Unraveling the Energetic Landscape of Perovskite Solar Cells: A Synergy of 2D Drift-Diffusion Simulations and Tapered Cross Section Photoelectron Spectroscopy

Interfaces are crucial elements that define the electronic properties of perovskite solar cells (PSCs). However, obtaining the band structure of a full PSC and accessing its buried layers and interfaces without modifying the device is challenging. A tapered cross section (TCS) of a PSC (i.e., a PSC polished under a very shallow angle) offers access to these buried parts on a width one or two orders of magnitude larger than the lateral resolution of a photoelectron spectroscopy (PES) set-up. In this work, we combine 2D numerical drift-diffusion simulations with TCS-PES measurements to access the electrostatic potential profile with high spatial resolution along the PSC, allowing us to construct the band diagram of our device. Thus, we experimentally confirm the presence of a band bending at the interfaces between perovskite and charge-transport layers and quantify it under various conditions relevant for solar cells operation. Such synergy between the TCS-PES approach and numerical simulation provides substantial information about the energetic landscape at the interfaces in PSCs and is essential for devices without mostly field-free layers. These insights for dark and illuminated conditions are central to understand the nature of interfaces within PSCs.