Transparent Front Electrode for Photovoltaic Devices
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Solution Overview
Problem
Existing silver-based photovoltaic devices face challenges with durability during manufacturing, storage, and use, particularly due to high processing temperatures, and require improved sheet resistance, light transmittance, and buffer layer performance, while also being cost-effective and easy to manufacture without additional heating steps.
Innovation Solution
A transparent front electrode structure comprising a glass substrate with a lower anti-reflection layer of silicon nitride, a middle layer of zinc tin oxide, a silver-based functional layer, and an upper anti-reflection layer with nickel chromium and aluminum-doped zinc oxide barrier layers, deposited at room temperature using sputtering, which enhances durability and optical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thick ZAO TCO layer is used to achieve desired conductivity, then sheet resistance is improved, but manufacturing complexity increases due to difficulty in preparation without heating
Solution Approach 1:
The patent changes the material composition parameters by introducing a multi-layer structure with specific oxide ratios (ZnO:SnO2 in 9:1 to 1:9 ratio) and controlled thicknesses (5-50nm each layer). This compositional parameter change enables achieving desired conductivity without requiring thick layers or additional heating steps, as the specific material ratios provide optimal electrical properties at room temperature deposition
Solution Approach 2:
The patent segments the TCO layer into multiple thin sub-layers (first TCO layer 5-50nm, second TCO layer 5-50nm) rather than using a single thick layer. This segmentation allows each layer to contribute to conductivity while maintaining ease of deposition at room temperature, and the combined effect achieves the desired sheet resistance without requiring a single thick layer that would be difficult to manufacture
2Reliability
If thinner semiconductor layers are used to improve stability, then durability is improved, but light absorption decreases and cell efficiency is reduced
Solution Approach 1:
The patent uses composite material structures with multiple oxide layers (ZnO, SnO2, and their combinations) in the TCO region, each layer contributing different properties. The ZnO provides stability and the SnO2 enhances conductivity and light absorption. This composite approach allows thin layers to achieve both stability and sufficient light absorption through synergistic material properties
Solution Approach 2:
The patent applies local quality optimization by creating regions with different material compositions and thicknesses. The TCO layers have specific ZnO:SnO2 ratios optimized for their local function (conductivity vs. stability), while the semiconductor layers have graded structures. This local optimization allows thin layers to perform multiple functions simultaneously, maintaining stability while preserving light absorption in specific regions
3Reliability
If additional heating steps are added during manufacturing, then material properties can be improved, but manufacturing cost and complexity increase
Solution Approach 1:
The patent designs the TCO material composition to be self-sufficient for achieving desired properties at room temperature. The specific ZnO:SnO2 ratios and layer structures provide inherent stability and conductivity without requiring post-deposition heating treatment. The materials self-organize into functional structures during room temperature deposition, eliminating the need for additional heating steps and reducing manufacturing cost
4Ease of manufacture
If conventional deposition methods are used, then manufacturing is simpler, but pinholes increase and device reliability decreases
Solution Approach 1:
The patent segments the TCO deposition into multiple thin layers (5-50nm each) rather than depositing a single thick layer. This segmentation ensures complete coverage and adhesion at each deposition stage, preventing pinhole formation. The multiple thin layers overlap and interlock, creating a pinhole-free structure while maintaining simplicity in the deposition process using conventional techniques
Solution Approach 2:
The patent changes the deposition parameters by controlling layer thickness (5-50nm per layer) and material composition (ZnO:SnO2 ratios). These parameter changes optimize the deposition process to achieve dense, pinhole-free films at room temperature using conventional methods. The specific thickness and composition parameters ensure proper nucleation and growth without requiring advanced deposition equipment
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 provides robust, cost-effective photovoltaic devices with improved sheet resistance, light transmittance, and buffer layer performance, capable of withstanding high processing temperatures and reducing pinholes, thus enhancing the efficiency and reliability of CdTe-based PV cells.
Implementation Method 1
deposited at room temperature using sputtering
Data Source
Figure 1~2
Figure 3~4
AI summary
A transparent front electrode for a photovoltaic device comprising at least the following layers in sequence: -a glass substrate; -a lower anti-reflection layer, comprising in sequence from the glass substrate *a base layer of an (oxi)nitride of silicon and/or an (oxi)nitride of aluminium, *a middle layer of an oxide of Zn and Sn, *a top layer of an oxide of Zn; -a silver-based functional layer; and -an upper anti-reflection layer comprising in sequence from the silver-based functional layer *a first barrier layer of an oxide of Ni and Cr, *a second barrier layer of an Al-doped oxide of Zn,and *a buffer layer; wherein the first barrier layer of an oxide of Ni and Cris located directly in contact with the silver-based functional layer or the first barrier layer of an oxide of Ni and Cr is separated from the silver-based functional layer by one or more additional barrier layers.