Electrical properties of organic light emitting diodes with post fabrication heat and electric field treatments

The current work presents post-fabrication heat treatment and a combined external electric field-heat post-fabrication treatments for organic light emitting diodes (OLEDs). The devices were fabricated in the same run with a standard device without annealing for comparison, with an identical structure of ITO/PVK/Rhodamine B/Pb. After depositing the Rhodamine B layer on the PVK film, the samples were thermally annealed at different temperatures before depositing Pb. Some of the samples were thermally annealed without any external electric field while others were treated by an external electric field during heating. It is found that the annealing temperature of PVK/Rhodamine B layers increases the turn-on voltage of the device. On the other hand, in the electric field-heat treatment, the turn-on voltage is observed to decrease and the maximum current density of the device is dramatically enhanced

Influence of Copper Phthalocyanine (CuPc) Thin Layer on Capacitance-Voltage Characterization of a Device Consisting of ITO/CuPc/PVK/Rhodamine B Dye Layers

In this paper, the influence of copper-phthalocyanine (CuPc) hole-injection layer on the capacitance-voltage (CV) characteristic performance of ITO/CuPc/PVK/Rhodamine B/Pb devices was investigated. The thickness of the CuPc layer was varied form 5 nm to 50 nm. The thin films were deposited on the PVK layer by thermal vacuum deposition at 1.0 × 105 torr using MiniLab 080 system. The thicknesses were measured using using FILMETRICS F20-UVX thin-film analyzer. It was found that as the thickness of CuPc layer decreases the transition voltage (VT) and built-in voltage (Vbi) decrease except for a thickness 5 nm, which shows negative differential resistance (NDR)

Capacitance-voltage measurements of hetero-layer OLEDs treated by an electric field and thermal annealing

Capacitance-voltage (C-V) characterization of organic light-emitting diodes (OLEDs) having the structure ITO/ PVK (poly (9-Vinylcarbazole)/Rhodamine B dye/Pb is reported. The C-V curves provide more understanding about processes occurring in OLEDs like the voltages at which holes and electrons start flowing from the two electrodes through the OLED layers and the voltages at which emission starts. The OLEDs were fabricated under the same annealing conditions with an additional standard device without annealing for comparison. After depositing the Rhodamine B dye layer on the PVK thin film, samples were thermally annealed at different temperatures. The Pb layer was then deposited. Some samples were thermally annealed without applying any field, while others were annealed at the same temperatures under an external electric field. It was found that devices treated by only thermal annealing and those annealed under an electric field do not show any light emission whereas the standard device fabricated without any annealing does. The main difference between devices fabricated by exposure to an electric field while annealing and other devices is the lower turn-on voltages of the former devices

The Influence of Thin Layer Copper Phthalocyanine on the Performance of PVK/ Rhodamine B Device

In this paper, the influence of copper-phthalocyanine (CuPc) hole-injection layer on the current voltage characteristic and the electroluminescence performance of ITO/CuPc/PVK/ Rhodamine B/Pb devices was investigated. The characteristics were measured at room temperature and without glove box with a thickness variation of CuPc layer. The results showed that the turn-on voltage of the devices can be dramatically lowered by inserting the CuPc layer