Understanding and control over defects in halide perovskites through defect chemical studies combined with in situ optical characterization and detailed optical spectroscopy

由于卤化物钙钛矿优异的光电性能，它们作为一种高效的半导体材料在太阳能电池、发光二极管或光、X射线和伽马辐射探测器中的应用正在被讨论。在此背景下，卤化物钙钛矿的一个显着特征是对固有离子点缺陷的高耐受性和自我修复能力。然而，这些缺陷会影响光电性能，例如，当施加电势差时，会导致离子通过卤化物钙钛矿，导致效率损失和基于卤化物钙钛矿的光电子器件的性能下降。因此，本项目的目标是深入了解卤化物钙钛矿中的各种点缺陷是如何影响其光电性能的，并了解如何通过对钙钛矿进行可控的修饰来调谐点缺陷浓度。实现这些目标的关键是将缺陷化学研究与对具有明确性质的卤化物钙钛矿样品进行光学测量相结合。基本研究包括精确设置碘分压，这将导致钙钛矿与碘的热力学相互作用，从而得到依赖于碘分压和温度的点缺陷的平衡浓度。这种方法是氧化物钙钛矿的标准方法。在上一个项目中，也成功地证明了这种方法对甲基铵-碘化铅是可行的。在拟议的延续计划中，将通过电导测量产生的点缺陷浓度，而这些点缺陷对光电性能的影响将直接通过原位光学表征来研究，即通过测量薄膜形成过程中的吸收和发射。此外，还将使用掺杂来确定缺陷浓度，以完善缺陷化学模型，并定量确定生成热。为了阐明激发态的性质及其弛豫，识别缺陷和杂质，并确定缺陷在带隙中的位置，使用了强大的光学非原位测量方法，如瞬时吸收、光致发光的温度相关和时间相关的测量和热刺激发光。总之，结合现场和非现场调查，将建立一个全面的缺陷化学模型，该模型将能够针对缺陷浓度，了解对光电性能的影响，并改进光电子器件。

Due to the excellent optoelectronic properties of halide perovskites, their use as an efficient semiconductor material in many applications such as solar cells, light-emitting diodes, or in detectors for light, X-rays and gamma radiation is being discussed. A remarkable feature of halide perovskites in this context is their high tolerance and self-healing ability towards intrinsic ionic point defects. Nevertheless, these defects can affect the optoelectronic properties and, for example, cause ions to move through the halide perovskite when a potential difference is applied, leading to efficiency losses and degradation of the properties of optoelectronic devices based on halide perovskites. Therefore, the goal of this project is to gain a deep understanding of how various point defects in halide perovskites affect their optoelectronic properties and to understand how point defect concentrations can be tuned through controlled modifications of the perovskites. Key to achieving these goals is the combination of defect chemistry studies with optical measurements on halide perovskite samples with well-defined properties. The basic investigations involve the precise setting of an iodine partial pressure that leads to a thermodynamically defined interaction of the perovskites with iodine and thus to an equilibrium concentration of point defects that depends on the iodine partial pressure and the temperature. Such an approach is standard for oxide perovskites. In the previous project, it was also successfully demonstrated for methylammonium lead iodide that such an approach can work. In the proposed continuation project, the resulting point defect concentrations will be measured via the electrical conductivity, while the effects of these point defects on the optoelectronic properties will be studied directly via in-situ optical characterization, i.e., via the measurement of absorption and emission during film formation. In addition, doping will be used to target the defect concentrations in order to refine the defect chemical model and to determine quantitatively formation enthalpies. In order to make statements about the nature of the excited states and their relaxation, to identify defects and impurities, and to determine the location of defects in the band gap, powerful optical ex-situ measurement methods, such as transient absorption, temperature-dependent and time-dependent measurement of photoluminescence and thermally stimulated luminescence, are used. Overall, with the combination of in-situ and ex-situ investigations, a comprehensive defect chemical model will be established, which will allow to target defect concentrations, to understand the effects on optoelectronic properties, and to improve optoelectronic devices.