Although three-dimensional (3D) organic-inorganic perovskites (OIP) produced a remarkable solar cell power conversion efficiency (PCE) of over 25%, it still suffers from an inherent chemical and structural instability in atmospheric conditions. This is the major impediment for the commercialization of perovskite solar panels and other electronic products. A practical approach to tackle this challenge is to reduce the dimensionality of the OIP to two-dimensions (2D). However, the improved stability comes at the expense of the PCE, which is due to the inherent anisotropic charge-transport properties in 2D HP caused by the out-of-plane quantum and dielectric confinement of the long-chain organic cations. A resolve to this would be to deposit a 2D/3D layered OIP material. Chemical vapour deposition (CVD) is an established solvent-free technique for the conformal deposition of air-stable perovskite layers and devices. We report on the low-pressure CVD of a 2D OIP thin film, using butylammonium (BA) as the long-chain organic cation to produce BA₂PbI₄, followed by its exposure to the traditional methylammonium (MA) small cation, to produce a layered BA₂PbI₄/MAPbI₃ structure. Absorption and emission spectroscopy confirm the presence of the constituent MAPbI₃ and BA₂PbI₄ peaks and the formation of a quasi-2D OIP material (BA₂MA_n-1Pb_nI_3n+1, n > 1). Synchrotron-based grazing incidence x-ray diffraction measurements from 50 – 300 K provides insight into the phase change of the material, whereas temperature-dependent photoluminescence was used to probe the phonon-exciton interaction of the constituent materials.

 

This work was supported by National Science Foundation under Grant No. DMR-1807263 and the Fulbright Research Scholar Program

Use of the Advanced Photon Source was supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357