Amorphous In2(S1-x,Se)x Buffer Layer for Solar Cells

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Solution Overview

Problem

Current thin-film solar cells based on Cu(In,Ga)(S,Se)2 require a buffer layer, but existing buffer materials like CdS are toxic, costly, and inefficient, leading to reduced solar cell efficiency and stability due to light, heat, and moisture exposure.

Innovation Solution

A layer system comprising an amorphous In2(S1-x,Se)x buffer layer with a chalcopyrite structure, which is deposited in a vacuum process, providing high efficiency and stability without toxic substances, and allowing for lower production costs and environmental impact.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If CdS buffer layer is used, then electronic matching between absorber and front electrode is improved, but toxicity and production costs increase

Engineering Contradiction:

Improveelectronic matchingVSAvoidtoxicity

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent replaces toxic CdS with In2(S1-x,Sex)3+δ which can be deposited as an amorphous layer without requiring the same level of safety precautions and waste disposal infrastructure, effectively substituting a harmful material with a benign alternative that achieves the same electronic matching function

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

Solution Approach 2:

The patent changes the material composition from cadmium-based to indium-based compounds, specifically using In2(S1-x,Sex)3+δ with adjustable sulfur and selenium content to optimize both the electronic properties and environmental compatibility of the buffer layer

Inventive Principle:

Principle #35Parameter changes

2Reliability

If CdS buffer layer is used, then electronic matching is improved, but manufacturing complexity and safety precautions increase

Engineering Contradiction:

Improveelectronic matchingVSAvoidmanufacturing complexity

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

Solution Approach 2:

Inventive Principle:

Principle #35Parameter changes

3Reliability

If CdS buffer layer is used, then buffer function is achieved, but light absorption increases reducing cell efficiency

Engineering Contradiction:

Improvebuffer functionVSAvoidlight absorption

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The patent modifies the band gap of the buffer layer by adjusting the sulfur and selenium content in In2(S1-x,Sex)3+δ, creating an optimal energy level alignment that maintains electronic function while minimizing optical absorption in the visible spectrum

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent uses a composite approach by combining indium sulfide and indium selenide in specific ratios within the In2(S1-x,Sex)3+δ structure, allowing simultaneous optimization of electronic band alignment and optical transparency properties

Inventive Principle:

Principle #40Composite materials

4Reliability

If CdS buffer layer is used, then buffer function is achieved, but stability under light, heat and moisture exposure deteriorates

Engineering Contradiction:

Improvebuffer functionVSAvoidstability

Core Design Contradiction:

ReliabilityVSStability of the object's composition

Solution Approach 1:

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

Inventive Principle:

Principle #40Composite materials

5Manufacturing precision

If wet-chemical CBD process is used for CdS deposition, then buffer layer quality is improved, but process compatibility with production flow deteriorates

Engineering Contradiction:

Improvebuffer layer qualityVSAvoidprocess compatibility

Core Design Contradiction:

Manufacturing precisionVSProductivity

Solution Approach 1:

The patent replaces the wet-chemical CBD process with a vacuum-based physical vapor deposition process for depositing In2(S1-x,Sex)3+δ, eliminating the need for aqueous chemistry and enabling direct integration into existing vacuum-based thin-film fabrication lines

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent uses vacuum deposition to create an inert environment during buffer layer formation, avoiding the need for chemical baths and enabling process integration with other vacuum-based semiconductor fabrication steps

Inventive Principle:

Principle #39Inert atmosphere (Inert environment)

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 amorphous In2(S1-x,Se)x buffer layer achieves solar cell efficiencies comparable to CdS, with improved stability against temperature, light, and moisture, and reduced light absorption, resulting in higher electrical output and cost-effectiveness.

Implementation Method 1

Thin-film systems for solar cells and solar modules are well known and available on the market in various designs, depending on the substrate and the materials applied. The materials are selected in such a way that the incident solar spectrum is used to the maximum.

Methodology Applied

Scientific EffectPhotovoltaic effect: Photovoltaic Effect

Implementation Method 2

CdS is a direct semiconductor with a direct electronic band gap of around 2.4 eV and is therefore already present in a Cu(In,Ga)(S,Se) 2/CdS/ZnO solar cell at CdS Layer thicknesses of a few 10 nm absorb the incident light.

Methodology Applied

Scientific EffectLight absorption: Absorption (EM radiation)

Implementation Method 3

It also offers protection against sputter damage in the subsequent process step of depositing the front electrode using DC magnetron sputtering.

Methodology Applied

Scientific EffectSputter damage protection: Sputtering

Data Source

PatentEP2281310B1Layer system for solar cells

Publication Date: 2019.09.25 CNBM RESEARCH INSTITUTE FOR ADVANCED GLASS MATERIALS GROUP CO LTD

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AI summary

The present invention relates to a layer system (1) for thin-film solar cells and solar modules based on CIS-absorbers (4). The layer system (1) according to the invention has a buffer layer (4) made of In2(S1−x,Sex)3+δ, wherein 0≦̸x≦̸1 and −1≦̸δ≦̸1. Additionally, the buffer layer (5) is amorphously designed. With this buffer layer (5), the disadvantages of CdS-buffers frequently used to date, namely toxicity and poor process integration, are overcome, whereby in addition to high efficiency, high long-term stability is also achieved; and thus again the disadvantages of conventional buffer layers alternative to CdS do not exist.