The process of the underpotential deposition (UPD) of Pb adatoms (Pbad) onto Se was used to produce nanocomposite films consisting of amorphous Se and nanosized PbSe clusters distributed throughout the film bulk. It was found that doping lead into Se films modifies their optical and photoelectrochemical properties and increases the efficiency of the charge transfer both in the film bulk and through the semiconductor | electrolyte interface. Introducing lead into the bulk of Se films significantly promotes the process of Pbad UPD onto Se surface. The underpotentially deposited Pbad interact chemically with Se surface atoms, resulting in the formation of a PbSe monolayer. The PbSe formed can be identified by the anodic peak corresponding to its electrochemical oxidation.