Patrick Cimo

Electrophoretic Displays Fabricated on Ultra-Slim Flexible Glass Substrates

Ultra-slim flexible glass substrates enable high performance displays and electronic devices through their inherent benefits of a high-quality surface, process compatibility, thermal and dimensional stability, optical transmission, and barrier properties. This study demonstrates use of flexible glass as a backplane substrate for both active matrix displays with organic thin-film transistors (TFTs) as well as segmented displays. The demonstrated 4.7-inch active matrix VGA displays have a resolution of 170 dpi (640×480 pixels), pixel size of 150 μm × 150 μm, and aperture ratio of 40%. The dimensional stability benefit of flexible glass was clearly observed when compared to the registration of polymer substrate devices. This study demonstrates the capability and benefits of flexible glass substrates in devices fabricated with solution-based processing as a step toward roll-to-roll flexible electronic fabrication.

Strained Growth of Aluminum-Doped Zinc Oxide on Flexible Glass Substrate and Degradation Studies Under Cyclic Bending Conditions

Aluminum-doped zinc oxide (AZO) thin films have been used in low cost transparent conductive oxide (TCO) applications. For flexible electronics, the devices are subjected to cyclic bending during manufacturing and usage, which may lead to both electrical and optical degradation of TCO thin films. This paper was designed to investigate the effect of the strained growth and normal growth methods on the electrical and optical degradation under diverse cyclic bending conditions. The AZO thin films were deposited on a 100 μm thick Corning Willow Glass flexible substrate by using an RF-magnetron sputtering technique. The design of experiments technique was applied to analyze the significant factors that can affect the electrical and optical performance of AZO thin films. The experimental factors include growth methods, bending radius, and tension. From the analysis of the X-ray diffraction technique, the AZO thin films grown by the normal method have dominant (0 0 2) orientation, but the AZO thin films prepared by the strained growth method show other orientations, including (0 0 2) orientation. Although the strained growth method does change the AZO thin film properties, the strained growth method does not significantly improve the reliability of the AZO thin film after a 2000 cycle bending fatigue test.

Cholesteric Liquid Crystal Display With Flexible Glass Substrates

Cholesteric liquid crystal (ChLC) bi-stable displays were fabricated on 100 μm thick flexible glass front- and backplane substrates. The flexible glass substrates were 250 mm × 300 mm in size, and the displays were fabricated using Gen2 equipment by temporarily attaching the substrates to processing carriers. No significant fabrication issues were encountered that would limit process optimization of these devices. Benefits of the flexible glass substrates observed compared to previously evaluated polymer film substrates include both thermal capability and dimensional stability. The fabricated flexible glass ChLC displays included both 5-inch color and 10.4-inch monochrome devices with resolutions of 80 ppi and 40 ppi, respectively. The displays had a total thickness of 204 μm.

Flexible CZTS solar cells on flexible Corning ® Willow ® Glass substrates

Cu₂ZnSnS₄ (CZTS) thin film solar cells were successfully fabricated on Corning^® Willow^® Glass substrates coated with a Molybdenum (Mo) back contact. The CZTS thin films were deposited by using magnetron sputtering followed by annealing in sulfur vapor for 30 minutes. The best conversion efficiency achieved of the flexible CZTS solar cell was 3.08%, with an active area of 0.45cm². The conversion efficiency was reduced by 20% when the cell was bent to a 50mm radius. The degradation is caused by higher series resistance, which can be due to the degradation of the TCO layer and the damage in the CZTS/Mo interface.

The use of Corning® Willow™ glass for flexible CdTe solar cells

New flexible glass products should enable the fabrication of high efficiency, flexible CdTe devices because of their high optical transmission and compatibility with the high temperature processing conditions often used for making high performance CdTe solar cells. Here, we will report on our preliminary results using Corning® Willow™ Glass in a high temperature CdTe device fabrication process. For all device studies, we used MOCVD deposited SnO2:F/SnO2 bilayers as the transparent conducting oxide/buffer. We investigated CdS window layers deposited by both room temperature sputtering and chemical bath deposition (CBD). Using 550°C CdTe layers deposited by close-spaced sublimation (CSS) on both types of CdS layers, we made CdTe devices with efficiencies above 12% with Willow Glass. These efficiencies are comparable to identically processed devices on rigid glass, confirming that Willow Glass is compatible with all high temperature CdTe processing steps.

High-efficiency flexible CdTe superstrate devices

Flexible, superstrate CdTe devices combine the advantages of a commercially demonstrated, low-cost manufacturing process with a lightweight, flexible form factor. Here, we present data on cell efficiencies greater than 16%, and the critical processing changes that have enabled recent efficiency increases. The devices in this study were made on Corning® Willow® Glass, which is a highly transparent, flexible, hermetic, and dimensionally stable substrate that can withstand high processing temperatures. To date, we have produced devices with several different combinations of front and back contacts on this glass and have found that it is compatible with most of our standard processing steps. One of our best devices to date has a certified efficiency of 16.2%, with a short-circuit current density (Jsc) of 25.6 mA/cm2, an open-circuit voltage of 820 mV, and a fill factor (FF) of 77.3%. The increased Jsc in this cell is due to an improved sputtered CdS:O deposition process, and the high FF is due to a co-evaporated ZnTe:Cu back contact.

Performance of transparent conductors on flexible glass and plastic substrates for thin film photovoltaics

High-performance transparent conductive indium-tin-oxide (ITO) films on flexible glass have been flextested to 25-50k bend cycles without breakage, and with ~0.1% change in sheet resistance. In contrast, commercial ITO/PET samples undergo ~50-100% increase in sheet resistance in the same test, indicating that such coatings/substrates may not be acceptable for use in some products or fabrication procedures. The flexible glass substrate enables high-temperature processing, which facilitates the high performance of the coatings. Measurements of the volume resistivity and water vapor transmission rate (WVTR) indicate that Corning® Willow® Glass is suitable as a PV substrate material without need for barrier coatings or glass lamination.

Ultrafast Laser Fabrication of 3D Photonic Components in Flexible Glasses

We demonstrated the first flexible photonics lightwave circuits in glasses. The waveguide was written in ≤100μm thick Corning® Willow® Glass by a spatially and temporally shaped femtosecond ultrafast laser beam with processing speed up to 50mm/s. The flexible glass waveguide shows superior loss performance of 0.11dB/cm at λ=1550nm, with negligible bending loss down to a radius of 6.7cm.