Reaction between Pyridine and CH₃NH₃PbI₃: Surface-Confined Reaction or Bulk Transformation?

Abstract

Pyridine molecules have been used to passivate surface Pb sites of CHNHPbI, to recrystallize CHNHPbI, and to bleach CHNHPbI. However, these results contradict each other, as recrystallization and optical-bleach require transformation of bulk CHNHPbI, but surface passivation demands the confinement of the reaction at the surface region. The underlying mechanism for these seemly contradicting results is not yet understood. In this paper, we show, at 25 °C, partial pressure of pyridine vapor is a determining factor for its reaction behaviors with CHNHPbI: one can modify the surface region of CHNHPbI by using pyridine vapor of pressure 1.15 torr or lower but can transform the whole bulk CHNHPbI film with a pyridine vapor of 1.3 torr or higher. Our result is the first demonstration that the reaction modes, i.e., surface-confined reaction and bulk transformation, are very sensitive to the partial pressure of under-saturated pyridine vapor. Despite the different reaction behaviors, it is interesting that in all pressure ranges, pyridinium ion is a main product from the reaction between pyridine and CHNHPbI. The bulk transformation is due to the formation of a liquid-like film, which increases the mobility of species to catalyze the reaction between pyridine and CHNHPbI. It is important to note 1.3 torr is much smaller than the saturated vapor pressure of pyridine (20 torr at 25 °C). These findings provide a guidance in applying pyridine and other amines to functionalize and transform CHNHPbI and other hybrid halide perovskites. It also highlights the critical role of fundamental studies in controllably modifying CHNHPbI.

Amino-Deliquescence and Amino-Efflorescence of Methylammonium Lead Iodide

“…The MA 0 liquefaction and recrystallization cycling process has been used to alter film crystallographic orientation, increase grain size, reduce grain boundary defect density, , improve interfacial quality, heal degraded films, , and facilitate cation exchange. − Moreover, liquefaction of MAPbX 3 (and non-perovskite precursors such as NH 4 PbX 3 or HPbX 3 ) under a MA 0 atmosphere has been reported for X = Cl, X = Br, ,, and X = I. ,, Although generally described as intercalation and off-gassing of amine molecules participating in hydrogen bonding with the organic cation, , the origin, driving force, and kinetics of these liquefaction and recrystallization processes have remained unclear. Here, we monitor in situ the liquefaction and recrystallization of MAPbI 3 thin films in a MA 0 atmosphere using extinction spectroscopy and optical microscopy under controlled temperature and pressure conditions.…”

Improve the Stability of Hybrid Halide Perovskite via Atomic Layer Deposition on Activated Phenyl-C61 Butyric Acid Methyl Ester

“…Figure shows the IR spectra of the CH 3 NH 3 PbI 3 /PCBM sample before and after 200 cycles ALD ZnO. The locations of characteristic peaks of CH 3 NH 3 PbI 3 in fresh CH 3 NH 3 PbI 3 /PCBM align well with those from the pure CH 3 NH 3 PbI 3 . , The small positive peak at 1735 cm –1 is due to the CO bonding of PCBM . The 200 ZnO ALD cycles do not change the locations and intensity of the peaks from CH 3 NH 3 PbI 3 , confirming that the PCBM layer protects the underlying CH 3 NH 3 PbI 3 from being corroded by the DEZ/H 2 O chemistry at 80 °C for at least 200 cycles.…”

“…shows the IR spectra of the CH 3 NH 3 PbI 3 /PCBM sample before and after 200 cycles ALD ZnO. The locations of characteristic peaks of CH 3 NH 3 PbI 3 in fresh CH 3 NH 3 PbI 3 / PCBM align well with those from the pure CH 3 NH 3 PbI 3 15,16. …”