A Review of Intercalation in Heavy Metal Iodides

Abstract

This review outlines the work to date concerning the mysteries of both the large optical effects and the bonding mechanisms involved with intercalation in heavy metal iodide systems. Such a system exhibits unusual shifts of the optical band edge to higher energies upon intercalation. The shift depends on which host-guest combination is used. Several models have been developed to describe this system. The bonding mechanism for this system is not clear because some data appear to support a model based on a polarization interaction between the guest and host material whereas other data support a charge transfer or quantum confinement model. There appear to be several different systems being formed by intercalation of the same substances that have different stoichiometry. This riddle may be solved by investigations of the particular methods of intercalation.

Morphology-photovoltaic property correlation in perovskite solar cells: One-step versus two-step deposition of CH3NH3PbI3

“…Insufficient coverage in one-step coating is probably related to wettability, associated with high ionic strength (1.25M of CH 3 crystal with dimension of about 100-150 nm is induced by two-step method, which indicates that spin-coating of 20 μl of 1M solution of PbI 2 in DMF covers fully the TiO 2 film. PbI 2 is layered structure and well known to undergo intercalation reaction, 15 in which Lewis base molecules such as pyridine and methylamine were found to be intercalated into interlayer of PbI 2 . It was mentioned that charge transfer was not obvious during intercalation reaction and the dipole moment of Lewis base molecule or hydrogen bonding by the N-H bond was necessary requirement for intercalation.…”

Quantum confinement in PbI2 nanodisks prepared with cucurbit[7]uril

“…1.9 nm for PbI 2 ), 21,22 although literature reveals that PbI 2 absorption edge shifts can be assigned to many other factors, from intercalation of electron-donor species between the iodide layers in few atoms clusters to ripening processes, and in low-polarity solvents. 1,25 In fact, all these phenomena are interconnected and the shift is always related to quantum confinement mechanisms. Normally, low-polarity solvents tend to stabilize larger colloidal particles in detriment of the smaller ones as shown by Sandroff et al, 24 but also change the dielectric constant of the medium.…”

“…25 Using the effective mass approximation model, it is possible to estimate the crystallite size and thickness, as did Sandroff et al 24 and others. 21,22 Thus, in such anisotropic nanomaterial, the equation governing the band-gap shifts has the form: (1) where the effective reduced masses of the electron-hole pairs in the xy plane and in the axis perpendicular to them are represented by µ xy and µ z , respectively, and L xy and L z are the dimensions of the crystallites. The reduced masses have been experimentally determined as 0.32 (µ xy ) and 1.4 (µ z ) electron mass units, according to magneto-optic experiment data.…”

“…Therefore, each layer can be described as a I-Pb-I sequence layer. 1 Very interesting materials can be obtained by diminishing the PbI 2 particle size to the nanoscale in order to favor the appearance of new properties resultant of quantum confinement, such as those observed in zero-dimensional solids, quantum dots and other N-dimensional, quantumconfined nanomaterials. Quantum dots encounter many applications in several technological fields such as sensor devices and anti-counterfeiting systems, illumination (as high efficiency white-light emitting diodes), medicine (as cellular markers), lasers, solar cells and others.…”

“…[2][3][4][5] Another important property of lead iodide is its ability to form intercalation compounds with many chemical species, such as hydrazine, ammonia, aniline, butylamine, pyperidine and quinoline, among others. 1 The insertion of guest molecules in the interlamellar gap considerably affects the chemical and physical properties of the material.…”