Core-Shell Nanoparticles for CIGS Solar Cells
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Solution Overview
Problem
Conventional solution-phase deposition methods for CIGS thin-film photovoltaic devices face challenges such as gallium migration, uneven gallium distribution, and the need for harsh selenization processes, which affect the efficiency and cost-effectiveness of the solar cells.
Innovation Solution
The development of CIGS-type core-shell nanoparticles with a quaternary or ternary metal chalcogenide core surrounded by a binary metal chalcogenide shell, which are deposited and fused into thin films, preventing gallium migration and allowing for copper-rich environments without the need for harsh selenization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If solution-phase deposition is used to deposit CIGS nanoparticles, then fabrication cost is reduced, but gallium migration occurs during grain growth resulting in uneven gallium distribution
Solution Approach 1:
The patent extracts gallium into a separate shell layer surrounding the CIGS core, creating a core-shell structure where the shell serves as a gallium reservoir. This prevents gallium migration during grain growth by providing a controlled diffusion source, thereby maintaining uniform gallium distribution while using low-cost solution-phase deposition.
Solution Approach 2:
The patent performs preliminary gallium enrichment by forming a gallium-containing shell around the CIGS core nanoparticles before the grain growth process. This preliminary action ensures that gallium is pre-positioned around the grains, preventing migration and compositional gradients during subsequent thermal processing.
2Shape
If copper-rich environment is used to promote grain growth, then grain size increases, but electronic performance deteriorates due to excess copper
Solution Approach 1:
The patent introduces a gallium-containing shell as an intermediary between the copper-rich growth environment and the CIGS core. The shell acts as a buffer that allows copper to be present during grain growth without allowing excess copper to contaminate the core, thus enabling large grain formation while maintaining electronic performance.
Solution Approach 2:
The patent creates local quality differences by having a copper-rich environment externally while maintaining a controlled stoichiometry within the core-shell structure. The shell region accommodates the copper-rich conditions necessary for grain growth, while the core maintains the proper Cu:In:Ga ratio for optimal electronic performance.
3Shape
If harsh selenization process is used to achieve volume expansion, then grain growth is improved, but PV cell contact is inadvertently selenized impeding its electronic performance
Solution Approach 1:
The patent extracts the volume expansion function from the harsh selenization process by incorporating pre-formed shell structures that provide the necessary volume increase during controlled annealing. This eliminates the need for aggressive selenization that would otherwise be required to achieve sufficient grain growth, thereby preventing contact selenization.
Solution Approach 2:
The patent changes the processing parameters by using core-shell nanoparticles with controlled shell thickness and composition, allowing volume expansion and grain growth to occur at lower temperatures and shorter times compared to conventional selenization, thus avoiding damage to the PV cell contact.
4Loss of substance
If KCN etching is used to remove unwanted copper, then copper is removed from the film, but the process is time-consuming and inefficient
Solution Approach 1:
The patent performs preliminary copper removal by controlling the nanoparticle synthesis to prevent excess copper formation in the first place, rather than requiring subsequent etching steps. The core-shell structure is formed with controlled stoichiometry that minimizes unwanted copper, eliminating or reducing the need for time-consuming KCN etching processes.
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
This approach results in high gallium content, enhanced grain growth, improved electrical properties, and reduced processing costs by preventing gallium migration and eliminating the need for harsh selenization, leading to increased efficiency and cost-effectiveness in solar cell production.
Implementation Method 1
The solution-phase deposition may be done using oxide particles of the component metals followed by reduction with H2 and a reactive sintering with a selenium containing gas
Implementation Method 2
the nanoparticles coalesce to form large-grained thin films. The deposited particles may then be melted or fused into a thin absorber film
Implementation Method 3
During grain growth gallium particles tend to migrate towards one film side resulting in an uneven gallium distribution
Implementation Method 4
gallium particles tend to migrate towards one film side
Implementation Method 5
Volume expansion may be achieved by reacting the relatively small (ionic radius) sulfide with the larger selenide (e.g., react sulfide with selenium atmospheres)
Implementation Method 6
a reactive sintering with a selenium containing gas (e.g., H2Se)
Data Source
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AI summary
A method for the preparation of CIGS-type core-shell nanoparticles produces core-shell nanoparticles that may include a quaternary or ternary metal chalcogenide core. The core may be substantially surrounded by a binary metal chalcogenide shell. A core- shell nanoparticle may be deposited on a PV cell contact (e.g., a molybdenum electrode) via solution-phase deposition. The deposited particles may then be melted or fused into a thin absorber film for use in a photovoltaic device.