Study On Carrier Injection And Transport Behaviors Of Quantum Dot Light Emitting Diodes

The phenomenon of electroluminescence was first discovered in 1936 by G.de Stril.As an electroluminescent device,quantum dot light-emitting diodes(QLEDs)displays have shown good promise in the field of display technology due to their wide color gamut,high color purity of light,relatively simple processing,low energy consumption and high stability.In addition,QLEDs is considered to be a “green” light source that can replace conventional lighting materials due to its good luminous performance and long service life.Since the first QLEDs was born in 1994,researchers have improved and designed new functional layer materials,optimized device structures and used new preparation processes to increase the external quantum efficiency(EQE)of electroluminescent devices from the initial0.01 % to over 20 % today.In contrast to the rapid development of QLEDs device performance,there are still many unexplained aspects about QLEDs device physics,such as the carrier injection and transport properties of quantum dot light-emitting diodes.It is known that these behaviors play a crucial role in the operation of QLEDs.Based on this,this thesis revisits the hole injection mechanism in QLEDs through a combination of experiments and simulations,and explores the transition of temperature-dependent charge transport mechanisms in core/shell colloidal quantum dot films,and the results are important for optimizing QLEDs and understanding the impact of carrier dynamics on device performance.In the third section,the hole injection mechanism in QLEDs is revisited by a combination of experiments and simulations.The results show that the applied bias significantly reduces the barrier height between the HOMO level of the HTL and the valence band of QDs,which is conducive to hole injection.The bending of the LUMO energy level of the HTL at the HTL/QD interface can confine the electrons in the quantum dot emitting layer and reduce leakage current,while the triangle-shaped potential barrier resulting from the bending of the VB energy level of the QD is favorable for hole tunneling injection.In addition,both theoretical simulations and experimental data demonstrate that the pathway for holes to be injected from the HTL to QDs in the QLED device is thermally-assisted tunneling.In the fourth section,the charge transport properties of luminescent core/shell colloidal quantum dot films over a wide temperature range are characterized and analyzed based on single carrier devices,and the charge transport mechanism is investigated.The results show that the Poole-Frenkel emission conduction mechanism is applicable to the high temperature range.As the temperature decreases,the measured currents can be described by the EfrosShklovskii variable range hopping model.It is worth noting that in both cases,defect states and disorder in quantum dot films play a very important role in the charge transport process.