Fluorinated Polymer Charge Transport Layer for Organic EL Light Extraction
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Solution Overview
Problem
The low light-extraction efficiency of organic electroluminescence (EL) devices is attributed to the high refractive index of organic semiconductor materials, which leads to light loss through total reflection at interfaces, and existing methods to improve this efficiency are either costly or complex.
Innovation Solution
A composition comprising a fluorinated polymer, an organic semiconductor material, and a dopant is used to create a charge transport layer with a low refractive index, achieved through co-deposition of these components, which reduces the refractive index and enhances light-extraction efficiency without compromising electrical conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a fluorinated polymer is mixed with organic semiconductor material and dopant to form a charge transport layer, then the refractive index is lowered and light-extraction efficiency is improved, but the electrical conductivity may be compromised
Solution Approach 1:
The patent creates a composite charge transport layer by mixing fluorinated polymer (low refractive index material) with organic semiconductor material and dopant. This composite structure allows simultaneous optimization of optical properties (light extraction) and electrical properties (charge transport) through careful selection and proportioning of components.
Solution Approach 2:
The patent systematically varies the composition ratios of fluorinated polymer, organic semiconductor material, and dopant to optimize both refractive index and electrical conductivity. By adjusting these parameters, the invention achieves a balance between reducing light loss and maintaining adequate charge transport capability.
2Loss of energy
If conventional methods such as microlens substrates or scattering substances are used to improve light-extraction efficiency, then the light extraction performance is enhanced, but the production cost and process complexity increase significantly
Solution Approach 1:
The patent extracts the light-extraction enhancement function from complex structural modifications (microlenses, scattering layers) and integrates it directly into the charge transport layer material composition. This simplifies the overall device structure by eliminating separate optical enhancement components while maintaining improved light extraction through the fluorinated polymer's inherent low refractive index.
Solution Approach 2:
The charge transport layer is designed to simultaneously perform multiple functions: charge transport (via organic semiconductor material and dopant), light extraction enhancement (via fluorinated polymer's low refractive index), and structural integrity. This multi-functionality eliminates the need for separate dedicated optical enhancement layers or components.
3Loss of energy
If the refractive index of the charge transport layer is reduced to improve light extraction, then light loss by total reflection decreases, but the electrical conductivity of the layer may deteriorate
Solution Approach 1:
The patent applies local quality by assigning different functional roles to different components within the charge transport layer: fluorinated polymer provides low refractive index for light extraction, organic semiconductor material provides charge transport capability, and dopant enhances electrical conductivity. Each component contributes its specific property locally within the composite structure.
Solution Approach 2:
The composite nature of the charge transport layer allows combining materials with complementary properties: fluorinated polymer for optical optimization and organic semiconductor material with dopant for electrical optimization. The synergistic interaction in the composite enables simultaneous achievement of low refractive index and adequate electrical conductivity.
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 approach effectively lowers the refractive index of the charge transport layer, improving light-extraction efficiency and reducing driving voltage, while maintaining the basic performance of the organic EL device, and can be produced using simple and cost-effective methods.
Implementation Method 1
The light-extraction efficiency of an organic EL device remains usually at a level of from 20 to 30%, and its improvement is greatly expected. The essential reason of the low light-extraction efficiency of e.g. an organic EL device is a high refractive index of an organic semiconductor material constituting an emissive layer and a charge transport layer. If the refractive index on the light-emitting side is high, light is lost by total reflection or the like at an interface having a different refractive index
Implementation Method 2
If the refractive index on the light-emitting side is high, light is lost by total reflection or the like at an interface having a different refractive index, whereby the light-extraction efficiency is lowered
Implementation Method 3
as a means to improve the electrical conductivity of a charge transport layer of an organic semiconductor device such as an organic EL device, a method of mixing an additive called a dopant in an organic semiconductor material which is a material of e.g. the charge transport layer has been known
Implementation Method 4
A composition comprising a fluorinated polymer, an organic semiconductor material and a dopant... which has a surface roughness of at most 1.0 nm by RMS... A method for producing a layer comprising the composition as defined in any one of [1] to 10], which comprises co-depositing the fluorinated polymer, the organic semiconductor material and the dopant
Data Source
AI summary
To provide a composition having a very low refractive index, an organic photoelectronic element using the composition, and simple methods for producing such a composition and an organic photoelectronic element.A composition comprising a fluorinated polymer, an organic semiconductor material and a dopant.