Modelling charge carrier dynamics in metal halide perovskites for next-generation solar cells

金属卤化物钙钛矿由于其在高效率、易制造的太阳能电池中的应用潜力，近年来引起了人们极大的研究兴趣。然而，在对这些材料的光电性质和它们内部电荷传输的性质的理解方面仍然存在很大的差距。这种差距的例子包括关于实验迁移率测量的不同寻常的温度依赖性的物理起源的争论，以及与传统半导体相比，热载流子的缓慢冷却。关于引起这种观测的基本物理问题，人们提出了各种说法。该小组之前的工作已经仔细审查了其中的一些断言。特别是，研究了大极化子的形成和Fröhlich耦合到多个极性光学声子模对于理解这些材料中迁移率测量的重要性。还探讨了载流子-载流子散射在瞬变动力学背景下的意义，并对屏蔽载流子Fröhlich散射的后果进行了一些研究。该小组开发了世界领先的蒙特卡罗系综程序BoltMC，用于进行此类研究。这使得可以在原子和连续谱长度尺度之间进行建模，这一方法对于正确理解器件物理是必不可少的。第一年这项研究项目的第一阶段将涉及全面理解目前正在编写的BoltMC，并从去年开始继续研究三碘化铅中电荷载流子与多极光学声子模的Fröhlich耦合，预计将发表一篇论文。BoltMC将被扩展到考虑极化子散射。在这个子项目之后，与慕尼黑大学费利克斯·德施勒的实验小组合作，将推进该小组先前关于瞬时载流子动力学的工作。计划还将进一步研究载流子的屏蔽Fröhlich散射，因为早期结果表明，这可能对解决围绕这类材料迁移率的温度依赖关系的持续问题很重要。从长远来看，该项目将寻求显著扩展BoltMC，以允许研究异质性以及电子和离子运动的耦合。后一种方法需要将蒙特卡罗方法和漂移扩散模型结合起来。还有可能进一步扩展代码以实现全器件规模的建模。总体而言，该项目有可能在理解卤化物钙钛矿太阳能电池的运行方面提供重要的发展。这是在最终确立这项技术的商业可行性的道路上迈出的重要一步。

Metal halide perovskites have attracted significant research attention in recent years, owing to their potential for use in the active layer in high-efficiency and simple-to-fabricate solar cells. However, there remain significant gaps in the understanding of the optoelectronic properties of these materials and the nature of charge transport within them. Examples of such gaps include the debate over the physical origin of the unusual temperature-dependence of experimental mobility measurements and the slow cooling of hot carriers compared with conventional semiconductors. Various claims have been made regarding the essential physics giving rise to such observations. Previous work from the group has scrutinised some of these assertions. In particular, the importance of the formation of large polarons and Fröhlich coupling to multiple polar optical phonon modes to an understanding of mobility measurements in these materials has been studied. The significance of carrier-carrier scattering within the context of transient dynamics has also been explored, and some investigation has been performed into the consequences of screening of the Fröhlich scattering of carriers. The group has developed a world-leading ensemble Monte Carlo code, BoltMC, with which such investigations are performed. This allows for modelling in between the atomistic and continuum length scales, an approach that is essential for a proper understanding of device physics.The initial phase of this research project in year 1 will involve developing a full understanding of BoltMC as it is currently written and continuing work from the last year investigating the Fröhlich coupling of charge carriers to multiple polar optical phonon modes in methylammonium lead triiodide, from which a publication is expected to result. BoltMC will be extended to account for polaronic scattering. Following this subproject, previous work by the group relating to transient carrier dynamics will be advanced, with a collaboration with the experimental group of Felix Deschler at the University of Munich in development. It is planned that the screened Fröhlich scattering of carriers will also be studied further, since early results suggest this may be important in resolving ongoing questions surrounding the temperature-dependence of the mobility in this class of materials. In the longer term, this project will look to significantly extend BoltMC to allow for the investigation of heterogeneity and the coupling of electronic and ionic motion. The latter of these will require the marriage of the Monte Carlo approach of BoltMC and drift-diffusion modelling. There is also the further possibility of extending the code to enable full device-scale modelling.Overall, this project has the potential to provide important developments in the understanding of the operation of halide perovskite solar cells. This is an important step on the road to ultimately establishing the commercial viability of this technology.