Solar Cell Texturing via Parallel Conduit Mask Printing
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Solution Overview
Problem
Current methods for generating light trapping structures on multi-crystalline silicon wafers are cost-inefficient and fail to achieve optimal light trapping properties compared to pyramidal or trough structures, with conventional mask printing techniques being slow, fragile, or unable to meet minimum linewidth specifications.
Innovation Solution
A method involving the use of an array of closely-spaced parallel elongated conduits to print a liquid mask material onto the wafer, allowing for high-speed, single-pass mask printing of patterned light trapping structures such as pyramids or troughs, using capillary channels and a printhead with micro-spring conduits or polyimide cantilevers, enabling efficient etching of exposed areas with HF/Nitric/Acetic Acid mixture.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional mask printing techniques (ink jet, screen printing, flexography) are used, then the process is simple and cost-effective, but the minimum linewidth specifications cannot be met
Solution Approach 1:
The printing system is segmented into multiple independent nozzle arrays arranged in parallel, each capable of depositing mask material with high precision. This segmentation allows each nozzle to target specific linewidth requirements while maintaining overall system simplicity and cost-effectiveness.
2Manufacturing precision
If newer mask printing techniques (micro contact printing, dip pen nanolithography, MEMS approaches) are used, then the linewidth specifications are met, but the processes are too slow, fragile or don't provide sufficient vertical clearance over large areas
Solution Approach 1:
Multiple nozzle arrays are merged into a single integrated printing head that operates simultaneously across large wafer areas. This combination provides sufficient vertical clearance while maintaining high printing speed and meeting linewidth specifications through the coordinated action of multiple nozzles.
Solution Approach 2:
The printing system transitions from single-point or single-line printing to area-wide parallel printing by arranging nozzles in multiple arrays across the wafer surface. This dimensional expansion enables high-speed printing that meets both linewidth specifications and productivity requirements.
3Ease of manufacture
If isotexture process is used, then the process is cost-effective, but the light trapping properties are far from optimal compared to patterned features
Solution Approach 1:
A mask pattern is printed on the wafer surface before the etching process. This preliminary masking action defines the precise locations where etching will occur, enabling the formation of patterned light trapping features (such as pyramids or troughs) that provide superior optical performance while maintaining cost-effectiveness through a straightforward two-step process.
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 significantly increases mask printing speeds, meets minimum linewidth specifications, and reduces production costs, facilitating the creation of high-efficiency patterned light trapping structures on multi-crystalline silicon wafers, improving solar cell efficiency by up to 0.8% absolute compared to isotextured surfaces.
Implementation Method 1
Each conduit includes a capillary channel extending between a base portion and its tip portion... causing sufficient liquid mask material to flow along the capillary channels such that the ejected mask material portions form a mask feature
Data Source
AI summary
Multicrystalline silicon (mc-Si) solar cells having patterned light trapping structures (e.g., pyramid or trough features) are generated by printing a liquid mask material from an array of closely-spaced parallel elongated conduits such that portions of the mc-Si wafer are exposed through openings defined between the printed mask features. Closely spaced mask pattern features are achieved using an array of conduits (e.g., micro-springs or straight polyimide cantilevers), where each conduit includes a slit-type, tube-type or ridge/valley-type liquid guiding channel that extends between a fixed base end and a tip end of the conduit such that mask material supplied from a reservoir is precisely ejected from the tip onto the mc-Si wafer. The exposed planar surface portions are then etched to form the desired patterned light trapping structures (e.g., trough structures).