Organic EL Hole Injection Layer Conductivity Gradient
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Solution Overview
Problem
Conventional organic electroluminescence (EL) elements face issues with leak current due to insufficient confinement of carriers, leading to decreased luminous efficiency and increased operation voltage, which cannot be effectively suppressed despite attempts to improve conductivity.
Innovation Solution
An organic EL element structure is introduced with a hole injection layer having varying conductivity in its thickness direction, forming regions of carrier depletion to reduce leak current while maintaining improved conductivity and suppressing operation voltage, along with an electron injection transport layer and hole transport layer to enhance carrier confinement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If acceptor is doped in the hole transport layer to improve conductivity, then operation voltage is reduced and efficiency is increased, but leak current is generated due to insufficient carrier confinement
Solution Approach 1:
The hole transport layer is divided into multiple sub-layers with different acceptor doping concentrations. The first hole transport layer has higher acceptor concentration for improved conductivity and lower operation voltage, while the second hole transport layer has lower acceptor concentration to suppress leak current and improve carrier confinement. This segmentation allows each sub-layer to perform its specific function optimally.
Solution Approach 2:
Different regions of the hole transport layer are assigned different acceptor doping concentrations based on their functional requirements. The region adjacent to the luminescent layer uses lower doping to confine carriers, while the region adjacent to the hole injection layer uses higher doping to facilitate hole injection and reduce operation voltage. This local quality variation resolves the contradiction between conductivity and carrier confinement.
2Object-generated harmful factors
If electron injection suppression layer is added to suppress leak current, then carrier confinement is improved, but device complexity increases
Solution Approach 1:
The second hole transport layer serves multiple functions simultaneously: it acts as an electron injection suppression layer to confine carriers and reduce leak current, while also maintaining hole transport capability and contributing to overall layer stability. This multi-functionality eliminates the need for a separate electron injection suppression layer, thereby reducing device complexity while achieving the desired leak current suppression.
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 effectively suppresses leak current, maintains high conductivity, and reduces operation voltage, thereby enhancing luminous efficiency and extending the life of the organic EL element while minimizing crosstalk.
Implementation Method 1
holes are injected into the organic EL layer from the positive electrode and electrons are injected thereinto from the negative electrode, and the organic EL layer emits light through recombination of the injected holes and electrons
Data Source
AI summary
An object of the present invention is to enable suppression of a leak current of an organic EL element while improving a conductivity of the organic EL element and suppressing an operation voltage thereof. An organic EL element is used which comprises at least a luminescent layer, a hole transport layer adjacent to a positive-electrode side of the luminescent layer, and an electron injection transport layer adjacent to a negative-electrode side of the luminescent layer, wherein a hole injection layer is provided between the hole transport layer and the positive electrode, and the conductivity of the hole injection layer continuously changes along a thickness direction of the hole injection layer.