Comparative Studies of the Properties of ZnO Sprayed Thin Films on Different Polymer Substrates for Flexible Solar Cell Applications

Abstract

Zinc oxide (ZnO) thin films have been deposited onto polyethylene terephthalate (PET) and polyimide (PI) substrates using the chemical spray pyrolysis technique in order to explore their potential use as transparent window materials for solar cells. The substrate temperature along deposition of the material was maintained at 250 °C. The effects of substrate types on the structural and optical characteristics of the formed films were studied. X-ray diffraction patterns confirm the proper phase formation of crystalline ZnO films. Films deposited on PI exhibited a larger roughness compared to those deposited onto PET substrates because of the large particles adsorbed on the former. Optical transmittance values exceeding 80% in the visible and infra-red (IR) region on both substrates were registered. Optical band gaps (Eg) from Tauc plots for ZnO films on PET achieved values of ca. 3.2 eV whilst on PI were ca. 3.3 eV. Surface reflectance shows that ZnO on PI has consistently a higher surface reflectance of ca. ~2% throughout the spectral region compared to ZnO films on PET substrates while both showed a parasitic absorbance below 10% within the region of interest.