Single layer devices of indium tin oxide/Alq3∕Al were constructed with varying the active areas from 1to8mm2 and the thicknesses from 30to50nm. Average electric field across the Alq3 layer during the transient state was estimated from the accumulated charges at the interfaces of the devices. The electron mobility could thus be calculated by assuming that the injected charge carriers moved under the average electric field rather than the instantaneous field. The resulting mobility could be determined uniquely in a device thickness. The electron drift mobility was shown to behave similarly to the time-of-flight results.
A ''fuzzy-junction'' organic light-emitting device ͑OLED͒ containing a graded organic-organic interface is reported. Such graded junction is effectively produced utilizing interdiffusion through an ultrathin interfacial fusing layer sandwiched between two functional layers. With a glass transition temperature (T g) lower than remaining layers, this fusing layer permits smooth interdiffusion and mixing of neighboring layers by annealing above its T g. With appropriate material combinations, fuzzy-junction OLEDs thus prepared exhibit both reduced voltage and enhanced emission efficiency in comparison with conventional abrupt-junction devices. As an instance, a green fluorescent OLED with such fuzzy junction shows a high peak power efficiency of ϳ20 lm/W, substantially higher than ϳ14 lm/W of a corresponding abrupt-junction device.
In this letter, we report a promising type of electrically programmable, i.e., reconfigurable, organic light-emitting devices ͑OLEDs͒ incorporating a thin carrier-blocking layer as the sacrificial fusing layer. In such devices, the carrier-blocking layer has a lower glass transition temperature than neighboring layers. By raising the internal temperature of the device above the transition temperature of the carrier-blocking layer with a large enough current, interdiffusion between organic layers could occur through such a layer. As a consequence, neighboring layers are fused and a new path for carrier transport is formed, bypassing the carrier-blocking property and altering the device characteristics. A device that emits blue light as fabricated but can be transformed into a green-emitting one is demonstrated. Such a type of device may be used for color pixels in OLED displays, user-programmable OLED applications, and nonvolatile memory devices.
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