Top Emission OLED Buffer Layer Oxide Protection
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Solution Overview
Problem
Conventional top emission organic light emitting display apparatus face challenges in maintaining low voltage light emission due to oxidation of the organic layer during the formation of the upper transparent electrode, leading to reduced aperture ratio and increased light emission voltage.
Innovation Solution
Incorporating a buffer layer made of a conductive oxide with stronger oxygen bonding force or lower Gibbs free energy than the upper electrode material between the organic light emitting layer and the upper electrode to prevent oxidation, and using dopants and specific materials for the hole and electron transport layers to enhance efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a top emission type organic light emitting element is used with a transparent upper electrode, then light can be emitted from the transparent upper electrode side, but the organic layer is oxidized when the upper electrode is formed, leading to elevated light emission voltage
Solution Approach 1:
A buffer layer made of oxide is introduced between the upper transparent electrode and the organic light emitting layer. This buffer layer acts as an intermediary that protects the organic layer from oxidation during the formation of the upper electrode, thereby preventing the elevation of light emission voltage while maintaining the top emission structure.
Solution Approach 2:
The buffer layer is formed in advance before the upper electrode is deposited. This preliminary action creates a protective barrier that prevents oxygen from the upper electrode formation process from reaching and oxidizing the organic layer, thus maintaining low light emission voltage from the outset.
2Ease of manufacture
If the upper electrode is made transparent using ITO or IZO by sputtering, then light emission from the upper electrode side is enabled, but the organic layer cannot be protected from oxidation during upper electrode formation
Solution Approach 1:
The buffer layer serves as a protective intermediary between the sputtered transparent upper electrode and the organic layer. It allows the easy formation of transparent electrodes via sputtering while simultaneously shielding the organic layer from the harmful oxidation effects during this manufacturing process.
Solution Approach 2:
The buffer layer, made of oxide material, utilizes the oxygen present in the sputtering process to protect the organic layer. The oxide buffer layer acts as an oxygen sink, converting the potentially harmful oxygen from the sputtering atmosphere into a protective function that prevents organic layer oxidation.
3Reliability
If a buffer layer made of oxide is provided to protect the organic layer from oxidation, then light emission voltage can be maintained, but the buffer layer itself may be oxidized during upper electrode formation
Solution Approach 1:
By carefully selecting oxide materials with appropriate stability characteristics for the buffer layer and controlling the sputtering process parameters, the buffer layer can withstand the formation conditions of the upper electrode without significant oxidation. The oxide material is chosen to have sufficient thermal and chemical stability to protect the organic layer while remaining stable itself during the deposition 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 approach effectively suppresses the rise in light emission voltage, maintains high transmittance, and ensures efficient hole and electron injection, enabling low-voltage light emission while preventing organic layer oxidation.
Implementation Method 1
a buffer layer principally made of an oxide producing less oxygen by decomposition in the layer forming process than the upper electrode material is formed between the organic light emitting layer and the upper electrode
Implementation Method 2
A side of the organic layer which is in contact with the buffer layer or the lower electrode is doped with an electron donative or hole donative dopant
Data Source
AI summary
The present invention provides a top emission type organic light emitting display apparatus in which manufacture it is possible to prevent the organic film from being oxidized when the upper transparent electrode is formed, and which is capable of emitting light at a low voltage. This organic light emitting display apparatus includes an organic light emitting layer and an upper electrode and a lower electrode sandwiching the said organic light emitting layer between them, and is of a structure in which the light emitted from the organic light emitting layer is taken out from the upper electrode side, wherein a buffer layer mostly made of an oxide with its Gibbs free energy generated at around the melting point being lower than −300 kJ/mol is provided between the organic light emitting layer and the upper electrode, the side of the organic layer which is in contact with the buffer layer being doped with an electron donative dopant.