No abstract

single-photon emitters have been considered for applications in quantum information processing, quantum cryptography and metrology. For the sake of integration and to provide an electron photon interface, it is of great interest to stimulate single-photon emission by electrical excitation as demonstrated for quantum dots. Because of low exciton binding energies, it has so far not been possible to detect sub-Poissonian photon statistics of electrically driven quantum dots at room temperature. However, organic molecules possess exciton binding energies on the order of 1 eV, thereby facilitating the development of an electrically driven single-photon source at room temperature in a solid-state matrix. Here we demonstrate electroluminescence of single, electrically driven molecules at room temperature. By careful choice of the molecular emitter, as well as fabrication of a specially designed organic lightemitting diode structure, we were able to achieve stable single-molecule emission and detect sub-Poissonian photon statistics.

Photoluminescence quenching of single dibenzoterrylene (DBT) dye molecules in a polymeric organic light-emitting diode was utilized to analyze the current dynamics at nanometer resolution. The quenching mechanism of single DBT molecules results from an increase in the triplet-state population induced by charge carrier recombination on individual guest molecules. As a consequence of the long triplet-state relaxation time, its population results in a reduced photoluminescence of the dispersed fluorescent dyes. From the decrease in photoluminescence together with photon correlation measurements, we could quantify the local current density and its time-dependent evolution in the vicinity of the single-molecule probe. This optical technique establishes a non-invasive approach to map the time-resolved current density in organic light-emitting diodes on the nanometer scale.

We have analyzed the tendency of crystallization and the thermal activation of ordering processes in rubrene thin films. As we will demonstrate, a crystalline phase with a unit cell in agreement to the bulk structure can be stabilized upon heating of amorphous rubrene layers previously capped by a sputtered SiOx layer. This encapsulation significantly enhances the thermal stability of the organic film by about 150 °C. We compared this approach with crystallization initiated by the presence of a pentacene seed layer during rubrene deposition. Thin film transistors prepared by this route showed hole mobilities of 0.01 cm2/Vs which are four orders of magnitude higher than for their amorphous counterparts. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Single molecule studies are limited to a defined class of organic dye molecules inserted into respective host materials. Basic requirements for suited material combinations include high photon emission rates and long term photostability. A majority of known aromatic host-guest systems employ crystalline organic matrices to prevent dye molecules from uncontrolled reactions with contaminants. However, in terms of device fabrication and technological potentials it is often desirable to use polymers as room temperature host matrices. Unfortunately, single dye molecule investigations in polymers at room temperature usually report orders of magnitude lower photostabilities compared to their crystalline molecular counterparts, leading to a reduced interest in organic thin film applications. In this report, we exemplary demonstrate the feasibility of engineering a host-guest system based on dibenzoterrylene dye molecules which were diluted into the polymer poly-( p-phenylene-vinylene) (PPV) possessing very low photobleaching probabilities at room temperature. By controlling the oxygen exposure during manufacturing the number of emitted photons prior to photobleaching was significantly increased from 10 6 up to 10 11 photons. Employing suited encapsulation techniques to prevent oxygen penetration after host-guest preparation, photostable devices over prolonged time periods on the order of months to years could be achieved. Therefore, this approach grants access to a variety of new polymer based combinations of host-guest systems for studying single molecular quantum emitters inside organic electronic devices and nanostructured polymer films with sufficient count rates and long-term stability at room temperature.