Baumeler, Thomas PaulAlharbi, Essa Awadh RKakavelakis, GeorgeFish, George CameronAldosari, Mubarak T.Albishi, Miqad S.Pfeifer, LukasCarlsen, Brian IrvingYum, Jun HoAlharbi, Abdullah S.Mensi, Mounir DrissGao, JingEickemeyer, Felix ThomasSivula, KevinMoser, Jacques-EdouardZakeeruddin, Shaik MohammedGraetzel, Michael2023-05-132023-05-132023-05-0410.1021/acsenergylett.3c00609https://infoscience.epfl.ch/handle/20.500.14299/197661Metal 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-FAPbI3, 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.Perovskite solar cellsSurface passivationX-ray diffractionX-ray photoelectron spectroscopyKelvin probe force microscopyElectroabsorption spectroscopytext::journal::journal article::research article