Proceedings of Online School on Fundamentals of Emerging Solar Cells (PVSCHOOL)
DOI: https://doi.org/10.29363/nanoge.pv school.2021.002
Publication date: 29th January 2021
Design and modification of interfaces has always been a critical issue for semiconductor devices. Today interface optimization has evolved into a primary tool to harness the full potential of metal halide perovskite (MHP)-based solar cells. In particular, the outstanding improvements in solar cell performance and stability can be primarily ascribed to a careful choice of the interfacial layout in the layer stack featuring novel intermediate layers and surface treatments. In this lecture, I will describe the unique challenges and opportunities of these approaches. For this purpose, I will first introduce the basic physical and chemical properties of the exposed MHP thin film and crystal surfaces, including topics such as surface termination, surface reactivity, and electronic structure. Next, I will lay out experimental characterization methods and results on the energetic alignment processes at the interfaces between the perovskite and transport and buffer layers. This part includes understandings reached as well as commonly proposed and applied models, especially the often-questionable validity of vacuum level alignment, the importance of interface dipoles, and band bending as the result of interface formation. I will follow this by discussing the impact of the interface formation on device performance, considering effects such as chemical reactions and surface passivation on interface energetics and stability. On the basis of these concepts, we will jointly look at a roadmap for the next steps in interfacial design for perovskite solar cells with emphasis on the importance of achieving control over the interface energetics and chemistry (i.e., reactivity) to allow predictive power for tailored interface optimization.