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. Herein, 2D numerical drift‐diffusion simulations are combined 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 device. Thus, it is confirmed experimentally that the presence of a band bending at the interfaces between perovskite and charge‐transport layers and quantified under various conditions relevant to solar cell 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.