Coupled experimental and theoretical investigation of the process parameters controlling the perovskite structure formation: towards thick defect-free layers

有机-无机钙钛矿混杂材料已迅速成为硅太阳能电池的一种极具前景的替代材料。然而，在光活性薄膜的溶液处理过程中，薄膜形成机制的基本性质仍然知之甚少，这阻碍了具有优异半导体质量的厚实的、垂直的单块钙钛矿薄膜的发展。在这个项目中，我们的主要目标是建立一个精确的模型来预测溶液处理的钙钛矿薄膜的成膜过程，控制基本的调控机制，从而改善薄膜的形貌。我们将开发并使用现场测量室在受控条件下监测薄膜的形成，同时我们将对钙钛矿晶体在干燥和后处理过程中的成核和生长进行相场模拟。这将使我们深入了解干燥薄膜的形貌形成过程，以及干燥薄膜的结构特征，如表面覆盖率、粗糙度、晶体尺寸和堆积。我们的目标是建立有关工艺参数(如溶剂选择、淬火温度、速度和方法以及干燥后步骤)对最终薄膜质量的影响的机理规则。我们还将研究如何在溶液中或在基片上引入成核剂来监控成核和提高薄膜质量。为油墨配方和工艺参数建立的基于物理的设计规则将用于演示实验上无缺陷的多晶膜结构，即使是对于厚层和不同的前体溶液配方。选定的钙钛矿型薄膜将完成对太阳能电池的改造，以验证形貌改善对光伏性能的影响。

Hybrid organic-inorganic perovskite materials have rapidly emerged as a highly promising alternative to silicon solar cells. However, the fundamental properties of the film formation mechanisms during solution-processing of the photoactive layers still remain poorly understood, which hinders the development of thick, vertically monolithic perovskite films with superior semiconducting quality. In this project, the main goal is to develop a precise model predicting film formation of solution-processed perovskite films, gain control over the fundamental governing mechanisms, and subsequently improve the film morphology.We propose a coupled approach where experimental measurements and simulation results complement each other. We will develop and use an in-situ measurement chamber to monitor the film formation under controlled conditions and in parallel we will perform phase field simulations of the nucleation and growth of perovskite crystals upon drying and post-processing. This will give insight into the morphology formation process, as well as into structural features of the dried film such as surface coverage, roughness, crystal sizes and stacking. We aim at establishing mechanistic rules regarding the impact of process parameters such as solvent choice, quenching temperature, rate and method, and post-drying steps on the final film quality. We will also investigate how nucleation agents introduced in the solution or at the substrate can be used to monitor nucleation and improve the film quality. The established physics-based design rules for ink formulation and process parameters will be used to demonstrate experimentally defect-free polycrystalline film structures, even for thick layers and for different precursor solution formulations. Selected perovskite films will be completed to solar cells in order to validate the impact of the morphology improvement on the photovoltaic performance.