XPS SPECTRA AS A TOOL FOR STUDYING PHOTOCHEMICAL AND THERMAL DEGRADATION IN APbX3 HYBRID HALIDE PEROVSKITES

Our results show that the resistance of hybrid lead halide perovskites to stress factors (light or heat) is gradually increased while substituting the A-site cation going from CH3NH3+ to CH(NH2)2+ and then to Cs+.This study was supported by Russian Foundation for Basic Research (grants 20-24-660003 and 21-52-52002)

Probing local photocurrent in inorganic CsPbBr3 perovskite films by scanning probe microscopy

Hybrid organic-inorganic halide perovskites are among the most promising materials for solar cells. Rapid growth of their power conversion efficiency (PCE) from 3.8% in 2009 [1] to more than 22% in 2017 [2] made them attractive for commercial applications. However, rapid degradation of organic-inorganic perovskites under operating conditions – photon flux, electric field, heating – remains unsolved in spite of tremendous research effort [3,4]. Their fully inorganic counterparts possess similar optoelectronic properties [5] and better stability [6]. Still, their PCE is below 10%, which requires further investigation and optimization

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

Measurements of XPS survey, core levels (N 1s, O 1s, Pb 4f, I 3d), and valence band (VB) spectra of CH3NH3PbI3 (MAPbI3) hybrid perovskite prepared on different substrates (glass, indium tin oxide (ITO), and TiO2) aged under different light-soaking conditions at room temperature are presented. The results reveal that the photochemical stability of MAPbI3 depends on the type of substrate and gradually decreases when glass is replaced by ITO and TiO2. Also, the degradation upon exposure to visible light is accompanied by the formation of MAI, PbI2, and Pb0 products as shown by XPS core levels spectra. According to XPS O 1s and VB spectra measurements, this degradation process is superimposed on the partial oxidation of lead atoms in ITO/MAPbI3 and TiO2/MAPbI3, for which Pb–O bonds are formed due to the diffusion of the oxygen ions from the substrates. This unexpected interaction leads to additional photochemical degradation. © 2021 by the author. Licensee MDPI, Basel, Switzerland.Funding: The sample preparation, aging experiments, UV‐vis, XRD, and SEM characterization were supported by Russian Science Foundation (project No. 19‐73‐30020). The XPS measurements were supported by the Ministry of Education and Science of the Russian Federation (project FEUZ‐2020‐0060), Theme ‘Electron’, no. AAAA‐A18‐118020190098‐5 and Russian Foundation for Basic Research (projects No. 21‐52‐52002/21 and 20‐42‐660003). C.‐C.C. acknowledges the financial support from the Ministry of Science and Technology in Taiwan (MOST 110‐2923‐E‐002‐007‐MY3) and the Top University Project from National Taiwan University (110L7836 and 110L7726)

Temperature Dependence of Photochemical Degradation of MAPbBr3 Perovskite

The experimental results of X-ray diffraction (XRD), optical absorbance, scanning electron microscopy (SEM), and X-ray photoelectron spectra (XPS) of the core levels and valence bands of MAPbBr3 (MA-CH3NH3+) perovskite before and after exposure to visible light for 700 h at temperatures of 10 and 60 °C are presented. It reveals that the light soaking at 60 °C induces the decomposition of MAPbBr3 perovskite accompanied with the decay of organic cation and the release of a PbBr2 phase as a degradation product whereas the photochemical degradation completely disappears while the aging temperature is decreased to 10 °C. © 2022 by the authors.Russian Foundation for Basic Research, РФФИ: 21-52-52002; Ministry of Education and Science of the Russian Federation, Minobrnauka: AAAA-A18–118020190098-5, FEUZ 2020-0060; Ministry of Science and Technology, Taiwan, MOST: 110-2923-E-002-007-MY3; Russian Science Foundation, RSF: 19-73-30020I.S.Z. and A.I.K. thank the Ministry of Science and Higher Education of the Russian Federation (Ural Federal University Program of Development within the Priority-2030 Program) for support.This work was supported by the Russian Science Foundation (Project 19-73-30020) at IPCP RAS. The XPS measurements were supported by the Ministry of Science and Higher Education of the Russian Federation under the theme “Electron” No. AAAA-A18–118020190098-5 and Project FEUZ 2020-0060 as well as the Russian Foundation for Basic Research (Project No. 21-52-52002). The research fundings from the Ministry of Science and Technology in Taiwan (MOST 110-2923-E-002-007-MY3) are gratefully acknowledged

Tuning hardness in calcite by incorporation of amino acids

Structural biominerals are inorganic/organic composites that exhibit remarkable mechanical properties. However, the structure–property relationships of even the simplest building unit—mineral single crystals containing embedded macromolecules—remain poorly understood. Here, by means of a model biomineral made from calcite single crystals containing glycine (0–7 mol%) or aspartic acid (0–4 mol%), we elucidate the origin of the superior hardness of biogenic calcite. We analysed lattice distortions in these model crystals by using X-ray diffraction and molecular dynamics simulations, and by means of solid-state nuclear magnetic resonance show that the amino acids are incorporated as individual molecules. We also demonstrate that nanoindentation hardness increased with amino acid content, reaching values equivalent to their biogenic counterparts. A dislocation pinning model reveals that the enhanced hardness is determined by the force required to cut covalent bonds in the molecules

