| Metal halide perovskite is an emerging material possessing superior optoelectronic properties.Based on the excellent optoelectronic and lighting properties of perovskite materials,perovskite light-emitting diodes（Pe LEDs）have great potential to be the foremost next-generation light-emitting diode（LED）.So far,the external quantum efficiencies of near-infrared,red,and green devices have reached to over 20%.However,the performance of blue Pe LEDs still significantly lags behind.Therefore,it is urgent to demonstrate high-efficiency blue Pe LEDs.In addition,the integration of red,green,and blue sub-devices into white light Pe LEDs is also a challenge in this field.Based on the inferior performance of blue and white Pe LEDs,the research demonstrated in this thesis focuses on the improvement of blue Pe LEDs and the integration of multi-color Pe LEDs to generate white light,especially on the key aspects covering perovskite material design,device architecture optimization,and optical analysis.In chapter Ⅱ,we demonstrated that the efficiency of blue perovskite LEDs can be improved by combining three key strategies:composition engineering,dimensional engineering and modulation of recombination zone position.First,through composition and dimensional engineering,we prepared quasi-two-dimensional perovskite thin films with improved blue emission,taking advantages of reduced trap density and enhanced photoluminescence properties.Second,we observed that the perovskite crystals are non-uniformly distributed in the PEDOT:PSS/perovskite hybrid film along the vertical direction.Therefore,by systematically modulating the position of the recombination zone through controlling the charge injection property of the devices,we enabled the majority of carriers recombining at the perovskite crystal-rich region,and thus demonstrated the most efficient blue perovskite light-emitting diode to date with emission peak at 480 nm,record luminance of 3780 cd m-2 and record external quantum efficiency of 5.7%.The demonstration of efficient blue perovskite LEDs paves the way for the realization of full-color displays and white-light illumination with perovskite LEDs.In chapter Ⅲ,we focused on the spectral stability issue in blue Pe LEDs.In our previous work,wo found that perovskite utilizing mix-halide would be confronted with the undesirable spectral shift during continuous operation.When increasing the testing bias or measuring time,the emission peak tended to red-shift.To address this issue,we combined pure-halide CsPbBr3with PEABr together,but found out that only green emission could be obtained due to the fast energy and/or charge transfer process in the quasi-2D composition.Instead,through substituting IPABr with certain amount of PEABr,we could suppress the domain of low-dimensional component and therefore modulate the phases with different n values in the films.Futhermore,by means of interfacial modification,we modulated the hole transporting properties within the device,which resulted in external quantum efficiency over 8%and stable spectra during operation.In charpter Ⅳ,we designed a novel device structure that is composed of a blue perovskite LED and red or green perovskite phosphor powders.We reported a simple and efficient approach to construct high-performance white Pe LEDs with much-enhanced light extraction efficiency（LEE）by coupling a blue Pe LED with a layer of red perovskite nanocrystal（Pe NC）down-converter through a rationally designed multilayer semitransparent electrode（Li F/Al/Ag/Li F）.The red Pe NC layer allows the extraction of the trapped waveguide mode and surface plasmon polariton mode in a blue Pe LED and converts them to red emission,resulting in over 50%LEE improvement.Simultaneously,the complementary emission spectrum of blue photons and down-converting red photons contributes to a white Pe LED with a high external quantum efficiency and luminance of more than 12%and approximately 2000 cd m-2,respectively,which represent state-of-the-art results in this field. |
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