IR Spectroscopic Degradation Study of Thin Organometal Halide Perovskite Films

Abstract

The advantages of IR spectroscopy include relatively fast analysis and sensitivity, which facilitate its wide application in the pharmaceutical, chemical and polymer sectors. Thus, IR spectroscopy provides an excellent opportunity to monitor the degradation and concomitant evolution of the molecular structure within a perovskite layer. As is well-known, one of the main limitations preventing the industrialization of perovskite solar cells is the relatively low resistance to various degradation factors. The aim of this work was to study the degradation of the surface of a perovskite thin film CH3NH3PbI3-xClx caused by atmosphere and light. To study the surface of CH3NH3PbI3-xClx, a scanning electron microscope, infrared (IR) spectroscopy and optical absorption were used. It is shown that the degradation of the functional layer of perovskite proceeds differently depending on the acting factor present in the surrounding atmosphere, whilst the chemical bonds are maintained within the perovskite crystal structure under nitrogen. However, when exposed to an ambient atmosphere, an expansion of the NH3+ band is observed, which is accompanied by a shift in the N–H stretching mode toward higher frequencies; this can be explained by the degradation of the perovskite surface due to hydration. This paper shows that the dissociation of H2O molecules under the influence of sunlight can adversely affect the efficiency and stability of the absorbing layer. This work presents an approach to the study of perovskite structural stability with the aim of developing alternative concepts to the fabrication of stable and sustainable perovskite solar cells.

Characterization Tools to Probe Degradation Mechanisms in Organic and Perovskite Solar Cells

“…Many studies have also used FTIR to study the structure and functional groups of perovskites. [176][177][178] Recently, Darkhan et al [179] studied the degradation of the perovskite thin film (CH 3 NH 3 PbI 3Àx Cl x ) in the presence of different stressors using FTIR and SEM. Figure 12 shows the FTIR spectra of the freshly prepared samples versus degraded ones either in air (Figure 12a), by irradiation (Figure 12b), or in a nitrogen atmosphere (Figure 12c).…”

“…The strongest vibrational modes, which correspond to the symmetric and asymmetric N–H stretching modes (associated with NH 3 + ), were seen in the fresh perovskite thin film at frequencies of 3132 and 3179 cm −1 . [ 179 ] The fresh films did not exhibit any feature, pointing to O–H stretching vibrations in the 3400–3700 cm −1 that would suggest the presence of a functional hydroxyl group (hydrates, hydroxide, and water). [ 179 ] The perovskite film was exposed to 50 ± 5% RH.…”

“…[ 179 ] The fresh films did not exhibit any feature, pointing to O–H stretching vibrations in the 3400–3700 cm −1 that would suggest the presence of a functional hydroxyl group (hydrates, hydroxide, and water). [ 179 ] The perovskite film was exposed to 50 ± 5% RH. When exposed to the atmosphere, the N–H stretching mode shifts toward higher frequencies, and the NH 3 + band widens (as shown by the blue curve of Figure 12a).…”

“…Also, the peak at 961 cm −1 (C–N stretch) shifted to 990 cm −1 due to the destruction of the crystalline structure. [ 179 ] The deprotonation of CH 3 NH 3 + , caused by hydration, forms new chemical bonds within the perovskite crystal structure. In a nitrogen environment, the chemical bonds of the crystal structure are maintained.…”

“…FTIR spectra of CH 3 NH 3 PbI 3-x Cl x single crystal samples: a) as-cast (red) and degraded (blue) perovskite film, b) as-cast (red) and exposed to illumination (yellow),and c) as-cast (red) and exposed to nitrogen (purple). Reproduced with permission [179]. Copyright 2023, MDPI.…”