Organic–Inorganic Halide Perovskite Formation: In Situ Dissociation of Cation Halide and Metal Halide Complexes during Crystal Formation

Abstract

Organic−inorganic halide perovskites have shown great promise as photovoltaic materials that bridge the gap between facile and low-cost fabrication and exceptional solar cell performance. Manipulation of the stoichiometry and chemistry of the precursors is among the main techniques for controlling the structural properties of perovskite layer. Herein we report that when a precursor solution containing excess cation halides (CH 3 NH 3 I) is utilized for perovskite formation, in situ dissociation of cations (CH 3 NH 3 + ) occurs. The excess iodide ions(I − ) mostly participate in the formation of iodoplumbate complexes such as PbI 3 − and PbI 4 2−. It is shown that the released energy from the crystal formation reaction can dissociate the free CH 3 NH 3 I molecules and iodoplumbate complexes into smaller molecules such as CH 3 I and NH 3 . When the I − concentration in the precursor is increased, more complexes are formed and subsequently more dissociations occur. The produced components are mostly trapped in the perovskite crystals and can act as defects.

High Power UV-Light Irradiation as a New Method for Defect Passivation in Degraded Perovskite Solar Cells to Recover and Enhance the Performance

“…When the MAI molecule reacts with PbI 2 and perovskite forms, almost all MAI peaks are shifted to other frequencies because of the change in the force constant of the bonds. The absorption peaks at 2961 and 1404 cm −1 are an asymmetric stretch and an asymmetric bend of CH 3 of MAI 14 , respectively. Also, the broad peak at 3095 cm −1 is related to the symmetric and asymmetric stretching modes of NH 3 .…”

“…It is known that the degradation and lifetime of a device are strongly dependent on all its components, fabrication process, and storing conditions 7,8 . In the case of the complete device degradation, several reasons are expressed for perovskite solar cell degradation such as the degradation of each device component 9,10 , the UV irradiation, chemical reaction between the perovskite layer and metal contacts, water molecules diffusion 11–14 , and the surface and grain boundaries defects 15 . These defects originate from the low thermal stability, or low formation energy of perovskite materials that cause instability issues, comprising ion migration and associated current hysteresis that lead to the degradation of the device 15 .…”

Effect of non-stoichiometry of initial reagents on morphological and structural properties of perovskites CH3NH3PbI3

“…It has been shown that other possible products of the decomposition of perovskite CH 3 NH 3 PbI 3 , except for the phase of PbI 2 , are CH 3 NH 2 and HI [42, 43]. Authors [44] have been shown that in the Fourier-transform infrared spectroscopy (FTIR) spectra of the products, there are bands indicating the presence of a C-I bond. Therefore, the reaction of the decomposition of organic-inorganic perovskite can be written as:…”

“…4c). Intermediate phases (CH 3 NH 3 ) 3 PbI 5 and (CH 3 NH 3 ) 2 PbI 4 were described in [44, 45]. With the increasing of the temperature of heat treatment up to 170 °C, a single-phase perovskite structure is formed.…”

“…Indeed, intense laser radiation can lead to the destruction of chemical bonds in CH 3 NH 3 PbI 3 , and to the excitation of the electronic subsystem of individual structural units, which contributes to the formation of a metastable structure. In particular, such a state may be the result of the intercalation of the compound formed due to the partial destruction of the perovskite into PbI 2 [44]. The change in the form of Raman spectra of films in such a metastable state is observed directly in the process of their measurements.…”