Metal halide perovskites (MHPs) have recently become an important class of materials for use in solar cells, light emitting devices (LEDs), photodetectors and other optoelectronic devices. Perovskite LEDs have the potential to be used for building displays, using red, green and blue (RGB) light emitting pixels. In this thesis, we report the synthesis and characterization of a series of low-dimensional metal halide perovskites and the fabrication of blue (460– 480 nm) and sky-blue (480– 500 nm) light emitting devices (LEDs) using these materials. An inclusive introduction will be given into metal halide perovskites, including the working principles and development of perovskite light-emitting devices (peLEDs), followed by the characterization methods used in peLED research. In the first...[ Read more ]

Metal halide perovskites (MHPs) have recently become an important class of materials for use in solar cells, light emitting devices (LEDs), photodetectors and other optoelectronic devices. Perovskite LEDs have the potential to be used for building displays, using red, green and blue (RGB) light emitting pixels. In this thesis, we report the synthesis and characterization of a series of low-dimensional metal halide perovskites and the fabrication of blue (460– 480 nm) and sky-blue (480– 500 nm) light emitting devices (LEDs) using these materials. An inclusive introduction will be given into metal halide perovskites, including the working principles and development of perovskite light-emitting devices (peLEDs), followed by the characterization methods used in peLED research. In the first project, a specific class of peLEDs using Ruddlesden-Popper phase low-dimensional perovskites to achieve sky-blue electroluminescence. We then attempted various strategies to improve the performance and stability of blue peLEDs by adding external metal dopants and investigating the various mechanisms by which these dopants enhance the device function. We find that quasi-2D systems can be used as spectrally stable and efficient sky-blue peLEDs. Mn²⁺ dopant ions were studied as a showcase material to elucidate the mechanism of device improvement. With subsequent optimizations of these peLEDs, a high external quantum efficiency (EQE) of 7.5% at 487 nm was obtained with a stable spectrum against voltage and over time. In the second project, we focus on achieving deep-blue emission (sub-475 nm) by using Dion-Jacobson phase perovskites. We then investigated the optical and structural changes when DJ-phase precursors are mixed with RP phase perovskites and were able to propose a mechanism for the observed blue-shift in the emission spectrum. Further device optimization led to an LED with EQE 1.5% at 469 nm as the first report on deep-blue Dion-Jacobson type peLED. In the third project, we endeavoured to further enhance sky-blue peLED performance via cation engineering and further device optimizations. A triple cation system, GA-Rb-Cs (GRC) was explored and the role of each cation studied using optical, electrical and structural analysis. We also improved the hole-transporting layer (HTL) via a lithium dopant. An efficient sky-blue peLED with EQE of 9.0% at 492 nm was recorded with the optimized GRC system, and this improvement was accompanied by prolonged device lifetime over 18 minutes with the modified HTL. The thesis concludes with future directions for this technology and for perovskite displays in general. The limitations of blue peLEDs at this stage are also discussed, with some preliminary results shown in the Appendix suggesting some future directions for the field.