Organic Electroluminescent Element Light-Emitting Layer Charge Transport
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Solution Overview
Problem
Organic electroluminescent elements face challenges in achieving good current-voltage characteristics due to charge trap levels in the light-emitting layer, which increase luminescent efficiency but worsen electrical performance.
Innovation Solution
Incorporating multiple charge transport materials in the light-emitting layer, with a total of 5 or more kinds, and controlling their ionization potential and electron affinity differences to prevent material aggregation and crystallization, thereby improving charge transport routes and reducing charge traps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If charge trap levels are provided inside the light-emitting layer to keep charges staying, then luminescent efficiency is improved, but current-voltage characteristics worsen
Solution Approach 1:
The patent uses composite materials by combining multiple charge transport materials (three or more kinds) with different molecular weights in the light-emitting layer. This composite approach creates multiple charge transport routes with different energy levels, allowing charges to be effectively transported while maintaining good current-voltage characteristics, thus resolving the contradiction between luminescent efficiency and electrical performance.
Solution Approach 2:
The patent changes the parameter of molecular weight distribution by using charge transport materials with different molecular weights (specifically, the ratio of maximum to minimum molecular weight is 5 or more). This parameter change creates diverse charge transport pathways with varying trap levels, enabling both efficient charge retention for luminescence and smooth current-voltage characteristics.
2Reliability
If multiple charge transport materials are used in the light-emitting layer, then charge transport routes are improved, but material aggregation and crystallization may occur
Solution Approach 1:
The patent controls the molecular weight parameter of charge transport materials, using materials with molecular weights of 10,000 or less and specific molecular weight ratios. This parameter control prevents material aggregation and crystallization while maintaining multiple charge transport routes, thus improving charge transport characteristics without compromising composition stability.
Solution Approach 2:
The patent applies local quality by having different charge transport materials with different molecular weights distributed in the light-emitting layer. Each material component provides specific local charge transport properties, and the combination creates overall improved charge transport while maintaining homogeneous composition through careful selection of molecular weight parameters.
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 results in organic electroluminescent elements with enhanced current-voltage characteristics, enabling high luminescent efficiency and low driving voltage, suitable for applications in flat panel displays and other light-emitting devices.
Implementation Method 1
when multiple charge transport materials are used and the level of the charge transport routes thereof are controlled, then it is possible to obtain an organic electroluminescent element having good current-voltage characteristics
Implementation Method 2
in the light-emitting layer, the charges are recombined to emit light
Data Source
Figure 1
AI summary
The objection of invention is to provide an organic electroluminescent element having an excellent current-voltage property. The organic electroluminescent element of the invention comprises an anode, a light emitting layer and a cathode, in this order, wherein a total number of kinds of an electron transport material and a light emitting material contained in the light emitting layer is five or more. Preferably, a total number of kinds of an electron transport material contained in the light emitting layer is four or more, and at least one of an ionization potential and an electron affinity of three kinds or more of the electron transport materials contained in the light emitting layer is different from each other.