Organic EL Element Suppressing Surface Plasmon Loss
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Solution Overview
Problem
The micro cavity organic electroluminescence (EL) elements with a λ/4 interference condition face significant surface plasmon (SP) loss, limiting their luminous efficiency, especially in strong cavity constructions, where existing methods to suppress SP loss are inadequate.
Innovation Solution
An organic EL element design with a specific electrode structure and optical path lengths that satisfy certain relationships between the interfaces, including a first and second charge transport layer and an out-coupling layer, to minimize SP loss and enhance light extraction efficiency, particularly for blue light emission in the 440-470 nm range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a micro cavity system with λ/4 interference condition is used to improve luminous efficiency, then light radiation intensity is increased through optical interference, but surface plasmon loss becomes large due to the small distance between the emission layer and metal reflective layer
Solution Approach 1:
The patent changes the optical path length parameter L to satisfy a specific relationship that simultaneously achieves λ/4 interference condition and suppresses surface plasmon loss. By optimizing the optical path length rather than simply increasing the physical distance, the patent maintains the beneficial interference effect while reducing SP loss.
Solution Approach 2:
The patent introduces a new dimension of control by considering the wavenumber difference between surface plasmons at different interfaces. Instead of only adjusting the vertical distance between layers, the patent optimizes the wavenumber matching condition to suppress SP loss while maintaining optical interference benefits.
2Object-generated harmful factors
If the distance between the emission layer and metal reflective layer is increased to suppress surface plasmon loss, then SP loss is reduced, but the interference effect is sacrificed and luminous efficiency improvement is limited
Solution Approach 1:
The patent optimizes the optical path length parameter L to satisfy a specific relationship that simultaneously achieves λ/4 interference condition and suppresses surface plasmon loss. By optimizing the optical path length rather than simply increasing the physical distance, the patent maintains the beneficial interference effect while reducing SP loss.
Solution Approach 2:
The patent introduces charge transport layers and an out-coupling layer as intermediary structures between the electrodes and emission layer. These intermediate layers help control the optical path and surface plasmon behavior, enabling simultaneous achievement of interference effect and SP loss suppression.
3Loss of energy
If a strong cavity construction with semi-transparent metal thin film is used to enhance interference effect, then luminous efficiency can be improved remarkably, but surface plasmon loss becomes even more significant
Solution Approach 1:
The patent optimizes the optical path length parameter L to satisfy a specific relationship that simultaneously achieves λ/4 interference condition and suppresses surface plasmon loss. By optimizing the optical path length rather than simply increasing the physical distance, the patent maintains the beneficial interference effect while reducing SP loss.
Solution Approach 2:
The patent introduces charge transport layers and an out-coupling layer as intermediary structures between the electrodes and emission layer. These intermediate layers help control the optical path and surface plasmon behavior, enabling simultaneous achievement of interference effect and SP loss suppression.
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 proposed design effectively suppresses SP loss, leading to improved luminous efficiency and enhanced performance in light-emitting apparatuses, such as display and imaging devices, by optimizing the interaction between surface plasmons at the electrodes.
Implementation Method 1
Light emitting molecules have a feature of radiating light strongly toward a space in which 'enhancing interference' of light occurs. Specifically, the radiation rate of excitons can be increased and the radiation pattern thereof can be controlled through use of optical interference.
Implementation Method 2
it is known that, in the case where a distance d0 between the metal reflective layer and the emission layer satisfies the condition: d0=λ/(4n0) (hereinafter, referred to as λ/4 interference condition), a radiation intensity is increased most by an interference effect.
Implementation Method 3
The SP loss is a phenomenon in which an SP of metal is excited by excitation energy of light emitting molecules, and as a result, the excitation energy is transformed into Joule heat.
Implementation Method 4
the element causing light emitted by the emission layer to exit from a side of the second electrode... the real part of a wavenumber of a surface plasmon generated at the second interface is represented by ks[rad/m], the following relationship is satisfied: −4.5×106≦kr−ks≦2.1×106
Data Source
AI summary
Provided are organic electroluminescence elements that suppress SP loss even in a strong cavity satisfying a λ/4 interference condition, thereby being improved in luminous efficiency. The organic electroluminescence elements emit light having a peak wavelength of 440 nm or more to 470 nm or less, in which a wavenumber difference δk (Re) between surface plasmons generated at respective reflecting electrode and transparent electrode falls within a specific range.