Organic EL Element Bipolar Charge Generation Layer
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Solution Overview
Problem
Organic EL elements are susceptible to degradation due to oxygen and moisture, leading to the formation of non-light-emitting 'dark spots' due to oxidation of electrodes and heat-reducible metals, which conventional sealing structures fail to completely prevent, especially in flexible substrates.
Innovation Solution
Incorporating a bipolar charge generation layer between the light-emitting layer and the second electrode, which functions as a hole-receiving electrode, formed from materials that generate electrons and holes under bias voltage, using high work function materials for electrodes to reduce oxidation and increase resistance to oxygen and moisture.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a film sealing structure is used to suppress oxidation of the cathode, then oxidation resistance is improved, but dark spots still occur and expand due to infiltration through pin holes and cracks
Solution Approach 1:
An electron transport layer is introduced as an intermediary between the cathode and the light-emitting layer. This layer acts as a protective barrier that prevents oxygen and moisture from reaching and oxidizing the cathode, while still allowing electron injection to proceed effectively. The intermediary layer thus decouples the protective function from the electron injection function, solving the problem of dark spots caused by cathode oxidation.
2Productivity
If a heat-reducible metal layer is used in the hole-electron current conversion layer, then current conversion efficiency is improved, but the metal is easily oxidized causing deterioration
Solution Approach 1:
The electron transport layer serves as a protective intermediary that shields the heat-reducible metal layer from oxygen and moisture infiltration. This allows the metal layer to maintain its excellent electron injection and current conversion properties without suffering from oxidation-induced deterioration, thus preserving both high productivity and reliability.
Solution Approach 2:
The electron transport layer creates an inert environment for the heat-reducible metal layer by blocking the penetration of oxygen and moisture. This protective atmosphere allows the metal to function at its full potential without undergoing oxidative degradation, maintaining both conversion efficiency and long-term stability.
3Ease of operation
If low work function materials are used for the cathode to obtain good electron injection, then electron injection is improved, but the cathode is easily oxidized by oxygen and moisture
Solution Approach 1:
The electron transport layer functions as a protective intermediary that separates the low work function cathode material from the harmful oxygen and moisture environment. This allows the cathode to maintain its excellent electron injection capability while the intermediary layer prevents oxidative degradation, thus resolving the contradiction between ease of operation and reliability.
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 suppresses the occurrence and expansion of dark spots, enhances the stability of organic EL elements against oxygen and moisture, and maintains light emission even when exposed to air, potentially extending the element's lifespan.
Implementation Method 1
a bipolar charge generation layer which generates electrons and holes
Implementation Method 2
An organic EL (electroluminescence) element has a structure in which an organic functional layer including a light-emitting layer is sandwiched by an anode and a cathode. In this structure, when a voltage is applied, holes and electrons injected from the anode and cathode into the light-emitting layer recombine to self-emit light.
Data Source
AI summary
A technology having resistance to moisture and oxygen, and in which the occurrence and expansion of non-light-generating portions, such as dark spots, are suppressed is provided. An organic EL element in which an organic functional layer including at least one or more light-emitting layers is arranged between a first electrode and a second electrode, wherein the organic functional layer includes a bipolar charge generation layer which generates electrons and holes, and one of the first electrode and the second electrode is a hole-receiving electrode.