Microcavity Organic Light-emitting Diode Design And Performance

Recently, organic light-emitting diodes(OLEDs) based on organicmaterials are one of the most promise technology for flat-panel displays.However, the broad emission spectra result in difficulties in developingfull color displays. So many researchers explore many approaches tonarrow the emission spectra and consider that the microcavity structure isa main method with most potential and extensive. The experiments provethat introduction of the microcavity structure into OLEDs not only narrowemission, and enhance the color purity, but also enhance device efficiency.It can be noticed that microcavity structures have greatly influence on theperformance of OLEDs.In this thesis, we simply analyzed the transmission theory of opticalthin film, and discussed the transmission characteristics of distributedBragg reflectors (DBR) and Ag film which were the reflectors in the textbased on the transmission matrix model using Matlab software. Thereflectivity, transmittance of Ag film and the relation between reflectivephase shift and the thickness of Ag film were studied and the relationbetween reflectivity, reflective bandwidth and refraction index difference,layer number and sequence of high-low medium of DBR were alsostudied. The obtaining result provided theoretical advices for actualdesign of the microcavity formed by reflective mirrors in OLEDs.Microcavity OLEDs formed by metal electrode silver (Ag) and DBRmirrors were designed. Some effects of cavity lengths, thickness of theemission layer, the interface of TPD/Alq3 and the emission region on theelectroluminescent (EL) spectrum and performance were investigated. Itwas found theoretically that the introduction of the microcavity intoOLEDs narrows emission spectra, and also significantly enhances theemissive intensity. The emitted radiation strongly depended on theemission region and the position of the emissive layer inside the cavity.Finally, the emission region should be narrow with its center at theantinode of the electric field in the resonant cavity to optimize MOLEDs.The negative refractive index dielectric (NRID) was introduced into the microcavity OLEDs. Two kinds of diodes containing thin negativerefractive index dielectric layer were designed. Firstly, the transmissionmatrix model of the negative refractive index dielectric was presented bythe classical electrodynamics theory. And then we theoretically studiedluminescence characteristics and EL spectra of the microcavity OLEDsbased on the transmission matrix model. The result shows that it's a newway to enhance device efficiency, color purity and thinned the thicknessof the MOLEDs.