Solar Cell Buffer Layer Segmentation for Efficiency
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Solution Overview
Problem
The use of zinc sulfide (ZnS) as a buffer layer in solar cells results in high resistance, limiting its thickness and potentially damaging the upper layers during subsequent processing, which affects the photoelectric conversion efficiency.
Innovation Solution
A method of forming multiple buffer layers, including zinc sulfide (ZnS) and zinc oxide (ZnO), by adjusting the ammonia water concentration in the deposition process, allowing for simultaneous deposition of the first and second buffer layers to compensate for the thinness of the ZnS layer and reduce damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If zinc sulfide (ZnS) is used as the buffer layer, then the buffer layer can be formed without cadmium (Cd), but the resistance of the buffer layer becomes higher, limiting its thickness and potentially damaging the upper layers during subsequent processing
Solution Approach 1:
The buffer layer is divided into multiple layers: a first buffer layer (ZnS) deposited at a first temperature, and a second buffer layer (ZnO or Zn(OH)2) deposited at a second temperature higher than the first. This segmentation allows each layer to perform its specific function - the ZnS layer provides Cd-free buffering while the ZnO/Zn(OH)2 layer compensates for thickness limitations and protects against damage during processing.
Solution Approach 2:
The deposition temperature is changed between forming the first and second buffer layers. The first buffer layer is deposited at a lower temperature, while the second buffer layer is deposited at a higher temperature. This parameter change enables control over the crystal structure and properties of each layer, optimizing both the Cd-free requirement and the damage prevention capability.
2Object-affected harmful factors
If the thickness of the ZnS buffer layer is increased to reduce damage, then the resistance problem worsens, but if the thickness is reduced to maintain low resistance, then the protective function is compromised
Solution Approach 1:
The buffer layer is divided into multiple layers: a first buffer layer (ZnS) deposited at a first temperature, and a second buffer layer (ZnO or Zn(OH)2) deposited at a second temperature higher than the first. This segmentation allows each layer to perform its specific function - the ZnS layer provides Cd-free buffering while the ZnO/Zn(OH)2 layer compensates for thickness limitations and protects against damage during processing.
Solution Approach 2:
The buffer layer is formed as a composite structure combining ZnS and ZnO/Zn(OH)2 layers. This composite approach leverages the advantages of both materials - ZnS provides effective buffering without cadmium, while ZnO/Zn(OH)2 offers better electrical properties and structural stability, allowing the composite layer to protect against damage without excessive resistance.
3Reliability
If multiple buffer layers are formed separately, then the photoelectric conversion efficiency improves, but the fabrication process becomes more complex and costly
Solution Approach 1:
The formation of the first buffer layer (ZnS) and the second buffer layer (ZnO or Zn(OH)2) is merged into a single continuous deposition process. The substrate is sequentially exposed to different deposition conditions without removing it from the deposition chamber, combining what would traditionally be separate fabrication steps into one integrated process, thereby reducing complexity while maintaining the benefits of multiple layers.
Solution Approach 2:
The deposition apparatus is designed to perform multiple functions: it can deposit different materials (ZnS and ZnO/Zn(OH)2) and control different deposition temperatures within the same processing cycle. This multi-functionality allows the single deposition process to achieve what would otherwise require multiple separate equipment and process steps, reducing overall fabrication complexity.
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 enhances the photoelectric conversion efficiency of solar cells, reduces process costs, and improves overall efficiency by allowing for the formation of multiple buffer layers in a single process, minimizing damage to the light absorbing layer.
Implementation Method 1
A method of forming multiple buffer layers, including zinc sulfide (ZnS) and zinc oxide (ZnO), by adjusting the ammonia water concentration in the deposition process
Data Source
AI summary
A solar cell includes a substrate, a back electrode layer on the substrate, a light absorbing layer on the back electrode layer, a buffer layer on the light absorbing layer, and a front electrode layer on the buffer layer. The buffer layer includes at least one of zinc sulfide (ZnS), zinc oxide (ZnO) and zinc hydroxide (Zn(OH)2). A method of fabricating the solar cell includes forming a back electrode layer on a substrate, forming a light absorbing layer on the back electrode layer, forming a first buffer layer on the light absorbing layer, and forming a second buffer layer on the first buffer layer. The first buffer layer or the second buffer layer includes at least one of zinc sulfide (ZnS), zinc oxide (ZnO), and zinc hydroxide (Zn(OH)2).