Organic Microcavity Electroluminescent Physics And Devices

Zhao Jiamin(Condensed Matter Physics)Directed by Prof. Wang LijunThe organic electroluminescence(EL) device with microcavity(MOLED) can take on some new characteristics, such as narrowed spectrum, intensity enhancement, sharply directed emission in space, due to the microcavity effects compared with the common device without cavity(OLED). These changes in emission quality have significant application values. In this paper, a few physical issues are discussed and several device design methods are proposed on MOLED. Firstly, the optical characteristics of microcavity are calculated by characteristic matrix and some calculated results obtained using MATLAB language are presented.Then some cavity quantum electro-dynamic (CQED) effects are studied by experiment. The photoluminescence(PL) intensity enhancement at resonance wavelength and suppression at off-resonance wavelength, emission spectrum narrowing as well as emission intensity redistribution in space are observed in the microcavity device fabricated with distributed Bragg reflector(DBR) and silver mirror as well as that done with two silver mirrors. In the cavity with DBR, the reduced radiative lifetime is obtained. By introduction of two LiF layers, the adjustment of the position of thin layer Alq3 in the microcavity is achieved and the effect of the coupling strength between the emissive dipole and vacuum electric-field on the emission intensity in (/2-length microcavity is studied for the first time. This result is instructive to designing efficient mirocavity luminescent device. The optical characteristics of metal silver film used as the reflective mirror of microcavity are calculated by characteristic matrix method and it is shown that the thickness of metal mirror affects not only the reflectivity but also the penetration depth and thus the cavity mode. This conclusion is confirmed by experiment.Using the typical MOLED structure Glass/DBR/ITO/HTL/EML(ETL)/Al,the EL spectrum narrowing, intensity enhancement in the normal direction as well as emission intensity redistribution in space are observed. By the introduction of single layer silver film instead of the DBR/ITO multilayer, a (/2-length cavity is obtained. Using this kind of microcavity, three-color single mode PL from a single material Alq and three-color single mode EL from double layers PVK/Alq are achieved for the first time. By the introduction of chirped DBR with three reflective bands, a new kind of microcavity is fabricated and multi-mode PL is obtained. It is promising to realize white emission by this special microcavity.