Method for Aluminum Oxide Thin Films Prepared through Low Temperature Atomic Layer Deposition for Encapsulating Organic Electroluminescent Devices.

Hui-Ying Li,Yu Duan,Yun-Fei Liu,Yi-Nan Lu,Yong-Qiang Yang

doi:10.3390/ma8020600

Abstract

Preparation of dense alumina (Al2O3) thin film through atomic layer deposition (ALD) provides a pathway to achieve the encapsulation of organic light emitting devices (OLED). Unlike traditional ALD which is usually executed at higher reaction n temperatures that may affect the performance of OLED, this application discusses the development on preparation of ALD thin film at a low temperature. One concern of ALD is the suppressing effect of ambient temperature on uniformity of thin film. To mitigate this issue, the pumping time in each reaction cycle was increased during the preparation process, which removed reaction byproducts and inhibited the formation of vacancies. As a result, the obtained thin film had both high uniformity and density properties, which provided an excellent encapsulation performance. The results from microstructure morphology analysis, water vapor transmission rate, and lifetime test showed that the difference in uniformity between thin films prepared at low temperatures, with increased pumping time, and high temperatures was small and there was no obvious influence of increased pumping time on light emitting performance. Meanwhile, the permeability for water vapor of the thin film prepared at a low temperature was found to reach as low as 1.5 × 10−4 g/(m2·day) under ambient conditions of 25 °C and 60% relative humidity, indicating a potential extension in the lifetime for the OLED.

Highlights

Research areas and novel applications focusing on organic light emitting devices (OLEDs) have developed rapidly [1,2,3,4]
OLEDs worked, it was essential to inject electrons into the cathode, requiring cathode metals with lower work functions such as aluminum, magnesium, calcium. These metals readily react with any water vapor which is introduced into the devices, causing the notable decline in OLEDs lifetime
Using the atomic layer deposition (ALD) method, 80 nm Al2O3 thin films were formed on Si substrate at both 80 nm-thickness low temperature ALD (80 °C) and 200 °C

Summary

Introduction

Research areas and novel applications focusing on organic light emitting devices (OLEDs) have developed rapidly [1,2,3,4]. Effective encapsulation of OLEDs is required to isolate each functional layer from water vapor and oxygen in air, prolonging the lifetime of the devices. Kyokyun [10] took advantage of electron beam physical vapor deposition to prepare magnesium oxide thin films with a thickness of 2100 nm They reported an obtained water vapor transmission rate (WVTR) decline to 0.2 g/(m2·day), which prolonged the lifetime of prepared OLED device by five times. The compatibility of the low temperature Al2O3 for organic electronics was studied by measuring I-V-L and lifetime of OLEDs. The results demonstrate ALD process at 80 °C, did not cause damage to the organic functional layers, providing a favorable barrier properties for OLEDs

Experimental Section

Results and Discussion

Conclusions