Surface Passivation of FAPbI<sub>3</sub>-Rich Perovskite with Cesium Iodide Outperforms Bulk Incorporation
Thomas Baumeler, Essa A. Alharbi, George Kakavelakis, George C. Fish, Mubarak T. Aldosari, Miqad S. Albishi, Lukas Pfeifer, Brian Carlsen, Jun‐Ho Yum, Abdullah Alharbi, Mounir Mensi, Jing Gao, Felix T. Eickemeyer, Kevin Sivula, Jacques‐E. Moser, Shaik M. Zakeeruddin, Michaël Grätzel
Abstract
Metal halide perovskites (MHPs) have shown an incredible increase in efficiency, reaching as high as 25.7%, which now competes with traditional photovoltaic technologies. Herein, we excluded CsX and RbX (X = I –, Br –, Cl – ), the most commonly used cations to stabilize α-FAPbI 3, from the bulk of perovskite thin films and applied them on the surface as passivation agents. Extensive device optimization led to a power conversion efficiency (PCE) of 24.1% with a high fill factor (FF) of 82.2% upon passivation with CsI. We investigated in depth the effect of CsI passivation on structural and optoelectronic properties using X-ray diffraction (XRD), angle-resolved X-ray photoelectron spectroscopy (ARXPS), Kelvin probe force microscopy (KPFM), time-resolved photoluminescence (TRPL), photoluminescence quantum yield (PLQY), and electroabsorption spectroscopy (TREAS). Furthermore, passivated devices exhibit enhanced operational stability, with optimized passivation with CsI leading to a retention of ∼90% of the initial PCE under 1 sun illumination with maximum power point tracking for 600 h.