STABILITY STUDIES OF ALD FILMS AND INFILTRATED HYBRID MATERIALS

Author
Selma Raquel Fairach
Year
2022
Thesis name in original language
STABILITY STUDIES OF ALD FILMS AND INFILTRATED HYBRID MATERIALS
Abstract & Cover

Over the years, depositing metal oxides onto the surface of organic substances has been favored by a lot of industries to create products with a longer life cycle. The renewable energy sector has seen a lot of improvement in their power conversion efficiency (PCE) of perovskite solar cells (PSC) through the incorporation of metal oxides either through atomic layer deposition (ALD) or vapor phase infiltration (VPI). ALD has also supported the structural modification and pore selectivity of synthetic membranes used in water filtration systems, catalytic reactors, gas and liquid purification systems, batteries, sensors, fuel cells, and barrier layers. Among all the possible thin film oxides that can be deposited through ALD, aluminum oxide (or “alumina”) is a popular choice for moisture and chemical barrier applications. It is often chosen as a thin film oxide due to its film thickness uniformity, lack of pinhole defects, and transparency (ALD-alumina is a colorless thin film oxide). Depositing ALD-alumina on a substrate surface will prevent the said material to oxidize future, allowing it to preserve its natural surface chemistry and all the optomechanical properties that come with it. However, the behavior of ALDalumina in various aqueous solutions are still contested in the field, with various researchers reporting different trends of ALD-alumina behavior in solution. This can pose a problem, as a lot of applications that utilize ALD-alumina are immersed in water, or other liquids, for extended periods of time. Due to a lack of understanding of the ALD-alumina degradation behavior, this factor is often ignored in applications. This could be a problem that affects the accuracy in other fields of research. ix The purpose of this thesis is to study and determine factors that affect ALD-alumina film chemistry in aqueous solutions. A set of dissolution trials have been setup with solutions of different volumes, concentration, and pH. ALD-alumina, synthesized through the reaction of trimethylaluminum (TMA) and water (H2O), is deposited on an air-plasma cleaned silicon substrate. The deposition temperature is kept at 150 °C for 400 cycles of ALD, resulting in ~48 nm of alumina thin film oxide. These samples will then be immersed in different volumes of Type 1 DI water (DIW) and different moles of NaCl solution. This is done to understand the impact of water volume and salt concentration on the degradation rate of ALD-alumina. To eliminate other factors that could affect the thin film behavior, the samples are kept in tightly sealed vials that are stored in a dark space at room temperature. Throughout this project, the specific film thicknesses of our ALD-alumina samples will be tracked across time in days. The surface chemistry will also be analyzed to XPS deconvolution of the oxygen and aluminum spectra peaks. As an extension of ALD applications as a protective coating, this thesis will also investigate the effect of VPI on the PCE stability of PSCs. The charge transport layer, Spiro-OMeTAD, will be infiltrated by TiCl4 to create a hybrid organic-inorganic layer that prevents degradation due to Au diffusion into the layer or crystallization effects when exposed to high heat. By introducing TiOx into the layer, the Spiro-OMeTAD layer will have better thermal stability and have an improved PCE stability under high illumination and humidity. 

University
Georgia Institute of Technology
(Atlanta, United States)
External Link
Read Thesis
LinkedIn
linkedin invite