Growth and properties of ZnO films on polymeric substrate by spray pyrolysis method

• ZnO:In layers were grown on polyimide substrate by spray pyrolysis.
• The buffer layer morphology is controlled by the layer thickness and spray rate.
• ZnO/ZnO:In bilayer morphology is dependent on the surface of buffer layer.
• Rough buffer layer leads to rough bilayer with scrolled belts (diameter of 2–6 μm).
• Due to scrolled belts layers show no preferential growth yet highly scatter light.

The growth of ZnO layers deposited by spray pyrolysis on polymeric substrate was studied. Zinc acetate precursor solution was sprayed onto preheated polyimide (PI) and glass reference substrates at 380 °C. The structural, morphological, optical and electrical properties of the layers were measured by X-ray diffraction, scanning electron microscopy, optical spectroscopy and van der Pauw and Hall method. ZnO:In layers could be grown on PI when deposited onto undoped ZnO layer acting as a buffer layer on PI. Independent of the substrate type, the ZnO/ZnO:In bilayer showed a mixed morphology from smooth canvas-like surface to large scrolled belt grains dependent on buffer layer morphology. Due to the formation of scrolled belts, the ZnO:In layer shows no preferential orientation, yet the preferred orientation of the ZnO buffer crystallites is (100) plane parallel to the substrate. The bilayers deposited on PI exhibit high light scattering capability (haze factor of 85–95% in the spectral region of 350–1500 nm). The resistivity of the ZnO:In film in bilayer on PI is 4.4 × 10− 2 Ω cm mainly due to low carrier mobility of 1.5 cm2/Vs, the carrier concentration is 1020 cm− 3.