Potential was studied as a function of temperature during charge generation in poly(vinyl alcohol) films containing ammonium heptamolybdate, copper nitrate, and polyoxometalate (NH4)42[Mo72VIMo60VO372(HCOO)30(H2O)72] · 30HCOONH4 · 250H2O. The range of the strongest charge generation and its bounds were determined. The results are matched to thermal analysis data. Charge generation correlates with evolution of volatiles from the films.