Investingation Of Performance And Ncapsulation Of OLED With Sulfide Glass Hin Film

Organic light-emitting devices （OLEDs） are a kind of device that externalelectric field drive the carrier in the organic material in the transmission andcomposite, which convert electrical energy into light energy. Compared with theother displays, OLEDs have many advantages, such as near180°viewing angle,self light luminescence, faster response, low power consumption and flexibledisplays. But the unencapsulated OLEDs are exposure of the organic-metalcathode interface to atmospheric oxygen and water vapor. This leads to oxidationand delamination of the metal cathode as well as chemical reactions within theorganic layers. So the operating life of devices is difficult to achieve therequirements in application. In this paper, MgF₂and Se thin films were used toencapsulate OLEDs by vacuum evaporation and the operating life was improved.The encapsulation thin films were obtained by vacuum vapor depositionand accomplished by in-situ encapsulation on OLEDs, using MgF₂and Se as theoriginal evaporation materials. Performances of insulation, transmission andbarrier of water/oxygen of different thickness of MgF₂thin film and Se/MgF₂,MgF₂/Se thin films were investigated in this paper. In addition, the influence ofMgF₂/Se films encapsulation layer on OLEDs was discussed in details, includingthe characteristics of current density-voltage-luminance, EL spectrum andoperating life.The phase structure, micro-morphology, thickness, optical transmission,resistance change rate of films of encapsulation layer and the corrosion of Cafilm were characterized by X-ray Diffraction （XRD）, atomic force microscopy（AFM）, ellipsometer, plane grating sensor, digital multi-meter and opticalmicroscope, respectively. EL spectrum and chrome, density of current, voltageand luminance of encapsulated OLEDs were measured by luminance spectrometer, DC power, optical power meter and photometer, respectively. Themain results of research were list below.（1） The XRD analysis showed that MgF₂and MgF₂/Se thin films wereamorphous. The main phase of Se film was hexahedron crystal of Se. The AFManalysis revealed that the surface of MgF₂thin film showed a compact columnarstructure, the Se film surface was no pores and smooth in some degree, and thesurface of MgF₂/Se thin films showed a dense cloth-like structure. The surfaceroughness of MgF₂, Se and MgF₂/Se thin films were2.43nm,1.37nm and1.92nm, respectively.（2） Research of the insulation property of thin films indicated the resistancevalue of MgF₂, Se/MgF₂and MgF₂/Se thin films were over2×10⁸, showingexcellent insulating properties. The resistance value of Se film reduced to2×10⁵from initial2×10⁸after480h, which revealed the insulation of Se filmwas instable. The burning of Se film caused by evaporation temperature could beavoided through using MgF₂/Se films structure instead of structure of Se/MgF₂.（3） Research of the optical transmission of thin films indicated thetransmission of MgF₂thin film was quite good and over85%in visible region.The transmission of Se thin film was poor and below60%in visible region. Andthe transmission of MgF₂/Se thin films was less than40%when the wavelengthwas under350nm, but the transparence was good and over75%when thewavelength was400-600nm.（4） Research of the barrier property of water/oxygen of thin films indicatedthe resistance change rate of the sample without MgF₂thin film reached149%in350h, so it did not have barrier property of water/oxygen. The barrier property ofwater/oxygen of the sample which used200nm MgF₂film was optimum and theresistance change rate was less than30%within300h. The barrier property ofwater/oxygen of the sample with Se/MgF₂films was quite well and the resistancechange rate was25.3%at300h. The barrier property of water/oxygen of thesample with MgF₂/Se films was quite better than the sample with MgF₂andSe/MgF₂thin films because the resistance change rate was less than4%within300h.（5） The Ca degradation test indicated the surface of the sample encapsulatedby MgF₂/Se thin films was corroded slightly in5h and began to appear a lot of dark spots in50h. And it appeared spot-like transparent region in200h.Moreover, the middle of transparent region was corroded relatively seriously.The surface almost changed to transparent and the film was corroded badly in300h.（6） Research of the performance of device encapsulated by MgF₂/Se thinfilm indicated the coordinate of the encapsulated device was almost no changeand still in the green region. The density of current-voltage characteristic ofencapsulated device was slightly lower, while the affects of other photoelectricproperties of device, such as luminance-voltage characteristic, luminance-densityof current characteristic, EL spectrum and chromaticity coordinate, were little.Furthermore the operating life of device is improved significantly, which is1.7times higher than non-encapsulated devices.