The effect of illumination intensity P(in) on the cell parameters of a silicon solar cell has been investigated based on one diode model. The variation of slopes of the I-V curves of a cell at short circuit and open circuit conditions with intensity of illumination in small span of intensity has been applied to determine the cell parameters, viz, shunt resistance R(sh), series resistance R(s), diode ideality factor n and reverse saturation current I(o) of the cell. The dependence of cell parameters on intensity has been investigated for a fairly wide illumination intensity range 15-180 mW/cm(2) of AM1.5 solar radiations by dividing this intensity range into a desirable number of small intensity ranges for measurements of the slopes of the I-V curves at short circuit and open circuit conditions. Initially R(sh) increases slightly with P(in) and then becomes constant at higher P(in) values. However, R(s), n and I(o) all decrease continuously with P(in), but the rate of decrease of each of these becomes smaller at higher P(in) values. Theoretical values of open circuit voltage V(oc), curve factor CF and efficiency eta calculated using the cell parameters determined by the present method match well with the corresponding experimental values. (C) 2010 Elsevier B.V. All rights reserved.