TH4E-(17)-6
RECONFIGURABLE ORGANIC LIGHT-EMITTING DIODES
Chieh-Wei Chen, Ting-Yi Cho, Chung-Chih Wu*
Department of Electrical Engineering, Graduate Institute of Electro-optical Engineering and
Graduate Institute
of
Electronics Engineering, National Taiwan University,
Taipei, Taiwan 10617, Republic of China
addrcss:[email protected]
EXTENDED ABSTRACT
Organic light-emitting diodes (OLEDs) based on either low-molecular-weight compounds or polymers have amacted worldwide interest due to their applications in efficient, low-voltage, large-area and full-color
displays [I-21. For most of OLEDs reported to date, the device configurations and consequently device characteristics are determined on completion of fabrication, not reconfigurable or programmable afterward. Reconfigurable OLEDs may have some interesting applications due to their programmability, such as color pixels in OLED displays, user programmable OLED displays and nonvolatile optical memory devices.
In this a i d e , we report a promising type of reconfigurable OLEDs incorporating a thin carrier-blocking layer as the sacrificial fusing layer. In such devices, the carrier-blocking layer has lower glass transition temperature than neighboring layers. By raising the intemal temperature of the device above the transition temperature of the camer-blocking layer, interdiffusion between organic layers could occur through such layer. As a consequence, neighboring layers are fused and a new path for carrier transport is formed, bypassing the carrier-blocking propelty and altering the device characteristics. A device that emits blue light as fabricated but can be transformed into a green-emitting one is demonstrated (Fig.1). Such type of devices may be used for color pixels in OLED displays, user-programmable OLED applications, and nonvolatile memory devices.
Moreover, a “fuzzy-junction” OLED containing a graded organic-organic interface is also demonstrated utilizing the concept of reconfigurable OLEDs. The ultra-thin sacrificial fusing layer permits smooth interdiffusion and mixing of neighboring layers by annealing above its Tg. With appropriate material combinations, fuzzy-junction OLEDs thus prepared exhibit both reduced voltage and enhanced emission efficiency in comparison with conventional abrupt-junction devices (Fig.2 and 3). As an instance, a green fluorescent OLED with such fuzzy junction shows a high peak power efficiency of -20 I”,substantially higher than -14 lmMr of a corresponding abNpt-junction device.
Fig: 1 Electroluminescence of pristine (square), Fig, 3 power eficiensy for &.viccs in ~ i ~ , electrically reconfigured (circle) and thermally symbols) characteristics for a doped 2. inset: EL sFcm of ~ 5 4 5 ~ ,+,pd reconfigured (triangle) devices. conventional devicc (downward triangles) devices,
Fig. 2 I-V (close symbols) and L-V (open
and P doped Iiuzy-junction device (squares). Inset: cmeiency for devices in Fig. 2.
REFERENCES
[I] C. W. Tang and S . A. VanSlyke, Appl. Phys. Lett. 51,913 (1987).
[2] J. H. Burroughes, D. D. C. Bradley, A. R. Brown, R. N. Marks, K. Mackay, R. H. Friend, P. L. Bums, and A.
B. Holmes, Nature 347, 539 (1990).
0-7803-7766-4103R17.00 02003 IEEE
