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This is not a ‘frog turned into a prince’ story, but a very long quest by technologists.

Technologists and, yes, advertisers, started dreaming about printed and flexible electronics decades ago, as early as 1970s. Products they wanted to develop evolved over time, but the core requirement of such printed electronics remained the key. The quest for large and flexible banners that could deliver interactive ads, and tablecloths that could be computer displays, evolved into the search for phones that could be folded up like handkerchiefs and flexible digital watches that would cling to your wrists. This continues to grow into more complex goals like flexible body implants and printable human tissues.

What makes today different from 1970s, however, is that dreams are seasoned with reality now. With several commercial products, demonstrations and promising researches, it is evident that printed, flexible and even organic electronics are fast becoming a rampant reality.

Research in this area predominantly classifies under manufacturing methods and processes, both lab-scale and large-scale, materials for substrates and inks, as well as designs. In this story, let us take a look at some such interesting projects transpiring at universities and other research and development (R&D) centres across the world.

Leaf-shaped, decorative, organic solar panel developed by VTT, Finland. Each leaf has an active surface of 0.0144m2 and includes connections and a decorative part
Leaf-shaped, decorative, organic solar panel developed by VTT, Finland. Each leaf has an active surface of 0.0144m2 and includes connections and a decorative part

Printed spacecrafts and atmospheric confetti
How small would space centres become if spacecrafts could be printed? Well, we would know soon enough. NASA’s Jet Propulsion Laboratory (JPL) has been exploring the idea of designing and fabricating a spacecraft entirely with flexible substrate printed electronics. The idea is to print a two-dimensional sheet with all the functional subsystems of a typical spacecraft, right from measurements to communications.

At the end of the project’s first phase, the team reports, “Atmospheric confetti. Inchworm crawlers. Blankets of ground-penetrating radars. These are some of the unique mission concepts that could be enabled by a printable spacecraft.” The low mass, volume and cost of printed spacecrafts makes NASA believe that, network missions would transform from a few discrete measurements to millions of platforms, achieving greater areal density and system reliability. Printed platforms could be released not just into space but also into volcanic plumes to measure composition and impact energies. These could be fitted in smart solar sails or areal balloons to monitor erstwhile unreachable areas and parameters.

The final report of the project’s second phase affirms that, it is feasible to build an entire spacecraft out of printed electronics, but it raises doubts about launching such a spacecraft off a rocket and having it orient and propel itself to the intended destination. In the near term, applications might be simpler, such as sensors.

Printing power, literally
Last year, California based Imprint Energy demonstrated the print manufacturing of ultra-thin, flexible and rechargeable batteries. This was part of a larger project by FlexTech Alliance to show that multiple key components, such as power source, display and other electronics, can be incorporated onto a flexible substrate to produce a product.

Imprint’s printed ZincPoly 60mWh rechargeable battery powered all components, including the wireless communication module of a wrist-worn device that conforms to a minimum 25mm bend radius, which is considered to be the typical bend radii for wrist-worn wearable electronics. While developing the printed power source, Imprint worked towards multiple technical goals including the ability to scale the manufacturing process, increase single-cell discharge capacity and rate capability, develop flexibility test protocols and equipment, and so on.

Printed electronics is also expected to be very helpful in the printing of flexible solar panels, which can power not just small devices but even cars.

One interesting research in this space is the development of a mass production method for printing decorative, organic solar panels by VTT Technical Research Centre of Finland Ltd. So far, it has been possible to pattern organic photovoltaic (OPV) panels only into strips, but this new method offers complete design freedom, so that panels can be used on surfaces of not just small, decorative objects but also large areas like cars or even exteriors of buildings.

The new solar panels, printed with VTT’s gravure and screen-printing technologies are only around 0.2mm thick and include electrodes and polymer layers, where the light is collected. Graphics can be printed to make the solar panels decorative too. Each leaf printed as a feasibility test has an active surface of 0.0144m2. These include connections and a decorative part. One square-metre of an active solar panel surface comprising approximately 200 OPV leaves generated 3.2 amperes of electricity with 10.4 watts of power at Mediterranean latitudes, where it was tested.

Although efficiency of organic solar panels is lower than traditional silicon based ones, these are more flexible, light, affordable and recyclable, which justifies the growing market for this segment.

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