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Color-selective organic light sensors are produced by inkjet printing with semiconductor inks.
Light sensing is one of the fundamental pillars of modern technology, shaping our information-based society through fiber-optic communication (that super-fast internet connection), storing terabytes of data, allowing us to ” explore space, improve our ability to diagnose and monitor disease, and develop remote sensing technologies such as LiDAR to map our planet and monitor the weather.
Sophisticated light sensors are what make all of this possible, and they play an important role in initiating future developments such as visible light communication (VLC). Current WiFi networks use radio waves to provide wireless connections, while VLC or Li-Fi uses the light emitted by common LED bulbs to enable data transfer at speeds of up to 224 gigabits per second.
In order to facilitate the transition to this technology, a team of researchers from the InnovationLab in Heidelberg and the Karlsruhe Institute of Technology (KIT) have developed a new method of producing light sensors capable of detecting light in the visible spectrum thanks to a 3D printing process to use.
Their research – recently published in Advanced materials – is based on the reuse of materials already well suited to the development of these specialized sensors. In particular, the team points out that organic photodiodes – already used in light sensing devices – are particularly attractive for this purpose because they are lightweight, flexible, and their properties are easily adjusted at the material and device level.
Although wavelength-specific organic photodiodes have been reported in the scientific literature, commonly used manufacturing techniques present challenges that limit their transfer to industrial scale 3D printing. and reformulating the ink at each step to control the properties of the material.
3D printing would allow high throughput production of devices with complete freedom of design – the trick is to minimize the complexity of production.
To overcome this hurdle, the team developed a new material based on the concept of massive heterojunctions, which are devices commonly used in organic solar cells. They have an absorption layer made of a donor and acceptor material which, when stimulated by different wavelengths of light, allows the transfer of electrons and the generation of an electric current.
In the present study, the material is composed of an optically transparent donor polymer and a non-fullerene electron acceptor, each of which controls a specific property of the device: the polymer dictates the physical properties of the ink while the non-fullerene acceptor controls the wavelength detection range.
This ability to separate these properties removes any interdependence between the manufacturing process and the desired optical properties of the printed material, essentially eliminating the need to reformulate a new ink for a specific device at a different wavelength. The team was able to produce a multi-channel VLC system using a two-color inkjet printer, on both large and small areas. Many of these variously designed photodetectors have been printed on flexible and lightweight materials.
“The simplicity of our approach, simultaneously addressing functionality and manufacturing, provides a general method for easy integration of wavelength-selective optical sensing elements in future printed electronics applications,” said the study authors. . “Particularly, in those requiring a high degree of customization, high manufacturing throughput and high cost efficiency, such as wearable devices, mobile sensor nodes or healthcare monitoring systems. ”
Research article available at: N. Strobel, et al. Advanced materials, 2020, doi.org/10.1002/adma.201908258
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