Photoelectric Conversion Element Electron Blocking Layer
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Solution Overview
Problem
Photoelectric conversion elements face challenges in achieving high photoelectric conversion efficiency and fast responsivity while minimizing dark current, especially when subjected to heat treatment, due to limitations in charge transportability and heat resistance of existing materials.
Innovation Solution
A compound with a specific structure, where fused diarylamines are connected through a divalent linking group, enhancing heat resistance and charge transportability without impairing high-speed responsivity and low dark current characteristics, is used as an electron blocking layer to prevent charge injection and reduce dark current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a voltage is externally applied to improve photoelectric conversion efficiency or enhance response speed, then photoelectric conversion efficiency and response speed are improved, but dark current increases due to charge injection from electrode
Solution Approach 1:
An electron blocking layer comprising a specific compound (formula 1) is introduced as an intermediary between the electrode and the photoelectric conversion layer. This layer has high ionization potential (5.0-6.0 eV) that prevents electron injection from the electrode into the photoelectric conversion layer, thereby blocking the harmful injected carriers that cause dark current while allowing the application of external voltage for improving photoelectric conversion efficiency and response speed
2Object-generated harmful factors
If conventional electron blocking materials are used to suppress charge injection, then dark current is reduced, but heat resistance deteriorates
Solution Approach 1:
The invention changes the key parameter of ionization potential to a specific range (5.0-6.0 eV) and introduces a specific molecular structure (formula 1 with fused diarylamine and divalent linking group) that provides both the required electrical properties for electron blocking and sufficient thermal stability. This compound maintains low dark current while exhibiting adequate heat resistance for practical device operation
3Power
If materials with high charge transportability are used to improve photoelectric conversion efficiency, then photoelectric conversion efficiency is improved, but dark current increases due to enhanced charge injection
Solution Approach 1:
The electron blocking layer acts as a selective intermediary that exploits the energy level difference (high ionization potential of 5.0-6.0 eV) to allow efficient charge transport in the photoelectric conversion layer while preventing charge injection at the electrode interface. This enables high photoelectric conversion efficiency through good charge transport in the conversion layer without the penalty of increased dark current from electrode injection
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 effectively reduces dark current and maintains performance even under heat treatment, enabling high photoelectric conversion efficiency and fast responsivity in imaging devices.
Implementation Method 1
an energy gap between WF of the electrode and LUMO of the fullerene (C 60 ) becomes small, as a result, particularly an electron is liable to be injected from the electrode into the photoelectric conversion film and a significant increase of dark current is caused
Implementation Method 2
photoelectric conversion sites are two-dimensionally arrayed in a semiconductor to form pixels and a signal generated by photoelectric conversion in each pixel
Data Source
Figure 1(a)~2
Figure 3~4
AI summary
To provide a photoelectric conversion element capable of functioning as a photoelectric conversion element when a compound having a specific structure is applied to the photoelectric conversion element, causing the element to exhibit a low dark current, and reducing the range of increase in the dark current even when the element is heat-treated, and an imaging device equipped with such a photoelectric conversion element. A photoelectric conversion element having a photoelectric conversion film which is sandwiched between a transparent electrically conductive film and an electrically conductive film and contains a photoelectric conversion layer and an electron blocking layer, wherein the electron blocking layer contains a compound having, as a substituent, a substituted amino group containing three or more ring structures.