The behavior of thin film solar cells is reviewed by an equivalent circuit. In this   circuit as element is included that represents lost by recombination celi. With the   equivalent circuit obtained we give a physical interpretation of the characteristic   parameters, as well as the constants taking part on the operation of a cell. The   Merten's method VIM (Variable Illumination Measurement) is used, that aflows us   measurements and analysis of the more significant parameters of a solar ceil in a   likely and fhst way. Wc measured different solar devices pin from a-Si.H celis in order to compare the results found by the VIM method and their simulation by   computer using the presented model.