OLED Light-Emitting Layer Narrow Stokes Shift Doping

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Solution Overview

Problem

The selection of materials for the light-emitting layer in organic electroluminescent devices is limited by strict rules regarding energy level matching between host and guest materials, which restricts the improvement of luminous efficiency and exciton energy transfer.

Innovation Solution

The use of a light-emitting layer comprising a first compound, a second compound with a narrow Stokes shift, and a third compound, where the second compound is doped in a mass ratio less than 50 wt%, and the triplet-state energy levels are strategically aligned to facilitate efficient exciton energy transfer, with the second compound emitting delayed fluorescence to prevent energy loss.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If traditional host-guest material matching is used in the light-emitting layer, then energy level matching can be achieved, but the selection range of materials is limited and luminous efficiency improvement is restricted

Engineering Contradiction:

Improveselection range of material systemVSAvoidenergy level matching requirement

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The light-emitting layer is segmented into three distinct compounds with different functions: first compound (host material), second compound (narrow Stokes shift emitter), and third compound (energy transfer acceptor). This segmentation allows each compound to be optimized independently for its specific function while maintaining overall system compatibility, thereby expanding material selection without compromising energy level matching

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The second compound with narrow Stokes shift acts as an intermediary between the first compound (host) and third compound (acceptor). It receives energy from the host and transfers it to the acceptor, mediating the energy transfer process and enabling broader material selection by providing a flexible intermediate energy level that bridges host and acceptor materials

Inventive Principle:

Principle #24Intermediary (Mediator)

2Productivity

If high doping ratio of second compound is used, then exciton energy transfer can be enhanced, but device efficiency decreases due to energy loss

Engineering Contradiction:

Improveexciton energy transfer efficiencyVSAvoidenergy loss from delayed fluorescence

Core Design Contradiction:

ProductivityVSLoss of energy

Solution Approach 1:

The doping ratio of the second compound is precisely controlled within the range of 1-49 wt%, optimizing the balance between exciton energy transfer efficiency and energy loss. This parameter optimization ensures sufficient second compound presence for effective energy transfer while preventing excessive concentration that would increase delayed fluorescence energy loss

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

Instead of using a high doping ratio to maximize energy transfer, the invention uses a moderate doping ratio (1-49 wt%) that provides sufficient energy transfer efficiency without the diminishing returns and increased energy loss associated with excessive doping. The third compound compensates for the moderate concentration of the second compound by having high energy transfer efficiency

Inventive Principle:

Principle #16Partial or excessive action

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 approach enhances luminous efficiency and widens the selection range of the material system, achieving improved device performance with increased spectral overlapping and efficient energy transfer, resulting in enhanced device efficiency and properties.

Implementation Method 1

the second compound has a characteristic of emitting delayed fluorescence

Methodology Applied

Scientific EffectDelayed fluorescence: Fluorescence

Implementation Method 2

an overlap ratio between the emission spectrum of the second compound and an emission spectrum of the first compound is greater than 30%

Methodology Applied

Scientific EffectEnergy transfer: Fluorescence

Data Source

PatentUS20230056639A1Organic electroluminescent device, display panel, and display device

Publication Date: 2023.02.23 BOE TECHNOLOGY GROUP CO LTD

AI summary

The present invention provides an organic electroluminescent device, a display panel, and a display device. An organic electroluminescent device, including: an anode and a cathode, arranged in opposite; a light-emitting layer, between the anode and the cathode; a first auxiliary function layer, between the light-emitting layer and the anode; and a second auxiliary function layer, between the light-emitting layer and the cathode; where the light-emitting layer comprises a first compound, a second compound and a third compound; a Stokes shift between an absorption spectrum of the second compound and an emission spectrum of the second compound is smaller than 70 nm; and a doping mass ratio of the second compound in the light-emitting layer is smaller than 50 wt %.