Resistive Transparent Buffer Layer for CdTe Photovoltaic Devices
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Solution Overview
Problem
Reducing the thickness of layers between the window glass and cadmium telluride in cadmium telluride photovoltaic devices to improve energy conversion efficiency is hindered by interface defects such as pinholes, which lower open circuit voltage and fill factor.
Innovation Solution
A method involving the deposition of a resistive transparent buffer thin film layer using cold sputtering with a water vapor atmosphere followed by annealing, which improves adhesion and reduces defects, allowing for a thinner cadmium sulfide layer without adverse effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the thickness of layers between window glass and cadmium telluride is reduced, then energy conversion efficiency is improved, but interface defects such as pinholes increase
Solution Approach 1:
A zinc tin oxide buffer layer is introduced as an intermediary layer between the cadmium sulfide layer and the cadmium telluride layer. This buffer layer prevents direct contact between the CdS and CdTe layers, eliminating pinhole formation while maintaining thin layer thickness for high efficiency. The buffer layer acts as a mediator that preserves interface quality without compromising the reduced thickness design.
Solution Approach 2:
The patent uses a composite structure comprising multiple materials (transparent conductive oxide, cadmium sulfide, zinc tin oxide buffer layer, and cadmium telluride) to achieve both thin layer thickness and high interface quality. The composite material system allows each layer to perform its specific function while working together to prevent defects and maximize energy conversion efficiency.
2Productivity
If the thickness of cadmium sulfide layer is reduced, then shorter wavelength radiation reaches cadmium telluride, but pinhole defects increase
Solution Approach 1:
The zinc tin oxide buffer layer serves as a protective intermediary between the thin cadmium sulfide layer and the cadmium telluride layer. It prevents pinhole formation at the interface while allowing the cadmium sulfide layer to remain thin for optimal shorter wavelength radiation transmission to the cadmium telluride layer.
3Productivity
If layer thickness is reduced, then radiation absorption is minimized, but adhesion between layers deteriorates
Solution Approach 1:
The zinc tin oxide buffer layer acts as an adhesion-promoting intermediary between layers. It provides a stable interface that enhances bonding between the cadmium sulfide and cadmium telluride layers, compensating for potential adhesion issues that arise from reduced layer thickness while maintaining optimal radiation transmission.
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 method enhances the adhesion and interaction between layers, reducing pinhole formation and improving the overall conversion efficiency and device lifetime by minimizing radiation absorption and maximizing blue light reach to the cadmium telluride layer.
Implementation Method 1
cold sputtering a resistive transparent buffer layer on a substrate
Implementation Method 2
The resistive transparent buffer layer can then be annealed at an anneal temperature of about 450° C to about 700° C
Data Source
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AI summary
Methods for depositing a resistive transparent buffer thin film layer (16) on a substrate (12) are provided. The methods can include cold sputtering a resistive transparent buffer layer on a substrate (e.g., at a sputtering temperature of about 10° C to about 100° C) in a sputtering atmosphere comprising about 0.01% to about 5% by volume water vapor (e.g., about 0.05% to about 1% by volume water vapor). The resistive transparent buffer layer can then be annealed at an anneal temperature of about 450° C to about 700° C. The methods of depositing a resistive transparent buffer thin film layer on a substrate can be used in a method of manufacturing a cadmium thin film photovoltaic device by forming cadmium sulfide layer (18) on the resistive transparent buffer layer, and forming a cadmium telluride layer (22) on the cadmium sulfide layer.