Heated Pocket Deposition for Uniform CdTe Thin Film Growth
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Solution Overview
Problem
The manufacturing of cadmium telluride (CdTe) photovoltaic modules faces challenges in achieving high deposition rates and uniformity of thin films using existing vacuum deposition techniques, which are costly and inefficient, limiting their competitiveness with fossil fuel technologies.
Innovation Solution
The use of a thermal sublimation source block with an array of holes in a vacuum chamber for heated pocket deposition, where the deposition material sublimates uniformly from each hole, maintaining a constant sublimation surface area and rate, and radiative heat transfer is controlled to ensure consistent film deposition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional vacuum deposition techniques are used, then deposition can be performed in modest vacuum levels, but deposition rates are low and manufacturing costs are high
Solution Approach 1:
The source block is segmented into multiple cavities, each containing deposition material in a separate pocket. This segmentation allows multiple deposition zones to operate simultaneously, increasing overall deposition rate while maintaining control over each individual zone
Solution Approach 2:
The deposition material is nested within cavities that are formed into the source block. The material is positioned inside these nested structures, allowing the source block to maintain a compact form while providing controlled sublimation surfaces at multiple levels
2Manufacturing precision
If conventional deposition techniques are used, then equipment complexity can be reduced, but film uniformity and deposition rate are insufficient
Solution Approach 1:
Different cavities in the source block can contain different deposition materials (e.g., CdS in some cavities, CdTe in others), allowing local customization of deposition properties. Each cavity is optimized for its specific material, ensuring uniform film formation across the entire substrate surface
Solution Approach 2:
The source block is designed with multiple cavities that can be independently controlled or selectively activated. This dynamic configuration allows adjustment of deposition parameters for different regions, maintaining film uniformity while managing structural complexity
3Productivity
If higher deposition rates are achieved, then productivity increases, but deposition uniformity and control are compromised
Solution Approach 1:
Multiple cavities in the source block sublime deposition material simultaneously and continuously, providing a sustained high-rate deposition process. The continuous operation of multiple zones maintains both high productivity and uniform film formation across the substrate
Solution Approach 2:
The output from multiple cavities is merged onto a single substrate surface, combining the deposition flux from several sources. This merging effect increases overall deposition rate while the distributed source configuration maintains uniformity across the film
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 method achieves high deposition rates for CdTe and CdS thin films, ten to one hundred times higher than other techniques, with uniformity and efficiency, reducing costs and improving the competitiveness of CdTe/CdS photovoltaic modules.
Implementation Method 1
a heat source configured to apply a heat flux to the thermal sublimation source block to sublimate the material within each of the plurality of holes
Implementation Method 2
the source block is configured such that radiative heat transfer between a portion of the surface of the substrate and the material within each of the plurality of holes is substantially constant during exposure of the substrate
Implementation Method 3
vacuum sublimation of CdS and CdTe thin films can result in thin-film deposition rates ten to one hundred times higher than other suitable deposition techniques
Data Source
AI summary
An apparatus and method for manufacturing thin-film CdS/CdTe photovoltaic modules in a vacuum environment. The apparatus deposits CdS and CdTe layers onto a substrate using heated pocket deposition, a form of physical vapor deposition (PVD) in which a material thermally sublimes from a thermal sublimation source block and is deposited onto a substrate. The thermal sublimation source block includes a pocket having a lower surface into which an array of holes is formed to house plugs of deposition material. Upon heating, deposition material sublimes from a surface of each plug of deposition material, and the surface of each plug regresses into its corresponding hole while maintaining a constant surface area. The sublimation surface area of deposition material across the pocket remains substantially constant during an extended deposition process, and the deposition material is substantially free of undesired thermal radiation from the substrate. As such, the thermal sublimation source block provides a temporally- and spatially-uniform thin film deposition rate across the lower surface of the substrate.