Light-Emitting Layer for Bright Luminescence via Energy Segmentation
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Solution Overview
Problem
Opto-electronic devices, such as OLEDs, face challenges in achieving high luminescence efficiency and emitting light of shorter wavelengths due to issues like self-quenching, triplet-triplet annihilation, and bathochromic shift, leading to reduced brightness and operational lifetimes.
Innovation Solution
A light-emitting layer comprising two emitter compounds with specific energy level configurations and intersystem crossing rates, where the energy level of S1(a) is higher than S1(b), and the rate of reverse intersystem crossing from T1(a) to S1(a) is greater than the excitation energy transfer rates, allowing for efficient energy recycling and reduced non-radiative decay.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If emitter compounds with strong spin-orbit interaction are used to increase intersystem crossing rate, then quantum yield is improved, but self-quenching occurs at high densities leading to reduced quantum yield
Solution Approach 1:
The system divides the emitter population into two distinct compounds with different energy levels. Compound (a) with higher S1 and T1 energy levels serves as the primary emitter, while compound (b) with lower energy levels acts as an energy acceptor. This segmentation prevents self-quenching by distributing excitons across two species with optimized concentrations.
Solution Approach 2:
Compound (b) functions as an intermediary that accepts energy from compound (a) and emits light with higher efficiency. The energy transfer from (a) to (b) mediated through dipole-dipole coupling or exchange interaction reduces the burden on compound (a), allowing lower concentrations and reduced self-quenching while maintaining high quantum yield.
2Illumination intensity
If high densities of emitter compounds are used to increase brightness, then illumination level is improved, but triplet-triplet annihilation occurs leading to reduced device lifetime
Solution Approach 1:
The triplet states are segmented between two compounds: compound (a) generates triplet states that rapidly transfer to compound (b), while compound (b) hosts the triplet states at lower concentrations. This segmentation reduces triplet-triplet annihilation by distributing triplet populations across two species with optimized density ratios.
Solution Approach 2:
The system establishes continuous energy flow from singlet to triplet states and from compound (a) to compound (b), maintaining steady-state triplet populations that avoid accumulation and subsequent annihilation. The rapid energy transfer ensures continuous utilization of triplet states for light emission without excessive buildup.
3Use of energy by moving object
If energy transfer to lower T1 level of emitter compound is used to achieve phosphorescence, then quantum yield is improved, but bathochromic shift occurs reducing emission of shorter wavelengths
Solution Approach 1:
The system changes the energy level parameters by introducing compound (b) with specifically tuned S1 and T1 energy levels that are lower than compound (a) but maintain appropriate gaps. This parameter optimization allows energy transfer while preserving the ability to emit at shorter wavelengths through compound (a)'s higher energy states.
Solution Approach 2:
The system adds a second energy transfer dimension: in addition to the conventional S1→T1 phosphorescent pathway, it introduces S1(a)→S1(b) and T1(a)→T1(b) energy transfer pathways. This multi-dimensional energy management allows simultaneous optimization of quantum yield through phosphorescence and wavelength control through the higher energy states of compound (a).
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 luminescence efficiency and enables the emission of light across a broader spectrum, including shorter wavelengths, while minimizing triplet-triplet annihilation and extending device operational lifetimes.
Implementation Method 1
the rate of reverse intersystem crossing from T1(a) to S1(a) is higher than the rate of excitation energy transfer from S1(a) to S1(b) and/or the rate of excitation energy transfer from T1(a) to T1(b)
Implementation Method 2
the rate of excitation energy transfer from S1(a) to S1(b) and/or the rate of excitation energy transfer from T1(a) to T1(b)
Implementation Method 3
emitter compounds having a comparably strong spin-orbit interaction and thus an increased intersystem crossing (ISC) rate between the excited singlet energy level S1 to the excited triplet energy level T1 and vice versa
Implementation Method 4
Too high densities of emitters often lead to self-quenching resulting in a lower quantum yield. Therefore, often host molecules spatially separating the single molecules of the emitter compound from another are used.
Implementation Method 5
Some of the hosts used in the art can also improve the efficiency of the opto-electronic device due to energy transfer from the host to the emitter compound
Implementation Method 6
blue phosphorescent OLEDs (PHOLEDs)
Implementation Method 7
the emission of light from the excited singlet and triplet states of the first emitter compound and/or from the excited singlet and triplet states of the second emitter compound
Implementation Method 8
this may, under certain circumstances, even lead to the occurrence of triplet-triplet annihilation (TTA) effects that are so strong that the device is entirely inoperative for higher electrical current flows or longer-lasting illumination
Data Source
AI summary
The present invention relates to a light-emitting layer B comprising a first emitter compound (a) having a non-exited state S0(a), a first excited singlet state S1(a) and a first excited triplet state T1(a); a second emitter compound (b) having a non-exited state S0(b), a first excited singlet state S1(b) and a first excited triplet state T1(b), wherein the energy level of S1(a) is higher than that of S1(b), the energy level of S1(b) is higher than that of T1(b) and wherein the rate of reverse intersystem crossing from T1(a) to S1(a) is higher than the rate of excitation energy transfer from S1(a) to S1(b) and/or the rate of excitation energy transfer from T1(a) to T1(b), and/or wherein the energy level of T1(b) is higher than that of T1(a). Further, the present invention also refers to an opto-electronic device comprising such light-emitting layer B and use thereof.