Crystal domain size control in organometal halide perovskite materials and its effect on ion and defect migration as well as its optoelectronic properties for photovoltaic application

基于有机金属卤化物的钙钛矿材料，如甲基铵碘铅(MAPI)，最近在太阳能领域引起了极大的关注。他们在报告的设备效率方面的发展是史无前例的，2012年的效率约为3%，最近的效率超过了21%。它们的一般元素丰度和低成本溶液处理的潜在可行性使其成为非常有希望的第三代光伏以及发光器件的候选材料。尽管取得了快速发展，但仍存在许多根本性问题。我们已经表明，可以获得令人惊讶的高质量的晶体半导体，然而，晶界的影响以及它们对稳定性、陷阱态、无序、离子和缺陷态迁移的整体影响还没有完全了解。本研究的目的是控制钙钛矿型薄膜中晶区尺寸的大小，并研究其对其光电性能的影响。本项目的第一部分重点研究了薄膜中有机金属卤化物微晶的尺寸控制及其晶体生长的相关机理。我们将建立一种方法，如何使用选定的溶剂蒸气的受控气氛在非常宽的范围内控制结晶动力学和晶粒度。利用这种方法，我们可以直接影响结晶过程、成核密度和结合，而不必改变前驱体成分。其目的是在从纳米到几十微米的广泛范围内提供对微晶尺寸的精确控制。光谱和显微方法跟踪各自的结果和动力学。使用X射线散射的原位结构表征将是该项目的第二部分，将提供关于结晶动力学的准确信息。该项目的第三部分集中于电光特性，并建立了与颗粒大小的最终关系。具体地说，该项目将使用与温度相关的电流瞬变，这使得人们能够了解离子迁移和滞后，以及吸收和光致发光光谱以及广域光致发光显微镜等光学技术。我的研究小组正在并将建立的其他方法，如电吸收和光电子能谱，也是可用的。结合这些方法，我们可以解决晶界对离子和缺陷迁移、陷阱态和无序以及太阳能电池器件性能的影响，即滞后、稳定性和电荷复合。这将为有机金属卤化物钙钛矿半导体在太阳能电池和相关器件中的应用提供更深层次的基础性认识，并制定相应的设计和工艺规则。

Perovskite materials based on organometal halides, such as methylammonium lead iodide (MAPI) found a lot of attention within the solar energy community in the very recent time. Their development in reported device efficiency is unprecedented, starting with an efficiency of around 3% in 2012 of more than 21% recently. Their general elemental abundancy and potential viability for low cost solution processing make them a very promising candidate for 3rd generation photovoltaics, but also light emitting devices. Despite this quick development, there are still many fundamental question remaining. We have shown that surprisingly high crystalline semiconductor qualities are achievable, however, the effect of grain boundaries and their overall effect on stability, trap states, disorder, ion and defect state migration has not completely understood. Object of this proposal is the control of crystalline domain sizes in a wide range within the perovskite films, and to investigate the subsequent effects on its optoelectronic properties. The first part of this project focuses on the crystal size control of organometal halide crystallites in thin films and their related mechanism for crystal growth. We will establish a method how to control the crystallisation kinetics and the crystal grain sizes on a very broad range using controlled atmospheres of selected solvent vapour. With this method we directly influence the crystallisation process, nucleation density and coalescence without having to alter precursor compositions. The aim is to provide a precise control of crystallite sizes on a broad range from nanometres to several tens of micrometers. Spectroscopic and microscopic methods track the respective results and kinetics. In-situ structural characterisation using X-ray scattering will be a second part of this project and will give precise information on the kinetics of crystallisation. The third part of this project focuses on the electro-optical characterisation and creates the ultimate relation to grain sizes. Specifically, this project will employ temperature dependent current transients, which allow an understanding for ion migration and hysteresis, as well as optical techniques such as absorption and photoluminescence spectroscopy as well as wide-field photoluminescence microscopy. Additional methods such as electro-absorption and photoelectron-spectroscopy, which are and will be established in my research group, are available as well. Combining these methods we can address the influence of grain boundaries on ion and defect migration, trap states and disorder as well as solar cell device performance, i.e. hysteresis, stability and charge recombination. This will provide a deep fundamental understanding on the thin film and material properties, and create respective design and processing rules for organometal halide perovskite semiconductors for their application in solar cells and related devices.