The Study Of The Influence Of Functional Layers On The Performance Of Phosphorescent Organic Light-emitting Diodes

Organic light-emitting diodes(OLEDs)have become the new generation display production after liquid crystal display and wide applications prospect in solid state lighting.The advantage of OLEDs are virtue of light weight,thin thickness,high brightness,flexible,broad visual angle,can work at low voltage and no need to prepare back light.In recent years,performances of organic light-emitting devices have been improved dramatically by developing new material and architectures.However,for OLEDs,the mobility of holes is often faster than that of electrons,which lead to unbalanced charge carries transport.Moreover,the excito n recombination region is often narrow in the multilayer device.These result in reduced efficiency and luminance.In this paper,we introduced a mixed interlayer between two emitting layers to achieve high efficiency,high luminanceand low turn on voltage of OLEDs.The emitting mechanism is also discussed.Firstly,we fabricated orange OLEDs by introducing an interlayer.The devices take advantage of red phosphorescent material and orange phosphorescent material.The result reveals that the performance of device with the mixed interlayer is higher than that of traditional interlayer.The maximum efficiency is 17.1 cd/A and 15.3 cd/W,respectively.And the turn on voltage is only 2.77 V.This can be attributed to the balanced charge carries and broader exciton recombination region.Then we fabricated white OLEDs by employing blue phosphorescent material and orange phosphorescent material.We find that excessive electron transport material block holes so that few holes can reach blue emission layer.The result device achieves high luminance of26530 cd/m~2 and also color stability in large voltage.We further treat the functional layer thickness optimism which is beneficial to the promote of OLED as the start point,probe the way to manufacture more efficient OLED and study the influence of functional layer on the performance of OLED.We found that Liq is dispensable after the analysis of the current density-voltage and luminance-voltage curves of four devices.The current density became very small and the luminance was pretty low without Liq.The absence of Liq made the injection and transport of electrons become difficult.we found the optimal thickness of 0.8 nm of Liq.We further focus on the thickness optimism of emitting laye and found the best thickness of 110 nm for luminance layer after the overall consideration.We also evaluated the devices from the aspects of current density,luminance,current efficiency,power efficiency and determined the optimal thickness of Bphen,we determined that the optimal thickness of Bphen in such a structure is10 nm.