Hybrid Organic/inorganic ?-nitride P-n Heterojunction Light-emitting Diodes

Revolutionary progress in ?-nitride-based light-emitting diodes(LEDs)has been seen over the last decades,leading to rapid growth in the fields of displays,solid-state lighting,visible light communication and so on.However,some critical problems,such as nitrides semiconductor materials with limited photoelectric properties,high cost,complicated fabrication process,prevent nitride-based LEDs from further development.To attain the long-term performance targets,great efforts need to be made.By contrast,organic semiconductor materials have attracted great interest and broad attention of scholars both at home and abroad owing to their advantages of simple fabrication,low cost and excellent optical property over the entire visible region.With active push to improve performance and extend the application range of In Ga N-based devices,as well as reach into new areas,the hybrid organic/inorganic systems may be a promising approach to combine the advantages of both organic and inorganic semiconductors to overcome their respective limitations,leading to excellent performance.Research in this area has made some progress,however,since this subject itself is more cross-cutting and complicated,high performance hybrid organic/inorganic LED is still rarely reported.Also,the working mechanism of the hybrid organic/inorganic LED is still underground.In this thesis,aiming at both targets,we have gradually developed a series of rather high-performance hybrid organic/inorganic p-n heterojunction LEDs through the rational design of device structure.We also performed lots of research work in revealing the working mechanism of the device,which can give us a complete picture of the hybrid organic/inorganic device operation and be helpful to the further optimization of the device structure.The main contents and results are shown below:1.By introducing organic p-type semiconductor 4,4'-cyclohexane-1,1-diylbis[N,N-bis(4-methylphenyl)aniline(TAPC),hybrid organic/?-nitride p-n junction LED with a p-type organic TAPC and n-type In Ga N/Ga N multiple quantum wells(MQWs)was fabricated.The TAPC used here is one of the most widely used hole-injection/transporting and electron-blocking material in organic LEDs.Through a rational device-structure designing,the hole and electron distribution within the device can be well controlled,thus better charge balance would be achieved.It's shown that the hybrid LED achieves peak current efficiency of 24.8 cd/A and external quantum efficiency of 20.5%,much better than those without TAPC.Such remarkable results demonstrate that TAPC is a promising alternative to inorganic p-type semiconductor and electron blocking materials,which provides an attractive route for cost-effective and high-performance simplified nitride-based LED sources.2.The hybrid organic/inorganic ?-nitride white LED(WLED)based on Rubrene/In Ga N/Ga N multi quantum wells(MQWs)was designed and fabricated.By optimizing the hybrid WLED structure,a nearly purity white-light emission was produced by hybridizing the blue light emitted from the In Ga N/Ga N MQWs and the yellow-red light emitted at the F8T2/p-Ga N interface by electroluminescence(EL).The resulting hybrid WLED with color coordinates of(0.31,0.33)shows a maximum current efficiency of 15.2 cd/A and excellent long lifetime stability.To better understand the luminescence mechanism of Rubrene and the carrier transport and radiation mechanism of across the Rubrene/In Ga N/Ga N MQWs p-n heterojunction,ultraviolet-visible(UV-VIS),photo/electroluminescence(PL/EL),time-resolved PL(TRPL)measurements and carrier dynamics were systematic studied.Such productive results will be beneficial to accomplish the drawbacks of phosphor-based WLED,which will greatly promote the development of cost-effective and high-performance phosphor-free nitride-based WLED sources.3.The influence of the hole injection layer(HIL)on the hybrid organic/inorganic ?-nitride p-n heterojunction white LEDs were systematic investigated.Three kinds of HIL,i.e.Mo O₃?HAT-CN and TAPC/Mo O₃,were inserted between the p-type electrode and the emitting layer.As compared to the device without HIM,these hybrid WLEDs with HIL all exhibite improved performance.Among them,the hybrid WLED with TAPC/Mo O₃ show the best device performance,where it achieved a lowest turn-on voltage of 2.9 V,peak current efficiency of 20.6 cd/A and external quantum of 8.1%.The origin of the high performance is comprehensively unveiled.The TAPC/Mo O₃bilayer HIL with effective electron-blocking capability can flexibly manipulate the hole and electron distribution between the emitting layers,extend the exciton the exciton formation region and maintain the charge balance within the device,a high performance hybrid WLED with high color stable is realized.Therefore,the selection of suitable hole injection layer provides a theoretical and experimental basis for obtaining highly efficient organic/?-nitride p-n junction organic/inorganic WLED.