Investigation On Performance Tailoring Of Optoelectronic Devices By Using Transition Metal Chlorides Of MeCl_x(Me=Mo,W,Mn)

Organic light-emitting diode（OLED）receives increasing attentions due to its low power consumption,self-emission,flexibility and high luminance.Ultraviolet（UV）organic lighting is one of OLED research hotspots.It covers a wide range of applications in medical,information storage,chemical sensor and exciting lighting source.Wide bandgap of emissive molecule in UV OLED restricts hole injection and deteriorates carrier recombination,counteracting the development of UV OLED.Transition metal chloride（Me Cl_x,Me=Mo,W,Mn）materials are easily accessible,which also have kinds of chemical valence states and plenty coordination bonded anions.In this paper,using transition metal chloride as hole injection layer（HIL）with low cost and high throughout productable solution-processed techniques to enhance the hole injection ability of the UV OLED,and thus optimize device performance.Meanwhile,we use MnCl₂ to lower melting point of glass and modify electronic packaging paste.Some important results are summarized as followings:1)Solution-processed Mo Cl₅ and its composites of dual HILs（（poly（3,4-ethylenedioxythiophene）-poly（styrenesulfonate）PEDOT:PSS/Mo Cl₅ and Mo Cl₅/PEDOT:PSS）and doped composite HIL（PEDOT:PSS+Mo Cl₅）for tailoring hole injection in NUV OLEDs are demonstrated.The surface morphology,electronic properties and hole injection capability of these HILs are examined with Atomic Force Microscope（AFM）,X-ray photoelectron spectroscopy（XPS）,UV-Visible absorption and impedance spectroscopy analysis.The hole injection is enhanced by using Mo Cl₅,PEDOT:PSS/Mo Cl₅,Mo Cl₅/PEDOT:PSS and PEDOT:PSS+Mo Cl₅ in this order.Efficient NUV OLEDs from2-（4-biphenyl）-5-（4-tert-butylphenyl）-1,3,4-oxadiazole（PBD）molecule and HIL of PEDOT:PSS+Mo Cl₅ are demonstrated,showing maximum External Quantum Efficiency（EQE）of 2.2%,maximum radiance of 6.5 m W/cm²,full width at half maximum（FWHM）of 44 nm and electroluminescent（EL）peak of 407 nm.2）Solution-processed WCl₆ and its doping composite of PEDOT:PSS+WCl₆ are employed for tailoring hole injection of near UV OLED,and thus achieving high efficiency.X-ray photoelectron spectroscopy and UV-Visible absorption analysis show that WCl₆ and PEDOT:PSS+WCl₆ films behave exceptional electronic properties and superior optical transmittance.Current-voltage characteristics and impedance spectroscopy analysis confirm that the hole injection ability is enhanced in the order of WCl₆,PEDOT:PSS and PEDOT:PSS+WCl₆.Using PEDOT:PSS+WCl₆ as hole injection tailoring and PBD as emissive layer,the near UV OLED reaches maximum external quantum efficiency of 2.6%,radiance of 8.05 m W/cm²,FWHM of 45 nm and ELpeak of 405 nm.Device aging tests indicate that WCl₆ doped PEDOT:PSS considerably enhances the stability of near UV OLED.3)A kind of low melting point glass is developed by doping with MnCl₂ in purpose of reducing the sintering temperature of conductive paste.It is expected to apply in the low temperature packaging field of organic photoelectronic device.The X-Ray diffraction（XRD）shows a wide dispersion peak.The scanning electron microscope（SEM）measurement shows the MnCl₂ doped glass powders have smooth surface and uniform particle size distribution.Differential scanning calorimeter（DSC）characteristics confirm that MnCl₂ can effectively reduce the melting point of glass powders.