OLED Emissive Layer with Aligned Excimer Dipoles
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Solution Overview
Problem
Organic light emitting diodes (OLEDs) suffer from low external quantum efficiency due to light trapping in the stratified thin film structure, with maximum external quantum efficiency being significantly lower than inorganic LEDs, primarily due to losses via plasmon, organic, and substrate modes.
Innovation Solution
Incorporating square planar tetradentate platinum or palladium complexes in the emissive layer of OLEDs, with emitting dipoles aligned parallel to the substrate, to enhance photoluminescent efficiency and reduce light trapping, using concentrations ranging from 5 wt% to 100 wt% in neat or doped films with carbazole-based hosts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If phosphorescent emitters are used in OLEDs to achieve high electron-to-photon conversion efficiency, then internal quantum efficiency approaches 100%, but external quantum efficiency remains low (20-30%) due to light trapping in the stratified thin film structure
Solution Approach 1:
The patent changes the molecular orientation parameter of the phosphorescent emitter from random to aligned parallel to the substrate surface. This parameter change modifies the emission pattern and reduces light trapping in the stratified thin film structure, enabling external quantum efficiency to approach internal quantum efficiency of 100%.
Solution Approach 2:
The patent uses composite emissive layers combining square planar tetradentate platinum or palladium complexes with carbazole-based host materials. This composite structure facilitates both high electron-to-photon conversion and improved light extraction through the aligned excimer emission.
2Use of energy by moving object
If phosphorescent emitters are used in OLEDs, then electron-to-photon conversion efficiency approaches 100%, but device stability and luminance durability are limited
Solution Approach 1:
The patent changes the molecular orientation parameter of the phosphorescent emitter to align parallel to the substrate. This alignment stabilizes the excited state and reduces non-radiative decay pathways, extending device stability and luminance durability to over 13,000 hours while maintaining high efficiency.
3Ease of manufacture
If conventional OLED structures are used, then manufacturing is straightforward, but external quantum efficiency is limited to 20-30% due to light trapping
Solution Approach 1:
The patent modifies the molecular orientation parameter of the phosphorescent emitter without changing the basic OLED structure. This parameter change can be achieved through standard deposition techniques, maintaining ease of manufacture while dramatically reducing light trapping loss and improving external quantum efficiency.
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 alignment of emitting dipoles parallel to the substrate significantly improves the external quantum efficiency of OLEDs, achieving efficiencies approaching 40% and extending device stability, with peak efficiencies exceeding 28% and luminance durability of over 13,000 hours.
Implementation Method 1
Incorporating square planar tetradentate platinum or palladium complexes in the emissive layer of OLEDs, with emitting dipoles aligned parallel to the substrate, to enhance photoluminescent efficiency
Implementation Method 2
phosphorescent excimers with preferred molecular orientation as monochromatic emitters
Data Source
AI summary
An organic light emitting diode having a substrate, a first electrode, a hole transporting layer proximate the first electrode, a second electrode, an electron transporting layer proximate the second electrode, and an emissive layer between the hole transporting layer and the electron transporting layer. The emissive layer includes a square planar tetradentate platinum or palladium complex, and excimers formed by two or more of the complexes are aligned such that emitting dipoles of the excimers are substantially parallel to a surface of the substrate.