Open-air spray-plasma deposition of moisture barriers
Keywords: Humanities and Sciences.
Chemistry.

Emerging optoelectronic devices often require moisture barriers to prevent water ingress. While a variety of methods exist to limit moisture ingress including glass/glass encapsulation and multilayer films produced in vacuum environments, they present disadvantages in terms of rigidity, weight, cost and method of application. A compounding aspect of barrier evaluation is the need for a both accurate and high throughput methodology. In this dissertation, I will show the development of different types of thin film moisture barriers via plasma deposition in open-air and demonstrate a rapid testing methodology using infrared imaging to evaluate the moisture barrier efficacy. Firstly, I will demonstrate a spatially resolved imaging methodology for water vapor transmission rate (WVTR) testing that relies on quantified infrared characterization at water absorption bands. This technique is validated using a moisture barrier on a polymer substrate via calibration of the infrared image intensity with moisture content in the polymer substrate from images taken at different times. This method is compared to existing state of the art techniques such as membrane permeation measurement and optical calcium film testing. This fast, non-destructive and in-situ method enables defect visualization and shows the WVTR with a sensitivity limit of 5·10-5 g/m2/day. Secondly, I will describe the open-air spray plasma deposition of thin film moisture barriers. A commercially available precursor, 1,2-bis(triethoxysilyl)-ethane (BTESE), is used here in the open-air spray plasma processing. The deposited films are highly transparent, tunable in thickness and mechanical properties, and exhibiting a WVTR at about 1.5 g/m2/day under an accelerated aging condition of 38 °C and 90% relative humidity (R.H.), a tenfold increase in moisture barrier efficacy compared to bare polymer substrates. The barrier films are directly applied to perovskite solar devices and enable the devices to retain 80% of their initial performance for over 600 hours in ambient conditions, while the control devices decreased to 20% of their performance after 200 hours. Additionally, the barrier films are mechanically robust, exhibiting a threefold increase in adhesion energy and fourfold increase in Young's modulus compared to commercial polysiloxane coatings. Finally, I will present a multilayer moisture barrier design with alternating layers of inorganic SiO2 thin film and conformal organosilicate film to prevent moisture ingress. The inorganic layer effectively blocks moisture ingress and the organsilicate layer decouples any pinhole defects in the inorganic layer. A multilayer alternating barrier films with 900nm achieved WVTR on the order of 10-4 g/m2/day at an accelerated aging condition of 38°C and 90% R.H., with transparencies ranging from 99% to 75% depending on the number of layers. Perovskite solar cells with multilayer barriers retain over 80% of their initial performance for over 660 hours in a 50°C, 50%R.H. aging environment. The ability of the rapid deposition of high efficacy multilayer moisture barrier in open-air as well as the non-destructive and in-situ evaluation of its efficacy enabling device resistance to humid environments is crucial towards realizing longer operating lifetimes