Perfecting Halide Perovskites: From Precursor Ink Chemistry to Defect Control

卤化物钙钛矿是光电子应用中非常有前途的材料，并且已经被纳入到高效的光伏器件，发光二极管和激光器中。然而，尽管钙钛矿基器件的效率突飞猛进，但人们对钙钛矿薄膜结晶和缺陷形成的基本过程了解不足。本项目涉及化学、固态物理和材料科学的交叉研究，旨在实现以下目标：1)发展对钙钛矿前驱体油墨的胶体化学和溶剂-溶质相互作用的基本理解；2)阐明薄膜成核、结晶和缺陷形成的机制；3)开发减少缺陷形成和减轻其影响的方法；4)开发稳定高效的光伏器件和发光二极管。卤化物钙钛矿是钙钛矿材料的一个合成子类别，由于其显著的光电特性（即在可见光谱上的广泛吸收，长载流子扩散长度，双极性输运，高载流子迁移率等）以及通过简便的溶液处理生产高质量材料的能力而引起了人们的极大兴趣。在不到十年的时间里，基于钙钛矿的光电子技术已经在实验室规模上实现了超过25%的认证光伏功率转换效率（pce），超过了所有其他竞争的新兴光伏技术，并接近成熟薄膜技术的性能。在钙钛矿光电子学研究中，虽然效率记录经常被打破，但对钙钛矿薄膜中结晶和缺陷形成的基本过程缺乏详细的了解。这是至关重要的，因为对于相同的组成材料，不同的结晶策略已被证明可以产生具有显着不同光电性能，缺陷浓度甚至稳定性的薄膜。在缺乏对结晶和缺陷形成机制的牢固掌握的情况下，用于控制钙钛矿结晶和钝化电子和结构缺陷的各种干预措施在很大程度上是通过自上而下的试验和错误方法进行的。提出的研究旨在进行自下而上的调查，从而对钙钛矿结晶过程有一个基本的了解，从而提供控制、优化和定制钙钛矿薄膜光电性能的能力。此外，这将允许最大限度地减少结构和电子缺陷，不仅对提高钙钛矿光伏电池的性能和稳定性，而且对所有基于钙钛矿的光电子产品都具有重要意义。本项目旨在了解钙钛矿前驱体溶液的化学性质，绘制从前驱体溶液到晶粒的转化过程，并确定前驱体溶液、晶界和界面的化学性质如何影响缺陷的性质和浓度，以及钙钛矿薄膜的化学组成和光电性能。这种方法的一个重要方面是从基本的微观层面开始，然后将对相关过程的理解转化为宏观性质。理解和控制这些材料系统的能力不仅将导致钙钛矿光电子器件性能的显着改善，而且还允许合理设计新的溶剂系统，以及控制卤化物钙钛矿材料结晶的新方法。

Halide perovskites are exceptionally promising materials for optoelectronic applications, and have already been incorporated into efficient photovoltaic devices, light-emitting diodes and lasers. However, despite the skyrocketing efficiencies of perovskite-based devices, there is insufficient understanding of the fundamental processes governing crystallisation and defect formation in perovskite-thin films.This project involves research at the intersection of chemistry, solid-state physics, and materials science, geared towards achieving the following goals: 1) developing a fundamental understanding of the colloidal chemistry, and solvent-solute interactions of perovskite precursor inks, 2) elucidating the mechanisms of nucleation, crystallisation and defect formation of thin-films, 3) developing methods to reduce defect formation and mitigate its effects, and 4)the development of stable and efficient photovoltaic devices and light-emitting diodes.Halide perovskites are a synthetic sub-category of perovskite materials which have generated much interest due to their remarkable optoelectronic properties (i.e. broad absorption over the visible spectrum, long carrier diffusion lengths, ambipolar transport, high charge-carrier mobilities etc.) and the ability to produce high-quality material through facile, solution-based processing. In just under a decade, perovskite-based optoelectronics have achieved certified photovoltaic power conversion efficiencies (PCEs) exceeding 25% on a labscale, surpassing all other competing emerging photovoltaic technologies and approaching the performances of mature thin-film technologies. In perovskite optoelectronics research, while efficiency records are regularly broken, there is a lack of detailed understanding of the fundamental processes which govern crystallisation and defect formation in perovskite thin films. This is of paramount importance as, for the same composition material, different crystallisation strategies have been shown to produce films with significantly different optoelectronic properties, defect concentrations and even stability. In the absence of a firm grasp of the mechanisms of crystallisation and defect formation, the various interventions which have been applied to control perovskite crystallisation and passivate electronic and structural defects have been largely carried out through a trial and error, top-down approach. The proposed research aims to carry out a bottom-up investigation which yields a fundamental understanding of the perovskite crystallisation process, and hence provides the ability to control, optimise and tailor the optoelectronic properties of perovskite thin-films. Further, this will allow for minimising structural and electronic defects, having important implications, not just for improving both the performance and stability of perovskite photovoltaics, but for all perovskite-based optoelectronics. This project aims to develop an understanding the chemistry of the perovskite precursor solutions, map the conversion processes from precursor solution to crystal grains, and identify how manipulating the chemistry of the precursor solution, grain boundaries and interfaces affects the nature and concentration of the defects, and the chemical composition and optoelectronic properties of perovskite thin-films. An important aspect of this approach is starting on a fundamental microscopic level and then translating the understanding of the relevant processes into macroscopic properties. The ability to understand and control these material systems will not only lead to significant improvements in the performance of perovskite optoelectronic devices, but also allow for rational design of new solvent systems, and new approaches to controlling the crystallisation of halide perovskite materials.