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

近年来，金属卤化物钙钛矿因其在太阳能电池的活性层中具有高效和易于制造的潜力而引起了人们的广泛关注。然而，对这些材料的光电特性和电荷输运性质的理解仍然存在很大的差距。这种差距的例子包括对实验迁移率测量异常依赖温度的物理起源的争论，以及与传统半导体相比，热载流子的冷却速度较慢。关于引起这种观察的基本物理学，人们提出了各种各样的主张。该小组之前的工作已经对其中一些说法进行了仔细研究。特别是，研究了大极化子的形成和Fröhlich与多极光学声子模式的耦合对理解这些材料中的迁移率测量的重要性。本文还探讨了瞬态动力学背景下载流子-载流子散射的意义，并对筛选Fröhlich载流子散射的后果进行了一些研究。该小组开发了一个世界领先的集合蒙特卡洛代码，BoltMC，用它来进行这样的研究。这允许在原子和连续体长度尺度之间建模，这是正确理解器件物理所必需的一种方法。该研究项目在第一年的初始阶段将包括全面了解BoltMC，因为它目前正在编写，并继续去年的工作，调查三碘化甲基铵铅中Fröhlich载流子与多极光学声子模式的耦合，预计将发表一篇论文。BoltMC将被扩展以解释极化散射。在这个子项目之后，该小组与瞬态载流子动力学有关的先前工作将得到推进，并与慕尼黑大学Felix Deschler的研究组合作开发。计划还将进一步研究筛选的载流子Fröhlich散射，因为早期的结果表明，这可能对解决围绕这类材料迁移率的温度依赖性的持续问题很重要。从长远来看，该项目将显著扩展BoltMC，以允许研究非均质性和电子和离子运动的耦合。后者需要将BoltMC的蒙特卡罗方法与漂移扩散模型结合起来。还可以进一步扩展代码以实现完整的设备级建模。总的来说，这个项目有可能在理解卤化物钙钛矿太阳能电池的运作方面提供重要的发展。这是最终确立该技术商业可行性的重要一步。

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.