Influence of Ion Migration from ITO and SiO₂ Substrates on Photo and Thermal Stability of CH₃NH₃SnI₃ Hybrid Perovskite

Abstract

The influence of light soaking and heat stress on the degradation of indium tin oxide (ITO)/CH3NH3SnI3 and SiO2/CH3NH3SnI3 hybrid perovskite is studied. The measurements of X-ray photoelectron survey spectra (XPS) showed an increase in the concentration of substrate ions in the surface layer of ITO/CH3NH3SnI3 and reduction of N:Sn and I:Sn ratios after 500 h of white light irradiation and 200 h of annealing at 90 °C. The high-energy-resolved XPS Sn three-dimensional (3d) spectra of ITO/CH3NH3SnI3 indicated a consistent increase in the contribution of Sn4+ ions at these exposure times under light soaking and heat stress. Scanning electron microscopy (SEM) measurements show a violation of the continuity of the perovskite layer with the exposure time and an increase in the size of the voids, which is consistent with the indicated changes in the XPS spectra. On the other hand, we consider the effect of irradiation and annealing on the diffusion of the substrate elements and their chemical interaction with the overlying perovskite layers. The XPS Sn 3d, O 1s, and valence band (VB) measurements and density functional theory (DFT) calculations reveal that at the initial stages of CH3NH3SnI3 degradation, the SnI4 phase separation occurs and with a further increase in exposure time, tin is oxidized to form a SnO2 phase. In addition, we found that CH3NH3SnI3 perovskite prepared on a SiO2 substrate is more stable than on an ITO substrate, and the effect of the oxidation of tin atoms due to the migration of oxygen ions is very weak. The theoretical modeling demonstrates that the formation of SnI2 defects in CH3NH3SnI3 became irreversible due to the oxidation by the migration of the oxygen ions from the substrate. The calculated formation energy of an oxygen vacancy in ITO is about 2 times smaller than in SiO2 that explains the instability of ITO/CH3NH3SnI3.

Influence of Oxygen Ion Migration from Substrates on Photochemical Degradation of CH3NH3PbI3 Hybrid Perovskite

“…For ITO/MAPbI 3 , the N:Nb ratio decreases from 0.73 to 0.13, and the I:Pb ratio decreased from 2.70 to 1.56 while, for TiO 2 /MAPbI 3 , the N:Nb ratio is reduced from 0.90 to 0.24 and the I:Pb ratio is reduced from 2.89 to 1.24. As shown earlier [8][9][10], a decrease in the N:Nb ratio indicates the decomposition of the organic cation, whereas reduction of I:Pb suggests the formation of PbI 2 , a product of decomposition of hybrid perovskites. On the one hand, these conclusions fit well into the degradation scheme as proposed in [11,12]: Measurements of XPS N 1s, Pb 4d, and I 3d core-level spectra with a high energy resolution are capable to verify the validity of these conclusions.…”

The ultralow thermal conductivity and tunable thermoelectric properties of surfactant-free SnSe nanocrystals

“…The two components at 486.8 and 487.7 eV correspond to two oxidation states of Sn 2+ and Sn 4+ , respectively, that are bonded to Se 2À , and the third component at 488.4 eV is attributed to Sn 4+ bonded with iodide. 14,36,38 In the case of the MAI-treated NCs, the Sn 3d 5/2 peak was also found to have three components, shied by 0.2 eV towards higher binding energies, which was probably due to the increased oxidation of Sn 2+ to Sn 4+ . Notably, these shis are absent in Fig.…”

“…S7 †). 36,37 When the SnSe NCs were treated with MAI, the iodine 3d peak was more pronounced and non-symmetric; the I 3d 5/2 peak could be deconvoluted into two components at 620.4 eV and 621.2 eV (Fig. S7 †), which are attributed to iodide ions bonded with Sn 2+ and Sn 4+ , respectively.…”

Mixed Conductivity of Hybrid Halide Perovskites: Emerging Opportunities and Challenges

“…For instance, elevated temperatures during operation were found to induce ion migration from the neighboring layers, such as the counterelectrodes (e.g., Au) as well as dopants of the holetransporting material (e.g., Li + ), which act as defects in the active layer (Domanski et al, 2016). Similarly, ion migration and dopant reactivity are found to induce transformations in the selective charge-transport layers, such as the hole-transporting materials (Magomedov et al, 2018;Boldyreva et al, 2020), whereas electron-transporting layers were also found to affect the stability of hybrid perovskite devices through various (photo) redox processes (Akbulatov et al, 2020;Zhidkov et al, 2020). Moreover, photoinduced halide segregation results in gradual changes of the optoelectronic properties of the active layer, thereby affecting the resulting performances (Gratia et al, 2016;Slotcavage et al, 2016;Barker et al, 2017;Samu et al, 2017;Yoon et al, 2017).…”