Our model study shows that a spatial non-homogeneous, in particular one-sided, irradiation of a cesium-containing cell can generate a photo-electromotive force (EMF), similar to the well-known Dember’s effect in semiconductors. Data on the photo-EMF in an infinite slab cell with a width of L = 10^–2 m containing a pure cesium vapor and Cs–Ar mixtures were self-consistently determined at a gas temperature of Tg = 480 K. Cesium vapor pressure ranged from 0.007 to 0.11 torr, the argon to cesium vapor pressure ratio was from 0 to 103, and spectral flux density was F = 10?^2–3.7·10^3 W/(m2·nm) in a wavelength range of the D1 and D2 lines. A model for cesium photoplasma and an approach for determining the photo-EMF in the one-sided irradiated slab cell developed by us previously were used. An error was corrected in the formula for the electric potential in the plasma volume in the approach previously applied to the Na–Ar slab cell. Significant differences were found between data for the cesium- and sodium-containing cells for electron density and temperature and atomic and diatomic alkali ion densities. It was found that photo-EMF can be created in the cesium-containing cell at lower (by a factor of ten) alkali vapor pressure and resonance irradiation spectral flux density than in the sodium-containing cell. Non-monotonic dependencies of the potential change in the plasma volume, the potential drop near the cell walls, and, as a result, photo-EMF on gas component pressures and F were found and discussed. Maximum obtained photo-EMFs in the Cs–Ar and Na–Ar cells were about 0.65 V and 1 V, respectively. These results are of great interest for the application of alkali-containing gas plasmas, particularly in the development of photoelectric gas converters.