Monocrystalline Silicon Surface Preparation for Low Reflectance Texturing
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Solution Overview
Problem
Existing methods for preparing monocrystalline silicon solar cell surfaces for texturization often result in high reflectance and reflectance standard deviation due to the formation of silicate salts, which can be attributed to large pH and temperature differences between preparatory steps, leading to suboptimal light trapping and energy conversion efficiency.
Innovation Solution
A method involving a pre-cleaning step with ozonated deionized water, followed by a saw damage removal step using a diluted alkaline solution, and a rinsing step with a pH-adjusted aqueous medium to minimize pH shock, and subsequent oxidation with ozonated deionized water to create a clean and hydrophilic surface, reducing silicate salt formation and enhancing textural homogeneity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a pre-cleaning step with ozonated deionized water is applied before SDR, then surface contamination is removed, but silicate salts form on the surface due to large pH and temperature differences
Solution Approach 1:
The patent applies parameter changes by adjusting the pH of the rinsing water to be alkaline (pH 9-11) to match the SDR step conditions, and controlling the temperature difference between steps to be less than 10°C. This prevents silicate salt formation by eliminating the large pH and temperature shocks that cause precipitation, while still achieving effective surface cleaning through the pre-cleaning ozonated water step.
Solution Approach 2:
The patent introduces an intermediary rinsing step with alkaline pH water between the pre-cleaning and SDR steps. This intermediary step acts as a buffer that transitions the surface conditions gradually rather than directly exposing the surface to extreme pH changes, thereby preventing silicate salt precipitation while maintaining cleaning effectiveness.
2Manufacturing precision
If conventional SDR is performed with high concentration alkaline solution, then saw damage is removed, but reflectance remains high due to silicate salt formation
Solution Approach 1:
The patent changes the pH parameter of the rinsing water to alkaline range (pH 9-11) and controls temperature difference to prevent silicate salt formation. This eliminates the harmful reflectance effect caused by salt precipitation, while the SDR step with concentrated alkaline solution continues to effectively remove saw damage through chemical etching of the damaged silicon layer.
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 achieves a reflectance below 10% at 700 nm with reduced standard deviation, improving the energy conversion efficiency of monocrystalline silicon solar cells to up to 22.5% by ensuring a homogeneous distribution of pyramid sizes and spaces on the surface, while being cost-effective and compatible with current post-texturing processes.
Implementation Method 1
removing contaminants from the surface by contacting the surface with a cleaning solution
Implementation Method 2
contacting the surface with ozonated deionized water
Implementation Method 3
etching the pre-cleaned surface with an aqueous solution comprising from 12 to 19% by weight, preferably 13 to 18% of KOH and/or NaOH
Implementation Method 4
rinsing the etched surface with an aqueous medium at pH from 7 to 10, preferably from 7 to 8
Implementation Method 5
contacting the rinsed etched surface with ozonated deionized water at pH from 2 to 4.5
Implementation Method 6
creating a clean and hydrophilic surface
Data Source
Figure 1
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Figure 3a~3d
AI summary
A method for preparing a monocrystalline silicon substrate surface for a subsequent texturing step, the method comprising: a. removing contaminants from the surface by contacting the surface with a cleaning solution; b. etching the pre-cleaned surface with an aqueous solution comprising from 12 to 19% by weight, of KOH and/or NaOH; c. rinsing the etched surface with an aqueous medium at pH from 7 to 10; and d. contacting the rinsed etched surface with ozonated deionized water at pH from 2 to 4.5, thereby converting the rinsed etched surface into a prepared surface. A method for texturing the prepared surface is also provided.