ECCS-EPSRC: Superlattice Architectures for Efficient and Stable Perovskite LEDs

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This proposal will develop thin-film metal-halide perovskite light-emitting diodes (LEDs) with high efficiencies. Standard inorganic LEDs, such as blue indium-gallium nitride, rely on the ability to p-dope and n-dope the hole- and electron-injecting layers, and to construct multi-quantum-well structures within which electrons/holes are confined and emit light, all in a heteroepitaxial structure. This allows close to thermodynamic efficiency operation for red and blue, but not yet for green (where nitrides show substantial losses). In contrast, organic LEDs (OLEDs) are assembled as stacks of different molecular materials, with band-edge positions selected to allow electron or hole transport to the recombination zone. ‘Doping’ through charge-transfer reactions with redox-active additives is used to assist injection from electrodes, but is not possible in the bulk. Though commercialized for displays, OLEDs require drift fields to overcome injection barriers, show very low carrier mobilities, and operate at voltages well above the emission bandgap. As outlined in our ‘track-record’ above, the team successfully adopted the OLED architecture for thin-film LEDs made with metal-halide perovskites. The critical components in this work will be developing: (a) a 2D/3D superlattice that confines e-h pairs, but with a tuneable “well depth” in order to minimize drive voltage requirements will be used in these to achieve good charge trapping, (b) spacer layers of perovskite that keep charge carriers away from the transport layers to avoid quenching; (c) and (d) hole- and electron-transport layers engineered to give ohmic injection at the perovskite interfaces, through chemical tuning and doping (ensuring that trap/quenching states associated with doping are far enough away from the emissive perovskite zone) and designed to give ohmic contacts at the two electrodes. This requires advances across a range of materials chemistry, materials processing, and semiconductor engineering tasks, underpinned by advanced characterization techniques. Light-emitting diodes (LEDs) are devices that are used in many of today’s displays, such as those used in televisions and cell phones, and can also increasingly in lighting. For these applications red-, green-, and blue-emitting LEDs are needed. However, green-emitting LEDs that are energy efficient and that are stable are particularly challenging to develop. This proposal is focused on developing efficient green-emitting devices based on a class of materials known as metal-halide perovskites. In particular, teams at the Universities of Cambridge (UK), Oxford (UK), and Colorado (USA) will collaborate with one another to solve engineering problems facilitating such devices. This work may result in new commercially viable LED technologies, as well as other new applications for metal-halide perovskites. As well as having potential impacts on the emerging semiconductor industry in the UK and USA, this project will: provide a US postdoctoral researcher with experience in organic and metal-organic synthesis and a range of physical characterization methods, and with the opportunity to participate in a close international inter-institute collaboration; and help support the education and training of women and underrepresented minority students.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.