OLED Electropositive Metal Dopants for Low Voltage and Air Stability
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Solution Overview
Problem
Current organic light emitting diode (OLED) technologies face challenges with caesium as a dopant due to its high reactivity, volatility, and safety concerns, leading to difficulties in industrial application, and existing alternatives either have high costs, air and moisture sensitivity, or limited effectiveness in achieving low voltage and high efficiency.
Innovation Solution
The use of substantially air-stable metals like Li, Na, K, Be, Sc, Y, La, Lu, Ti, and V as n-dopants in OLEDs, combined with electron transport matrix compounds having specific reduction potentials and polar groups, to enhance electrical properties and stability, allowing for efficient charge injection and transport.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If caesium is used as n-dopant in OLEDs, then electrical conductivity and charge injection are improved, but safety hazards and handling difficulty increase due to high reactivity and air sensitivity
Solution Approach 1:
The patent changes the chemical parameter of the dopant from highly reactive caesium to less reactive electropositive metals (Li, Na, K, Be, Sc, Y, La, Lu, Ti, V), maintaining electrical conductivity while improving safety and stability parameters
Solution Approach 2:
The patent replaces expensive and hazardous caesium with cheaper, more stable electropositive metals that can be handled more easily, effectively substituting a problematic material with a superior alternative
2Reliability
If caesium is used as n-dopant, then doping effectiveness is achieved, but volatility increases under vacuum conditions
Solution Approach 1:
The patent changes the physical parameter of the dopant by selecting metals with higher boiling points and lower volatility (Li, Na, K, Be, Sc, Y, La, Lu, Ti, V) compared to caesium, eliminating volatility issues while maintaining doping effectiveness
3Stability of the object's composition
If electropositive metals are used as n-dopants, then air stability is improved, but cost and synthesis complexity increase for alternative dopants
Solution Approach 1:
The patent optimizes the stability parameter by selecting electropositive metals that naturally provide air stability without requiring complex protective measures or expensive synthesis procedures, achieving simplicity alongside stability
4Reliability
If conventional dopants are used, then charge injection is achieved, but operational voltage remains high
Solution Approach 1:
The patent changes the electronic parameter of the dopant system by selecting electropositive metals with appropriate ionization potentials that facilitate easier electron injection, thereby reducing the energy (operational voltage) required while maintaining effective charge injection
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables the production of OLEDs with improved electrical properties, specifically low operational voltage and high efficiency, while ensuring air stability and ease of handling, thus overcoming the limitations of previous dopants.
Implementation Method 1
The charge carrier injection is effected on the basis of an applied external voltage, the subsequent formation of excitons in a light emitting zone and the radiative recombination of those excitons
Implementation Method 2
The reason why such polar group often significantly improves the electron injecting and/or electron transporting properties of the semiconducting material is not yet fully understood. It is believed that the high dipole moment of the polar group plays somehow the positive role
Implementation Method 3
OLEDs emit light after the injection of charge carriers in the form of electrons from the cathode and in form of holes from the anode into organic layers arranged in between. The charge carrier injection is effected on the basis of an applied external voltage, the subsequent formation of excitons in a light emitting zone and the radiative recombination of those excitons
Data Source
Figure 1~2
Figure 3
AI summary
The present invention relates to an electronic device comprising at least one light emitting layer between the anode and an cathode, a device further comprising between the cathode and the anode at least one mixed layer comprising (i) in substantially elemental form, an electropositive element selected from Li, Na, K, Be, Sc, Y, La, Lu, Ti and V, and (ii) at least one substantially covalent electron transport matrix compound comprising at least one polar group selected from a) phosphine oxide group, wherein the reduction potential of the substantially covalent electron transport matrix compound, if measured by cyclic voltammetry under the same conditions, has the value which is more negative than the value obtained for 4,7-diphenyl-1,10-phenanthroline, preferably more negative than for (9-phenyl-9H-carbazole-2,7-diyl)bis(diphenylphosphine oxide), more preferably more negative than for (9,9-dihexyl-9H-fluorene-2,7-diyl)bis(diphenylphosphine oxide), highly preferably more negative than for 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene, even more preferably more negative than for 3-phenyl-3H-benzo[b]dinaphto[2,1-d:1',2'-f]phosphepine-3-oxide, most preferably more negative than for pyrene and still preferably more negative than for [1,1'binaphthalen]-2,2'-diylbis(diphenylphosphine oxide) or b) diazole group, wherein the reduction potential of the substantially covalent electron transport matrix compound, if measured by cyclic voltammetry under the same conditions, has the value which is more negative than the value obtained for 4,7-diphenyl-1,10-phenanthroline, preferably more negative than for (9-phenyl-9H-carbazole-2,7-diyl)bis(diphenylphosphine oxide), more preferably more negative than for (9,9dihexyl-9H-fluorene-2,7-diyl)bis(diphenylphosphine oxide), highly preferably more negative than for 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene, even more preferably more negative than for 3-phenyl-3H-benzo[b]dinaphto[2,1-d:1',2'-flphosphepine-3-oxide, most preferably more negative than for pyrene and still preferably more negative than for [1,1'-binaphthalen]-2,2'-diylbis(diphenylphosphine oxide).