Organic Electroluminescent Element Film Density Control
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Solution Overview
Problem
Conventional organic electroluminescent elements face challenges in achieving high luminance, minimizing voltage rise, preventing dark spots, and ensuring storage stability at high temperature and high humidity, particularly for blue light emission and large-area applications.
Innovation Solution
An organic electroluminescent element is developed with a substrate and organic layers, including a light-emitting layer incorporating a specific phosphorescent compound and host compound, with controlled film surface density and organic solvent content, and optionally featuring a gas barrier layer, to enhance light emission efficiency and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conventional organic electroluminescent elements are used for blue light emission, then light emission is achieved, but light emission efficiency is insufficient
Solution Approach 1:
The patent changes the chemical composition parameters of the organic layers, specifically using a host compound with high triplet energy level and a phosphorescent dopant with appropriate energy level matching, thereby improving light emission efficiency and reducing energy loss through optimized molecular energy level alignment
Solution Approach 2:
The patent employs composite material structures by combining host compounds (such as mCP or TCTA) with phosphorescent dopants (such as Ir(ppy)3 or Ir(piq)3) in the emission layer, creating a composite system that leverages the high triplet energy of the host and the phosphorescent properties of the dopant to achieve efficient blue light emission
2Power
If organic electroluminescent elements are driven at low voltage, then power consumption is reduced, but voltage rise occurs during operation
Solution Approach 1:
The patent optimizes the electrical parameters of the device by selecting organic materials with appropriate HOMO-LUMO levels and mobility characteristics, and by controlling the thickness and composition of charge transport layers, thereby achieving low operating voltage while maintaining voltage stability through balanced charge injection and transport
Solution Approach 2:
The patent applies different material compositions and structures to different layers (hole injection layer, hole transport layer, emission layer, electron transport layer, electron injection layer), with each layer optimized for its specific function, thereby achieving overall low voltage operation with stable performance through localized optimization of charge injection and transport properties
3Illumination intensity
If conventional organic electroluminescent elements are operated, then light emission is achieved, but dark spots form during operation
Solution Approach 1:
The patent controls the molecular weight, purity, and composition parameters of the organic materials, particularly using high-purity host and dopant compounds with controlled molecular weight distributions, thereby preventing material degradation and aggregation that lead to dark spots while maintaining uniform light emission
Solution Approach 2:
The patent uses composite material systems with carefully selected host-guest combinations where the host compound matrix provides structural stability and the phosphorescent dopant provides uniform distribution of emission centers, preventing aggregation-induced dark spots through proper phase separation and molecular dispersion control
4Reliability
If organic electroluminescent elements are stored at high temperature and high humidity, then environmental stability is tested, but storage stability deteriorates
Solution Approach 1:
The patent employs inert atmosphere packaging by filling the encapsulation space with nitrogen or other inert gases, and uses encapsulation layers that create a barrier against moisture and oxygen, thereby protecting the organic materials from degradation caused by high temperature and humidity during storage
Solution Approach 2:
The patent selects organic materials with high thermal stability parameters, including compounds with high glass transition temperatures, strong molecular bonds, and resistance to oxidation and hydrolysis, thereby maintaining storage stability even under elevated temperature and humidity conditions
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 solution results in high luminance, reduced voltage rise, prevention of dark spots, and improved storage stability at high temperature and high humidity, while enabling efficient blue light emission and large-area applications.
Implementation Method 1
An organic electroluminescent element is an element provided with a constitution comprising an emission layer containing a emitting substance being sandwiched with a cathode and an anode, and an exciton is generated by an electron and a positive hole being injected into the emission layer to be recombined, resulting emission utilizing light release (fluorescence-phosphorescence) at the time of deactivation of said exciton
Data Source
AI summary
An organic electroluminescent device having high luminance and long-term stability under high temperature, high humidity conditions. This organic electroluminescent device is suppressed in voltage increase and generation of dark spots when driven at a constant current. Additionally, a display and an illuminating device can be made using the organic electroluminescent device. The organic electroluminescent device is characterized in that at least one of organic layers constituting the device is a light-emitting layer containing a host compound and a phosphorescent compound of the general formula:and the at least one organic layer has a film surface density of 1.10-1.25 g/cm3.