Fabrication and Study of Polymer Light Emitting Devices

Background

Polymer based light-emitting diodes (LED) were discovered in 1990 by Friend et al. The first polymer LEDs used poly(phenylene vinylene) (PPV) as the emitting layer. Since 1990 many different polymers have been shown to emit light under the application of an electric field (electroluminescence, EL). PPV and its derivatives are still the most commonly used materials, but polythiophenes, polypyridines, poly(pyridyl vinylenes), polyphenylenes and copolymers of these materials are now being used. A large effort in industry and academia to improve stability, lifetime, and efficiency has prompted the study of a vast number unique and novel configurations in polymer devices.

Recent Advances

Figure 1
Our research efforts in the area of polymer light-emitting devices focuses on novel configurations using a variety of polymer and copolymer systems. Light-emitting devices consist of active/emitting layer(s) sandwiched between a cathode and an anode. Indium tin oxide (ITO) is typically used for the anode and aluminum or calcium as the cathode. Figure 1a (above) shows the structure of a simple (single layer) device with only the electrodes and a single active layer. Simple 'single' layer devices typically work only under a forward DC bias. Figure 1b shows a novel configuration: a symmetrically configured alternating current light emitting (SCALE) device, which works under AC as well as forward and reverse DC bias.

Figure 2
Figure 2 shows the response of a SCALE device driven at 60 Hz. The frequency of the light emission is 120 Hz.

Figure 3
Figure 3 is a picture of a 7-bar polymeric light emitting device display. The device configuration makes use of a polymer hole-transporting layer and a polymer emitting layer. We continue to develop new device configurations as well as improving device performance.

Publications

R.G. Sun, Y.Z. Wang, Q.B. Zheng, H.J. Zhang, and A.J. Epstein, 1.54 µm Infrared Photoluminescence and Electroluminescence from an Erbium Organic Compound, Journal of Applied Physics 87, 7589-7591 (2000).

R.G. Sun, Y.Z. Wang, D.K. Wang, Q.B.Zheng, E.M. Kyllo, T.L. Gustafson, and A.J. Epstein, High Luminescent Efficiency In Light-Emitting Polymers Due To Effective Exciton Confinement, Applied Physics Letters 76, 634-636 (2000).

Y.Z. Wang, R.G. Sun, F. Meghdadi, G. Leising, and A.J. Epstein, Multicolor Multilayer Light Emitting Devices Based on Pyridine-Containing Conjugated Polymers and Para-Sexiphenyl Oligomer, Applied Physics Letters 74, 3613-3615 (1999).

Y.Z. Wang, R.G. Sun, D.K. Wang, T.M. Swager and A.J. Epstein, Polarity and Voltage Controlled Color Variable Light Emitting Devices Based on Conjugated Polymers, Applied Physics Letters 74, 2593-2595 (1999).

R. Sun, Y. Wang, X. Zou, M. Fahlman, Q. Zheng, T. Kobayashi, T. Masuda, and A.J. Epstein, Electroluminescence of Carbazole Substituted Polyacetylenes, Proceedings, SPIE Conference on Optical and Photonic Applications of Electroactive and Conducting Polymers, San Diego, CA, 19-24 July 1998, Vol 3476, pp. 332-337 (1998).

Y.Z. Wang, R.G. Sun, F. Meghdadi, G. Leising, T.M. Swager, and A.J. Epstein, Color Variable Multilayer Light Emitting Devices Based on Conjugated Polymers and Oligomers, Synthetic Metals 102, 889-892 (1999).

A.J. Epstein and Y.Z. Wang, Interface Control of Polymer and Oligomer-Based Light Emitting Devices, Semiconductive Polymers, ACS Symposium Series 735, edited by Y. Wei and B. Hsieh (Oxford University Press, New York, 1999), Chapter 8,119-133 (1999).

Y.Z. Wang and A.J. Epstein, Interface Control of Light-emitting Devices Based on Pyridine-containing Conjugated Polymers, Accounts of Chemical Research 32, 217-224 (1999).

Y.Z. Wang, D.D. Gebler, D.-K. Fu, T.M. Swager, and A.J. Epstein, New Approach to Color Variable Light-Emitting Devices Based on Conjugated Polymers, Proceedings, International Society of Optical Engineers on Optical Probes of Conjugated Polymers, vol. 3148, 27 July-1 August 1997, San Diego, CA,117-123 (1998).

Y.Z. Wang, D.D. Gebler, D.K. Fu, T.M. Swager, A.G. MacDiarmid, and A.J. Epstein, Novel Light-Emitting Devices Based on Pyridine-Containing Conjugated Polymers, IEEE Transactions on Electron Devices 44 (8), 1263-1268 (1997).

Y.Z. Wang, D.D. Gebler, D.K. Fu, T.M. Swager, and A.J. Epstein, Color Variable Bipolar/AC Light-Emitting Devices Based on Conjugated Polymers, Applied Physics Letters 70 (24), 3215-3217 (1997).

Created by Darren Gebler. Maintained by John Rohrbacher. Last updated 10/21/96.