Light intensity effects on electrical properties of AgIn5S8 thin films

The light illumination effects on the current conduction mechanism in thermally annealed polycrystalline AgIn5S8 thin films has been investigated by means of dark and photoexcited conductivity measurements as a function of temperature. The dark electrical conductivity analysis in the temperature region of 30-300 K, reflected the domination of thermionic emission and variable range hopping of charge carriers over the grain boundaries above and below 90 K, respectively. Conductivity activation energies of similar to 155 and 78 meV (in the temperature regions of 230-300 K and 90-220 K. respectively), a density of localized states (evaluated assuming a localization length of 5A(0)) of 1.17 x 10(20) cm(-3) eV(-1), an average hopping distance of 41.51 A(0) (at 60 K) and an average hopping energy of 28.64 meV have been determined from the dark electrical measurements. When the sample was exposed to illumination at specific excitation intensity, the values of the conductivity activation energy, the average hopping energy and the average hopping range were decreased significantly. On the other hand, the density of localized states near the Fermi level increased when the light intensity was increased. Such behavior is attributed to the temporary shift in Fermi level and/or trap density reduction by electron-hole recombination. (C) 2011 Elsevier B.V. All rights reserved.