Development of a CVD Process for the Synthesis of CsPbBr3 Perowskites for Light Emitting Diodes

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Combining large quantum efficiencies, a tunable bandgap and narrow bandwidth emission, metal halide perovskites demonstrate excellent optoelectronic properties and thus represent a promising material class for light emission technologies. Electroluminescence devices based on perovskites (PeLEDs) by now achieve commercially relevant quantum efficiencies > 20%. However, in most PeLEDS the active layer is prepared via spin coating procedures, which are often highly complex and easily affected by variations in quality, impeding correlations between growth processes and material and device functionality. Thus, most spin coating processes are not industrially relevant. On the other hand, preparing perovskites with chemical vapor deposition (CVD) promises precise and independent control over different growth parameters and less complex synthesis procedures, resulting in highly reproducible processes. Development of CVD technology for perovskite growth is still in its infancy, with little knowledge about the influence of the different process parameters such as precursor ratios, material fluxes or temperature on the material properties, especial on the formation of defects and the optoelectronic functionality of the perovskites. The main goal of this project is the development of a CVD process enabling the growth of CsPbBr3 perovskite for PeLEDs in a Hot-Wall-Showerhead reactor. In this specifically designed reactor, material fluxes from independently operated sublimation sources are homogenized and directed onto the substrate with a showerhead, offering precise control over different process parameters and excellent reproducibility. A tight correlation between the variation of different process and growth parameters and the optical and structural analysis of the obtained perovskite layers will allow for an efficient optimization of the CsPbBr3 layer. To further improve the quantum efficiency of the active layer, we will develop the co-sublimation of organic-inorganic compounds (MaBr) as additives to passivate nonradiative defects in CsPbBr3. As a next step, the CVD-grown perovskite layers are embedded in a PeLED architecture to analyze non-radiative losses at the interfaces with neighboring charge transport layers and to characterize the efficiency and balance of the charge injection from those layers. Based on these results, the charge injection layers will be varied to optimize the figures of merit of the device with the goal of demonstrating a CVD-processed PeLED with external quantum efficiency > 1.5 %.