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

金属卤化物钙钛矿结合了高的量子效率、可调的带隙和窄带宽发射，表现出优异的光电性能，因此是一种很有前途的光发射技术材料。基于钙钛矿的电致发光器件(PeLED)现在达到了商业上相关的量子效率&gt；20%。然而，在大多数PELEDS中，有源层是通过旋涂工艺制备的，这通常非常复杂，并且容易受到质量变化的影响，阻碍了生长过程与材料和器件功能之间的关联。因此，大多数旋涂工艺在工业上并不相关。另一方面，用化学气相沉积(CVD)制备钙钛矿材料可以精确而独立地控制不同的生长参数，并减少复杂的合成过程，从而获得高度可重复性的过程。化学气相沉积(CVD)技术用于钙钛矿结构的研究还处于起步阶段，对前驱体比例、原料流量、温度等不同工艺参数对材料性能的影响，特别是对缺陷的形成和钙钛矿结构的光电性能的影响知之甚少。该项目的主要目标是开发一种CVD工艺，能够在热壁喷头反应堆中生长用于PeLED的CsPbBr3钙钛矿。在这个特别设计的反应器中，来自独立操作升华源的材料通量被均化，并通过喷头引导到衬底上，从而提供对不同工艺参数的精确控制和出色的重复性。不同工艺和生长参数的变化与所获得的钙钛矿层的光学和结构分析之间的紧密关联将允许对CsPbBr3层进行有效的优化。为了进一步提高有源层的量子效率，我们将发展有机-无机化合物的共升华作为钝化CsPbBr3中非辐射缺陷的添加剂。作为下一步，我们将CVD生长的钙钛矿层嵌入到PELED结构中，以分析与相邻电荷传输层的界面处的非辐射损失，并表征来自这些层的电荷注入的效率和平衡。基于这些结果，电荷注入层将被改变，以优化器件的品质因数，目标是展示经CVD处理的具有1.5%外部量子效率的Ped。

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 %.