Sputtering Target Barrier Layers for CIS Solar Cells
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Solution Overview
Problem
In the production of thin-film solar cells, the incorporation of iron (Fe), nickel (Ni), and chromium (Cr) impurities from stainless steel support structures into sodium-containing molybdenum sputtering targets leads to decreased conversion efficiency due to diffusion into the copper indium selenide (CIS) absorber layer, affecting the electrical and optical properties of the solar cell.
Innovation Solution
A sputtering target with a support structure comprising materials like Mo, W, Ta, V, Ti, or Zr, and additional barrier layers such as Cr and Nb are used to prevent the diffusion of Fe, Ni, and Cr into the alkali-containing transition metal sputtering layer, thereby minimizing their incorporation into the CIS absorber layer during the deposition process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If stainless steel support structures are used in sputtering targets, then mechanical strength and structural stability are improved, but iron, nickel, and chromium impurities diffuse into the CIS absorber layer causing decreased conversion efficiency
Solution Approach 1:
A diffusion barrier layer comprising tungsten, molybdenum, or their alloys is introduced as an intermediary between the stainless steel support structure and the CIS absorber layer. This barrier layer prevents the diffusion of Fe, Ni, and Cr impurities from the stainless steel into the absorber layer while maintaining structural integrity and mechanical strength of the overall target assembly.
Solution Approach 2:
The sputtering target is segmented into distinct functional layers: a stainless steel support structure providing mechanical strength, a diffusion barrier layer preventing impurity migration, and a CIS absorber layer for photovoltaic function. This segmentation isolates the harmful diffusion pathway while preserving the beneficial mechanical properties of stainless steel.
2Reliability
If barrier layers are added to prevent impurity diffusion, then conversion efficiency is improved, but device complexity and manufacturing steps increase
Solution Approach 1:
The barrier layer is optimized with specific thickness parameters (sufficient to block diffusion but thin enough to minimize complexity) and controlled composition ratios of tungsten, molybdenum, or their alloys. By carefully controlling these parameters, the barrier layer achieves effective impurity prevention while keeping the overall target structure manageable and manufacturable.
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 barrier layers significantly reduces the concentration of Fe, Ni, and Cr in the sputtering layer and subsequently in the solar cell, enhancing the performance and efficiency of the CIS-based solar cells by minimizing the negative impact of these impurities on the absorber layer.
Implementation Method 1
sputtering the first electrode comprising an alkali-containing transition metal layer from a target
Implementation Method 2
additional barrier layers such as Cr and Nb are used to prevent the diffusion of Fe, Ni, and Cr into the alkali-containing transition metal sputtering layer
Data Source
AI summary
A sputtering target, including a sputtering layer and a support structure. The sputtering layer includes an alkali-containing transition metal. The support structure includes a second material that does not negatively impact the performance of a copper indium selenide (CIS) based semiconductor absorber layer of a solar cell. The sputtering layer directly contacts the second material.