AVS 66 Session AS-ThA: Role of Surfaces and Interfaces in Energy Material and Industrial Problems

Glass has become the all-important interface between human users and information and communications in our daily lives. People not only want to look at bright, high-definition information-displays but also want to interact with and touch the displays. This has placed new requirements on the performance and durability of the surfaces we interact with.

Just below the outer boundaries of glass, the composition makes a transition from the surface that we interact with, defining the spatial limits of the solid, to the “bulk”-material that exhibits most of the macroscopic properties we experience that allow us to use it as building materials to construct displays, hand-held devices, smart-watches, etc.

The composition of the near-surface region, from a few nanometers to several micrometers generally governs the appearance and durability of these surfaces. It also is a critical component in the adhesion of thin films deposited to improve scratch resistance, cleanability, and optical performance.

We will review some compositional profiles of glass, thin films and other materials to understand how some of these surfaces appear, compositionally, and how this can inform us of chemistries and mechanical properties. I will review Secondary Ion Mass Spectrometry (SIMS) depth-profile data and its combination with data acquired by other methods that give us a more complete understanding of the optical surfaces we interact with.

Products that offer sensorial benefits in addition to cleaning are increasingly popular among consumers in the fabric care market. Such sensorial attributes are typically related to touch and smell and help provide a more enjoyable experience to the consumer both during and after the laundering process. This presentation will focus on the XPS and SIMS characterization of fabrics before and after washing with different liquid laundry formulations to determine the amount and distribution of different components on the fabric’s surface.

Surface analysts have a love-hate relationship with silicones. Silicones are widely used industrially for lowering surface energy, improving slip, coefficient of friction, mar and many other surface lubricity properties. Due to their low surface energies, and sometimes low viscosity or molecular weight, there is a tendency for them to spread over surfaces or be present as surface contaminants. In these cases a surface analyst may wish to remove them using a gas cluster ion beam source (GCIB). In other instances it may be desirable to understand the chemistry of a silicone coating as a function of depth. Unfortunately, GCIB profiling of silicones is not as straightforward as it is with other organic polymers.

Examples of depth profiles under different GCIB conditions from some reference silicones and silicone-containing coatings will be discussed in this presentation.

This work details the effect of underlying layers on the growth of CsGeI₃, a novel all-inorganic perovskite absorber. The hole-transport layer (HTL) and the underlying substrate were systematically varied. Surface and bulk properties of the film stack were characterized at every growth step. The choice of HTL affects the absorber film morphology, and resulting device efficiency. Further, this approach reveals that the choice of substrate can affect the properties of layers through the entire device.

Two common HTLs, PEDOT:PSS and MoO₃, were deposited on substrates with differing surfaces. Glass, ITO (indium tin oxide, a common thin film solar cell transparent electrode), and Si substrates were selected to explore how a range of surface structures, from amorphous to polycrystalline to crystalline, affects the subsequent layers. The vapor-deposited MoO₃ was further modified with gas-phase treatments (UV-ozone and O₂ plasma exposure) and small molecules (silanization). Specifically, an IPTMS ((3-iodopropyl) trimethoxysilane) silanization procedure was developed to produce an iodine-terminated surface, for improved adhesion of the CsGeI₃ absorber layer. A suite of materials characterization methods were applied to the samples after each step of device fabrication to assess the evolution of morphology and composition. Bulk, surface, and interface characteristics were probed using UV-Vis absorption measurements, X-ray photoelectron spectroscopy, scanning electron microscopy, optical profilometry, and spectroscopic ellipsometry. Notably, the absorber film morphology and ultimately the stability of the film stack is sensitive to not only the HTL, but the nature of the material under the HTL (ITO vs. glass), demonstrating the influence of surface/interface properties across multiple layers in a device.

We have used time-of-flight secondary-ion mass spectrometry (TOF-SIMS) at the National Renewable Energy Laboratory to investigate the performance and reliability of solar cell materials and devices, and we will present some recent work that highlights the versatility of TOF-SIMS. This work includes: 1) Multi-scale, multi-technique investigations of photovoltaic module failure including TOF-SIMS to enable insights into the root-cause mechanisms of module degradation at the nanoscale that are observed at the length scale of meters; 2) Investigations into the performance and stability of hybrid perovskite solar cell devices and 3) Using a combination of 1-D profiling and 3-D tomography to elucidate the fundamentals of incorporating dopants in CdTe solar cells.

Polymer electrolyte membrane fuel cells (PEMFCs) produce electricity with only heat and water as byproducts, but sluggish kinetics of the oxygen reduction reaction (ORR) at the cathode restrict widespread commercialization, motivating development of advanced catalysts such as the extended surface platinum nickel (PtNi) and platinum nickel cobalt (PtNiCo) nanowires investigated in this work.