Development Of High Performance White Organic Light-emitting Diodes

Organic light emitting diodes?OLEDs?have received a broad attention for consid-ered as ideal solid-state lightings owning to their superior energy conservation,envi-ronmental protection,healthy light,flexible feasibility.It presents a simultaneously pro-gress situation of research,development and industrialization.OLED illuminants have achieved certain significant progresses,there is still need to improve the technology for sustainable integrated development.That means under high brightness,it should realize large area lighting,high efficiency,superior white light quality,flexible lighting and low cost.From the perspective of the practical requirements in the field of lighting applica-tion,this thesis systematic studied the OLED devices with light quality,device efficien-cy,flexible lighting.Detail works in this thesis include:?1?By retionally selecting materials and designing device structures,high quality fluorescent/phosphorescent hybrid white OLED?WOLED?has been fabricated.At a high luminance of 5000 cd/m²,the WOLED yields outstanding lighting parameters in-cluding a CIE of?0.46,0.46?,a CCT of 2968 K and a CRI of 92.Comprehensive studies on the injection and transport of charge carrier can be in favor of deep understanding the charge transport process in the emissive layers and effective controlling the carriers and excitons,resulting in a complete scenario of the working mechanism.By using an in-tra-zone exciton harvesting scheme to directional control the excitons,providing a prac-tical method to tune the CCT without sacrificing the CRI value.Doping Ir?ppy?₂?acac?into the red emissive layer is of great benefit to the enhancement of excitons formation in the red emissive layer.By changing the doping concentration to increase the red color component and thus achieve a WOLED with CCT of²500 K.It provides a new idea for the development of low CCT WOLED devices.?2?It is discovered that in the Liq/Al/MoO₃-based tandem OLEDs,the use of a thicker Al layer in charge generation layer?CGL?apparently increases the vertical as well lateral electrical conductivity,resulting in a significant leaky lateral current spreading along the CGL,which is due to the formation of conductive interfacial MoO_3-x layer originating from the oxidation reduction reaction at the Al-MoO₃ interface.To prevent lateral electrical conductance in CGL,a C₆₀ buffer layer presenting high electron mobility and strong electron accepting ability is introduced in between the Al-MoO₃ interface.The corresponding tandem OLED exhibits high efficiency and low efficiency roll-off.The current efficiency of the tandem device is more than twice high-er than that of the single EL unit device related to optical cavity effect.Tandem device showed a current efficiency of 155.6 cd/A,and still maintained as high as 140.1 cd/A at a high luminance of 5000 cd/m².?3?It is indicated that the MoO₃?2 nm?/Al?2 nm?/MoO₃?5 nm??Layered Metal Ox-ides,LMO?stacked layers can be used as electrode in OLED devices due to its excel-lent electrical conductivity and optical properties.The performance of such OLEDs based on LMO field-effect electrodes are comparable to that of OLEDs made by con-ventional ITO electrodes.The LMO electrode structure shows excellent optical proper-ties;the transmittance is higher and the reflectance is lower than that of the ITO film across the visible spectra;the LMO-based OLED has emission spectra invariant of viewing angles,while the ITO-based OLED suffers from a relatively strong angular variation of the emission spectra.Finally,to illustrate the LMO's facile scale up poten-tial,a large area 30×35 mm² flexible OLED grew on a LMO-coated plastics?PET?sub-strate was successfully fabricated.