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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.

Gas barrier films are widely used in electronic and packaging applications. They are also critical components of flexible organic light-emitting diodes (FOLEDs) that require high gas barrier performance. Among the various film manufacturing techniques, solution-processed thin-film encapsulation (TFE) represents a low-cost FOLED fabrication method. The nanometerthick SiN films produced following the vacuum ultraviolet (VUV)-induced densification of solution-processed perhydropolysilazane (PHPS) films in a N 2 atmosphere can potentially serve as TFE barrier films. However, the nanometerthick PHPS densification process has not been examined in sufficient detail. We investigated and discussed the effects of the Si−N bond number, PHPS film composition, and free volume (present in the produced Si−N network) on the VUV-induced PHPS densification process. It was found that VUV irradiation caused rapid hydrogen release and film densification through the formation of Si−N bonds. The results obtained using the X-ray photoelectron spectroscopy and dynamic secondary ion mass spectrometry techniques, and the calculated residual hydrogen ratios, revealed that the film composition was strongly related to the number of residual hydrogen atoms and Si−N bonds. Notably, nanometer-thick PHPS film densification was a relatively slow process, in which the free volume in the Si−N network was considerably reduced by the atomic rearrangement induced by the simultaneous cleavage of several Si−N bonds during VUV irradiation. We believe that the results presented herein can potentially serve as a guideline for developing solution-processed nanometer-thick SiN films with relatively high density and excellent gas barrier performance (that is comparable to that exhibited by vacuum-processed barrier films).

Rationale Organic light‐emitting diode (OLED) products based on display applications have become popular in the past 10 years, and new products are being commercialized with rapid frequency. Despite the many advantages of OLEDs, these devices still have a problem concerning lifetime. To gain an understanding of the degradation process, the authors have investigated the molecular information for deteriorated OLED devices using time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS). Methods TOF‐SIMS depth profiling is an indispensable method for evaluating OLED devices. However, the depth profiles of OLEDs are generally difficult due to the mass interference among organic compounds, including degradation products. In this study, the tandem mass spectrometry (MS/MS) depth profiling method was used to characterize OLED devices. Results After degradation, defects comprised of small hydrocarbons were observed. Within the defect area, the diffusion of all OLED compounds was also observed. It is supposed that the source of the small hydrocarbons derives from decomposition of the OLED compounds and/or contaminants at the ITO interface. Conclusions The true compound distributions have been determined using MS/MS depth profiling methods. The results suggest that luminance decay is mainly due to the decomposition and diffusion of OLED compounds, and that OLED decomposition may be accelerated by adventitious hydrocarbons present at the ITO surface.

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