Tapered Cross‐Section Photoelectron Spectroscopy of State‐of‐the‐Art Mixed Ion Perovskite Solar Cells: Band Bending Profile in the Dark, Photopotential Profile Under Open Circuit Illumination, and Band Diagram. - Wussler, Michael; Mayer, Thomas; Das, Chittaranjan; Mankel, Eric; Hellmann, Tim; Prabowo, Chandra; Zimmermann, Iwan; Nazeeruddin, Mohammad Khaja; Jaegermann, Wolfram (Advanced Functional Materials, 2020)