Carbazole Charge Blocking Layer Reduces Dark Current
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Solution Overview
Problem
Conventional photoelectric conversion devices in solid-state imaging systems face challenges with reduced aperture ratio and light gathering efficiency due to small pixel sizes, leading to increased dark current caused by external voltage application, particularly when using fullerene-based materials, which require an effective charge blocking layer to suppress dark current without compromising heat resistance and molecular design freedom.
Innovation Solution
A photoelectric conversion device incorporating a compound with a specific carbazole structure as the charge blocking layer, which has a high electron affinity of 4.0 eV or more, is used to contact materials with deep electron affinity, effectively suppressing source charges and reducing dark current while maintaining high heat resistance and hole transportability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a voltage is externally applied to enhance photoelectric conversion efficiency or increase response speed, then photoelectric conversion efficiency is improved, but dark current increases due to injection of charge from electrode
Solution Approach 1:
An electron blocking layer is introduced as an intermediary between the electrode and the photoelectric conversion layer. This layer has electron blocking capability (electron affinity of 4.0 eV or more) to prevent electron injection from the electrode while allowing hole transport, thus reducing dark current without compromising photoelectric conversion efficiency.
2Object-generated harmful factors
If a charge blocking layer is provided to suppress injection of electric charge, then dark current is reduced, but heat resistance and molecular design freedom are compromised
Solution Approach 1:
The invention specifies a parameter range for electron affinity (4.0 eV or more) that provides the threshold for effective electron blocking. Within this framework, various carbazole-based compounds with different molecular structures can be selected, maintaining both electron blocking capability and heat resistance while allowing molecular design flexibility for specific applications.
3Productivity
If pixel size is reduced to increase multi-pixel system density, then number of pixels is increased, but aperture ratio and light gathering efficiency are reduced
Solution Approach 1:
The invention utilizes materials with high electron affinity (4.0 eV or more) in the electron blocking layer to achieve effective charge suppression with minimal layer thickness. This allows maintaining small pixel dimensions while compensating for reduced light gathering efficiency through improved charge management, thereby preserving aperture ratio benefits.
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 proposed solution significantly reduces dark current by suppressing source charges at the interface between different materials in the photoelectric conversion film, enhancing the photoelectric conversion efficiency and response speed while maintaining high heat resistance and molecular design flexibility.
Implementation Method 1
photoelectric conversion film contains a compound represented by formula (i)... significantly reduces dark current by suppressing source charges at the interface between different materials in the photoelectric conversion film, enhancing the photoelectric conversion efficiency
Implementation Method 2
providing a charge blocking layer to suppress the injection of an electric charge into the photoelectric conversion layer... the photoelectric conversion device... needs to maximize the photoelectric conversion efficiency and a voltage is sometimes externally applied so as to enhance the photoelectric conversion efficiency
Data Source
Figure 1A~1B
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AI summary
Provided is a photoelectric conversion device comprising a transparent electrically conductive film, a photoelectric conversion film, and an electrically conductive film, wherein the photoelectric conversion film contains a compound represented by the following formula (i): wherein each of R2 to R9 independently represents a hydrogen atom or a substituent, provided that each of at least two out of R3, R4, R7 and R8 independently represents an aryl group, a heterocyclic group or -N(Ra)(Rb), each of Ra and Rb independently represents a hydrogen atom or a substituent, and at least either Ra or Rb represents an aryl group or a heterocyclic group; and R1 represents an alkyl group, an aryl group or a heterocyclic group.