Vacuum Ultraviolet Photochemical Sol-Gel Processing of Zn, Sn, Zn-Sn Oxide Thin Films for Encapsulation of Organic Light Emitting Diodes

Abstract

Room temperature solution processing of highly compact, glass-like thin films of ZnO, SnO2 and Zn-Sn oxide was achieved for the purpose to use them as thin film encapsulations (TFEs) for organic light emitting diodes (OLEDs), by employing photochemical decomposition of metallorganic precursors under vacuum ultraviolet irradiation in dry N2. While hydration water in the source chemical strongly promoted granular crystal growth, anhydrous precursors achieved highly flat thin films without pinholes and cracks. The analysis by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and ellipsometry revealed fast decomposition of organic ligand and polycondensation into metal oxide/hydroxide thin films with high densities within 5 minutes. Transmission electron microscopic observation revealed crystallization in about 5 nm size in case of ZnO, whereas SnO2 remained totally amorphous. Mixing of the two precursors to yield Zn2SnO4 and ZnSnO3 was able to control the degree of crystallization vs. compactness of the thin film to maximize their ability as TFEs to extend the lifetime of OLEDs for about 4 times for operation under ambient air.

Passivation of CdS/Cu2ZnSnS4 Interface from Surface Treatments of Kesterite‐Based Thin‐Film Solar Cells

“…An analysis shows that two components are needed for a satisfactory fit of the spectra. Similarly, the O 1s spectrum for the AA sample shows an extra component at ≈530.5 eV (green), representative of a metal oxide (MeO x ) component, likely SnO x , [ 19 ] present at the CZTS surface. In addition to hydroxide (blue component at around 531.5 eV, with respect to MeO x ) and some weakly adsorbed species, probably H 2 O (red component at around 533 eV, with respect to MeO x ) [ 20 ] are also observed.…”

“…An analysis shows that two components are needed for a satisfactory fit of the spectra. Similarly, the O 1s spectrum for the AA sample shows an extra component at %530.5 eV (green), representative of a metal oxide (Me─O x ) component, likely SnO x , [19] [20] are also observed. Similar components were also observed for the nontreated (F) CZTS sample.…”

Photochemical Conversion of Ethanolamine-Zn2+ Complex Gel under Vacuum Ultraviolet Irradiation Associated with Color-Tunable Photoluminescence

“…Because the VUV processing is done in a dry N 2 glovebox, crystal growth by dissolution/recrystallization is practically forbidden. 28 These observations appear to rule out quantum size effect as the cause of color change of the PL.…”

“…The narrow absorption peak in the UV range clearly indicates the formation of ZnO NCs, as opposed to the typical broad band absorption of the annealed sample for which the X-ray diffraction (XRD) pattern also confirmed formation of ZnO as reported earlier. 28 The peak centered at ca. 290 nm shows almost no change in wavelength and only increases the overall absorbance upon increasing the VUV time.…”

“…We have recently reported photochemical dry gel conversion of metalorganic precursors into highly compact, flat, and transparent ZnO, SnO 2 , and Zn−Sn oxide thin films by employing vacuum ultraviolet (VUV) irradiation (λ = 172 nm, E ph = 7.2 eV) at room temperature in a N 2 -filled glovebox, for the purpose of thin-film encapsulation of organic light-emitting diodes (OLEDs). 28 Compared with the traditional sol−gel route based on hydrolysis of zinc salt in water and subsequent crystallization by heating, avoiding water content in the coating solution was important to suppress crystal growth of ZnO and protect underlying OLED materials from exposure to water. Coatings made from such dry gel were composed of extremely small ZnO NCs with less than 5 nm size, for which quantum size effect could certainly be expected.…”