N-Doped Semiconducting Material Using Phosphine Oxide Matrix
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Solution Overview
Problem
Current industrial processes for n-doping in organic electronic devices face challenges with caesium's high reactivity, volatility, and air/moisture sensitivity, leading to difficulties in handling and maintaining quality control, especially in thicker electron transporting layers, which limits the applicability of caesium-based doping in mass production.
Innovation Solution
The use of substantially air-stable metallic elements like Mg, Ca, Sr, Ba, Yb, Sm, and Eu as n-dopants, which form stable compounds in oxidation state II, co-evaporated with electron transport matrix compounds containing phosphine oxide groups, to achieve efficient electrical doping in organic semiconducting materials, particularly in thicker electron transporting layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If caesium is used as n-dopant in organic semiconducting materials, then electrical conductivity is improved, but handling difficulty and safety hazards increase due to high reactivity, volatility, and air/moisture sensitivity
Solution Approach 1:
The patent replaces caesium with divalent metals (Mg, Ca, Sr, Ba, Yb, Sm, Eu) that form stable compounds in oxidation state II. These metals are substantially air-stable and can be handled without special precautions, eliminating the safety hazards and handling difficulties associated with caesium while maintaining effective n-doping capability in phosphine oxide matrices
Solution Approach 2:
The patent changes the dopant material parameter from alkali metal (caesium) to divalent metal elements, and specifies that the matrix compound must have a reduction potential lower than certain reference compounds. This parameter change enables the use of air-stable metals while maintaining effective doping, as the divalent metals can still transfer electrons to the phosphine oxide matrix under the specified reduction potential conditions
2Reliability
If caesium is used as n-dopant, then electrical properties are improved, but quality control becomes difficult due to volatility under vacuum conditions
Solution Approach 1:
The patent replaces volatile caesium with divalent metals that have negligible volatility under vacuum deposition conditions. These metals can be co-evaporated with phosphine oxide matrix compounds at typical deposition temperatures (150-400°C) without significant evaporation loss, enabling precise control of doping concentration and consistent layer quality
Solution Approach 2:
The patent specifies that the matrix compound must have a reduction potential lower than tris(2-benzo[d]thiazol-2-yl)phenoxyaluminum, preferably lower than 9,9′,10,10′-tetraphenyl-2,2′-bianthracene or 2,9-di([1,1′-biphenyl]-4-yl)-4,7-diphenyl-1,10-phenanthroline. This parameter specification ensures that the phosphine oxide matrix can accept electrons from the divalent metal dopants, maintaining effective n-doping while using non-volatile metals that enable precise manufacturing control
3Reliability
If caesium is used as n-dopant, then doping effectiveness is achieved, but production costs increase due to safety and fire hazard mitigation requirements
Solution Approach 1:
The patent replaces caesium with divalent metals (Mg, Ca, Sr, Ba, Yb, Sm, Eu) that are substantially air-stable and do not require special handling facilities. These metals can be processed using standard vacuum deposition equipment without additional safety infrastructure, eliminating the costs associated with caesium safety and fire hazard mitigation while maintaining effective n-doping
Solution Approach 2:
The patent specifies that the matrix compound must have a reduction potential lower than certain reference compounds (tris(2-benzo[d]thiazol-2-yl)phenoxyaluminum, 9,9′,10,10′-tetraphenyl-2,2′-bianthracene, 2,9-di([1,1′-biphenyl]-4-yl)-4,7-diphenyl-1,10-phenanthroline). This parameter specification ensures that the phosphine oxide matrix has sufficient electron affinity to accept electrons from the divalent metal dopants, maintaining doping effectiveness while using cost-effective, air-stable metals
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 n-doped semiconducting materials with improved electrical properties, allowing for the creation of OLEDs with lower operational voltage and higher efficiency, while being more stable and easier to handle, thus overcoming the limitations of caesium-based doping.
Implementation Method 1
The metallic element is selected from elements that form in their oxidation number II at least one stable compound... co-evaporated with electron transport matrix compounds containing phosphine oxide groups, to achieve efficient electrical doping
Implementation Method 2
The reason why the phosphine oxide 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 phosphine oxide group plays somehow the positive role.
Implementation Method 3
An especially simple method for n-doping in ETLs prepared by the thermal vacuum deposition, which is currently the standard method most frequently used, e.g. in industrial manufacture of displays, is evaporation of a matrix compound from one evaporation source and of a highly electropositive metal from another evaporation source and their co-deposition on a solid substrate.
Data Source
AI summary
The present invention relates to an electrically doped semiconducting material comprising at least one metallic element as n-dopant and at least one electron transport matrix compound comprising at least one phosphine oxide group, a process for its preparation, and an electronic device comprising the electrically doped semiconducting material.