The Fabrication and Characterization of Silicon Surface Grooving Using the CV Etching Technique for Front Deep Metallic Contact Solar Cells

Round 1

Reviewer 1 Report (Previous Reviewer 2)

Comments and Suggestions for Authors

The author answered most of my previous concerns but not all. They claim a US$50 cost for their technique in the reviewer response but did not include that information in the manuscript. How did they calculate their costs? Are these just capital equipment costs?

2. While It is understandable that the authors do not have access to other methods of grooving, the lack of a proper control sample needs to be acknowledged. Also the language claiming an improvement form non-grooved samples needs to be removed from the abstract since it makes it sound like its due to their chemical vapor etching rather than just due to the addition of grooves. 

3. Also the addition of sample details in figure 6 makes me realize that the authors are not using an interdigitated front contact solar cells as the tittle suggests, but just a regular front grooves contact solar cell. An Interdigitated front contact solar cell has both n- and p-type contact on the front surface (see https://doi.org/10.1016/j.solener.2013.12.007), while theirs only has the n-type contact on the front. This lead to my confusion about the extra metal shadowing that is present in a interdigitated front contact solar cell. The tittle and references to interdigitated cells needs to be removed.

4. Also in line 167 the authors claim the thickness of 96.77 microns matches the thickness of the wafer, but they claim the wafer was 330 microns in line 100. Do the authors mean this is the thickness after etching in the grooves?

Author Response

Reply to the reviewer 1

Thank you for dedicating your time and expertise in reviewing our manuscript. Your comments are invaluable in enhancing the quality and rigor of our work.

A1: The $50 is just the equipment costs; two heating plates (≈ US$20), water bath (≈ US$5) Teflon cell (≈ US$25).

A2: Some sentences in the abstract have been changed to clarify the referee requested.

The solar cell technology based on a plated front metal contacts inside Chemical Vapors Etching -formed grooves. Chemical vapor etching was used to elaborate regular front grooves on mc-Si and then applicate for solar cell with front deep metallic contacts, in this case the deep metallic contacts fingers augment the collection of charge carriers at the front surface due to the increase in the collection surface and minimize the distance charge carriers need to travel to reach a contact and, which enhances the performance of multicrystalline solar cells.

A3: I am sorry for the confusion. I agree with the referee, the title and references were corrected in the revised paper

A4: 96.77 microns corresponds to the thickness of the wafer after etching in the grooves.it was clarified in the revised paper

We hope these amendments address the concerns raised adequately, and we appreciate the thorough scrutiny which has undoubtedly improved the quality of our work. Thank you for your invaluable input.

Reviewer 2 Report (New Reviewer)

Comments and Suggestions for Authors

This study explored chemical vapor etching for interdigitated metallic contacts in mc-Si solar cells. Silicon wafer thickness is critical for enhancing carrier collection through surface grooves. A cost-effective HNO3/HF etching method with an anti-acid mask created patterned grooves. The etching process showed a consistent rate, crucial for semiconductor fabrication. Interdigitated front contacts reduced carrier recombination and improved the solar cell's internal quantum efficiency by 35%. This approach enhances charge collection, reduces recombination losses, and boosts solar energy conversion efficiency, making it a promising strategy for mc-Si solar cell performance improvement. This work needs a revision before it can be published.

1.       How does the application of ultraviolet (UV) light to the anti-acid mask make it resistant to acid vapor, and what role does it play in the creation of grooves on mc-Si wafers?

2.       Can you elaborate on the specific chemical reactions involved in the CV-etching process, especially regarding the interaction between HNO3 and HF and their role in pattern formation on the silicon substrate?

3.       What are the key factors that ensure the controlled environment during the CV-etching process, and how do they contribute to minimizing contamination and interference from external factors?

4.       Could you explain the significance of maintaining different temperatures for the acid solution and the silicon substrate during the etching process? How does this temperature difference impact the efficiency and accuracy of groove formation?

5.       How is the thick, porous layer of powder formed as a byproduct during the acid vapor reaction, and how does its dissolution reveal patterned grooves on the silicon substrate? What are the potential applications of these patterned grooves in semiconductor devices?

6.       How does the use of chemical vapor etching impact the performance of multicrystalline silicon (mc-Si) solar cells with interdigitated metallic contacts?

7.       What role does the thickness of silicon wafers play in the production of solar cells with interdigitated front and back contacts?

8.       Can you explain the process of creating grooves on silicon wafers using the HNO3/HF chemical vapor etching technique and the anti-acid mask?

9.       How does the etching process's linear dependence on time contribute to its precision and reproducibility in semiconductor and microfabrication industries?

1.   How do interdigitated front contacts minimize the distance charge carriers need to travel and reduce carrier recombination within the silicon material?

1.   Can you elaborate on how interdigitated front contacts improve charge carrier collection and mitigate recombination losses in solar cells?

