Synthesis and characterization of flexible zinc oxide-based composites

Abstract

An organic flexible optoelectronic device (f-OLED), composed by a conductive polymeric substrate (PEDOT:PSS) and a composition-controlled semiconductive layer of ZnO was designed based on the industry’s requirements of mechanical flexibility and cost-effective optical properties. ZnO-PEDOT:PSS was chosen due to its expected mechanical flexibility, low absorbance over 400nm to 700nm and tunable conductivity. Zinc oxide (ZnO) was selected as a potential replacement to ITO (Iridium Tin Oxide) due to its less fragile (brittle) behavior, which is a basic requirement on flexible composites.

Based on the above considerations, nanocrystalline ZnO particles were dispersed at different loadings within the PEDOT:PSS matrix. The morphological, structural, mechanical and functional properties were determined for different w/w ratio of ZnO nanoparticles and overall film thickness. Two approaches were followed: A physical deposition of metallic Zn onto polymer surface and subsequent air oxidation, and a mechanical mixing of the ZnO nanocrystals with PEDOT:PSS matrix at the upper layers of the composite films.

The morphological structure of the flexible optoelectronic composites was characterized via optical microscopy and scanning electron microscopy (SEM) allowing to assess the cluster structures of ZnO nanoparticles randomly dispersed in the composite. The composition was inspected via Fourier transformed infrared spectroscopy (FT-IR) and x-ray diffraction (XRD) allowing to determine mechanical adhesion as the prevailing mechanism since no component was altered during the fabrication process. Optical properties were inspected using an ultraviolet-visible spectrometer (UV-VIS) and a photoluminescent spectrometer (PL) detailing the characteristic exciton of pure ZnO at 372nm and its corresponding fluorescent emission at 388nm. Mechanical test where performed according to ASTM D682-1a results on a 15% ZnO - 85% PEDOT:PSS indicate over 1.3 GPa of Young Modulus a notable increase compared with 0.89 GPa of pristine PEDOT:PSS. It is possible to conclude that vacuum dried components outperformed those generated with a slight increase in thermal load.