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过氧化物材料，例如甲基铵碘化铅（methylammonium lead iodide，缩写为CHI），最近在太阳能界引起了很多关注。他们在报告的设备效率方面的发展是前所未有的，从2012年的3%左右的效率开始，到最近的21%以上。它们的一般元素吸收和低成本溶液处理的潜在可行性使它们成为第三代光致发光器件以及发光器件的非常有前途的候选者。尽管发展迅速，但仍存在许多根本问题。我们已经表明，令人惊讶的高结晶半导体质量是可实现的，然而，晶界的影响和它们对稳定性、陷阱态、无序、离子和缺陷态迁移的整体影响还没有完全理解。该提案的目的是在钙钛矿薄膜内的宽范围内控制晶畴尺寸，并研究其光电性能的后续影响。本计画的第一部分主要探讨有机金属卤化物薄膜中微晶的晶粒尺寸控制及其相关的晶体成长机制。我们将建立一种方法，如何控制结晶动力学和晶粒尺寸在一个非常广泛的范围内使用选定的溶剂蒸气的控制气氛。通过这种方法，我们直接影响结晶过程，成核密度和聚结，而不必改变前体成分。其目的是在从纳米到几十微米的宽范围内提供对微晶尺寸的精确控制。光谱和显微镜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，并将提供结晶动力学的精确信息。该项目的第三部分侧重于电光特性，并创建与粒度的最终关系。具体而言，该项目将采用温度相关的电流瞬变，这使得离子迁移和滞后的理解，以及光学技术，如吸收和光致发光光谱以及宽场光致发光显微镜。其他的方法，如电吸收和光电子光谱，这是和将建立在我的研究小组，以及可用。 结合这些方法，我们可以解决离子和缺陷迁移，陷阱状态和无序以及太阳能电池器件的性能，即滞后，稳定性和电荷复合的晶界的影响。这将提供对薄膜和材料性质的深刻基础理解，并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创建相应的设计和加工规则。

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.