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

结合大的量子效率、可调带隙和窄带宽发射，金属卤化物钙钛矿表现出优异的光电性能，因此代表了用于光发射技术的有前途的材料类别。基于钙钛矿的电致发光器件（PeLED）现在实现了商业上相关的量子效率> 20%。然而，在大多数PeLED中，活性层是通过旋涂程序制备的，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相关性。因此，大多数旋涂工艺在工业上不相关。另一方面，用化学气相沉积（CVD）制备钙钛矿保证了对不同生长参数的精确和独立控制以及较不复杂的合成程序，从而导致高度可重复的工艺。用于钙钛矿生长的CVD技术的发展仍处于起步阶段，对于不同工艺参数（例如前体比率、材料通量或温度）对材料性质的影响，特别是对缺陷的形成和钙钛矿的光电功能性的影响知之甚少。该项目的主要目标是开发一种CVD工艺，使PeLED的CsPbBr 3钙钛矿在热壁淋浴头反应器中生长。在这个专门设计的反应器中，来自独立操作的升华源的材料通量被均匀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再现性。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相关性将允许CsPbBr 3层的有效优化。为了进一步提高有源层的量子效率，我们将开发有机-无机化合物（MaBr）的共升华作为钝化CsPbBr 3中的非辐射缺陷的添加剂。作为下一步，CVD生长的钙钛矿层嵌入PeLED架构中，以分析与相邻电荷传输层界面处的非辐射损耗，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，将改变电荷注入层以优化器件的品质因数，目的是展示具有> 1.5%的外部量子效率的CVD处理的PeLED。

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 %.