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2H-Benzotriazol-2-ylethylammonium bromide and iodide and its difluorinated derivatives are synthesized and employed as interlayers for passivation of formamidinium lead triiodide (FAPbI3) solar cells. In combination with PbI2 and PbBr2, these benzotriazole derivatives form two-dimensional (2D) Ruddlesden-Popper perovskites (RPPs) as evidenced by their crystal structures and thin film characteristics. When used to passivate n-i-p FAPbI3 solar cells, the power conversion efficiency improves from 20% to close to 22% by enhancing the open-circuit voltage. Quasi-Fermi level splitting experiments and scanning electron microscopy cathodoluminescence hyperspectral imaging reveal that passivation provides a reduced nonradiative recombi-nation at the interface between the perovskite and hole transport layer. Photoluminescence spectroscopy, angle-resolved grazing-incidence wide-angle X-ray scattering, and depth profiling X-ray photoelectron spectroscopy studies of the 2D/three-dimensional (3D) interface between the benzotriazole RPP and FAPbI3 show that a nonuniform layer of 2D perovskites is enough to passivate defects, enhance charge extraction, and decrease nonradiative recombination. The research has received funding from the Ministry of Education, Culture, and Science (Gravity program 024.001.035) and the Netherlands Organization for Scientific Research via a Spinoza grant. This work of B.T.v.G. is part of the Advanced Research Center for Chemical Building Blocks, ARC CBBC, which is cofounded and cofinanced by the Netherlands Organization for Scientific Research (NWO) and the Netherlands Ministry of Economic Affairs (project 2016.03.Tue). W.T.M.v.G., K.V.H., L.L., and D.V. acknowledge the Research Foundation Flanders (FWO) for the funding of the SBO project PROCEED (S002019N) and the senior FWO research projects G043320N and G0A8723N. A.M. acknowledges the FWO for the funding of his FWO fundamental research PhD grant (1115721N). This study was supported by the Special Research Fund (BOF) of Hasselt University (BOF22PD01). J.F.O. acknowledges funding from the Engineering and Physical Sciences Research Council (EPSRC) Nano Doctoral Training Centre (EP/L015978/1).

Research into 2D layered hybrid perovskites is on the rise due to the enhanced stability of these materials compared to 3D hybrid perovskites. Recently, interest towards the use of functional organic cations for these materials is increasing. However, a vast amount of the parameter space remains unexplored in multi-layered (n > 1) hybrid perovskites for solar cell applications. Here, we incorporate carbazole derivatives as a proof of concept towards the use of tailored functional molecules in multi-layered perovskites. Films of low-n carbazole containing perovskites show high photoconductivity half-lifetimes. Higher-n (〈n〉 = 40) multi-layered perovskite films possess charge carrier diffusion lengths comparable to MAPI thin films. Solar cells containing these materials have comparable efficiencies to our MAPI and phenethylammonium (PEA)-containing multi-layered perovskite reference devices. Moisture stability tests were performed both at the material and device levels. In comparison to MAPI and PEA-based materials and solar cells, the addition of a small percentage of the carbazole derivative to the perovskite material significantly enhances the moisture stability.