Tandem OLED Display with Charge Generation Layer for High Color Temperature White Light
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Solution Overview
Problem
Existing OLED displays face challenges in achieving high-definition images with white light emission having a high color temperature, particularly in expressing white colors with a color temperature of 6500K or more, due to limitations in blue light emission efficiency.
Innovation Solution
The OLED display incorporates a tandem structure with a charge generation layer between two light emitting units, each comprising hole and electron transport layers and organic light emitting layers, including blue and yellow phosphorescent or fluorescent materials, to emit white light with a high color temperature, and optionally uses a color filter substrate to enhance color accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a conventional OLED structure with single light emitting unit is used, then the device complexity is low, but the color temperature of emitted white light cannot reach 6500K or more
Solution Approach 1:
The OLED is divided into two separate light emitting units (first and second light emitting units) with distinct functions. The first light emitting unit emits blue light while the second emits yellow light, allowing independent optimization of each unit's characteristics to achieve high color temperature white light emission.
Solution Approach 2:
The patent transitions from a single-layer light emitting structure to a multi-layer tandem structure by stacking two light emitting units with different emission characteristics. This dimensional expansion in the vertical direction enables simultaneous achievement of high blue light content and efficient light extraction.
2Temperature
If blue light emitting layer efficiency is increased to achieve high color temperature, then the color temperature increases, but the overall light emission efficiency decreases
Solution Approach 1:
The patent separates the blue light emission function and yellow light emission function into different light emitting units. The first light emitting unit is optimized for blue light with high efficiency phosphorescent materials, while the second unit provides yellow light to balance the spectrum, allowing each unit to operate at optimal efficiency.
Solution Approach 2:
The patent employs composite phosphorescent materials in the light emitting layers, combining host materials with guest phosphors (e.g., Ir(ppy)3 for blue, Ir(piq)3 for yellow) to achieve both high quantum efficiency and appropriate color emission, resolving the trade-off between efficiency and color temperature.
3Temperature
If a tandem structure with two light emitting units is used, then white light with color temperature of 6500K or more is emitted, but the manufacturing process becomes more complex
Solution Approach 1:
The tandem structure is designed with clearly defined functional layers that can be fabricated using sequential deposition processes. Each light emitting unit contains complete sets of hole transport, light emitting, and electron transport layers, allowing modular manufacturing and quality control.
Solution Approach 2:
A charge generation layer is introduced between the two light emitting units to serve as an intermediary that generates and balances charges. This layer facilitates efficient charge injection into both units without requiring complex external control mechanisms, simplifying the overall manufacturing process.
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 allows for the emission of white light with a color temperature of 6500K or more, effectively improving the display's ability to express high-definition colors by balancing blue and yellow light intensities, thereby overcoming the limitations of conventional OLEDs in achieving high color temperatures.
Implementation Method 1
a first organic light emitting layer between the first hole transport layer and the first electron transport layer... a second organic light emitting layer and a third organic light emitting layer between the second hole transport layer and the second electron transport layer
Implementation Method 2
The second organic light emitting layer may include a first phosphorescent light emitting material and the third organic light emitting layer may include a second phosphorescent light emitting material
Implementation Method 3
The first organic light emitting layer may be a blue fluorescent light emitting layer
Data Source
AI summary
An organic light emitting diode display includes: a substrate; a first electrode on the substrate; a second electrode opposed to the first electrode; a first light emitting unit and a second light emitting unit between the first electrode and the second electrode; and a charge generation layer between the first light emitting unit and the second light emitting unit. The first light emitting unit includes a blue fluorescent light emitting layer. The second light emitting unit includes a blue light emitting layer and a yellow light emitting layer.