Featured Research

from universities, journals, and other organizations

Organic Light-Emitting Diodes: Tailor-Made Polymers For Better Flat-Panel Displays

Date:
June 12, 2000
Source:
Max Planck Society
Summary:
A novel approach reducing the power consumption and improving the efficiency of organic light-emitting diodes (OLEDs) is reported by researchers at the Ludwig-Maximilians University at Munich in collaboration with the University of Potsdam and the Max Planck Institute of Polymer Research at Mainz.

A novel approach reducing the power consumption and improving the efficiency of organic light-emitting diodes (OLEDs) is reported by researchers at the Ludwig-Maximilians University at Munich in collaboration with the University of Potsdam and the Max Planck Institute of Polymer Research at Mainz (NATURE June 8, 2000). Organic light-emitting diodes (OLEDs) represent a promising technology for flexible flat-panel displays. The discovery simplifies the manufacturing of monochrome gray-level displays. In the near future, it might become important for the realization of electrically-pumped "plastic lasers".

OLED devices consist of one or several semiconducting organic layer(s) sandwiched between two electrodes. When an electric field is applied, electrons are injected by the cathode, while at the anode they are taken from the semiconducting layer, yielding positively and negatively charged carriers, respectively. The charges migrate in opposite directions, the holes towards the cathode, the electrons towards the anode. When the two types of carriers encounter each other, the formed excitons may decay by emitting light. The emission color can be easily tuned by altering the chemical structure of the emitter.

The light exits the devices through a transparent electrode, most commonly through the anode made from indium tin oxide (ITO). Recently, "doped" (i.e., oxidized) conducting polymers (e.g. derivatives of polyaniline or polythiophene) have been used as alternative anodes for improved hole injection and extended operational life time of OLED devices.

However, the performance of OLED containing polymeric anodes varies quite strongly from device to device depending on the preparation conditions. Klaus Meerholz, the leader of the Munich team states: "We had speculated for quite some time already, that this might be a result of not properly controlling the redox state of the polymer. None of the previous studies had given or considered this aspect, though it has been long known that the doping level is correlated to the electrochemical equilibrium potential of the polymer, which in turn is often used to estimate the 'work function' of a material. Vice versa, these considerations suggested to us that it should be possible to actively influence the work function of such anodes by specifically adjusting the doping level of the polymer."

Indeed, the authors demonstrate that there is a relation between the degree of oxidation and the work function of polymeric anodes. They found, that positive carriers can be injected much more efficiently into organic semiconductors using highly doped anodes.

To take further advantage of the new principle, blue-emitting OLEDs based on a polyfluorene derivative synthesized at Max Planck Institute for Polymer Research in Mainz were investigated. By highly doping the polymeric anode not only the onset field for light emission was reduced, on top of that the efficiency of the devices at a given current density was increased. This was attributed to the more balanced number density of the two carrier types inside the luminescent layer (a ratio 1:1 would be ideal). The speed up the time consuming search for the optimum doping level of their polymer, the researchers used "combinatorial devices", a matrix of small devices which can be adjusted individually.


Story Source:

The above story is based on materials provided by Max Planck Society. Note: Materials may be edited for content and length.


Cite This Page:

Max Planck Society. "Organic Light-Emitting Diodes: Tailor-Made Polymers For Better Flat-Panel Displays." ScienceDaily. ScienceDaily, 12 June 2000. <www.sciencedaily.com/releases/2000/06/000612085405.htm>.
Max Planck Society. (2000, June 12). Organic Light-Emitting Diodes: Tailor-Made Polymers For Better Flat-Panel Displays. ScienceDaily. Retrieved September 16, 2014 from www.sciencedaily.com/releases/2000/06/000612085405.htm
Max Planck Society. "Organic Light-Emitting Diodes: Tailor-Made Polymers For Better Flat-Panel Displays." ScienceDaily. www.sciencedaily.com/releases/2000/06/000612085405.htm (accessed September 16, 2014).

Share This



More Matter & Energy News

Tuesday, September 16, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Manufacturer Prints 3-D Car In Record Time

Manufacturer Prints 3-D Car In Record Time

Newsy (Sep. 15, 2014) — Automobile manufacturer Local Motors created a drivable electric car using a 3-D printer. Printing the body only took 44 hours. Video provided by Newsy
Powered by NewsLook.com
Refurbished New York Subway Tunnel Unveiled After Sandy Damage

Refurbished New York Subway Tunnel Unveiled After Sandy Damage

Reuters - US Online Video (Sep. 15, 2014) — New York officials unveil subway tunnels that were refurbished after Superstorm Sandy. Nathan Frandino reports. Video provided by Reuters
Powered by NewsLook.com
Frustration As Drone Industry Outpaces Regulation In U.S.

Frustration As Drone Industry Outpaces Regulation In U.S.

Newsy (Sep. 14, 2014) — U.S. firms worry they’re falling behind in the marketplace as the FAA considers how to regulate commercial drones. Video provided by Newsy
Powered by NewsLook.com
Smart Gun Innovators Fear Backlash From Gun Rights Advocates

Smart Gun Innovators Fear Backlash From Gun Rights Advocates

Newsy (Sep. 14, 2014) — Winners of a contest for smart gun design are asking not to be named after others in the industry received threats for marketing similar products. Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins