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Research

Research Areas

Stretchable and Flexible Organic Optoelectronics

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    Recently, the demand for stretchable and flexible electronics increased a lot for the next generation electronics application. Especially, research about stretchable and flexible displays and solid-state lighting devices based on organic light emitting diodes (OLED) has been stimulated. Moreover, stretchable and flexible energy conversion devices such as organic/polymer photovoltaic cells (OPVs) are also important area in flexible electronics.

     With this movement in flexible device technology, many demonstrations has been made by several companies and research groups. However, new stretchable and flexible electrode materials instead of using conventional brittle transparent oxide conductors are essentially needed for highly efficient electronic device applications. Therefore, our group has been developing stretchable and flexible soft anode material replacing conventional indium tin oxide (ITO) electrode.

  • Stretchable and Flexible OLEDs & Stretchable electrode

We developed a highly efficient Intrinsically stretchable organic light-emitting diodes (ISOLED) that uses 2D-contact stretchable electrodes (TCSEs) as the anode and cathode (Figure 1A). The TCSE includes a layer of graphene and graphene scrolls on top of embedded AgNW networks in the styrene–ethylene–butadiene–styrene (SEBS) elastomer matrix. The graphene layer modifies the WF, promotes charge spreading, and impedes inward diffusion of oxygen and moisture, and thereby achieving significant improvement in charge injection and environmental stability
 

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  • Intrinsically Stretchable OLED

We devekioed a ISOLED with an unprecedently high current efficiency of 20.3 cd A−1 , which even exceeds that of an otherwise-identical rigid ITO based counterpart. Also, a 3 inch five-by-five passive matrix ISOLED is demonstrated using convex stretching
 

[References]

1. Advanced Materials, 34, 31, 2203040 (2022)

  • Flexible Anode

  We developed self-organized conducting polymer anode material which has tunable work-function (we call AnoHIL) for application to flexible OLED display. The work function value of the flexible AnoHIL has the range of 4.7~5.8eV which is actually the highest value among flexible anodes for current organic devices. In right scheme, AnoHIL has a role of transparent anode. 

 

     Moreover, AnoHILs do not need additional hole injection layer (HIL) and it means simplifying of device structure as shown in the following figure

AnoHILs have important three advantages better than ITO electrodes.

1) Transmittance over 95% in all the visible range
2) Ohmic contact between organics and the AnoHIL layer
3) Improvement of luminous efficiency and device lifetime.

[References]

1. Science (2015), 350, 1222 

2. NPG Asia Materials (2017) 9, e411

  • Flexible Stretchable OLEDs

We developed self-organized conducting polymer anode material which has tunable work-function (we call AnoHIL), and modified CVD-grown graphene anode for application to flexible OLED display. 

We are developing stretchable electrode using composite electrode composing AgNWs, graphene, and conducting polymer

[References]

1. Nature Photonics (2012), 6, 105

  • Flexible Solar Cells

We are also endeavoring to achieve highly efficient flexible energy device using organic/polymer photovoltaic (OPV) device. 

    The OPVs using our flexible AnoHIL anodes showed high power conversion efficiency which is comparable to the conventional ITO/PEDOT:PSS based OPV. As the work-function of anode increases, holes can be extracted efficiently from the photoactive layer in the OPV devices. 

    We hope to attain further highly improved flexible 

Photovoltaic device in the near future.

[References]

1. Advanced Energy Materials (2016), 6, 1600172

2. Nanotechnology (2014), 25, 014012 

  • Solid State Lighting

Solid-state lighting (SSL) refers to a type of lighting that uses semiconductor light-emitting diodes (LEDs), organic light-emitting diodes (OLED), or polymer light-emitting diodes (PLED) as sources of illumination rather than electrical filaments, plasma (used in arc lamps such as fluorescent lamps), or gas. When compared to the incandescent or fluorescent lamp, OLED does not contain environmental hazardous materials, e.g., Hg, and also it can save up to 70% of power consumption of fluorescent lamp, 90% of that of incandescent lamp. Hence, in the near future, the incandescent lamp and the fluorescent lamp through the world will be replaced with environment-friendly solid-state white lighting source based light-emitting diodes. 
    Among the Solid State Lightings, OLED is the best candidate for the lighting application. When compared to the inorganic LED, it has various advantages since it can realize the 3 dimensional lighting, very thin device thickness, soft light similar to the sun and flexible lighting, etc.

    The development of OLED lighting source is getting more and more important. Until now, researchers in this field have tried to improve the luminous efficiency and the device lifetime, which have been the most important issues, by making tandem OLED structures. However, when we produce the OLED lighting panels based on tandem structures, we have to spend the more material cost and longer processing time. Therefore, to solve this importance issue, we tried to simplify the tandem white OLED devices.

  • Flexible Perovskite LED

    The development of OLED lighting source is getting more and more important. Until now, researchers in this field have tried to improve the luminous efficiency and the device lifetime, which have been the most important issues, by making tandem OLED structures. However, when we produce the OLED lighting panels based on tandem structures, we have to spend the more material cost and longer processing time. Therefore, to solve this importance issue, we tried to simplify the tandem white OLED devices.

[References]

1. Science (2015), 350, 1222

2. Advanced Materials (2017), 29, 1605587 

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