Three-Material Organic Photoelectric Conversion for Image Sensors
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Solution Overview
Problem
Existing solid-state imaging devices face challenges in achieving high sensitivity, high resolution, and fast response time due to reduced photon entry with pixel size reduction, leading to deteriorated spectroscopic shape, responsivity, and external quantum efficiency.
Innovation Solution
A photoelectric conversion element with a multilayer structure using three organic semiconductor materials with different mother skeletons, including a first organic semiconductor material with high electron mobility, a second material with high linear absorption coefficient, and a third material with high hole mobility, forming a photoelectric conversion layer that enhances electron and hole mobility, maintaining a sharp spectroscopic shape and improving charge transport efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a color filter including a two-dimensional array of primary-color filters is used for colorization, then color signals can be generated, but sensitivity is reduced because green light and blue light are absorbed by the color filter in red pixels
Solution Approach 1:
The patent transitions from a planar color filter array to a stacked three-dimensional configuration of multiple photoelectric conversion layers. Each layer is specialized for detecting specific wavelength ranges (blue, green, red), allowing simultaneous color discrimination and high sensitivity without light absorption losses from color filters.
Solution Approach 2:
The photoelectric conversion function is segmented into multiple specialized layers, with each layer optimized for specific wavelength detection. This segmentation allows each layer to operate at peak sensitivity for its designated wavelength range, collectively achieving full-color detection with high overall sensitivity.
2Measurement precision
If pixel size is reduced to increase resolution, then the number of pixels increases, but the number of photons entering each pixel decreases, resulting in reduced sensitivity and S/N ratio
Solution Approach 1:
The patent changes the structural parameters of the photoelectric conversion system by introducing multiple stacked layers with different optical and electrical characteristics. This allows each miniaturized pixel to capture photons more efficiently across multiple wavelength ranges simultaneously, maintaining high S/N ratio even as pixel size decreases.
Solution Approach 2:
The patent employs a composite structure combining multiple organic photoelectric conversion materials with different spectral responses in a stacked configuration. This composite approach enables each pixel to function as a multi-wavelength detector, improving photon capture efficiency and signal quality in small pixels.
3Measurement precision
If interpolation of pixels is performed to generate each color signal, then color images can be reconstructed, but false color artifacts occur
Solution Approach 1:
The patent performs color separation at the photoelectric conversion stage itself, before signal processing and image reconstruction. By physically separating wavelength detection in dedicated layers, the system obtains accurate color signals directly from the sensor, eliminating the need for post-capture interpolation that causes false color artifacts.
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 improves spectroscopic shape, responsivity, and external quantum efficiency by optimizing electron and hole mobility, resulting in a photoelectric conversion element with superior performance.
Implementation Method 1
In the imaging element disclosed in PTL 2, most of incident light is subjected to photoelectric conversion and is read, which results in visible light use efficiency of nearly 100%.
Implementation Method 2
The second organic semiconductor material in a form of a single-layer film has a higher linear absorption coefficient of a maximal light absorption wavelength in a visible light region
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
A photoelectric conversion element according to an embodiment of the present disclosure includes: a first electrode and a second electrode facing each other; and a photoelectric conversion layer provided between the first electrode and the second electrode, and including a first organic semiconductor material, a second organic semiconductor material, and a third organic semiconductor material that have mother skeletons different from one another. The first organic semiconductor material is one of fullerenes and fullerene derivatives. The second organic semiconductor material in a form of a single-layer film has a higher linear absorption coefficient of a maximal light absorption wavelength in a visible light region than a single-layer film of the first organic semiconductor material and a single-layer film of the third organic semiconductor material. The third organic semiconductor material has a value equal to or higher than a HOMO level of the second organic semiconductor material.