Switchable organic electroluminescence

The vacuum deposited amorphous organic thin film melamine cyanurate (MC) is found to possess an electrical switching property. The as-fabricated fresh thin film is at a semiconductor state and shows a rectification property in a range of several voltages. Under a higher applied voltage, the resistance of the film changes to a lower value, and shows linearity in its current–voltage relationship. After the application of a negative driving voltage for no more than 100 s, the MC film returns from the resistor state to the semiconductor state with a higher impedance. Based on this reproducible switching phenomenon, a type of voltage-controlled switchable organic electroluminescence device was fabricated by inserting the MC layer between the anode indium tin oxide (ITO) and the hole transport layer ${\mathrm{N,N}}^{\prime }$ -bis (3-methylphenyl)-${\mathrm{N,N}}^{\prime }$ -diphenyl-benzidine (TPD). In the forward driving voltage scan (for example, increasing the driving voltage from 0 to 16 V), the impedance is higher and the current density is lower; then the scan is backward (decreasing the driving voltage from 16 to 0 V), the impedance becomes lower and the current density becomes higher. Corresponding to the two different current density states at the same driving voltage, the device luminance also reaches two different states, one is lower and another is higher. This transition from a high (ON) to low luminance (OFF) renders a prototype to realize a switchable organic electroluminescence.