Morphological and Optical Properties of ZnO Thin Films Prepared by Spray Pyrolysis on Glass Substrates at Various Temperatures for Integration in Solar Cell

Abstract

ZnO thin films are widely used as antireflection layer in solar cells and can be grown by various techniques implemented at various temperatures. In this contribution, we present the morphological and optical properties of ZnO thin films prepared by spray pyrolysis on glass substrates at various growth temperatures from 350 to 550°C. The surface morphology of the films, analysed by scanning electron microscopy SEM, is modified with substrate temperature. Optical characterizations of ZnO films as a function of temperature were carried out by transmittance and photoluminescence (PL) measurements. Main optical properties are as follow: All the films are highly transparent in the visible region of the electromagnetic spectrum. The average transmission in the visible range (400–800nm) was greater than 80%. The band gap of ZnO films increases with increasing substrate temperatures attributed to the increase of the grain size of thesample.PL spectrum of ZnO films can be divided into the UV emission and the visible broadband emission attributed to the near band edge emission (NBE) and to the deep level emissions (DLE), respectively. The biggest ratio of UV emission on visible emission of the PL intensity is observed for the ZnO thin film deposited at 550°C by the spray pyrolysis technique. Therefore, we suggest that this original result indicate the most suitable growing conditions for obtaining high quality sprayed ZnO thin films with higher luminescence performances.