Сбалансированность регионального и муниципального бюджетов как инструмент обеспечения экономической безопасности территории на примере Красноярского края

In modern conditions, the problems of economic security of socio-economic systems of various levels are in the focus of attention of Russian and foreign scientists. These problems are particularly acute for territories that have a pronounced source of raw materials and underdeveloped high-added value industries. Economic security of the city and the region cannot be ensured without due regard to the sectoral structure of the economy and the balance of budgets of all levels. An important indicator of the budget balance is the structure of the regional budget revenue, or, particularly, the structure of tax revenues to the budget, as well as the expenditure structure. The article discusses the distinctive formation features of revenue and expenditure parts of the regional and local budgets, analyses the most typical sources of revenue for different territories. The consolidated budget structure for the region and some municipalities based on the example of the Krasnoyarsk Territory (Krai) is analysed. The dynamics of revenues and expenditures is considered, the limitations stipulated by the regional law on intergovernmental relations are examined. As a result of the study, the authors arrived at the conclusions about the lack of balance between the analysed budgets, their inconsistency with the needs of the region, and, as a result, the existing threats to the economic security of the territory in question. The article contains recommendations on the development of economic activities in the Krasnoyarsk Territory that take into account the specifics of the studied region and that can improve the balance of local and regional budgetsВ современных условиях проблемы экономической безопасности социально-экономических систем различного уровня находятся в сфере пристального внимания российских и за- рубежных ученых. Особенно остро данные проблемы стоят перед территориями, име- ющими выраженную сырьевую направленность и недостаточный уровень развития производств с высокой добавленной стоимостью. Экономическая безопасность города и региона не может быть обеспечена без учета отраслевой структуры экономики и сба- лансированности бюджетов всех уровней. Важным индикатором сбалансированности бюджета является структура доходной части регионального бюджета, или, более точ- но, структура налоговых поступлений в бюджет, а также структура расходов. В статье рассматриваются особенности формирования доходной и расходной частей региональных и местных бюджетов, анализируются наиболее типичные источники доходной части для различных типов территорий. Авторы приводят анализ структуры консолидированного бюджета региона и ряда муниципальных образований на примере Красноярского края. Рассматривается ди- намика доходов и расходов, исследуются ограничения, предусмотренные региональ- ным законом о межбюджетных отношениях. В результате исследования авторами получены выводы об отсутствии сбалансированности анализируемых бюджетов, их несоответствии потребностям региона и, как следствие, о существующих угрозах экономической безопасности рассматриваемой территории. Статья содержит рекомендации по развитию на территории Красноярского края видов экономической деятельности, учитывающих специфику исследуемого региона и способных повысить сбалансированность местных и регионального бюджето

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

Measurements of XPS survey, core levels (N 1s, O 1s, Pb 4f, I 3d), and valence band (VB) spectra of CH3NH3PbI3 (MAPbI3) hybrid perovskite prepared on different substrates (glass, indium tin oxide (ITO), and TiO2) aged under different light-soaking conditions at room temperature are presented. The results reveal that the photochemical stability of MAPbI3 depends on the type of substrate and gradually decreases when glass is replaced by ITO and TiO2. Also, the degradation upon exposure to visible light is accompanied by the formation of MAI, PbI2, and Pb0 products as shown by XPS core levels spectra. According to XPS O 1s and VB spectra measurements, this degradation process is superimposed on the partial oxidation of lead atoms in ITO/MAPbI3 and TiO2/MAPbI3, for which Pb–O bonds are formed due to the diffusion of the oxygen ions from the substrates. This unexpected interaction leads to additional photochemical degradation

XPS evidence of degradation mechanism in CH3NH3PbI3 hybrid perovskite

In this study, we investigate the photo-/thermal degradation mechanism of hybrid perovskites by using x-ray photoelectron (XPS) valence band (VB) spectra coupling with density functional theory (DFT) calculations. Herein, CH3NH3PbI3 is respectively subjected to irradiation with visible light and annealing at an exposure of 0-1000 h. It is found from XPS survey spectra that, in both cases (irradiation and annealing), a decrease in the I:Pb ratio is observed with aging time, which unambiguously indicates the formation of PbI2 as the product of photo/thermal degradation. The comparison of the XPS VB spectra of irradiated and annealed perovskites with the DFT calculations of CH3NH3PbI3 and PbI2 compounds have showed a systematic decrease in the contribution of I-5p states, which allows us to determine the respective threshold for degradation, which is 500 h for light irradiation and 200 h for annealing. This discrepancy might be due to the fact that the relaxation of thermal excitations of the system is carried out only by the phonons (which are non-radiative physical processes) while the radiative processes occurred during the photoexcitation will elastically or inelastically divert part of the external energy from the system to reduce its impact on perovskite degradation. © 2019 IOP Publishing Ltd