Paper electronics: a new challenge for materials a new opportunity for devices II

Resume : Conductive paper has been made by adding carbon nanotubes and other conducting nano – materials to the pulp fiber suspension. In another approach nano fibrillated cellulose films (also called micro fibrillated cellulose) have been made electrical conductive using metallic nanowires and carbon nanotubes. In the first case the whiteness of the paper suffered dramatically especially when carbon nanotubes are used. In the second case the transparency of the nano fibrillated cellulose films decreases markedly with the loading of nano – materials. In addition, nano fibrillated cellulose is not available in large scales and requires a lot of energy in production. In the research presented here we used regenerated cellulose films as substrates. The advantage of these films is that the raw material cellulose is available in a large scale, as it is produced industrially. The regenerated cellulose films are made by spin coating trimethylsilylcellulose (TMSC) onto silicon wafer substrates and subsequent regeneration with gaseous hydrochloric acid. The free standing regenerated cellulose films are coated with silver nanowires to obtain transparent conductive cellulose films. The procedure of film formation is presented. The electrical- and optical properties of the uncoated and coated regenerated cellulose films will be discussed. It will be shown that silver nanowire coated regenerated cellulose films have electrical and optical properties that are comparable to indium tin oxide (ITO). However, in contrast to ITO and thin ITO films on plastic substrates, the regenerated cellulose films are completely flexible.

Resume : Solution-processing of raw graphite to graphene and subsequent printing on paper is aimed at low-cost, high-volume applications such as RFID devices, thus, improving their recyclability. We have demonstrated the feasibility of ink-jet printing of graphene-based inks on paper substrates (K. Arapov et al. Farad. Discuss., 173, 2014). An interesting feature of paper for printing is the filtration of the ink, which leaves the micrometer-sized 2D sheets stacked on top rather than penetrating into the pores, as seen for metal inks. This leads to less ink spreading, thus higher printing definition and a more efficient use of the conductive particles, improving cost-effectiveness. An aspect of our approach is to avoid non-conductive intermediates, e.g., graphene oxide, during processing to maximize the conductive properties of the 2D colloids together with the exfoliated state in the suspension/ink. We now extend this work to high graphene content inks suitable for screen printing, which have shown for bar coated films sheet resistances of less than 5 Ω/□/1 mil, which brings replacement of metal leads in RFID devices, photovoltaic backsheets and other applications closer within reach.

Resume : The objective of the A3PLEc project is to develop the next generation of sustainable paper-based products with specific autonomous functionalities aiming at interacting with their users and/or reporting changes in their environment. A major focus is placed on the development of new and flexible manufacturing concepts based on printing technology to produce large area hybrid organic/inorganic papers with improved performance at competitive cost. To this aim, the A3PLE project is focused on 1) the integration of recent advances in functional materials (paper, fibres, inks) and functional components (battery, sensors, display, memory) and their production process upscale and 2) the development of innovative, flexible and cost-effective manufacturing processes based on printing and embedding techniques for the integration of all these functional components on the smart paper substrate.

Resume : Composite pulps of tetrapodal zinc oxide whiskers (ZnO-Ts) and cellulose have been found to form paper sheets by scalable manufacturing methods. To probe the optoelectronic properties of the so formed composite paper sheets, the UV-sensing properties of the composite paper were investigated. The composite sheets were found to be suitable as substrates for screen printing, and screen printing was used to create a UV-sensor by printing an interdigit electrode pattern with a carbon ink. Composite papers were manufactured with different grammage and the effect of paper making additives on the UV-sensing properties was investigated. The responsivity of the composite paper UV-sensor typically exceeds 0.1 A/W at the responsivity maximum at 384 nm. The UV-sensing function demonstrates the functionality of the composite papers, which together with scalable low cost manufacturing methods indicate a new route to low cost large area devices.

Resume : Nowadays electrochromic devices, characterized by a reversible change in optical properties under an electrical stimulation, have entered the market of electronic paper. In this presentation, we report, novel design, fabrication and characterization of printed electrochromic devices, ECDs, on paper substrate. The simplification of a 5-layer-battery-type architecture results from the use of a metallic layer both as electronic conductor and counter electrode, (referred as 4-layer ECDs) while a further step was achieved by using in addition a conductive and electrochromic material as working electrode (referred as 3-layer ECDs). 4-layer ECD, using lithium-based ionic liquid membrane electrolyte and a combination of silver metal and poly(3,4-ethylenedioxythiophene) (PEDOT) based materials, shows a color change from light to deep blue, for an operational potential lower than 1 V. Further optimization of the electrolyte layer in composition and processing leads to printed ECDs, successfully colored using the power of a smart phone offering an interesting counterfeit tool. Acknowledgements : The authors wish to thank the ANR PEPS for financial support.

Resume : Wood cellulose – natural, abundant, inexpensive, bio-degradable – desirable properties for a substrate material for flexible organic electronics. Still, while the use of paper in simple device structures like capacitors or conductors is no obstacle, its applicability for more advanced systems, like thin film diode architectures is challenging. Common approach is the use of smoothing fillers and plastic coatings before actual diode deposition. Unquestionably the natural structure of the material is lost in that process. Here, we present an approach, which allows the use of rough unmodified kraft pulp fiber networks as carrier of a diode architecture. Silver nanowires are wrapped around the cellulose fibers, adsorbed to their surface by its naturally present hydroxyl groups. This structure forms the semi-transparent anode of the photovoltaic device. The organic semiconductor layer is simply deposited as a mantle to the fibers of the network. A metal back electrode is applied only to one side of the paper network. We demonstrate that realizations of cellulose fiber photovoltaic devices with P3HT:PCBM standard active layer, show decent performance with fill factors and open-circuit voltages comparable to planar substrate cells without optimization. Thereby it will be highlighted that the rough structure of wood cellulose is indeed an advantage, especially in the capture of straylight with these photovoltaic cells, compared to common planar devices.

Resume : The present development of non-wafer-based photovoltaics (PV) allows supporting thin film cells on a wide variety of low-cost recyclable and flexible substrates such as paper; thereby extending PV solutions to a broad range of consumer-oriented indoor disposable applications where autonomous energy harvesting is today a bottleneck issue. However, their fibrous structure makes it quite challenging to fabricate good-performing inorganic PV devices like thin film silicon cells on such substrates. The advances presented in this article demonstrate the viability of fabricating thin film silicon PV cells on a paper coated with a layer of a hydrophilic mesoporous (HM) material and liquid packaging cardboard (LPC). Such substrates can, not only withstand the cells production temperature (150 °C), but also provides an adequate paper sealing and surface finishing for the deposition of the cell’s layers. The substances released from the paper substrate were continuously monitored during the cell deposition by mass spectrometry analysis, which allowed adapting the deposition procedures to mitigate any possible contamination from the substrate. In this way, a proof of concept solar cells with a 3.4% cell efficiency (with 41% fill factor, 0.82V open circuit voltage and 10.2mA/cm2 short-circuit current density) was attained on HM paper, while efficiencies of 4% were attained for the LPC paper, opening the door to the use of paper as a reliable low cost substrate to fabricate inorganic PV cells for a plethora of indoors applications with tremendous impact in multisectorial fields such as the food, pharmacy and security.