Top-Emitting White OLED Emissive Construct with Blocking Layer
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Top-emission white organic light-emitting diode (OLED) devices face challenges in efficiency, color stability, and complexity due to issues like light trapping, microcavity effects, and material limitations, which affect their performance for lighting applications.
Innovation Solution
The emissive construct comprising a fluorescent emissive layer, a blocking layer, and phosphorescent emissive layers, with specific energy levels and thicknesses, is used to enhance light extraction and color tuning, allowing for efficient electron and hole recombination and improved power efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional emissive structure is used in top-emission white OLEDs, then the device structure is simpler, but light extraction efficiency is poor due to light trapping and microcavity effects
Solution Approach 1:
The emissive construct is divided into multiple discrete layers including fluorescent emissive layers, phosphorescent emissive layers, and blocking layers with specific T1 energy level relationships. This segmentation allows each layer to perform its specific function optimally, with the blocking layer preventing triplet exciton migration and the phosphorescent layers harvesting triplet excitons for light emission, thereby improving overall light extraction efficiency while maintaining manageable structural complexity
Solution Approach 2:
The blocking layer acts as an intermediary between the fluorescent and phosphorescent emissive layers. It has a T1 energy level higher than or equal to the fluorescent emitter, which prevents triplet exciton migration from the fluorescent layer to the phosphorescent layer, thereby maintaining color stability and improving light extraction efficiency without requiring complete structural redesign
2Loss of energy
If multiple emissive layers are added to improve light extraction, then power efficiency improves, but device complexity increases
Solution Approach 1:
Different regions of the emissive construct are assigned specific properties: fluorescent emissive layers with specific T1 values for singlet exciton emission, phosphorescent emissive layers for triplet exciton harvesting, and blocking layers with T1 ≥ fluorescent T1 to prevent triplet migration. This local differentiation of material properties allows each component to contribute optimally to power efficiency while maintaining a systematic rather than random complexity
Solution Approach 2:
The invention controls the T1 energy level parameter across different layers to achieve desired performance. The blocking layer is specifically designed with T1 ≥ fluorescent T1, and the phosphorescent layers are positioned to harvest triplet excitons. By systematically varying this key energy level parameter, the invention achieves high power efficiency (over 50 lm/W) while maintaining a structured approach to complexity
3Ease of manufacture
If conventional materials are used, then material selection is easier, but color stability deteriorates due to triplet exciton migration and microcavity effects
Solution Approach 1:
The blocking layer serves as an intermediary that stabilizes color by preventing triplet exciton migration. Its T1 energy level is specifically chosen to be higher than or equal to the fluorescent emitter, creating an energy barrier that blocks triplet exciton diffusion. This intermediary layer maintains color stability without requiring complete material system redesign
Solution Approach 2:
The emissive construct uses composite material architecture combining fluorescent and phosphorescent emitters with specific host materials. The fluorescent layers use emitters like BE-1 and BE-2 with defined T1 values, while phosphorescent layers use emitters like Ir(pq)2acac and YE-1. This composite approach, where materials are selected and combined based on their photophysical properties rather than using conventional single-material systems, achieves superior color stability
4Device complexity
If the OLED is designed for top-emission, then device structure is simplified, but angle dependency of color increases
Solution Approach 1:
The emissive construct is segmented into multiple layers with different emission characteristics. The fluorescent layers provide angle-independent emission while the phosphorescent layers are positioned to compensate for angle-dependent effects. The blocking layers are strategically placed to control exciton distribution, thereby reducing overall angle dependency while maintaining the simplified top-emission device structure
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 improves the power efficiency and color stability of top-emission white OLEDs, achieving high lumens per watt and extended device lifetime with reduced angle dependency on color, meeting DOE lighting requirements.
Implementation Method 1
a first phosphorescent emissive layer disposed over the blocking layer; wherein the emissive construct is configured to allow electrons to be transferred from the first phosphorescent emissive layer to the blocking layer
Implementation Method 2
a first fluorescent emissive layer comprising a first fluorescent emitter having a first T1; a second fluorescent emissive layer comprising a second fluorescent emitter having a second T1
Data Source
AI summary
The present disclosure relates to an emissive construct, which can be used in various OLED applications, for example, top-emission white organic light-emitting diodes. The emissive construct can include an optional second fluorescent emissive layer having an emitter with a second T1, a first fluorescent emissive layer having an emitter with a first T1, the first T1 being greater than the second T1 value, a hole-blocking layer, and a phosphorescent emissive layer.