OLED Emission Layer Dual-Host Delayed Fluorescence
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Solution Overview
Problem
Organic light-emitting devices (OLEDs) using delayed fluorescence face challenges in achieving high efficiency and minimizing efficiency roll-off due to the energy difference between triplet and singlet states, which affects charge transport and injection characteristics.
Innovation Solution
An OLED structure incorporating a dopant with a delayed fluorescence emitting material, a first host, and a second host, where the triplet energies of the hosts are equal to or greater than the dopant's triplet energy, and the energy gap between triplet and singlet energies of the dopant is within a specific range, facilitating efficient energy up-conversion and improved charge transport.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a luminescent material with small energy difference between triplet and singlet states is used to facilitate energy up-conversion, then delayed fluorescence efficiency is improved, but the triplet energy level becomes constrained which may limit charge transport characteristics
Solution Approach 1:
The patent employs a composite host system comprising multiple host materials with different triplet energy levels. This composite approach enables the system to simultaneously satisfy the energy up-conversion requirement (by having hosts with triplet energies matching the dopant's triplet state) and maintain good charge transport characteristics (by incorporating hosts with appropriate mobility properties), thereby resolving the contradiction between energy efficiency and charge transport adaptability.
Solution Approach 2:
The patent optimizes the triplet energy level parameter of the host materials to be equal to or greater than the triplet energy level of the dopant. This parameter adjustment enables efficient energy transfer from the host triplet state to the dopant triplet state, facilitating delayed fluorescence emission while maintaining compatibility with charge transport requirements through careful selection of host materials with appropriate energy and mobility parameters.
2Loss of energy
If a host with high triplet energy level is used, then energy up-conversion from triplet to singlet state is facilitated, but charge injection from adjacent layers becomes less effective due to large band gap energy
Solution Approach 1:
The patent uses a composite host system where different host materials with complementary properties are combined. This allows the system to achieve high triplet energy levels for efficient delayed fluorescence while incorporating components that maintain suitable band gap characteristics for effective charge injection from adjacent layers, thus resolving the contradiction between energy conversion efficiency and charge injection reliability.
3Loss of energy
If a host with short conjugation length is used, then triplet energy level is increased for better delayed fluorescence, but charge transport characteristics decrease
Solution Approach 1:
The patent employs a composite host system that combines materials with short conjugation lengths (providing high triplet energy for efficient delayed fluorescence) with materials that have good charge transport properties. This composite approach allows the system to simultaneously achieve high delayed fluorescence efficiency and maintain excellent charge transport characteristics, resolving the contradiction between the two performance parameters.
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 solution enhances luminescent efficiency and reduces efficiency roll-off in OLEDs, particularly for blue delayed fluorescence emission, by optimizing the energy levels and charge transport properties of the host materials.
Implementation Method 1
Delayed fluorescence refers to a fluorescent emission that activates an energy up-conversion from a lower energy excited triplet state to a higher energy excited singlet state
Implementation Method 2
When a voltage is applied between the anode and the cathode, holes provided from the anode are injected into the emission layer through the hole transport layer, and electrons provided from the cathode are injected into the emission layer through the electron transport layer. In the emission layer, the holes and the electrons are recombined to produce excitons, which then radiatively decay to emit light
Data Source
AI summary
An organic light-emitting device includes a first electrode; a second electrode facing the first electrode; and an emission layer between the first electrode and the second electrode, the emission layer including a dopant, a first host, and a second host. The dopant is a delayed fluorescence emitting material, and a triplet energy of the first host, EH1(T1) and a triplet energy of the second host, EH2(T1) are each equal to or greater than a triplet energy of the dopant, ED(T1). The triplet energy of the first host, EH1(T1) is in a range of about 2.6 eV to about 3.1 eV.