The charge carrier transport in a solar cell is studied taking into account the dependence of the minority carrier lifetime on the injection level. The nonlinear continuity equation so obtained is solved by using a perturbative method. The spectral response of a silicon solar cell at high light intensity is evaluated on the basis of the proposed model. Theoretical results agree very well with some recently reported experimental data, for silicon solar cells at high intensity. However, there is evidence that in the light intensity range where our perturbative approach can be applied, the effect of the nonconstant minority carrier lifetime on the total short circuit current of the solar cell is quite small.