Roll‐to‐Roll processing of flexible devices and components

Next generation consumer electronic devices, including wearables are placing an ever increasing emphasis on form factor. This has resulted in an increase in the number of polymeric films used in their construction. As most of these polymeric materials are initially manufactured in the form of a roll, there has been a drive towards the utilization of so called roll‐to‐roll processing (R2R) in order to reduce both manufacturing line setup, cleanroom and materials costs. This paper will therefore describe some of the most important advances made in this field, including improvements in stack processing for the production of ITO based touch panel devices, the development of new processing platforms for high performance, low defectivity stacks for barrier film & patterning for R2R manufacture of thin film transistors.     

Enhanced Photodetection Properties of Tellurium@Selenium Roll‐to‐Roll Nanotube Heterojunctions

Non‐layered tellurium (Te) is a promising material for applications in transistor and optoelectronic devices for its advantages in excellent intrinsic electronic and optoelectronic properties. However, the poor photodetection performance and relatively uncertain stability of tellurene under ambient conditions greatly limit the practical applications. In order to improve the performance of tellurene‐based materials, Te@Se roll‐to‐roll nanotubes with different selenium (Se) contents synthesized by epitaxial growth of Se on Te nanotubes are, for the first time, employed to fabricate working electrodes for photoelectrochemical (PEC)‐type broadband photodetection. They exhibit not only a preferably enhanced capacity for self‐powered broadband photodetection but also significantly improved photocurrent density and stability in various aqueous environments (HCl, NaCl, and KOH solutions), compared to tellurene‐based photodetectors. It is anticipated that the present work can open up new possibilities for high‐performance tellurene‐based optoelectronic devices.     

Large‐Scale Roll‐to‐Roll Patterned Oxygen Indicators for Modified Atmosphere Packages

We demonstrate roll‐to‐roll fabrication of ultraviolet A light‐activated colorimetric oxygen indicators on paper and plastic substrates. Such large‐scale, cost‐effective and non‐toxic oxygen indicator and production method can find applications as a very low‐cost leakage indicator for modified atmosphere packages by printing the material directly or gluing the pre‐printed indicator label inside the lid. The introduction of leakage indicators onto all modified atmosphere packages could result in improved food safety and reduced food spoilage. Copyright © 2017 John Wiley & Sons, Ltd.     

Roll‐to‐Roll Production of Graphene Hybrid Electrodes for High‐Efficiency,Flexible Organic Photoelectronics

Despite nearly two decades of research, the absence of ideal, flexible, and transparent electrodes has been the biggest bottleneck for realizing flexible and printable electronics via roll‐to‐roll (R2R) method. A fabrication of poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate):graphene:ethyl cellulose (PEDOT:PSS:G:EC) hybrid electrodes by R2R process, which allows for the elimination of strong acid treatment. The high‐performance flexible printable electrode includes a transmittance (T) of 78% at 550 nm and a sheet resistance of 13 Ω sq⁻¹ with excellent mechanical stability. These features arise from the PSS interacting strongly with the ethyoxyl groups from EC promoting a favorable phase separation between PEDOT and PSS chains, and the highly uniform and conductive G:EC enable rearrangement of the PEDOT chains with more expanded conformation surrounded by G:EC via the π–π interaction between G:EC and PEDOT. The hybrid electrodes are fully functional as universal electrodes for outstanding flexible electronic applications. Organic solar cells based on the hybrid electrode exhibit a high power conversion efficiency of 9.4% with good universality for active layer. Moreover, the organic light‐emitting diodes and photodetector devices hold the same level to or outperform those based on indium tin oxide flexible transparent electrodes.     

Roll‐to‐Roll Production of Transparent Silver‐Nanofiber‐Network Electrodes for Flexible Electrochromic Smart Windows

Electrochromic smart windows (ECSWs) are considered as the most promising alternative to traditional dimming devices. However, the electrode technology in ECSWs remains stagnant, wherein inflexible indium tin oxide and fluorine‐doped tin oxide are the main materials being used. Although various complicated production methods, such as high‐temperature calcination and sputtering, have been reported, the mass production of flexible and transparent electrodes remains challenging. Here, a nonheated roll‐to‐roll process is developed for the continuous production of flexible, extralarge, and transparent silver nanofiber (AgNF) network electrodes. The optical and mechanical properties, as well as the electrical conductivity of these products (i.e., 12 Ω sq^?1 at 95% transmittance) are comparable with those AgNF networks produced via high‐temperature sintering. Moreover, the as‐prepared AgNF network is successfully assembled into an A4‐sized ECSW with short switching time, good coloration efficiency, and flexibility.     

