2D hybrid halide perovskites with the formula (A′)2(A)n-1PbnI3n+1 have remarkable stability and promising efficiency in photovoltaic and optoelectronic devices, yet fundamental understanding of film formation, key to optimizing these devices, is lacking. Here, in situ grazing-incidence wide-angle X-ray scattering (GIWAXS) is used to monitor film formation during spin-coating. This elucidates the general film formation mechanism of 2D halide perovskites during one-step spin-coating. There are three stages of film formation: sol–gel, oriented 3D, and 2D. Three precursor phases form during the sol–gel stage and transform to perovskite, first giving a highly oriented 3D-like phase at the air/liquid interface followed by subsequent nucleations forming slightly less oriented 2D perovskite. Furthermore, heating before crystallization leads to fewer nucleations and faster removal of the precursors, improving orientation. This outlines the primary causes of phase distribution and perpendicular orientation in 2D perovskite films and paves the way for rationally designed film fabrication techniques.
Bibliographical noteFunding Information:
This work was supported by the Office of Naval Research (ONR) under grant N00014‐20‐1‐2725. This project was supported in part by a fellowship award through the National Defense Science and Engineering Graduate (NDSEG) Fellowship Program, sponsored by the Air Force Research Laboratory (AFRL), the Office of Naval Research (ONR) and the Army Research Office (ARO). This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE‐AC02‐06CH113. Part of this work was done through Dr. Hsinhan Tsai’s user proposal (GUP‐61829) at Beamline 8‐ID‐E of the Advanced Photon Source at Argonne National Laboratory. N.C.F is partially supported by the Center for Light Energy Activated Redox Processes (LEAP), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award # DE‐SC0001059. L.X.C. is partially support by the Solar Energy Photochemistry program of the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, through Argonne National Laboratory under Contract No. DE‐AC02‐06CH11357. Use of the Center for Nanoscale Materials, an Office of Science user facility, was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE‐AC02‐06CH11357.
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- 2D halide perovskites, film formation
- spin-coating, thin films