Photo thermoelectric generators (PTEGs) are solid state heat engines that generate electricity from concentrated sunlight. In this paper, we developed a novel detailed balance model for PTEGs and applied this model to both state-of-the-art and idealized materials. This model uses thermoelectric compatibility theory to provide analytic solutions to device efficiency in idealized materials with temperature-dependent properties. The method for the theoretical calculation of the mechanism of absorption and refraction of light radiation of a selected wavelength in the volume of a photoelectric converter and the design of an effective photo thermal converter with a fixed slit are presented in the article. Direct- and non-direct-electron transitions from the valence band to the conduction band are analyzed. The possibility of optimal distribution of the light spectrum on the frontal surfaces of the solar cell and thermoelectric converter is shown. According to the results of experimental studies, a conclusion was made that the efficiency of a photo converter increases by a factor of three as compared with analogues, but operating without a thermal converter.