Development of In-situ Photoluminescence Spectroscopy to Investigate the Ion Coordination in Solution-Derived Perovskites

Description

Solution-derived organometal halide perovskites are an intriguing class of materials for opto-electronic applications. Recently, a high power conversion efficiency over 25% has been achieved in photovoltaic devices. However, stability and toxicity still pose a threatto the commercialization of the technology. Theoretically, perovskite compositions with more stable crystal structure and nvironmentally friendly elements have been predicted. However, there is only little success in experiment to obtain high quality perovskite crystals and films. Thus, understanding the ion coordination and crystallization processes is essential to overcome the aforementioned challenges.In this proposed research, we are aiming at developing an in-situ photoluminescence (PL) technique to monitor ion coordination during the perovskite formation process, from solution preparation to spin-coating and thermal annealing. The proposed in-situ PL is fast (millisecond-scale) and capable to detect non-crystalline phase compositions. Notably, the intermediate state formed at the beginning of the crystallization process is crucial for the final perovskite composition and film quality. The preliminary results of the study on a multiple-ion composited perovskite material support the aforementioned statement. Technically, we will setup a high-sensitivity in-situ PL technique inside a nitrogen-filled glovebox. The probe will be equipped with a motorized translation stage to reduce any possible damage from photo-excitation. Scientifically, we will apply the technique to systemically investigate the crystallization process in multiple-ion composited perovskites and to understand the origin of the enhanced crystallinity with polymer additives. In order to have a qualitative understanding of the intermediate states, density-functional-theory (DFT) will be used to identify the ossible compositions. The theoretical results will be further correlated to the experimental results obtained by the in-situ PL. Ultimately, the key formation step or composition of the intermediate state can be identified, and bring insight into the fabrication process of high quality new erovskite materials.