Halogen-Enriched 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 buffer layer, with CdS being toxic and inefficient alternatives showing instability and lower efficiencies, leading to increased production costs and environmental concerns.
Innovation Solution
A layer system with a halogen-enriched Zn x In 1-x S y buffer layer, where the halogen mole fraction is higher at the interface with the absorber layer, enhancing open-circuit voltage and efficiency, and incorporating zinc to increase short-circuit current, using metal halide compounds like sodium chloride for deposition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If CdS buffer layer is used, then good cell efficiency is achieved, but toxic heavy metal cadmium requires increased safety precautions and higher production costs
Solution Approach 1:
The invention extracts and removes the harmful cadmium element from the buffer layer composition while retaining the essential functional properties. The buffer layer is reformulated using only zinc, indium, sulfur, and halogen elements, completely eliminating cadmium from the solar cell structure while maintaining good cell efficiency.
Solution Approach 2:
The invention changes the chemical composition parameters of the buffer layer by replacing cadmium-containing compounds with cadmium-free zinc indium sulfide halide compounds. The specific compositional ranges (0.1 ≤ x ≤ 0.9 for Zn x In 1-x S y Zr w) and halogen content (0.01 ≤ z ≤ 0.5) are optimized to achieve both non-toxicity and high efficiency.
2Object-affected harmful factors
If alternative buffer materials like ZnMgO or In(O,OH) are used, then cadmium toxicity is reduced, but excessive instabilities and hysteresis effects occur
Solution Approach 1:
The invention creates a composite buffer layer material combining zinc indium sulfide with halogen elements (chlorine, bromine, or iodine). This composite structure integrates the stability of zinc sulfide with the beneficial electronic properties introduced by indium and halogen, achieving both non-toxicity and enhanced reliability under various environmental conditions.
3Use of energy by moving object
If CdS buffer layer is used, then light absorption occurs, but most absorbed light is lost due to immediate charge carrier recombination in the buffer layer
Solution Approach 1:
The invention applies local quality optimization by creating a buffer layer with specific compositional gradients and controlled thickness (5-50 nm). The halogen content and zinc-indium ratio are locally optimized to minimize recombination centers while maintaining necessary optical absorption, ensuring that light absorption does not lead to excessive recombination losses.
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 achieves high efficiency and stability for thin-film solar cells, reducing production costs and environmental impact by eliminating toxic substances and improving performance through targeted halogen and zinc distribution in the buffer layer.
Implementation Method 1
most of the incident light is absorbed even with a CdS layer thickness of a few 10 nm. The light absorbed in the buffer layer is lost for the electrical yield, since the generated charge carriers recombine in this layer immediately
Implementation Method 2
using various non-wet chemical methods, for example thermal evaporation, ion layer gas reaction, cathode sputtering (sputtering), atomic layer deposition (ALD) or spray pyrolysis
Data Source
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AI summary
The invention relates to a layer system (1) for thin-film solar cells (100) and solar panels, said system comprising an absorber layer (4) containing a chalcogenide semiconductor and a buffer layer (5) which is arranged on the absorber layer (4) and contains halogen-enriched ZnxIn1-xSy where 0.01 <= x <= 0.9 and 1 <= y <= 2. The buffer layer (5) consists of a first layer region (5.1) adjoining the absorber layer (4) and containing a halogen mole fraction Ai and a second layer region (5.1) adjoining the first layer region (5.2) and containing a halogen mole fraction A2. The ratio of A1/A2 is >= 2 and the layer thickness (d1) of the first layer region (5.1) <= 50% of the layer thickness (d) of the buffer layer (5).