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nano tech 2024 (January 31 - February 2, 2024)


nano tech 2024 AIST and Yamagata University proposed new technologies for organic device one after another

January 31 - February 1-3, 2024, nano tech 2024 was held in Tokyo Big Sight. Main topics are picked up.


Electrode of organic device is modified by use of component of coffee


Fig 1. Molecule structure of coffeic acid and carrier density
distribution (upper), Array of coffeic acid molecule on surface of
electrode (under)
With respect to organic device, National Institute of Advanced Industrial Science and Technology (AIST) proposed a unique technology using component of coffee due to enhancement of carrier injection property. Surface of electrode on organic device is modified by making use of coffeic acid, is include of coffee, potato, sunflower oil and so on.

Figure 1 shows its mechanism. Molecule with dipole moment is oriented side by side by priority adsorption of catechol group include of coffeic acid on surface of electrode. As a result, work function of electrode is increased at 0.5 eV and over. In short, hole injection barrier of electrode and upper organic semiconducto is reduced, in a word, current into organic semiconductor is greatly increased. Material dependence is not almost. In fact, work function of main electrode materials, such as, Au, Ag, Cu, ITO, Al confirmed to be increased. In this experiment, a simple diode (ITO/coffeic acid/P3HT organic semiconductor/Al) was pilot produced. As figure 2Ccurrent density was 100 times than that of device without coffeic acid.


Fig 2. Current density-voltage characteristic of P3HT diode
Commercial coffeic acid was used in this experiment, but it will derive from plant itself in the near future. By the way, coffeic acid can be deposited not only by coating methods, but also vacuum evaporation method.

IPCE of perovskite solar cell is increased by making use of SAM as HTL

As concerns perovskite solar cell, Yamagata University reported a research result of use of SAM (Self Assembled Monolayers) as hole transport layer (HTL).

In this experiment, phosphonic series SAM was spin-coated on ITO electrode at 1-2 nm thickness, and then, CsPbI perovskite was spin-coated and annealed at 100 Ž. The next, C60 and BCP were evaporated as electron transport layer. Finally, Al electrode was evaporated. As a result, incident photon-to-current efficiency (IPCE) of this device was increased from 18 % (reference with TFB HTL) to 20 %.

This is reason why;‡@Characteristics are uniformed because of enhancement of coatability of HTL in ITO surface, ‡AWettability of perovskite liquid is enhanced because of low contact angle (13.8 %) of surface of SAM.

Emissive polymer appears as new lighting device based on triboluminescence

As regards unique device and technology, Okinawa Institute of Science and Technology introduced an emissive smart polymer. Itfs an emissive device based on triboluminescence by use of frictional excitation. In short, this device is emitted by excitation of frictional heat. For example, if colored plane by highlighter pen is scrubbed, it's emitted.

In this experiment, fluorescent pigment layer was covered with PVC cover film as electric device. Off course, emission color can be changed by kind of fluorescence material, and emission strength is basically proportional with fritional force. However, effective application is not found yet.

Fine Cu wiring is printed by screen off-set printing

As concerns printing process, AIST appealed manufacturing technology of fine Cu wiring by screen off-set printing method.


Pic.1 Printing resolution of screen printing method (left) and screen off-set printing method (right)
In this process, ink is printed on a silicon rubber transfer roll by conventional screen printing method, and then, it's transferred to a substrate. Solvent in ink is adsorbed into silicon rubber, and then, bleeding of ink is suppressed. As a result, it's possible to print fine pattern same as 10 ƒÊm and under. Picture 1 shows printing resolution of screen printing method (left) and screen off-set printing method (right). You can confirm that printing resolution of this method is surely higher than that of conventional screen printing method. However, total throughput becomes to be lower because of necessity of 2 times transfer process and cleaning work (annealing or sweeping) of silicon rubber each time of printing.

Method
Temperature (Ž)
Time (min)
Specific resistance
(ƒÊƒ¶¥cm)
 Sticking force (N/‡o)
Superheated steam anneal
  
350
10
4.2
 0.27 
300  10 10.0 -
250 10 12.4 -
Low temperature plasma anneal
250
30
3.3
 -

Tab 1. Characteristics comparison
Cu ink (JX Metals) was introduced in the booth, too. Main component is pure Cu, as table 1, high purity Cu wiring oxidation-free can be formed by superheated steam anneal method or low temperature plasma anneal method. Its specific resistance is relatively low such as 3.3 - 12.4 ƒÊƒ¶¥cm. By the way, screen off-set printing system will be released by Mino Group and Sotaworks.

High viscosity ink can be discharged by IJ method

On the other hand, Yamagata University tried to drop high viscosity ink by ink-jet printing (IJ) method. High viscosity ink same as 219 mPa¥s could be stably discharged by devising operation process, for example, increase of amount of displacement of PZT by applying high voltage. As you know, low viscosity ink same as approximate 20 mPa¥s should be used in IJ method heretofore. In short, inks for gravure printing and flexo printing can be used in this technology. In this research, 6 nozzles could be stably dropped.

Two PI films is adhered by simple annealing

Okayama University proposed new technology about direct adhesion of polyimide (PI) film and PI film without pre-treatment in the booth of New Energy and Industrial Technology Development Organization (NEDO). As you know, PI film is easily carbonized before melting because thermal decomposition temperature is greatly near melting temperature. For this reason, in case of adhering PI film, before adhesion, surface plasma is treated, or adhesive is used in the past.


Fig 3. Adhesion using heated mold
On the other hand, this research team succeeded to directly adhere two PI films without pre-treatment and adhesive. In this experiment, commercial PI films Tg-free were used. As figure 3, PI film and PI film were adhered for mere 1sec in atmosphere by heat press using a mold. On the other hand, it can be adhered by laser annealing. By the way, it's effective for flexible wiring substrate, flexible flat cable, and so on.

Transparent organic and inorganic hybrid glass is useful for light encapsulation

Ishizuka Glass appealed an original organic and inorganic hybrid glass. Its main component is SiO. It's relatively high viscosity ink before cure, but it becomes to be flexible and transparent glass-like compact after annealing at 200Ž for 2h. High transmittance same as approximate 90 % in wide range (UV, NR, and IR) is obtained. Furthermore, heat resistance is high same as 300 Ž order. Flexible property can be adjusted by composition.


Pic.2 Samples of organic and inorganic hybrid glass
It's suitable for various encapsulations, lens, transparent adhesive, and so on. However, gas barrier property is not sufficient for encapsulation use, it had better use as light encapsulation use instead of acrylic and silicon.

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