ABSTRACT
A flexible supercapacitor (SC) is an attractive energy storage device for powering low-power sensors, since it can be built using only nontoxic and sustainable materials. In this study, the advantages of using biodegradable polylactic acid (PLA) substrate for printed SC are investigated by studying the SC's cyclic bending reliability, failure mechanism, and the impact of the bending radius. The results confirm that the SCs with laminated PLA with polymer barrier substrate exhibited the highest bending reliability, stability, and capability in preventing liquid electrolyte evaporation among the investigated substrates. Besides, the reliability decreased with the decreasing bending radius only when the strongly impacted areas lie on the electrode, the flaking and cracking of which was found to be the failure mechanisms of the tested SCs, except for the SCs with PLA/Al substrate, which failed due to the Al cracking. This research suggests that using PLA/barrier substrate, developing more robust activated carbon electrodes, developing cellulose paper with more dense fiber structure and smaller porous areas, and controlling the bending radius are crucial to improving the SC's reliability.
ABSTRACT
Printed flexible hybrid electronics (FHE) is finding an increasing number of applications in the fields of displays, sensors, actuators and in energy harvesting and storage. The technology involves the printing of conductive and insulating patterns as well as mounting electronic devices and circuits on flexible substrate materials. Typical plastic substrates in use are, for example, non-renewable-based poly(ethylene terephthalate) (PET) or poly(imides) (PI) with high thermal and dimensional stability, solvent resistance and mechanical strength. The aim of this study was to assess whether renewable-based plastic materials can be applied on sheet-to-sheet (S2S) screen-printing of conductive silver patterns. The selected materials were biaxially oriented (BO) bio-based PET (Bio-PET BO), poly(lactic acid) (PLA BO), cellulose acetate propionate (CAP BO) and regenerated cellulose film, NatureFlex™ (Natureflex). The biaxial orientation and annealing improved the mechanical strength of Bio-PET and PLA to the same level as the reference PET (Ref-PET). All renewable-based substrates showed a transparency comparable to the Ref-PET. The printability of silver ink was good with all renewable-based substrates and printed pattern resistance on the same level as Ref-PET. The formation of the printed pattern to the cellulose-based substrates, CAP BO and Natureflex, was very good, showing 10% to 18% lower resistance compared to Ref-PET and obtained among the bio-based substrates the smallest machine and transverse direction deviation in the S2S printing process. The results will open new application possibilities for renewable-based substrates, and also potentially biodegradable solutions enabled by the regenerated cellulose film and PLA.
ABSTRACT
In our research on sustainable solutions for printed electronics, we are moving towards renewable materials in applications, which can be very challenging from the performance perspective, such as printed circuit boards (PCB). In this article, we examine the potential suitability of wood-based materials, such as cardboard and veneer, as substrate materials for biodegradable solutions instead of the commonly used glass-fiber reinforced epoxy. Our substrate materials were coated with fire retardant materials for improved fire resistance and screen printed with conductive silver ink. The print quality, electrical conductivity, fire performance and biodegradation were evaluated. It was concluded that if the PCB application allows manufacturing using screen printing instead of an etching process, there is the potential for these materials to act as substrates in, e.g., environmental analytics applications.
ABSTRACT
Recent advances in perovskite solar cells (PSCs) have resulted in greater than 23% efficiency with superior advantages such as flexibility and solution-processability, allowing PSCs to be fabricated by a high-throughput and low-cost roll-to-roll (R2R) process. The development of scalable deposition processes is crucial to realize R2R production of flexible PSCs. Gravure printing is a promising candidate with the benefit of direct printing of the desired layer with arbitrary shape and size by using the R2R process. Here, flexible PSCs are fabricated by gravure printing. Printing inks and processing parameters are optimized to obtain smooth and uniform films. SnO2 nanoparticles are uniformly printed by reducing surface tension. Perovskite layers are successfully formed by optimizing the printing parameters and subsequent antisolvent bathing. 2,2',7,7'-Tetrakis-(N,N-di-4-methoxyphenylamino)-9,9'-spirobifluorene is also successfully printed. The all-gravure-printed device exhibits 17.2% champion efficiency, with 15.5% maximum power point tracking efficiency for 1000 s. Gravure-printed flexible PSCs based on a two-step deposition of perovskite layer are also demonstrated. Furthermore, a R2R process based on the gravure printing is demonstrated. The champion efficiency of 9.7% is achieved for partly R2R-processed PSCs based on a two-step fabrication of the perovskite layer.
ABSTRACT
Understanding the phenomena at interfaces is crucial for producing efficient and stable flexible organic solar cell modules. Minimized energy barriers enable efficient charge transfer, and good adhesion allows mechanical and environmental stability and thus increased lifetime. We utilize here the inverted organic solar module stack and standard photoactive materials (a blend of poly(3-hexylthiophene) and [6,6]-phenyl C61 butyric acid methyl ester) to study the interfaces in a pilot scale large-area roll-to-roll (R2R) process. The results show that the adhesion and work function of the zinc oxide nanoparticle based electron transport layer can be controlled in the R2R process, which allows optimization of performance and lifetime. Plasma treatment of zinc oxide (ZnO) nanoparticles and encapsulation-induced oxygen trapping will increase the absolute value of the ZnO work function, resulting in energy barriers and an S-shaped IV curve. However, light soaking will decrease the zinc oxide work function close to the original value and the S-shape can be recovered, leading to power conversion efficiencies above 3%. We present also an electrical simulation, which supports the results. Finally, we study the effect of plasma treatment in more detail and show that we can effectively remove the organic ligands around the ZnO nanoparticles from the printed layer in a R2R process, resulting in increased adhesion. This postprinting plasma treatment increases the lifetime of the R2R printed modules significantly with modules retaining 80% of their efficiency for â¼3000 h in accelerated conditions. Without plasma treatment, this efficiency level is reached in less than 1000 h.
ABSTRACT
A printed energy harvesting and storage circuit powered by ambient office lighting and its use to power a printed display is reported. The autonomous device is composed of three printed electronic components: an organic photovoltaic module, a carbon-nanotubes-only supercapacitor and an electrochromic display element. Components are fabricated from safe and environmentally friendly materials, and have been fabricated using solution processing methods, which translate into low-cost and high-throughput manufacturing. A supercapacitor made of spray-coated carbon nanotube based ink and aqueous NaCl electrolyte was charged using a printed organic photovoltaic module exposed to office lighting conditions. The supercapacitor charging rate, self-discharge rate and display operation were studied in detail. The supercapacitor self-discharge rate was found to depend on the charging rate. The fully charged supercapacitor was used as a power source to run the electrochromic display over 50 times.
