Unlike the broadband, diffuse emission from organic light-emitting diode (OLED) displays, a new type of emitter made using standard OLED manufacturing processes and materials releases only distributed single photons upon electrical excitation of the active layer.1 Designed by researchers at the University of Stuttgart (Stuttgart, Germany), the University of Ulm (Ulm, Germany), and the University of Würzburg and ZAE Bayern (both in Würzburg, Germany), the single-photon emitter also operates at room temperature (unlike semiconductor quantum dots), offering numerous opportunities for applications in secure communications and cryptography.
Because fluorescent molecules embedded in polymer or photonic-crystal matrices have inefficient electroluminescent properties, the researchers chose an iridium (Ir)-based organometallic complex—specifically, Ir(piq)3 (tris(1-phenylisoquinoline)iridium) molecules—that emits single photons at 613 nm with almost 100% internal quantum efficiency via phosphorescence in a polymer matrix.
The emission is successful based on two key fabrication steps: First, the red-light-emitting molecules are dispersed evenly in a blue-light-emitting host polymer; and second, a low-work-function barium metal is used as the cathode to ensure adequate charge-carrier densities suitable for electron injection and, hence, electrically driven single-photon emission at room temperature. Photon-correlation measurements confirm single-photon emission from the distributed Ir-based molecules with lifetime values ranging from 1.0 to 1.4 μs using a 12 V input. Contact Maximilian Nothaft at [email protected].