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Chemical Analysis of the Interface between Hybrid Organic-Inorganic Perovskite and Atomic Layer Deposited Al₂O₃.

ABSTRACT: Ultrathin metal oxides prepared by atomic layer deposition (ALD) have gained utmost attention as moisture and thermal stress barrier layers in perovskite solar cells (PSCs). We have recently shown that 10 cycles of ALD Al₂O₃ deposited directly on top of the CH₃NH₃PbI_{3- x}Cl _x perovskite material, are effective in delivering a superior PSC performance with 18% efficiency (compared to 15% of the Al₂O₃-free cell) with a long-term humidity-stability of more than 60 days. Motivated by these results, the present contribution focuses on the chemical modification which the CH₃NH₃PbI_{3- x}Cl _x perovskite undergoes upon growth of ALD Al₂O₃. Specifically, we combine in situ Infrared (IR) spectroscopy studies during film growth, together with X-ray photoelectron spectroscopy (XPS) analysis of the ALD Al₂O₃/perovskite interface. The IR-active signature of the NH₃⁺ stretching mode of the perovskite undergoes minimal changes upon exposure to ALD cycles, suggesting no diffusion of ALD precursor and co-reactant (Al(CH₃)₃ and H₂O) into the bulk of the perovskite. However, by analyzing the difference between the IR spectra associated with the Al₂O₃ coated perovskite and the pristine perovskite, respectively, changes occurring at the surface of perovskite are monitored. The abstraction of either NH₃ or CH₃NH₂ from the perovskite surface is observed as deduced by the development of negative N-H bands associated with its stretching and bending modes. The IR investigations are corroborated by XPS study, confirming the abstraction of CH₃NH₂ from the perovskite surface, whereas no oxidation of its inorganic framework is observed within the ALD window process investigated in this work. In parallel, the growth of ALD Al₂O₃ on perovskite is witnessed by the appearance of characteristic IR-active Al-O-Al phonon and (OH)-Al?O stretching modes. Based on the IR and XPS investigations, a plausible growth mechanism of ALD Al₂O₃ on top of perovskite is presented.

SUBMITTER: Koushik D

PROVIDER: S-EPMC6369720 | biostudies-literature | 2019 Feb

REPOSITORIES: biostudies-literature

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Chemical Analysis of the Interface between Hybrid Organic-Inorganic Perovskite and Atomic Layer Deposited Al2O3.

Koushik Dibyashree D Hazendonk Lotte L Zardetto Valerio V Vandalon Vincent V Verheijen Marcel A MA Kessels Wilhelmus M M WMM Creatore Mariadriana M

ACS applied materials & interfaces 20190124 5

Ultrathin metal oxides prepared by atomic layer deposition (ALD) have gained utmost attention as moisture and thermal stress barrier layers in perovskite solar cells (PSCs). We have recently shown that 10 cycles of ALD Al2O3 deposited directly on top of the CH3NH3PbI3- xCl x perovskite material, are effective in delivering a superior PSC performance with 18% efficiency (compared to 15% of the Al2O3-free cell) ...[more]

PMID: 30624886

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Project description:Atomic-layer-deposited alumina (ALD Al2O3) can be utilized for passivation, structural, and functional purposes in electronics. In all cases, the deposited film is usually expected to maintain chemical stability over the lifetime of the device or during processing. However, as-deposited ALD Al2O3 is typically amorphous with poor resistance to chemical attack by aggressive solutions employed in electronics manufacturing. Therefore, such films may not be suitable for further processing as solvent treatments could weaken the protective barrier properties of the film or dissolved material could contaminate the solvent baths, which can cause cross-contamination of a production line used to manufacture different products. On the contrary, heat-treated, crystalline ALD Al2O3 has shown resistance to deterioration in solutions, such as standard clean (SC) 1 and 2. In this study, ALD Al2O3 was deposited from four different precursor combinations and subsequently annealed either at 600, 800, or 1000 °C for 1 h. Crystalline Al2O3 was achieved after the 800 and 1000 °C heat treatments. The crystalline films showed apparent stability in SC-1 and HF solutions. However, ellipsometry and electron microscopy showed that a prolonged exposure (60 min) to SC-1 and HF had induced a decrease in the refractive index and nanocracks in the films annealed at 800 °C. The degradation mechanism of the unstable crystalline film and the microstructure of the film, fully stable in SC-1 and with minor reaction with HF, were studied with transmission electron microscopy. Although both crystallized films had the same alumina transition phase, the film annealed at 800 °C in N2, with a less developed microstructure such as embedded amorphous regions and an uneven interfacial reaction layer, deteriorates at the amorphous regions and at the substrate-film interface. On the contrary, the stable film annealed at 1000 °C in N2 had considerably less embedded amorphous regions and a uniform Al-O-Si interfacial layer.

Project description:Perovskite photovoltaics has achieved conversion efficiencies of 26.0% by optimizing the optoelectronic properties of the absorber and its interfaces with charge transport layers (CTLs). However, commonly adopted organic CTLs can lead to parasitic absorption and device instability. Therefore, metal oxides like atomic layer-deposited (ALD) SnO2 in combination with fullerene-based electron transport layers have been introduced to enhance mechanical and thermal stability. Instead, when ALD SnO2 is directly processed on the absorber, i.e., without the fullerene layer, chemical modifications of the inorganic fraction of the perovskite occur, compromising the device performance. This study focuses on the organic fraction, particularly the formamidinium cation (FA+), in a CsFAPb(I,Br)3 perovskite. By employing in situ infrared spectroscopy, we investigate the impact of ALD processing on the perovskite, such as vacuum level, temperature, and exposure to half and full ALD cycles using tetrakis(dimethylamido)-Sn(IV) (TDMA-Sn) and H2O. We observe that exposing the absorber to vacuum conditions or water half-cycles has a negligible effect on the chemistry of the perovskite. However, prolonged exposure at 100 °C for 90 min results in a loss of 0.7% of the total formamidinium-related vibrational features compared to the pristine perovskite. Supported by density functional theory calculations, we speculate that FA+ deprotonates and that formamidine desorbs from the perovskite surface. Furthermore, the interaction between TDMA-Sn and FA+ induces more decomposition of the perovskite surface compared to vacuum, temperature, or H2O exposure. During the exposure to 10 ALD half-cycles of TDMA-Sn, 4% of the total FA+-related infrared features are lost compared to the pristine perovskite. Additionally, IR spectroscopy suggests the formation and trapping of sym-triazine, i.e., a decomposition product of FA+. These studies enable to decouple the effects occurring during direct ALD processing on the perovskite and highlight the crucial role of the Sn precursor in affecting the perovskite surface chemistry and compromising the device performance.

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Dataset Information

Chemical Analysis of the Interface between Hybrid Organic-Inorganic Perovskite and Atomic Layer Deposited Al₂O₃.

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Chemical Analysis of the Interface between Hybrid Organic-Inorganic Perovskite and Atomic Layer Deposited Al<sub>2</sub>O<sub>3</sub>.

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