Three-stage growth of Cu–In–Se polycrystalline thin films by chemical spray pyrolysis

Structural, optical and electrical properties of polycrystalline Cu–In–Se films, such as CuInSe2 and ordered vacancy compounds (OVC), prepared by three-stage process of sequential chemical spray pyrolysis (CSP) of In–Se (first stage), Cu–Se (second stage) and In–Se (third stage) solutions have been studied in terms of substrate temperature at the second stage (TS2). The films grown at TS2⩽420 °C exhibited larger grains in comparison with the Cu–In–Se films grown by the usual CSP method. Optical gap energy was approximately 1.06 eV for 360 °C⩽TS2⩽420 °C, but increased dramatically from 1.06 to 1.35 eV when the TS2 rose from 420 to 500 °C. Conductivity type was p-type for TS2<420 °C, but n-type for TS2>420 °C.