We have fabricated single-layer sandwich cells containing photoactive molecular layer (vanadyl phthalocyanine complex) and tested them in various environments. In contrast with dry gases, such as argon, oxygen, and ammonia, which cause the changes mainly in the first quadrant of J-V plots, addition of water vapor resulted in appearance of significant dark short-circuit currents and open circuit voltages. These values were amplified by the presence of mixed water and ammonia vapors. The observed effect is explained by the near-electrode reactions and by the existence of ionic component of conductivity in phthalocyanine layer, which give rise to generation of output electrical power in the dark. The power conversion efficiency under the white light illumination does not follow this trend being the highest in an inert atmosphere (argon). Changing the material of the top metal electrode from aluminum or indium to gold terminates both photovoltaic and dark power generating processes, though sensitivity of the current to vapors holds out.