Study Of Blue Organic Light-Emitting Diodes By Adopting Dopant

Organic light-emitting diodes(OLEDs)are regarded"Fantasy Monitor"and"Photovoltaic Industry Star of Tomorrow"for their thin thickness,fast response,low driving voltage,wide operating temperature range,self-luminescence,low power consumption,and the ability to fabricate flexible devices,which is one of the hot topics in the field of display and lighting research widely.High-performance red,green,and blue(RGB)organic electroluminescent diodes(OLEDs)are important for achieving high-quality full-color display and high-efficiency white light emission.However,state-of-the-art blue OLEDs have relatively poor performance compared with their red and green counterparts in terms of luminous efficiency,color purity and operational lifetime.The doping method is considered to be one of the effective ways to improve the performance of blue OLEDs there are two kinds of luminescence mechanisms such as excitons energy transfer and carrier trapping in that devices.The concentration and different host materials are closely related to these two luminescence mechanisms.Therefore,it is very important to study the concentration of dopants and different host materials for the preparation of efficient and stable blue OLEDs.Compared with phosphorescent materials,fluorescent materials have the advantages of long exciton lifetime and low cost.BCzVBi is a highly efficient and thermally stable blue fluorescent small molecule luminescent material.In this paper,BCzVBi is used as a doping molecule,and small molecules mCP and CBP are used as host materials to prepare two different host-dopant devices(mCP-BCzVBi:Type-I;CBP-BCzVBi:Type-II),it has been found that changing the concentration of dopants and using different host materials have a greater impact on the optoelectronic properties of the device.The main work is summarized as follows:First,based on BCzVBi,two different types of devices,Type-I and Type-II,were prepared by vacuum thermal evaporation.The specific structure of the device is:ITO/NPB(40 nm)/host:x wt.%BCzVBi(30nm)/TPBi(40 nm)/LiF(0.5 nm)/Al(100 nm),host is mCP or CBP.Secondly,the prepared Type-I and Type-II blue OLED devices were characterized by voltage-current density,voltage-current density-photocurrent,brightness,color purity and stability.The following conclusions were obtained:(1)As the concentration of BCzVBi increases from 5 to 100 wt%,the on-voltage of Type-I and Type-II devices drops by at most 2.1 V,and the electroluminescence spectrum shows a red shift of up to 14 nm.(2)The saturation point of Type-I blue-light device appears at~50 wt%.At 50mA/cm~2 current density,the luminance of the device is 2533 cd/m~2,and the current efficiency is 5.10 cd/A;the doping concentration is~15 wt%,the maximum luminance of the Type-II device is 2940 cd/m~2 driven by a current density of 50 mA/cm~2.Third,the electron transport layer and hole transport layer of the device were optimized.TAPC and Bphen with higher carrier mobility were used as the hole transport layer and electron transport layer,respectively.Different devices have drawn the following conclusions:(1)When TPBi is used as the electron transport layer,the device with MoO3 as the hole transport layer shows a good JV characteristic curve;the device with TAPC as the hole transport layer has the highest brightness,when 50 mA/cm2 It is 2905 cd/m2.(2)When Bphen is used as the electron transport layer,the maximum brightness of the device is 3630 cd/m2,which is 24.9%higher than that of the TPBi device.The above research shows that different host-guest doping structures have different brightness bands,quantum efficiency,and stability due to their unique energy band arrangement.By studying the performance of devices with different doping concentrations,the design and preparation of high efficiency Durable blue OLED devices lay the foundation.