Top Emitting OLED Viewing Angle Correction via High Refractive Index HIL
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Solution Overview
Problem
Top emitting OLED devices experience deviations in luminance and chrominance when the viewing angle changes, due to the micro-cavity effect which affects their viewing angle characteristics.
Innovation Solution
A top emitting OLED device structure is implemented with a second electrode having a light transmittance of no less than 25%, a hole injection layer with refractive indices of N≥2.0 for blue, N≥1.9 for green, and N≥1.8 for red pixels, and an optical compensation layer with specific molecular orbital energy level differences, along with a light output coupling layer to inhibit multi-beam and wide-angle interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a top emitting OLED structure with micro-cavity effect is used to increase luminance efficiency, then luminance efficiency is improved, but viewing angle characteristics deteriorate due to multi-beam interference causing luminance deviation and chrominance shifting
Solution Approach 1:
The patent changes the refractive index parameter of the hole injection layer to N≥1.8 (specifically N≥2.0 for blue, N≥1.9 for green, N≥1.8 for red pixels) to suppress the micro-cavity effect. This parameter change modifies the optical path difference within the device, reducing multi-beam interference and improving viewing angle characteristics while maintaining acceptable luminance efficiency
Solution Approach 2:
The patent applies different refractive index requirements to different color pixels (blue: N≥2.0, green: N≥1.9, red: N≥1.8) based on their specific optical path requirements. This local quality approach allows each color sub-pixel to optimize its viewing angle characteristics according to its wavelength-specific interference patterns
2Manufacturing precision
If the thickness of the organic layer is adjusted to meet optical path requirements for different colors, then chrominance purity is improved, but device structure complexity increases
Solution Approach 1:
The patent makes the hole injection layer serve multiple functions: it maintains its essential role in hole injection while simultaneously acting as an optical compensation layer to suppress micro-cavity effects. This multi-functionality eliminates the need for separate compensation layers, reducing structural complexity while achieving chrominance purity through refractive index control
3Length of stationary object
If the HIL thickness is increased to achieve the required optical path length, then optical path requirement is met, but drive voltage increases and current carrier equilibrium is negatively affected
Solution Approach 1:
The patent changes the refractive index parameter of the HIL to N≥1.8, which allows achieving the required optical path length with a thinner layer. Since optical path length equals physical thickness multiplied by refractive index, the high refractive index compensates for reduced thickness, maintaining optical performance while improving electrical performance through thinner layer design
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 configuration improves viewing angle characteristics by reducing interference effects, maintaining high refractive indices for the hole injection layers, and using optical compensation layers to meet spectral requirements, thereby enhancing the overall optical performance and material efficiency.
Implementation Method 1
the light emitted by the organic material undergoes interference within the optical micro-cavity so as to obtain higher efficiency and purer chrominance
Implementation Method 2
the hole injection layer has a refractive index no less than 1.8
Implementation Method 3
a top emitting device comprises an anode with a reflective layer and a cathode which is semi-transparent semi-reflective, so that an optical micro-cavity is formed
Data Source
AI summary
A top emitting OLED device for improving viewing angle characteristics, comprising a substrate, a first electrode, a hole injection layer, a hole transport layer, a light-emitting layer, an electron transport layer, a second electrode and a light output coupling layer sequentially stacked on the substrate, wherein the second electrode has a light transmittance no less than 25%, and the hole injection layer has a refractive index no less than 1.8.