Optical and morphological properties of ZnO and Alq3 incorporated polymeric thin layers fabricated by the dip-coating method

Abstract

In this report, we present the influence of polymer matrix on morphological and optical properties of thin films containing zinc oxide (ZnO), tris(8-hydroxyquinolinato)aluminium (Alq3) and ZnO:Alq3. Polyvinylpyrrolidone (PVP) and poly(methyl methacrylate) (PMMA) dissolved in isopropanol and tetrahydrofuran, respectively, were used as polymeric matrices of fabricated composites. The analysed thin layers were deposited on Si substrates using a dip-coating method and characterized by Fourier-Transform Infrared Spectroscopy (FTIR), Energy-Dispersive X-ray spectroscopy (EDX), Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), Spectroscopic Ellipsometry (SE) and photoluminescence (PL). It was found that adding the polymer to Alq3 causes a blueshift in absorption compared to pure Alq3 layers. We also observed photoluminescence in the region of 2.2–2.8 eV for ZnO:Alq3:PMMA and ZnO:Alq3:PVP, as well as for Alq3:PMMA at room temperature. PL measurements showed that adding ZnO to Alq3:polymer matrix did not result in any shift in PL spectra compared to the results of Alq3:polymer layer. AFM and SEM measurements show that relatively smooth films were obtained in the case of composites based on PVP and PMMA. Moreover, a change in the size of ZnO agglomerates depending on polymer used is observed for the three-component layers. We also noticed that the values of the refractive index are higher for the samples in the PVP matrix. However, the opposite behaviour was observed in the case of the extinction coefficient.