Organic Photoelectric Element with Blocking Layer for Dark Current Reduction
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Solution Overview
Problem
Conventional photoelectric elements used in solid-state imaging devices face challenges with reduced sensitivity due to smaller pixel sizes, increased dark current from charge carrier injection, and lack of heat resistance, especially during processing steps like color filter formation and soldering, which affect their performance and storage stability.
Innovation Solution
A photoelectric element is designed with a conductive layer, an organic photoelectric layer having a p-type material with a glass transition temperature of 100°C or higher, and a blocking layer with a triarylamine material having a glass transition temperature of 140°C or higher, along with a transparent conductive layer, to enhance heat resistance and reduce dark current while maintaining high photoelectric conversion efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the pixel size is reduced to increase the number of pixels, then the productivity and resolution are improved, but the aperture ratio and light collection efficiency are reduced
Solution Approach 1:
The patent employs a composite photoelectric layer combining p-type organic photoelectric material and n-type semiconductor material (fullerene or derivative) to create a bulk heterojunction structure. This composite material approach enables high photoelectric conversion efficiency while maintaining the ability to function in small pixel areas, thus resolving the contradiction between increasing pixel count and maintaining aperture ratio.
2Measurement precision
If an external voltage is applied to improve photoelectric conversion efficiency or response speed, then the sensitivity is improved, but charge carrier injection from electrodes increases dark current
Solution Approach 1:
The patent introduces a blocking layer as an intermediary component between the electrode and the photoelectric layer. This blocking layer selectively prevents charge carrier injection from the electrode into the photoelectric layer, thereby reducing dark current while allowing the application of external voltage to maintain high photoelectric conversion efficiency and response speed.
Solution Approach 2:
The patent modifies the energy level parameters by selecting materials with specific work functions and LUMO levels. The blocking layer material is chosen to have a work function that creates a large energy gap with the photoelectric layer's LUMO level, preventing electron injection. This parameter optimization allows external voltage application for high efficiency while minimizing dark current through proper energy level alignment.
3Ease of manufacture
If conventional electrode materials with work function of 4.5 eV are used, then the ease of manufacture is improved, but electron injection into fullerene photoelectric layer increases dark current
Solution Approach 1:
The blocking layer serves as an intermediary between the conventional electrode material and the fullerene photoelectric layer. This intermediate layer prevents direct interaction between the electrode and photoelectric layer, blocking electron injection while allowing the use of conventional, easy-to-manufacture electrode materials like ITO with work function of 4.5 eV.
Solution Approach 2:
The patent changes the energy level parameter at the electrode-photoelectric layer interface by introducing the blocking layer. The blocking layer's work function is selected to create a large energy barrier (greater than 2 eV gap with LUMO level) that prevents electron injection, while maintaining compatibility with conventional electrode materials for ease of manufacture.
4Ease of manufacture
If the photoelectric element is subjected to heating steps for manufacturing, then the manufacturing process is completed, but heat resistance is insufficient causing performance degradation
Solution Approach 1:
The patent optimizes the thermal parameters of the organic photoelectric material by selecting compounds with glass transition temperatures (Tg) of 100°C or higher. This parameter change ensures the material maintains its structural integrity and photoelectric properties during manufacturing heating steps (color filter formation, protective film formation, soldering) without performance degradation.
Solution Approach 2:
The patent uses a composite structure combining the organic photoelectric material with the blocking layer material, where both components are selected for their thermal stability. The blocking layer material with Tg of 140°C or higher provides additional thermal resistance, protecting the photoelectric layer during manufacturing processes while maintaining overall device 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
The solution achieves high external quantum efficiency, low dark current, and improved heat resistance, ensuring the photoelectric element's performance stability throughout manufacturing processes and storage, even at elevated temperatures.
Implementation Method 1
photoelectric conversion units (pixels) are two-dimensionally arrayed in a semiconductor, and a signal charge generated by photoelectric conversion in each pixel is transferred and read out
Implementation Method 2
providing a charge blocking layer for efficiently blocking injection of charges into a photoelectric layer thereby to reduce dark current
Data Source
AI summary
A photoelectric element includes a conductive layer, an organic photoelectric layer, a blocking layer and a transparent conductive layer, the organic photoelectric layer contains a p type organic photoelectric material having a glass transition temperature of 100° C. or higher and forms an amorphous layer, and the blocking layer contains a blocking material having a glass transition temperature of 140° C. or higher.