Organic Electroluminescent Display Reverse Bias Luminance Compensation
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Solution Overview
Problem
Organic electroluminescent displays experience a decrease in average luminance due to the accumulation of fixed negative and positive carriers at the anode and cathode electrodes, reducing the movement of electrons and holes and thus the light emission efficiency.
Innovation Solution
The introduction of a reverse bias voltage is applied to the organic electroluminescent element through a second voltage line, allowing a reverse current to flow and reducing the number of fixed carriers, thereby compensating for the decrease in luminance by increasing the movement of carriers to the light-emitting layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a voltage is supplied to the anode electrode to be higher than that supplied to the cathode electrode, then holes are supplied to the light emitting layer and electrons are supplied to the light emitting layer, but negative carriers accumulate in the anode electrode and positive carriers accumulate in the cathode electrode, causing the average luminance to decrease
Solution Approach 1:
The patent applies periodic action by alternating the voltage polarity between positive and negative. The driving unit supplies a positive voltage to the anode electrode during a first period, then switches to supplying a negative voltage during a second period. This periodic voltage switching causes carriers to oscillate between accumulation and movement states, preventing permanent accumulation at electrodes and maintaining sustained light emission efficiency.
Solution Approach 2:
The patent changes the voltage parameter from a static unidirectional voltage to a dynamic bidirectional voltage. By controlling the voltage polarity to switch between positive and negative states, the system modifies the carrier transport behavior. This parameter change enables the same electrode structure to function differently at different times, preventing carrier accumulation while maintaining productive carrier transport to the light emitting layer.
2Stability of the object's composition
If negative carriers are kept in the anode electrode and positive carriers are kept in the cathode electrode for long time, then the movement of electrons and holes is reduced, but the average luminance is decreased
Solution Approach 1:
The periodic voltage switching creates oscillating carrier distribution. During the positive voltage phase, carriers are pushed toward the cathode; during the negative voltage phase, they are pushed toward the anode. This periodic action prevents stable accumulation at either electrode, creating a dynamic equilibrium where carriers continuously move through the light emitting layer, maintaining both stability in the overall system and productivity in light emission.
Solution Approach 2:
The system transitions from a static carrier distribution state to a dynamic one. Instead of carriers remaining fixed at electrodes, the voltage switching induces continuous carrier movement. The carrier distribution becomes time-dependent, with carriers dynamically redistributing in response to changing voltage polarity, thereby maintaining sustained mobility and light emission 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
This approach effectively compensates for the decrease in average luminance by reducing the number of fixed carriers, enhancing the light emission efficiency of the organic electroluminescent display.
Implementation Method 1
An organic electroluminescent display is a display device for emitting light by electrically exciting fluorescent or phosphorescent materials
Implementation Method 2
emitting light by electrically exciting fluorescent or phosphorescent materials
Implementation Method 3
emitting light by electrically exciting fluorescent or phosphorescent materials
Implementation Method 4
allowing a reverse current to flow and reducing the number of fixed carriers
Implementation Method 5
The electron transport layer (ETL) accelerates the electrons supplied from a cathode electrode so that the electrons which are supplied from the electron transport layer (ETL) collide with the light emitting layer (EML)
Implementation Method 6
The hole transport layer (HTL) is supplied to the light emitting layer from the anode electrode by accelerating the supplied holes
Data Source
AI summary
An organic electroluminescent display that can prevent decreases in an average luminance of an organic electroluminescent element thereof includes: a data line to supply a data signal; a scan line to supply a scan signal; a first switching element having a control electrode electrically coupled to the scan line, to transfer the data signal from the data line; a first driving transistor having a control electrode electrically coupled to the first switching element, to control a driving current of a first voltage line; a first capacitive element having a first electrode electrically coupled to the first voltage line and having a second electrode electrically coupled to a control electrode of the first driving transistor; an organic electroluminescent element, electrically coupled to the first driving transistor and a third voltage line, to display an image in response to a current supplied from the first driving transistor; and a second voltage line to supply a reverse bias voltage of a second voltage line to the organic electroluminescent element.