Zinc Oxide Intermediate Layer for Tandem OLED Driving Voltage
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Solution Overview
Problem
Tandem-type organic electroluminescence devices face challenges with high driving voltage and reduced luminescent efficiency due to the use of intermediate units with transparent conductive films like ITO and IZO, which suffer from plasma damage, and other materials that form high-resistant layers or absorb visible light, leading to suboptimal performance.
Innovation Solution
Incorporating a zinc oxide layer or a zinc-containing complex oxide layer as the intermediate unit, which is formed by evaporation methods to prevent damage to adjacent organic layers and reduce reflectivity differences, allowing efficient electron and hole injection while minimizing leak current and interaction between electron accepting and donating materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If transparent conductive films like ITO and IZO are used in the intermediate unit, then charge injection function is provided, but plasma damage occurs and driving voltage increases
Solution Approach 1:
The patent introduces an organic compound layer as an intermediary between the transparent conductive film and the emitting layer. This intermediate layer acts as a buffer that protects the emitting layer from plasma damage during sputtering while still allowing the transparent conductive film to provide its charge injection function. The organic compound layer absorbs the harmful plasma effects without compromising the electrical functionality.
2Reliability
If ITO and IZO layers are used in the intermediate unit, then charge injection is enabled, but luminescent efficiency decreases
Solution Approach 1:
The organic compound layer serves as a mediator that optimizes the interface between the inorganic transparent conductive film and the organic emitting layer. This intermediate layer improves charge injection efficiency while minimizing energy loss, thereby maintaining high luminescent efficiency. The organic compound layer facilitates better charge transfer without the energy losses associated with direct ITO/IZO contact.
3Reliability
If alkali metal or alkali metal compound layers are laminated with organic compound layers, then charge generating function is provided, but highly resistant layer is formed
Solution Approach 1:
The patent modifies the composition and structure of the intermediate unit by using specific organic compounds with optimized properties. By changing the material parameters (selecting appropriate organic compounds with suitable HOMO/LUMO levels), the patent achieves effective charge generation without forming highly resistant layers, thus maintaining lower driving voltage.
4Ease of manufacture
If inorganic compounds are used for the intermediate unit, then manufacturing simplicity is improved, but charge injection efficiency decreases
Solution Approach 1:
The patent employs a composite structure combining organic and inorganic materials in the intermediate unit. Specifically, it uses transparent conductive films (inorganic) laminated with organic compound layers. This composite approach leverages the manufacturing simplicity of inorganic films while adding organic layers to enhance charge injection efficiency, achieving both ease of manufacture and high reliability.
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
The use of zinc oxide or zinc-containing complex oxide layers in the intermediate unit enables low driving voltage and high luminescent efficiency by ensuring efficient charge injection and recombination in tandem-type organic electroluminescence devices, preventing leak current and maintaining high external quantum efficiency.
Implementation Method 1
Incorporating a zinc oxide layer or a zinc-containing complex oxide layer as the intermediate unit, which is formed by evaporation methods to prevent damage to adjacent organic layers
Data Source
AI summary
An organic electroluminescence device includes: an anode; a cathode opposed to the anode; and a plurality of emitting units including at least a first emitting unit and a second emitting unit. The plurality of emitting units each includes: an emitting layer; and an intermediate unit between the first emitting unit and the second emitting unit. The intermediate unit includes an electron injecting layer, a zinc oxide layer and a hole injecting layer in this sequence from the anode. The electron injecting layer contains an electron donating material and is adjacent to the first emitting unit. The hole injecting layer contains an organic electron accepting material and is adjacent to the second emitting unit.