Effect Of The Microcavity Effect On The Efficiency Roll-off Of Organic Light-emitting Devices

Great progress has been made in organic electroluminescent light emitting device(OLED). A lot of attentions from researchers have been paid to it due to the superiorfeatures of OLED. OLED is a kind of surface-emitting and self-luminescent device,and possesses wide viewing angle, high corresponding speed, low cost, and manyother advantages. In addition, bendable display devices can be developed whenorganic materials are fabricated on flexible substrates. There is a large space for thedevelopment of OLED in terms of display and lighting. However, there are still manyproblems in the practical application of OLED. Efficiency roll-off is considered to beone of the factors that constrain OLED development.The content of this article is dedicated to employ the micro-cavity effect to improvethe efficiency roll-off. Microcavity is defined as an optical resonant cavity composedof electrodes that have high emissive efficiency and thickness comparable to that ofthe visible light wavelength. Micro-cavity effect will have an impact on the lifetime ofexcitons. Thereby it’ll reduce the efficiency roll-off. We do multiple sets ofcomparative experiments. According to the strength of the micro-cavity effect, weproduce three groups of devices, a group of Sm: Ag electrode top-emitting deviceswith weak micro-cavity effect, a group of Ag cathode top-emitting devices with strongmicro-cavity effect, and a group of bottom-emitting devices without micro-cavityeffect.In order to study the performance of different devices and simplify the testing workwe produce organic luminescence integrated test system based on MFC. The systemmeets the requirement completely. By using this system to compare the differentintensities of OLED microcavity we find that micro-cavity effect influences theefficiency roll-off of devices. At a certain brightness efficiency roll-off can beweakened in weak microcavity but strengthed when the brightness exceeds this value.We attribute this to that in weak micro-cavity effect device Sm: Ag electrode sheetresistance is large, and the light absorption of the electrode is strong. However, in Ag-electrode device with strong micro-cavity effect, we demonstrate thatmicro-cavity effect greatly improves the efficiency roll-off of the device.