory is not valid because the concentration of excess photogenerated carriers may be comparable or exceed the thermal equilibrium value of the carrier concentration. The open-circuit voltage, short-circuit current, I-V curves, maximum power output, fill factor and efficiency of a 1 Omega cm solar cell have been calculated as a function of incident light intensity by solving numerically the nonlinear ambipolar equation and using the general boundary condition at the junction which is formally valid at all illumination intensities. The effect of the series resistance of the solar cell has been estimated by using the lump model and is discussed separately. Where possible, the theoretical results are compared with the experimental results.