Research Of Organic-inorganic Hybrid Perovskite Light-emitting Devices

Organic-inorganic halide perovskites are regarded as an important optoelectronic material that exhibits long free-carrier diffusion length,high charge-carrier mobility,tunable bandgap,and solution-processability.The hybrid perovskites also show high photoluminescence quantum yield(PLQY),high color purity and high brightness,making them desirable for display and lighting applications in the future.However,perovskite ligit emitting diode(PeLED)has lots of challenges:1)the need for further boosting the device efficiency to surpass organic LEDs(OLEDs and quantum-dot LEDs[17];and 2)the need for dramatic improvement in device stability.To tackle the above problems,in this thesis I mainly study the influence of the crystallization kinetics of organic-inorganic quasi-two-dimensional perovskite films on the performance of PeLED devices.My work includes the aspects of interface modification layer,charge injection,device structure design,etc.The relationship between the perovskite active layer and device performance provides a new research direction for improving the device efficiency of PeLED and overcoming the low stability of perovskite.Frist,we insert betaine,an interface buffer layer(BL),between the HTL and perovskite emitting film,which can control the surface wetting properties and increase the crystalline nucleation sites,leading to a uniform film formation and confined grain size.Due to the confinement of grain size,the perovskite film deposited on the stacked layers of PEDOT:PSS/HTL/BL shows a high exciton binding energy(Eb)of 84.5 meV and enhances PLQY significantly.By combining all the advantages of using betaine as the BL,the corresponding PeLEDs exhibit a dramatic enhancement in current efficiency and EQE.Furthermore,perovskites always suffer from poor operational stability and vulnerable chemical stability,especially after subjected to oxygen and moisture exposure.These shortages may be solved by proper encapsulation.However,the intrinsic properties such as ionic migration,phase segregation and electrostriction are hardly to be overcome.The above issues would be accelerated under a large electric field,and these finally cause device failure.In this thesis,I employ interfacial indicator to directly reveal electrical leakage location,and the quantitative interfacial Auger recombination(IAR)and the boundary conditions(interfacial majority carries exhaustion and interfacial minority earriers deficit models)are discussed according to interfacial drift-current ratio.Based on the above understanding,we can controllably tune IAR.Finally,the IAR-stimulated PeLEDs present superb operational stability benefiting from suppressed operational voltage(T50 over 11 h at 1000 cd/m2,10 times longer than the standard devices)and decent performance.With recombination region self-adjusting(RRSa)which is realized by mixing IAR and electrons injection-gain,such a device also shows negligible roll-off even at a luminance over 3 ×104 cd/m2.This work not only gives a deep view about IAR,but also sets up a direction to f-urther promote the next stride of PeLEDs.