NEST Light-Emitting Device Carrier Balance
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Solution Overview
Problem
Light-emitting devices using phosphorescent materials face efficiency roll-off at high luminance, and those with fluorescent materials have theoretical efficiency limits, while thermally activated delayed fluorescent (TADF) materials and negative singlet-triplet energy gap (NEST) materials offer potential but require optimization for improved performance.
Innovation Solution
A light-emitting device structure incorporating a light-emitting layer with specific organic compounds, including those with carbazole rings, aromatic amines, and π-electron deficient heteroaromatic rings, which form exciplexes to enhance carrier balance and efficiency, utilizing NEST materials with a T1 level higher than the S1 level to facilitate intersystem crossing and delayed fluorescence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If phosphorescent materials are used as light-emitting substances, then internal quantum efficiency can reach 100% theoretical limit, but efficiency roll-off occurs at high luminance
Solution Approach 1:
The patent changes the energy level parameters of the light-emitting substance by using NEST materials with inverted singlet-triplet energy levels (T1 > S1), which fundamentally alters the emission mechanism and enables efficient operation at high luminance without efficiency roll-off
Solution Approach 2:
The patent creates a composite light-emitting layer containing both the NEST material and a host material (first substance), where the host material facilitates energy transfer and carrier balance while the NEST material provides the inverted energy levels for efficient delayed fluorescence emission
2Device complexity
If fluorescent materials are used as light-emitting substances, then device structure is simple, but internal quantum efficiency is limited to 25% theoretical maximum
Solution Approach 1:
The patent fundamentally changes the energy level parameters by using NEST materials with inverted singlet-triplet levels (T1 > S1), which allows triplet excited states to contribute to light emission and achieve internal quantum efficiency exceeding the 25% theoretical limit of conventional fluorescent materials
Solution Approach 2:
The host material (first substance) acts as an intermediary that facilitates energy transfer from triplet excited states to the NEST material, enabling efficient energy utilization while maintaining a relatively simple device structure
3Ease of manufacture
If TADF materials are used to avoid heavy atoms, then cost is reduced, but emission efficiency and lifetime require optimization
Solution Approach 1:
The patent optimizes the energy level parameters of TADF materials by selecting NEST materials with specific inverted singlet-triplet level arrangements (T1 > S1), which fundamentally improves emission efficiency and lifetime while maintaining the advantage of avoiding heavy atoms
Solution Approach 2:
The patent replaces the need for heavy atom-based phosphorescent materials with TADF materials that utilize spin-orbit coupling through molecular structure design rather than heavy atoms, achieving similar or superior efficiency without the cost and complexity of noble metal complexes
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 device achieves favorable carrier balance, high efficiency at high luminance, and extended driving lifetime with reduced efficiency roll-off, providing a novel and efficient light-emitting solution.
Implementation Method 1
The TADF material can efficiently emit light by utilizing intersystem crossing from the triplet excited state to the singlet excited state
Implementation Method 2
a luminescence lifetime of delayed fluorescence caused by photoexcitation of the light-emitting substance is shorter at a first temperature than at a second temperature
Implementation Method 3
a NEST material, which is considered to have inverted energy levels of singlet and triplet excited states... a light-emitting device including a NEST material as a light-emitting substance, which utilizes intersystem crossing from a triplet excited state to a singlet excited state
Data Source
AI summary
A light-emitting device with favorable carrier balance is provided. The light-emitting device includes a light-emitting layer between a first electrode and a second electrode. The light-emitting layer includes at least a first substance and a light-emitting substance, the first substance includes an organic compound having one or more of a carbazole ring, an aromatic amine skeleton, and a π-electron deficient heteroaromatic ring, a luminescence lifetime of delayed fluorescence caused by photoexcitation of the light-emitting substance is shorter at a first temperature than at a second temperature, the first temperature is lower than the second temperature, and the first temperature and the second temperature are each higher than or equal to 10 K and lower than or equal to 300 K.