Effect of the solution pH on the growth of spray-deposited CuInS sub(2) thin films

The effect of solution pH on the growth of spray deposited CuInS sub(2) thin films has been investigated. Solutions with pH 1.5, 2.4, 3.5 and 4.5 are used to deposit the films on glass substrates held at 550 K. The films have been characterized using optical absorption, X-ray diffraction (XRD) and transmission electron microscopy (TEM) analysis. At pH 1.5, no film formation is observed. Films deposited from 2.4 pH solution contain binary phase Cu sub(2) sub(S). Near stoichiometric, single phase CuInS sub(2) films with chalcopyrite structure are formed when solution pH=3.5. Films deposited from 4.5 pH solution are also found to be single phase, near stoichiometric CuInS sub(2) and exhibited chalcopyrite structure. However, an additional optical absorption process is observed which is attributed to a sub-band gap absorption.