Hot-wall vacuum deposited n-CdS/p-CdTe thin-film solar cells with the graded-gap CdTe 1 - x S x , interfaces have been investigated. The CdTe 1 - x S x , interfaces have been studied by means of the measurement and subsequent computer simulation of the spectral photoresponse curves, as well as by the layer-by-layer laser mass-spectrometry analysis of the cells. The p-n junction optimization according to the simulation results has been carried out by means of the open-air annealing of the fresh-prepared solar cells.