ECCS-EPSRC Superlattice Architectures for Efficient and Stable Perovskite LEDs

Lead halide perovskites show real promise for use in solar cells, but are also very promising for use in LEDs, since they can show high luminescence quantum yields in thin film structures. The investigators were first to show LED operation using device architectures based off designs for organic LEDs and were able to lift quantum efficiencies to high values (close to 100% internal quantum efficiency). However, these devices require higher than optimum drive voltages that limit power efficiency and limit operational lifetime. In this project we will realise new perovskite LED architectures that deliver a step change in power efficiency and stability at display-relevant conditions.

We consider there is a real opportunity to build all-perovskite heterostructure semiconductor stacks that achieve local bandgap control through choice of 2D and 3D perovskite structures. We will develop and demonstrate new thin-film perovskite LED architectures that use controllably engineered 2D/3D 'superlattice' perovskite structures as the emissive layers and as charge transport layers -- inspired by commercial GaN quantum well technologies. We will develop layer by layer deposition of perovskite structures containing stacks of lower-bandgap 3D layers with larger gap 2D layers. These will be designed to cause charge recombination in a central 2D/3D superlattice, together with electron- and hole-transporting 2D perovskite layers to either side that confine the charge recombination zone away from quenching sites at the heterointerfaces to either side. Selective injection of electrons and holes to these structures will be provided by organic charge transport materials. These will be 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 project requires advances across a range of materials chemistry, materials processing and semiconductor engineering tasks, underpinned by advanced characterisation techniques. We will initially develop green LEDs, since the APbBr3 materials show close to ideal green CIE coordinates, and extend our designs to red and blue perovskite emitters in the second half of the project. We will stress-test isolated emission materials and LEDs, leveraging protocols we have established for the best-in-class perovskite solar cells but tailored here for light emission.

The objectives for the project will be the development of processing methodologies for growth of perovskite superlattice structures, their implementation in power-efficient LEDs, and the demonstration of enhanced operational stability, achieved through operation at low drive voltages. We target a step change in power efficiency and stability at display-relevant conditions. Besides academic impact, disseminated through publications and conferences, we will explore potential for industrial impact, building on the fundamental patent portfolio we have been establishing.