Study On Laser Radiation Of Waveguide Leakage Mode In Organic Light-Emitting Diode

So far,some progress has been made in the study of electro-pumped organic semiconductor lasers based on micro-cavity structure.However,with the increasing of current density,various loss mechanisms in the devices will gradually raise,which is a challenge to the study of electro-pumped organic lasers.When the leaked waveguide mode in the dielectric layer of organic light emitting diode（OLED）is very close to the cut-off wavelength of planar waveguide structure,the threshold of the propagation mode becomes low,and the radiate laterally from the substrate of OLED device,and its radiation spectrum becomes narrower than the front radiation spectrum.The light of lateral leaked mode is generated by the waveguide mode leaking into the substrate.Therefore,the light of the leaked mode can be increased by increasing the proportion of waveguide mode in the device.This can facilitate the light amplification which radiates laterally in the OLED substrate.In this paper,the laser radiation of waveguide leaked mode in OLED device is studied.The mirror of optical resonator is formed by the evaporated silver film on both sides of the quartz substrate in OLED device.Based on ensuring the electrical performance and quantum to realize the optical radiation of lateral leaked waveguide mode in the device substrate.Alq₃、CBP:Ir（ppy）₂（acac）（8wt%,15 nm）and Bepp₂:Ir（ppy）₂（acac）（8wt%,15 nm）were used as luminescence layers successively in this paper.Alq₃ can be used as both luminescent layer and electron transport layer with the thickness ranging from 60 nm to 280 nm.For phosphorescent devices,the thickness of the electron transport layer CBP and Bepp₂ varies from 40 nm to 140 nm.By changing the thickness of the electron transport layer,the proportion of the waveguide mode can be changed to improve the leaked mode,also more electrons can be combined with the hole.Appropriate host-guest doping system and guest doping ratio can be selected to optimize the charge transfer capacity of luminescent layer and energy transfer process,so as to improve the performances of phosphorescent OLED devices.The frontal emission spectrum and the lateral emission spectra of the quartz substrate with or without resonator are measured respectively.It is found that the lateral emission spectrum is narrower than that of the frontal emission spectrum,which is attributed to the fact that the wavelength of leaked mode is very close to the cutoff wavelength of metal cladding waveguide structure,The theoretical calculation is basically consistent with the experimental results.The TM and TE modes of the lateral emission spectrum belong to first order mode.In addition,the spectrum with cavity is slightly narrower than that of without cavity,which indicate that the cavity has a slight effect.