  We study experimentally the photoconductivity of CdS-CdSe sintered granular
films obtained by the screen printing method. We mostly focus on the
dependences of photoconductivity on film's microstructure, which varies with
changing heat-treatment conditions. The maximum photoconductivity is found for
samples with compact packing of individual grains, which nevertheless are
separated by gaps. Such a microstructure is typical for films heat-treated
during an intermediate (optimal) time. In order to understand whether the
dominant mechanism of charge transfer is identical with the one in
monocrystals, we perform temperature measurements of photoresistance.
Corresponding curves have the same peculiar nonmonotonic shape as in CdSe
monocrystals, from which we conclude that the basic mechanism is also the same.
It is suggested that the optimal heat-treatment time appears as a result of a
competition between two mechanisms: improvement of film's connectivity and its
oxidation. Photoresistance is also measured in vacuum and in helium atmosphere,
which suppress oxygen and water absorption/chemisorption at intergrain
boundaries. We demonstrate that this suppression increases photoconductivity,
especially at high temperatures.
