Study On The Improvement On OLED Performance By Employing CsN₃-doping Technology And The Fabrication Of Tandem Warm White OLED

Organic light-emitting devices?OLEDs?exhibit unique charms in the field of solid-state lighting and display owing to their special characteristics of compatibility with flexible substrates,environmental friendliness,low power consumption,high efficiency and rich colors etc.High efficiency and low power consumption have always been the common concern of OLED researchers.Served as efficient N-dopant,CsN₃ is able to enhance the electron conductivity of the electron-transporting layer and the current density of the device obviously,leading to the decrease in operating voltages as well as improvement on current efficiency and power efficiency.Warm white tandem OLEDs having stable emission spectra can be free of suffering from blue-light hazard,enabling people to feel comfortably and easily and being beneficial to health.In this paper,we studied the effect of CsN₃ as N-dopant on the device performance;A new type of charge generation unit?CGU?was proposed and a high-performance tandem green OLED and tandem warm white OLED were constructed,and the optical properties of the tandem warm white device were studied in detail.The main content of the paper is listed as follow:1.Employing CsN₃ as N-dopant in Bphen and B3PYMPM,respectively,and improving the device performance greatly.The experimental results show that CsN₃-doping can effectively enhance the electron conductivity of the electron-transporting layer as well as the current density of the device and reduce the electron injection barrier,resulting in the decrease of operating voltage and the improvement of device efficiency.Compared with the reference device,the boost of the electron conductivity is the responsible for the increase in device current density.The conductivity of CsN₃:Bphen is four orders of magnitude higher than that of the pristine Bphen,while the conductivity of CsN₃:B3PYMPM is five orders of magnitude higher than that of the undoped B3PYMPM.XPS measurements show that the chemical reaction occurs between Al,CsN₃ and organic molecular at the presence of Al,producing metallic Cs.The metallic Cs will donate free electrons to electron-transporting layer and finally enhance the electron conductivity of the electron-transporting layer and the current density of the device.2.We have fabricated an efficient tandem OLED based on Ir?ppy?₃ emitter adopting CsN₃:B3PYMPM/Al/HAT-CN as CGU.The processes of charge generation,separation and injection within the CGU have been demonstrated by studying the change in the emission spectra of the dual-color tandem device.The experimental results show that the charges were generated at the HAT-CN/NPB interface and can be separated and injected to the adjacent carrier-transporting layer efficiently.The thin layer of metal Al can reduce the electron injection barrier at the B3PYMPM/HAT-CN interface remarkably,promoting the electron injection and improving the brightness and efficiency of the device.The maximum current efficiency and power efficiency of the tandem device were 164.3 cd/A and 109.8lm/W,respectively.At a given current density of 5 mA/cm²,the current efficiency and brightness are about 2.7 times that of the single-unit device.3.A high-efficiency tandem warm white OLED with high-stable spectra was constructed and its optical properties were investigated systematically.Firstly,the microcavity effect exiting in the tandem device was confirmed by experiments.Then,guided by the theory on microcavity,a tandem warm white device satisfying the requirements of warm white emission on color coordinates and correlated color temperature was simulated using the Sim OLED software.Finally,an efficient tandem warm white OLED was constructed based on the simulation results and the microcavity effect within the device was studied in detail.