Achieving Efficient Polychromatic Electroluminescence in All Perovskite-Emitters Based Light Emitting Diodes

Professor Choy, Wallace Chik Ho   (Principal Investigator (PI))

Professor Yin Wanjian   (Co-Investigator)

Dr Gao Junling   (Co-Investigator)

36

2021-01-01

845055

Achieving Efficient Polychromatic Electroluminescence in All Perovskite-Emitters Based Light Emitting Diodes

interconnecting layer, perovskite LED device physics, perovskite nanomaterials, polychromatic EL, polychromatic perovskite LEDs

Photonics

Engineering (E)

17211220

General Research Fund (GRF)

2020

On-going

1) Coordinating the primary color light for an efficient polychromatic EL In order to achieve efficient polychromatic EL in PeLEDs for various target applications, the coordination of the primary color light is very important but has not been clearly studied. In this proposal, we propose the unique combination of q-2D perovskite (as the front short-wavelength light emitter) and NC perovskite (as the back long-wavelength emitter) to establish the novel polychromatic EL structure. The structure can also prevent the long-wavelength light absorption in the front emitter and take the advantage of the solvent compatibility between the two perovskites. As a case study, we will investigate white light emission to show the ways for achieving efficient polychromatic EL. (1) We will coordinate the primary colors by experimentally adjusting the stacking number of blue q-2D perovskites and the mixed halides ratio of red NC perovskites, and by conducting colorimetry calculation with CIE chromaticity plots. (2) We will enhance the primary color intensity by minimizing perovskite defects through introducing ionic liquids and metal dopants into the q-2D and NC perovskites respectively. (3) While the device-structure design for manipulating the carrier distribution in the emitters is crucial for realizing the white polychromatic EL, this issue is not thoroughly studied. We will conduct multi-physical (electrical and optical) studies for whole PC-PeLED device structures together with the measured material parameters. The theoretical results will be combined with experimental demonstration to finalize the design of PC-PeLEDs. 2) Designing an effective ICL for PC-PeLEDs For PC-PeLEDs constructed from the new polychromatic EL structure, such as PC-PeLED with an architecture of anode/ hole transport layer (HTL)/ q-2D perovskite/ ICL/ NC perovskite/ electron transport layer (ETL)/ cathode, the carrier transport mechanisms of ICLs which are important for understanding and optimizing device performances are yet to reach conclusive understanding. We will formulate targeted models based on our previous work and unveil the carrier transport mechanisms of different ICLs through rigorous simulations. Together with the theoretical results, PC-PeLEDs with different ICLs including layered and mixed material structures will be characterized and analyzed for ICLs optimization. To achieve effective ICLs, we will simultaneously address the ion-exchange and solvent incompatibility issues among perovskites and ICL materials by designing properly layered structures and selecting appropriate materials and solvents. Meanwhile, the electrical properties and band-alignment of the carrier transport materials of ICLs are very important to achieve the efficient and appropriate carrier transportation for suitable carrier distributions in the perovskite emitters. Besides studying commercially available materials, we propose to use our home-synthesized metal-oxide nanomaterials particularly ternary metal oxides featured with their adjustable bandgap and conductivity, low-temperature processes (for avoiding thermal damage of perovskites), and the use of perovskite and organic materials compatible solvents. 3 3. Achieving high-performance PC-PeLEDs To obtain high-performance PC-PeLEDs, we will focus on their EQE, spectral stability, and operational stability. For EQE, we will theoretically and experimentally analyze the EQE loss mechanisms and evaluate their effects on device performances, including non-radiative recombination loss, interfacial loss, optical loss, and the loss from detrimental carrier distribution. For the spectral stability, since the changes of carrier transportation governed by various mechanisms (as stated in Part II-2(b)2(1)) with external voltage biases and temperatures will be different, we will simulate PC-PeLED performances taking into account effects of various voltage biases and temperatures with different mechanisms. The corresponding PC-PeLED characterizations will be made and compared with theoretical results. Finally, we will establish a guideline for achieving spectrally stable PC-PeLEDs . *** To show our capability to manage the project, we have started to work on the project. The preliminary results show that, in Objective 1, by using a new ionic liquid and adjusting the q-2D perovskite, we enhance the blue PeLED intensity to 5737 cd m-2 luminance. In Objective 3, by forming a new co-ligand quasi-core/shell structure in NC perovskite, we enhance the red PeLED lifetime to 316.5 hrs. They are the best results in the correspondingly reported PeLEDs from our best knowledge as detailed in ""Research Plan and Methodology"".