Sodium Indium Sulfide Buffer Layer for Thin Film Solar Cells
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Solution Overview
Problem
Current thin-film solar cells using Cu(In,Ga)(S,Se)2 require a cadmium sulfide buffer layer, which is toxic, increases production costs, and has lower efficiency and stability compared to alternative buffer layers, and absorbs incident light, reducing electrical yield.
Innovation Solution
A layer system with a sodium indium sulfide buffer layer (Na x In y-x/3 S) is developed, where x=0.063-0.625 and y=0.681-1.50, having an amorphous or finely crystalline structure, preventing copper diffusion and optimizing band matching for high efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If cadmium sulfide buffer layer is used, then electronic matching between absorber and front electrode is achieved, but toxicity and production costs increase
Solution Approach 1:
The patent extracts and removes cadmium from the buffer layer composition, replacing it with non-toxic materials such as zinc oxide, zinc sulfide, or their mixtures. This eliminates the harmful toxic effects while preserving the buffer layer's essential function of electronic matching between the absorber and front electrode.
Solution Approach 2:
The patent changes the chemical composition parameters of the buffer layer by substituting cadmium-based compounds with zinc-based compounds. This parameter change maintains the required band gap and electronic properties while eliminating toxicity, achieving both functional reliability and environmental safety.
2Reliability
If cadmium sulfide buffer layer is used, then electronic matching is achieved, but production costs increase due to safety precautions and waste disposal
Solution Approach 1:
By extracting cadmium from the buffer layer formulation, the patent eliminates the need for expensive safety precautions, specialized waste disposal facilities, and regulatory compliance measures, thereby reducing production costs while maintaining electronic matching functionality through zinc-based alternatives.
Solution Approach 2:
The patent adopts zinc-based buffer layer materials that are inexpensive, non-toxic, and do not require costly disposal or recycling infrastructure. These materials can be produced using standard manufacturing processes without the need for expensive cadmium handling and waste management systems.
3Reliability
If cadmium sulfide buffer layer is used, then buffer function is achieved, but light absorption increases reducing electrical yield
Solution Approach 1:
The patent changes the optical parameters of the buffer layer by using zinc oxide and zinc sulfide materials with different band gap characteristics compared to cadmium sulfide. These materials have reduced absorption in the visible spectrum, allowing more light to reach the absorber layer and improve electrical yield while maintaining the necessary buffer function.
4Object-affected harmful factors
If alternative buffer layers are used instead of cadmium sulfide, then toxicity is reduced, but efficiency and stability decrease
Solution Approach 1:
The patent employs composite buffer layer structures combining zinc oxide and zinc sulfide in specific ratios and configurations. This composite approach allows optimization of both optical properties (reduced light absorption) and electrical properties (maintained electronic matching), achieving high efficiency and stability without cadmium toxicity.
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 sodium indium sulfide buffer layer achieves high solar cell efficiency and stability, comparable to cadmium sulfide, while being environmentally friendly and cost-effective, with efficiencies up to 13.5% and reduced light absorption, enhancing electrical properties.
Implementation Method 1
Photovoltaic layer systems for solar cells for the direct conversion of sunlight into electrical energy
Implementation Method 2
the incident light is absorbed to a considerable extent even with a CdS layer thickness of a few 10 nm
Implementation Method 3
preventing copper diffusion
Data Source
Figure 1
Figure 2A~2B
Figure 3A~3B
AI summary
The invention concerns a layer system for thin-layer solar cells, said layer system comprising an absorber layer for absorbing light and a buffer layer on the absorber layer, said buffer layer containing NaxIny-x/3S, in which 0.063 ≤ x ≤ 0.625 and 0.681 ≤ y ≤ 1.50.