Effect of the Large-Size A-Site Cation on the Crystal Growth and Phase Distribution of 2D/3D Mixed Perovskite Films via a Low-Pressure Vapor-Assisted Solution Process

Abstract

In this study, various concentrations of the largesized cation iodide, namely, phenylethylammonium iodide (PEAI), incorporated in lead iodide (PbI 2 ) solid films react with heated methylammonium iodide (MAI) to fabricate 2D/3D mixed perovskite films with vertical phase distribution, which are prepared by the low-pressure vapor-assisted solution process (LP-VASP). The 2D/3D mixed perovskite films exhibit multiple photoluminescence (PL) emissions that correspond to a 2D Ruddlesden−Popper layered perovskite of PEA 2 MA n−1 Pb n X 3n+1 with varying n values and a 3D MAPbI 3 perovskite. Their crystalline structure along with crystal orientation, surface morphology, and surface potential is examined by X-ray diffraction, grazing-incidence wide-angle X-ray scattering, and Kelvin probe force microscopy, respectively. Confocal PL microscopy, two-photon excitation microscopy, and scanning transmission X-ray microscopy are further conducted to map the spatial and energy spectral distribution of 2D layered perovskites in the resultant film. From these results, multiple 2D layered perovskites are presumably formed in the bulk, while a 3D perovskite is mainly produced on the surface. The dimensional variation across the vapor-treated film is attributed to the phenylethylamine vapor (PEA (g) ) evaporating from the PEAI-added PbI 2 film and the methylamine vapor (MA (g) ) reaction with the PEAI-added PbI 2 film initiated from the film surface. A gradient phase distribution from 2D (bottom) to 3D (surface) perovskites is intuitively fabricated.

Enhanced Charge Transport via Mixed-Dimensional Heterostructures in 2D–3D Perovskites and Their Relevance to Solar Cells

“…The lower-energy PL tail of low-dimensional perovskite material comes from the radiative recombination of trap states and/or strong phonon coupling with the distorted soft crystal structure. − A recent report by Chen et al suggested that PL peaks at 540, 580, 620, 680, and 700 nm in PEAI–MAPbI 3 mixed perovskites were assumed to be n = 1, 2, 3, 4, and 5, respectively. The n -value of the RP phase in the PEAI–MAPbI 3 mixed perovskite can be tuned by the reaction temperature . However, the PL spectra of our measurements do not match the high n values of the reported values.…”

“…The n-value of the RP phase in the PEAI−MAPbI 3 mixed perovskite can be tuned by the reaction temperature. 41 However, the PL spectra of our measurements do not match the high n values of the reported values. Our measurement data showed that n = 1 is observed at 510 nm and n = 2 is observed at ∼590 nm, but no peaks related to high n-values are observed around 620−700 nm.…”

Sequential Chemical Vapor Deposition of Two-Dimensional Sn–Pb Compound Perovskite Thin Films and Its Exciton Transport

“…Additional low-intensity peaks are also present at 22.5°and 26.5°in the 80 and 100 °C samples, which are ascribed to the presence of PEAI. 50 When the conversion temperature was further increased to 120 °C, the periodic peaks of the 2D perovskite disappeared, with only a low-intensity PbI 2 (100) peak present, which can be associated with an elevated temperature that results in the sublimation of PEAI from the 2D perovskite and/or the decomposition of the 2D perovskite.…”

Synthetic approaches for perovskite thin films and single-crystals

“…Furthermore, 2D/3D mixed perovskite films were developed using a low-pressure VASP, where phenylethylammonium iodide (PEAI) was added in PbI 2 and then the prepared film was reacted with methylamine (CH 3 NH 2(g) and MA (g) vapors). 151 It was demonstrated that the 3D MAPbI 3 perovskite was formed on the surface of multiple 2D RP perovskite layers of PEA 2 MA n −1 Pb n X3 n +1 with different n values, suggesting a vertical-gradient phase distribution, which could be effectively applied in perovskite optoelectronic devices. Moreover, quasi-2D PEA 2 (FAPbBr 3 ) n −1 PbBr 4 films prepared through the VASP were incorporated in perovskite light-emitting diodes, exhibiting not only high luminance and external quantum efficiency, but also good reproducibility.…”