RESUMO
We have investigated an effective and a single-step chemical vapor deposition (CVD) method to achieve conformal visible poly-dichloro-para-xylylene (parylene C) film for light extraction enhancement in bottom-emitting organic light-emitting diodes (OLEDs) at room temperature. We report that sublimed parylene dimers pyrolyzed between 400 °C and 500 °C resulted in visible parylene films with tunable transmittance and haze, exhibiting light scattering properties due to the formation of uniformly distributed dimer crystals. We achieved a novel conformal visible parylene film with total transmittance and high haze of 79.5% and 93.6%, respectively. It is observed that the outcoupling efficiency of the OLEDs employing the visible parylene film is enhanced up to 45.8%. Additionally, the OLED with the visible parylene light extraction film shows limited angle-dependency of emission spectrum over viewing angles. The single-step room temperature fabrication process of this conformal outcoupling film paves the way to achieving commercial high-performance OLEDs.
RESUMO
Poly-dichloro-para-xylylene (parylene-C) film is formed through a chemical vapor deposition process, where monomeric gases are polymerized on the target surface at room temperature and are used as transparent insulating coating films. The thin parylene-C films exhibit uniform conformal layers even when deposited on substrates or surfaces with fine cracks, structures, and bumps. However, the film is highly transparent in the visible range (transmittance > 90%); thus, it is difficult to visually identify, inspect the coating process and check for any defects when used as an insulation film. Some reports have demonstrated the deposition of visible (hazy) parylene films through the control of the vaporization or pyrolysis of the parylene-C powder and sublimed dimers, respectively. Even though these films have been applied as device substrates and light extraction layers in organic light-emitting diodes (OLEDs), their optical and electrical characteristics have not been extensively explored, especially for their applications as insulation coatings. In this study, the characteristics of visible parylene films produced by tuning the ratio of dimer to monomer gases via the adjustments of the pyrolysis temperature are analyzed with electrical and optical methods. Parylene-C films deposited within the pyrolysis temperature of 400−700 °C exhibited a haze range of 10−90%. A relative reflectance of 18.8% at 550 nm of the visible light region was achieved in the visible parylene film deposited with a pyrolysis temperature of 400 °C. Resistivity in the order of 1010 Ω cm was achieved for the visible parylene films measured with the transmission line measurement (TLM) method. The films can be applied in advanced insulation coatings for various optical systems and electronic devices.
RESUMO
Sputtering technique involves the use of plasma that locally heats surfaces of substrates during the deposition of atoms or molecules. This modifies the microstructure by increasing crystallinity and the adhesive properties of the substrate. In this study, the effect of sputtering on the microstructure of parylene-C was investigated in an aluminum nitride (AlN)-rich plasma environment. The sputtering process was carried out for 30, 45, 90 and 120 min on a 5 µm thick parylene-C film. Topography and morphology analyses were conducted on the parylene-C/AlN bilayers. Based on the experimental data, the results showed that the crystallinity of parylene-C/AlN bilayers was increased after 30 min of sputtering and remained saturated for 120 min. A scratch-resistance test conducted on the bilayers depicted that a higher force is required to delaminate the bilayers on top of the substrate. Thus, the adhesion properties of parylene-C/AlN bilayers were improved on glass substrate by about 17% during the variation of sputtering time.