Researchers from Ulsan National Institute of Science and Technology (UNIST) of South Korea have developed a new plasmonic material that can be applied to both polymer light-emitting diodes and polymer solar cells.  The new material and build process offers world-record high performance, through a simple and cheap process.

Polymer LED and Solar Cell Building.  Two in one solution for low cost polymer LEDs and solar cells.  Image credit: UNIST.  Click image for the largest view.

Polymer LED and Solar Cell Building. Two in one solution for low cost polymer LEDs and solar cells. Image credit: UNIST. Click image for the largest view.

Most semiconducting optoelectronic devices (OEDs), including photodiodes, solar cells, light emitting diodes (LEDs), and semiconductor lasers, are based on inorganic materials. Examples include gallium nitride for light-emitting diodes and silicon for solar cells.

The problem is the limited availability of raw materials and the complex processing required to manufacture OEDs based on inorganic materials and the cost of device fabrication is increasing.  There is great industrial and consumer interest in thin-film OED products that are made from alternative semiconductors.

Polymer light-emitting diodes (PLEDs) emit light while polymer solar cells (PSCs) absorb light.  The contrary demands of the two types of devices mean that there are few metal nanoparticles that can enhance performance in PLEDs and PSCs at the same time.

Of the list of potential materials, organic semiconductors have received much attention for use in next-generation OEDs because of the potential for low-cost and large-area fabrication using solution processing.

Despite extensive efforts to develop new materials and device architectures enhancing the performance of these devices, further improvements in efficiency are needed before there can be widespread use and commercialization of these technologies.

The material prepared by the UNIST research team is reportedly easy to synthesize with basic equipment and has low-temperature solution processability. This low-temperature solution processability enables roll-to-roll mass production techniques and is suitable for printed electronic devices.

Professor Byeong-Su Kim said, “Our work is significant also because it anticipates the realization of electrically driven laser devices by utilizing “carbon dot”-supported silver nanoparticles (CD-Ag NPs) as plasmonic materials. The material allows significant radiative emission and additional light absorption, leading to remarkably enhanced current efficiency.”

Carbon dots (CDs) consist of carbon, hydrogen, and oxygen with a quasi-spherical structure in which the carbon shows the character of crystalline graphite.

The team demonstrated efficient PLEDs and PSCs using surface Plasmon resonance enhancement with the CD-Ag NPs. The PLEDs achieved a remarkably high current efficiency (from 11.65 to 27.16 cd A-1) and luminous efficiency (from 6.33 to 18.54 lm W-1).

Surface Plasmon Resonance is an electro-magnetic wave propagating along the surface of a thin metal layer and the collective oscillation of electrons in a solid or liquid stimulated by incident light.  Surface Plasmon Resonance is the basis of many standard tools for measuring adsorption of materials onto planar metal (typically gold and silver) surfaces or onto the surface of metal nanoparticles.

The PSCs produced in this way showed enhanced power conversion efficiency (from 7.53 to 8.31%) and internal quantum efficiency (from 91 to 99% at 460 nm). The luminous efficiency (18.54 lm W-1) and IQE (99%) are among the highest values reported to date in fluorescent PLEDs and PSCs, respectively.

Professor Jin Young Kim expands on the facts with, “These significant improvements in device efficiency demonstrate that surface plasmon resonance materials constitute a versatile and effective route for achieving high performance polymer LEDs and polymer solar cells. This approach shows promise as a route for the realization of electrically driven polymer lasers.”

The work is likely to gain some industrial traction.  The research paper has been published at Nature Photonics. There is little doubt that the Korean team will get Korean industrial attention.

What isn’t known is the quality of the LEDs and solar cells that might come to market because the research is in the very beginning phase. But OLEDs have made a lot of hopeful news in the video business and everyone is waiting for the next technological leap to get that quality of electronics to consumers.

One way or another, technology of this type is coming.  We westerners have to give the easterners credit for staying on course and endlessly upgrading the ever more useful and energy efficient electronic devices of our time.


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