A. A. Vashchenko

Mechanism of electronic-excitation transfer in organic light-emitting devices based on semiconductor quantum dots

The results of an experimental study of organic light-emitting diodes (LEDs) with luminescent layers based on two types of CdSe/CdS semiconductor quantum dots (QDs) with an average CdSe core diameter of 3 and 5 nm and a characteristic CdS shell thickness of 0.5 nm are presented. The dependences of the LED efficiency on the QD concentration are determined. The experimental data are used to determine the mechanism of electronic-excitation transfer from the organic matrix to the semiconductor QDs. Ways of optimizing the design of the LEDs in order to improve their efficiency are suggested on this basis.

Effect of the length of ligands passivating quantum dots on the electrooptical characteristics of organic light-emitting diodes

The electrooptical characteristics of organic light-emitting diodes with quantum dots passivated with organic ligands of different lengths as emitting centers are investigated. It is established that the thickness of the ligand coating covering the quantum dots has little effect on the Förster energy transfer in the diodes, but significantly affects the direct injection of charge carriers into the quantum-dot layer. It is shown that the thickness of the passivation coating covering the quantum dots in a close-packed nanoparticle layer is deter- mined both by the length of passivating ligands and the degree of quantum-dot coverage with ligands.

Optimization of carrier mobility in luminescence layers based on europium β-diketonates in hybrid light-emitting structures

The hole conductivity in films of three compounds, complexes based on europium β-diketonates, deposited by vacuum evaporation is studied by the time-of-flight technique. It is shown that no carrier photogeneration is observed in films under pulsed excitation with 337 nm light. The introduction of pentacene-based photogeneration layers into the samples made it possible to observe transient-current curves. It was found that a dispersive component of the transient current, associated with hole transport, is observed in a complex of europium with an auxiliary ligand based on bathophenanthroline. These data were used to determine the hole mobility. No dispersive component of the transient current was observed in complexes with an auxiliary ligand based on phenanthroline. A conclusion is made that the latter is due to the low mobility in compounds of this kind. This is attributed to a decrease in the degree of conjugation of the aromatic system, which occurs on passing from bathophenanthroline to phenanthroline.

Organic light-emitting diodes based on a series of new polythienothiophene complexes and highly luminescent quantum dots

Experimental samples of organic light-emitting diodes with transport layers based on polythienothiophenes and using CdSe/CdS/ZnS semiconductor quantum dots with an internal quantum efficiency up to 85% in the emitting layer are investigated. It is shown that solubility and film-forming properties are key for using polythienothiophenes in light-emitting diodes. The most promising polythienothiophenes are identified on the basis of the results obtained.

Organic light-emitting devices with multi-shell quantum dots connected with polythiophene derivatives

The results of an experimental study of organic light-emitting diodes with poly-2,5-(3,4-diamino thieno[2,3-b]thiophene)-4,4’-amidoarylene transport layers and CdSe/CdS/ZnS quantum dots, the CdSe core of which has an average diameter of 4.1 nm, are presented. A suggestion is made regarding the possible conjugation of quantum dots and polythiophenes, which would substantially improve the characteristics of the light-emitting diodes in the case of optimization of their structure.

Energy transfer from TPD to CdSe/CdS/ZnS colloidal nanocrystals

The efficiency of electronic-excitation energy transfer from organic semiconductor TPD to CdSe/CdS/ZnS nanocrystals passivated with different organic ligands is investigated. It is shown that the rate of energy transfer from TPD to nanocrystals decreases with increasing thickness of the passivation coating. It is suggested that the Förster mechanism is responsible for the excitation transfer.

Hybrid organic–inorganic light emitting diodes

Specific features of plane-geometry nanocrystals (CdSe nanoplatelets) functioning in an organic–inorganic light emitting diode are analyzed.