The Encapsulated OLED For The Flexible Polymer Substrate

The study of organic light emitting diodes (OLEDs) has been a major area of the research onorganic semi-conducting materials and devices. Compared with inorganic devices, OLEDs hasmany advantageous features, such as full solid-state, ultrathin, active light emitting, highbrightness, high contrast ratio and more adaptability for flexible substrates, etc. However, thestability in air of OLEDs is limited by many reasons, and this is the main challenge to OLEDsindustry. The degradation of OLEDs mainly caused by water vapor and oxygen, to solve thisproblem, atomic layer deposition (ALD) is applied to encapsulate the devices. In this work, Al2O3film was fabricated at low temperature by ALD. By optimizing the parameters of depositionprocess, the overall deposition time is reduced. Finally, the stability in air of OLEDs is increasedby encapsulating with ALD method.First of all, the background of OLEDs was reviewed. The important of encapsulation forOLEDs was emphasized by introducing the decay mechanism of the devices. Then thedevelopment of encapsulation method for OLEDs was presented. The relevant principles wereintroduced from structures, materials, light emitting mechanism, which are the important tooptimize the OLED.In order to deposition Al2O3film at low temperature of80℃, the pumping gas time (PGT) wasincreased during each cycle to discharge the redundant precursor of H2O and Trinethyluminium(TMA). The Al2O3film, was measured by calcium corrosion method, displayed the water vaportransmission rate (WVTR) can reach to1.5×10-4g/(m2·day). The stability in air of OLEDincreased efficiently by encapsulating with ALD.To further improve the barrier property of Al2O3film, O3was introduced instead of H2O. Fromthe scanning electron microscopy (SEM) and atomic force microscopy (AFM) testing, the Al2O3film deposited by O3and TMA showed excellent homogeneous properties. However, the ALDprocess is relatively slower than other technologies. By decreasing the PGT of O3and TMA, thedeposition rate and barrier property of Al2O3film were increased, the WVTR of it can reach to8.7×10-6g/(m2·day). Meanwhile, the encapsulation film was fabricated on the top-emitting OLEDs(TE-OLEDs). The light emission extraction of device was improved. By calculating with thesoftware SimOLED, the theory simulation data were consistent with our experimental results.At the end the study of bending model, we fabricated flexible OLED on the polymersubstrate. The device was encapsulated by ALD process and the lifetime increased. However, the mechanism of polymer substrate was decayed during the encapsulation process. Compared to theOLED fabricated on the glass, the stability in air of flexible OLED decreased relatively. Thus, theflexible OLED with encapsulated structure was realized by the ALD method applied.