Air-Stable Methylammonium Lead Iodide Perovskite Thin Films Fabricated via Aerosol-Assisted Chemical Vapor Deposition from a Pseudohalide Pb(SCN)₂ Precursor

Abstract

Ambient-air-stable methylammonium lead iodide (MAPI) perovskite thin films have been fabricated via one-step aerosol-assisted chemical vapor deposition (AACVD) from a pseudohalide Pb(SCN) 2 precursor. We compare both the bulk and surface properties of the perovskite films grown using AACVD with those made by the widely used spin-coating method. Films with larger grain sizes and much better stability in ambient air can be obtained by AACVD. By addition of excess MAI to the precursor solution, MAPI films with negligible PbI 2 impurities, as determined by X-ray diffraction, are obtained. The AACVD-grown MAPI films retain high phase purity with limited PbI 2 formation after aging in air for approximately one month. The films exhibit an optical bandgap energy of ca. 1.55 eV and the expected nominal bulk stoichiometry (within error). In addition to probing bulk properties, we utilize X-ray photoelectron spectroscopy (XPS) to scrutinize the surface characteristics in detail. We find that the use of excess MAI results in formation of neutral CH 3 NH 2 molecules at the surface. With aging time in air, the concentrations of iodine and nitrogen drop with respect to that of lead, but these changes are less severe in the AACVD-grown films compared to the counterparts made by spin-coating. Near-ambient pressure XPS is utilized to examine the surface stability of AACVD-grown films on exposure to 9 mbar H 2 O vapor. The formation of CH 3 NH 2 molecules at the surface is observed, and the MAPI phase remains largely intact. The CH 3 NH 2 molecules may passivate the surfaces and protect MAPI from degradation, providing a rationale for the observed stability of MAPI films fabricated from Pb(SCN) 2 with excess MAI.

Bioinspired scaffolds that sequester lead ions in physically damaged high efficiency perovskite solar cells

“…31 This BE value also matches that reported for Pb absorbed by HAP 32 and is much higher than typical values for Pb-I bonds in halide perovskites (ca. 138.6 eV) 33 as well as PbI 2 (ca. 138.9 eV).…”

Surface Property Tuning of Methylammonium Lead Iodide by Plasma for Use in Planar Perovskite Solar Cells

“…The presence of (220), (310), (224), and (330) can be indexed to the CH 3 NH 3 PbI 3 . 24 No considerable changes were observed on the peak at 28.1°, but plasma treatment slightly increased the intensity of the peaks at 34.9 and 44.2°. The intensity of the peak at 31.5° enhanced after plasma treatment.…”

Pseudo‐Halide Perovskite Solar Cells

“…fabricated a pure MAPbI 3 film without PbI 2 impurities via vapor‐assisted aerosol chemical deposition (AACVD) from pseudo‐halide Pb(SCN) 2 and MAI as precursors. [ 92 ] In their study, there were no S 2s XPS signals detected in the perovskite film, indicating that the sulfur atoms from Pb(SCN) 2 were completely lost during the formation of MAPbI 3 film, as seen in the Equation (14). [ 57 ] It is worth mentioning that they used near‐ambient pressure X‐ray photoelectron spectroscopy (NAP‐XPS) to monitor the degradation of film surface.…”