Stacked OLED Common Electrode Work Function Tuning
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Solution Overview
Problem
Conventional stacked organic light emitting devices face limitations in color temperature control and display versatility due to high operational voltage and complex electrode structures, as well as restricted material selection for hole injecting layers, which affects light emitting efficiency and color calibration.
Innovation Solution
A stacked organic light emitting device design where each light emitting unit operates alternately with positive and negative voltages applied to conductive layers, forming an NP junction with n-type and p-type organic material layers to control color temperature and intensity, allowing for various display configurations using a common electrode material for both anode and cathode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a transparent electrode such as ITO is used as a common electrode, then the device can maintain transparency, but the operational voltage is greatly increased and light emitting efficiency is deteriorated
Solution Approach 1:
The patent changes the work function parameter of the common electrode by selecting materials with work functions between 4.0-4.5 eV (such as Ca, Mg, Al, Ag, Au, Pt, Ir, Pd, Ti, Hf, Ta, Mo, W, Nb, Cu, Zn, In, Ga, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Ti, Zr, Hf, Ta, Mo, W, Nb, Cu, Zn, In, Ga, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) instead of conventional high work function ITO electrodes. This parameter change enables effective electron injection while maintaining transparency, thereby reducing operational voltage and improving light emitting efficiency.
2Use of energy by stationary object
If a Mg:Ag alloy layer is used as a common electrode, then electron injection is improved, but the selection of hole injecting layer materials is limited
Solution Approach 1:
The patent broadens the work function parameter range of the common electrode to 4.0-4.5 eV, which is higher than conventional low work function materials like Mg:Ag (2.5-3.0 eV). This parameter change allows matching with a wider range of hole injecting layer materials having HOMO levels between 5.0-6.0 eV, thereby improving electron injection efficiency while maintaining material selection flexibility.
Solution Approach 2:
The patent creates a universal common electrode material system that can work with multiple types of hole injecting layers. By selecting materials with work functions in the 4.0-4.5 eV range, the common electrode can be paired with various hole injecting layer materials (such as TCTA, Alq3, BCP, AlN, BaF2, CaF2, SrF2, TiO2, HfO2, TaO2, MoO3, WO3, Nb2O5, CuO, ZnO, In2O3, Ga2O3, La2O3, CeO2, PrO2, NdO2, SmO2, EuO2, GdO2, TbO2, DyO2, HoO2, ErO2, TmO2, YbO2, LuO2) without requiring specific material matching, thereby achieving multi-functionality and versatility.
3Temperature
If complex electrode structures are used for color temperature calibration, then color control is improved, but the preparation process becomes complicated
Solution Approach 1:
The patent achieves color temperature control by changing the work function parameter of the common electrode material rather than using complex multi-layer electrode structures. By selecting materials with specific work functions in the 4.0-4.5 eV range, the patent can control the energy level alignment at the electrode-organic interface, thereby controlling color temperature without requiring complex structural configurations.
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
Enables effective color temperature control and diverse color displays by independently regulating each light emitting unit's operation, simplifying the device preparation process and improving hole injection efficiency with flexible material choices for electrodes.
Implementation Method 1
a stacked structure in which an anode electrode, a light emitting layer and a cathode electrode are typically sequentially repeated... light is emitted from several light emitting layers
Implementation Method 2
an n-type organic material layer adjacent to any one of the conductive layers, and a p-type organic material layer to form an NP junction with the n-type organic material layer
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
The present invention provides a stacked organic light emitting device, comprising a first conductive layer, at least one intermediate conductive layer and a second conductive layer, and light emitting units disposed between the conductive layers, wherein at least two non-neighboring conductive layers among the conductive layers are conductive layers belonging to Group 1 such that they are electrically connected with each other to a common potential; at least one non-neighboring conductive layer among the conductive layers which are not electrically connected with the conductive layers belonging to Group 1 to a common potential are conductive layers belonging to Group 2 such that they are electrically connected with each other to a common potential; and the conductive layers belonging to Group 1 and the conductive layers belonging to Group 2 are connected with each other via a voltage regulator for alternately applying a positive voltage and a negative voltage.