Titanium Nitride Electrode Adherence in Organic Photoelectric Conversion
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Solution Overview
Problem
The configuration of providing a pixel electrode composed of transparent conductive oxide (TCO) on a glass substrate suffers from decreased adherence to the organic photoelectric conversion layer, leading to increased dark current due to thermal expansion differences and surface unevenness, which deteriorates signal-to-noise ratio.
Innovation Solution
A photoelectric conversion element with a lower electrode made of titanium nitride (TiN) on a substrate enhances adherence to the organic layer and suppresses dark current by improving flatness and heat resistance, using a composition with 70% or more TiN and 10% or less titanium oxide, and a work function around 4.6 eV, deposited using chemical vapor deposition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If TCO is used for the pixel electrode on a glass substrate, then transparency and light transmittance are improved, but adherence to the organic photoelectric conversion layer deteriorates
Solution Approach 1:
The pixel electrode is constructed as a composite structure with multiple layers including TCO (for transparency), metal layers (for conductivity and mechanical strength), and adhesion promotion layers. This composite approach allows the electrode to simultaneously achieve high light transmittance through the TCO layer while maintaining strong adherence through the metal and adhesion layers, resolving the contradiction between transparency and adherence.
2Illumination intensity
If TCO is used for the pixel electrode, then light transmittance is improved, but dark current increases due to thermal expansion differences
Solution Approach 1:
The invention introduces intermediate layers with specific thermal expansion coefficients between the TCO pixel electrode and the glass substrate. These intermediate layers act as thermal expansion buffers, absorbing the stress caused by differential thermal expansion during heating processes. This parameter control approach prevents the formation of cracks and maintains the integrity of the TCO layer, thereby suppressing dark current while preserving light transmittance.
3Measurement precision
If pixel size is reduced for miniaturization, then resolution is improved, but aperture ratio decreases leading to reduced light sensitivity
Solution Approach 1:
The invention employs extremely thin film structures for the photoelectric conversion layer and electrode layers, allowing the pixel electrode to maintain high light transmittance even when pixel size is reduced. The thin film approach minimizes the thickness of non-light-receiving components, thereby maintaining a high aperture ratio despite pixel miniaturization, which preserves light sensitivity while enabling higher resolution.
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 use of titanium nitride as the lower electrode significantly enhances adherence to the organic layer and reduces dark current, maintaining high electrical conductivity and photoelectric conversion efficiency even at reduced pixel sizes, while minimizing thermal effects.
Implementation Method 1
a photoelectric conversion element where a pixel electrode is provided on a substrate, an organic layer containing a photoelectric conversion layer is provided on the pixel electrode, and a counter electrode is provided on the organic layer
Implementation Method 2
difference in the coefficient of thermal expansion between the pixel electrode and the organic layer causes the dark current to increase due to heat
Data Source
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AI summary
A photoelectric conversion element includes, in the following order: a substrate; a lower electrode containing titanium nitride; an organic layer including a photoelectric conversion layer; and an upper electrode containing a transparent electrode material.