Controlling structural and transport properties of organic-inorganic halide perovskite films using chemical vapor deposition

Chemical vapor deposition (CVD), a low-cost and a scalable deposition technique, allows the growth of methylammonium lead iodide (MAPbI₃) films without the use of solvents. This fabrication method substantially increases the air stability while also inducing the stable cubic phase at room temperature and at pressures as low as 0.25 GPa. MAPbI₃ thin films were grown by a facile two-step low-pressure vapor deposition process in a single reactor. This method results in films which are usually in the tetragonal phase (space group: I4/mcm) and occasionally in the cubic phase under ambient conditions. High-pressure synchrotron-based X-ray diffraction studies from CVD-grown MAPbI₃ crystallites show that the sample remains in the cubic phase (space group: Im3¯) between 0.25 and 3.0 GPa. Temperature-dependent transport measurements show sharp anomalies, correlating with the structural changes. For the room temperature cubic phase-film, a dramatic decrease in resistivity is observed in comparison with typical films, indicating the possible suppression of the ionic contribution to the transport. Additionally, a drastic decrease in resistivity is observed for MAPbBr₃ single crystals, produced by the ITC method, under low pressure. Mixed halide films that exhibit an unanticipated structural phase stability from 20 K to 300 K were also grown using CVD.