Optical Path Control Structure for OLED Light Extraction
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Solution Overview
Problem
Existing organic EL display devices face challenges in increasing light extraction efficiency due to total internal reflection at the interface between the base layer and protective layer, where the refractive index of the protective layer is higher than that of the base layer, hindering effective light emission.
Innovation Solution
The proposed solution involves a light emitting element with an intermediate layer and an optical path control unit having positive optical power, covered by a covering layer, where the refractive indices satisfy n0≥n1>n2, ensuring efficient light extraction by controlling the refractive index gradient.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a protective layer with higher refractive index than the base layer is formed, then the protective layer provides protection, but light incident from the base layer side is totally reflected at the interface and light extraction efficiency cannot be increased
Solution Approach 1:
The patent changes the refractive index parameter of the protective layer by introducing a low refractive index coating layer with refractive index lower than both the base layer and the optical path control unit. This parameter change transforms the interface from a high-to-low refractive index transition (causing total internal reflection) to a low-to-high transition, enabling light extraction.
Solution Approach 2:
The low refractive index coating layer acts as an intermediary between the base layer and the optical path control unit. This intermediate layer with refractive index n2 satisfying n0≥n1>n2 serves as a refractive index bridge, allowing light to pass through the interface without total internal reflection while still providing protective functionality.
2Device complexity
If the refractive index of the protective layer is higher than the base layer, then the protective layer structure is simple, but light extraction efficiency is reduced due to total internal reflection
Solution Approach 1:
The patent modifies the refractive index parameter of the protective layer structure by adding a low refractive index coating layer. This single parameter change (refractive index) resolves the contradiction by enabling light extraction without significantly increasing structural complexity.
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 enhances light extraction efficiency and front luminance by minimizing internal reflection, thereby improving the overall performance of the display device.
Implementation Method 1
an optical path control unit disposed on a part of the intermediate layer and having positive optical power
Implementation Method 2
when a refractive index of a material constituting a part of the intermediate layer in contact with the optical path control unit is represented by n0, a refractive index of a material constituting the optical path control unit is represented by n1, and a refractive index of a material constituting the covering layer is represented by n2, n0≥n1>n2 is satisfied
Data Source
AI summary
Light emitting elements and display devices with increased light extraction efficiency and front luminance are disclosed. In one example, a light emitting element includes a light emitting unit, an intermediate layer covering the light emitting unit, an optical path control unit disposed on a part of the intermediate layer and having positive optical power, and a covering layer covering an outer region of the intermediate layer surrounding a part of the intermediate layer on which the optical path control unit is formed.