Microcavity OLED Structure for Optical Cavity Length Tuning
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Solution Overview
Problem
Existing microcavity OLED designs face challenges in determining the optimum optical path length to decrease spectral bandwidth and output angle, with constraints on material choice and thickness for filler layers, particularly in light-field displays requiring high angular resolution and wide field of view.
Innovation Solution
Incorporating an intermediate electrode with an overhang region and connecting area to alleviate electron-hole balancing requirements, allowing for flexible material and thickness selection, and enabling blanket deposition methods for multi-colored microcavity pixel arrays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the optical path length of the microcavity is adjusted by changing the thickness of the filler layer, then the spectral bandwidth and output angle are decreased, but the material choice and thickness selection are constrained by electron-hole balancing requirements
Solution Approach 1:
The device is segmented into two functional zones: an active emission zone with the organic light-emitting diode stack and electrode interface, and a passive optical zone with the filler layer and distributed Bragg reflector. This segmentation allows the optical zone to be optimized independently for spectral control without compromising the electrical performance of the emission zone.
Solution Approach 2:
The intermediate electrode acts as a mediator that provides both electrical connection and optical functionality. It serves as the electrical contact for the OLED stack while simultaneously functioning as part of the optical cavity structure, thereby decoupling the electrical and optical design constraints.
2Manufacturing precision
If a thicker filler layer is used to achieve the desired optical path length, then the spectral bandwidth decreases, but optical loss increases due to light absorption
Solution Approach 1:
The design changes the optical parameters by optimizing the filler layer thickness to achieve the desired optical path length while maintaining material transparency. The distributed Bragg reflector is designed with specific layer thicknesses (one quarter of the resonance wavelength) to maximize reflectivity and minimize absorption losses.
3Manufacturing precision
If the microcavity is designed for color tuning, then the spectral bandwidth is decreased, but additional patterning steps are required after OLED patterning
Solution Approach 1:
The filler layer is deposited with the precise thickness required for the desired color tuning before the OLED stack is fabricated. This preliminary action establishes the optical cavity dimensions early in the fabrication process, eliminating the need for subsequent patterning steps to achieve color differentiation.
Solution Approach 2:
Color tuning is achieved by varying the thickness parameter of the filler layer in the vertical dimension rather than through lateral patterning. This dimensional approach allows different colors to be achieved through thickness variation alone, simplifying the fabrication process.
4Manufacturing precision
If the reflectance of the distributed Bragg reflector is increased to decrease output angle, then the spectral bandwidth decreases, but the device complexity increases
Solution Approach 1:
The output angle is controlled by optimizing the optical parameters of the distributed Bragg reflector, specifically the layer thicknesses and refractive index contrast. By carefully selecting these parameters, high reflectance and narrow beam divergence are achieved without requiring overly complex multi-layer structures.
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
Facilitates tuning of optical cavity length and material selection, reducing spectral bandwidth and output angle, and enabling high angular resolution and wide field of view in multi-view displays without additional patterning steps.
Implementation Method 1
The highest reflectivity is attained when the layer thicknesses are chosen such that the optical path length of each layer is one quarter of the resonance wavelength, commonly referred to as the Bragg Wavelength, λBragg.
Implementation Method 2
A DBR is an optical minor composed of multiple pairs of two different dielectric layers with different refractive indices in an alternating order.
Implementation Method 3
Light is generated in an OLED device when electrons and holes that are injected from the cathode and the anode (electrodes), respectively, flow through the ETL and the HTL and recombine in the EML.
Implementation Method 4
The wavelength of the light output by such a resonant OLED structure is dependent, in part, upon this optical path length of the microcavity.
Data Source
AI summary
A microcavity pixel design and structure allowing for tuning the optical cavity length of the microcavity of a microcavity pixel structure. This is achieved by including an intermediate electrode in the device which has an overhang region to form a connecting area to a bottom electrode, alleviating design restrictions in material type and dimensions throughout the optical microcavity tuning process. A method for the fabrication of a multi-colored microcavity pixel array facilitating the use of blanket deposition methods for select layers within a microcavity pixel structure.