Roll‐to‐roll coating of flexible glass

Flexible glass is a relatively new kind of substrate with a unique combination of properties that are, in different aspects, ideal for numerous applications. The material has aroused significant interest and has prompted activities in R&D communities dedicated to topics such as flexible electronics, flexible OLED and flexible PV. As a result, device demonstrators of considerable maturity have been created, some of which were even manufactured using a roll‐to‐roll (R2R) process. So far, these activities have not resulted in marketable final products that are produced in an industrial context. The key prerequisite for a widespread industrial adoption of R2R processing of flexible glass substrates is the availability of suitable and proven manufacturing equipment. The tools need to be able to handle and process this delicate material, taking into account its mechanical properties, which differ significantly from the typical flexible substrates such as paper, polymer film, or metal foil. This article discusses specific equipment aspects that need to be considered in the R2R handling of flexible glass, both in general and by taking the example of a roll‐to‐roll lab coating system. This tool has been designed specifically for handling flexible glass and will be available to the interested community from October 2016. Furthermore, it is shown how different processes such as R2R sputtering, evaporation, and flash lamp annealing can be used for potential flexible glass applications in flexible electronics, architecture, and energy conversion devices. Beyond that, related layer stacks deposited by vacuum coating will be discussed.     

Roll‐to‐Roll Production of Layer‐Controlled Molybdenum Disulfide: A Platform for 2D Semiconductor‐Based Industrial Applications

A facile methodology for the large‐scale production of layer‐controlled MoS₂ layers on an inexpensive substrate involving a simple coating of single source precursor with subsequent roll‐to‐roll‐based thermal decomposition is developed. The resulting 50 cm long MoS₂ layers synthesized on Ni foils possess excellent long‐range uniformity and optimum stoichiometry. Moreover, this methodology is promising because it enables simple control of the number of MoS₂ layers by simply adjusting the concentration of (NH₄)₂MoS₄. Additionally, the capability of the MoS₂ for practical applications in electronic/optoelectronic devices and catalysts for hydrogen evolution reaction is verified. The MoS₂‐based field effect transistors exhibit unipolar n‐channel transistor behavior with electron mobility of 0.6 cm² V^?1 s^?1 and an on‐off ratio of ≈10³. The MoS₂‐based visible‐light photodetectors are fabricated in order to evaluate their photoelectrical properties, obtaining an 100% yield for active devices with significant photocurrents and extracted photoresponsivity of ≈22 mA W^?1. Moreover, the MoS₂ layers on Ni foils exhibit applicable catalytic activity with observed overpotential of ≈165 mV and a Tafel slope of 133 mV dec^?1. Based on these results, it is envisaged that the cost‐effective methodology will trigger actual industrial applications, as well as novel research related to 2D semiconductor‐based multifaceted applications.     

Roll‐to‐Roll Cohesive,Coated, Flexible,High‐Efficiency Polymer Light‐Emitting Diodes Utilizing ITO‐Free Polymer Anodes

This paper reports solution‐processed, high‐efficiency polymer light‐emitting diodes fabricated by a new type of roll‐to‐roll coating method under ambient air conditions. A noble roll‐to‐roll cohesive coating system utilizes only natural gravity and the surface tension of the solution to flow out from the capillary to the surface of the substrate. Because this mechanism uses a minimally cohesive solution, the roll‐to‐roll cohesive coating can effectively realize an ultra‐thin film thickness for the electron injection layer. In addition, the roll‐to‐roll cohesive coating enables the fabrication of a thicker polymer anode film more than 250 nm at one time by modification of the surface energy and without wasting the solution. It is observed that the standard sheet resistance deviation of the polymer anode is only 2.32 Ω/□ over 50 000 bending cycles. The standard sheet resistance deviation of the polymer anode in the different bending angles (0 to 180°) is 0.313 Ω/□, but the case of the ITO‐PET is 104.93 Ω/□. The average surface roughness of the polymer anode measured by atomic force microscopy is only 1.06 nm. Because the surface of the polymer anode has a better quality, the leakage current of the polymer light‐emitting diodes (PLEDs) using the polymer anode is much lower than that using the ITO‐PET substrate. The luminous power efficiency of the two devices is 4.13 lm/W for the polymer anode and 3.21 lm/W for the ITO‐PET. Consequently, the PLEDs made by using the polymer anode exhibited 28% enhanced performance because the polymer anode represents not only a higher transparency than the ITO‐PET in the wavelength of 560 nm but also greatly reduced roughness. The optimized the maximum current efficiency and power efficiency of the device show around 6.1 cd/A and 5.1 lm/W, respectively, which is comparable to the case of using the ITO‐glass.