1.   The following relevant photovoltaics references shall be cited: Ultra-Fast-Responsivity with Sharp Contrast Integrated Flexible Piezo Electrochromic Based Tactile Sensing Display; Highly enhanced performance of integrated piezo photo-transistor with dual inverted OLED gate and nanowire array channel; Ultralarge Curvature and Extreme Rapid Degradable Porous Wood Based Flexible Triboelectric Sensor for Physical Motion Monitoring

Author Response

Reply to the reviewer 2

We are grateful for the insightful and detailed feedback provided. Your comments have significantly contributed to enhancing the rigor and clarity of our manuscript. Below are the responses to the issues raised:

A1: we used in this work a negative anti-acid mask, When UV light is applied to negative anti-acid mask-coated mc-Si substrate, it chemically changes the properties of the layer. that makes it insoluble in certain chemicals and resistant to removal by acid vapor. The anti-acid mask, serves as a protective barrier during the acid etching process. It defines the areas where material should be preserved and prevents the etchant (acid) from attacking those areas. The remaining areas of the mc-Si wafer are exposed to the acid, which selectively removes material, thus creating the desired grooves or patterns.

A2: chemical reactions involved in the CV-etching process

Si + 4HNO 3 + 4HF → SiF 4 + 4NO 2 + 4H2O

7Si + 4NO 2 + 12HF + 2H 2O → 2(NH 4)2 SiF6 + 5SiO2

For HNO3/HF acid mixture rich in HNO3, a significant amount of NO2 reacts with silicon in presence of HF, enabling the formation of (NH4) 2SiF6 powder as a byproduct during the etching reaction, which easily dissolved in water, leaving grooves areas

A3: The CV-etching process was performed in an airtight reactor placed in a chemical fume hood to protect from harmful chemical vapors and particles. which It provides a controlled environment for working with hazardous and noxious chemicals. This chemical fume hood minimizes contamination and interference from external factors

A4: At a given temperature, the volume of the free acid container part comprised between the acid solution surface and the substrate is saturated with acid vapors. As the temperature increases, the amount of the acid vapors may exceed the limit corresponding to saturation, and thus it forms a fog leading to the appearance of small drops on the container walls and particularly on the Si substrate, witch hinders to obtained a uniform grooves. for this reason, the temperatures of the acid solution and the silicon substrate were carefully controlled and being maintained at 30°C and 45°C, respectively, to helps prevent the vapor from condensing on the silicon surface during the engraving process

A5: Powder formed as a byproduct, because it is derived from a chemical reaction between HF and HNO3. For HNO3/HF acid mixture rich in HNO3, a significant amount of NO 2 reacts with silicon in presence of HF, enabling the formation of (NH4) 2SiF6 powder, which easily dissolved in water, leaving grooves areas. The precise and controlled creation of patterned grooves and structures on silicon wafers, enabling the fabrication of integrated circuits, solar cell with buried contacts

A6: “interdigitated metallic contacts “was corrected by "deep front metallic contacts" in revised paper

Chemical vapor etching was used to elaborate regular front grooves on mc-Si and then applicate for solar cell with front deep metallic contacts, in this case the deep metallic contacts fingers augment the collection of charge carriers at the front surface due to the increase in the collection surface and minimize the distance charge carriers need to travel to reach a contact and, which enhances the performance of multicrystalline solar cells.

A7: There is an optimal thickness that balances light absorption with carrier collection efficiency. Very thick wafers may absorb more light, but they can also increase recombination losses, reducing the overall efficiency. Therefore, the wafer thickness should be carefully chosen to strike a balance. The production of solar cells with deep front and back contacts can strike this balance

A8: The principle of the CV-etching method consists of exposing mc-Si wafers to acid vapors issued from a mixture of HNO 3 (65%) and HF (40%) which selectively etches away the unprotected silicon areas by the anti-acid mask induces the formation of an (NH4)2SiF6 powder, this powder can be easily dissolved in water leaving grooves areas

A9: The linear dependence of the etching process on time is advantageous for achieving precision and reproducibility in the semiconductor and microfabrication industries. It provides a straightforward and reliable means of controlling etching depth and, as a result, the dimensions and properties of fabricated structures and devices. additional, the Precise and reproducible etching is essential for quality assurance. Manufacturers in the semiconductor and microfabrication industries must meet strict standards and specifications, and linear etching processes contribute to achieving these quality goals.

A10: The deep front metallic contact improves the probability of collect by reducing carrier travel distances, you minimize the chances of carriers recombining before they can be collected, which enhances the efficiency of the solar cell

A11: The short distances between adjacent deep fingers metallic contacts minimize the distance charge carriers need to travel to reach a contact and shorter travel distances reduce the likelihood of recombination.

A12: We appreciate your suggestion and have enriched paper by incorporating the recommended references concerning photovoltaics, (1) Ultra-Fast-Responsivity with Sharp Contrast Integrated Flexible Piezo Electrochromic Based Tactile Sensing Display; (2) Highly enhanced performance of integrated piezo photo-transistor with dual inverted OLED gate and nanowire array channel; (3) Ultralarge Curvature and Extreme Rapid Degradable Porous Wood Based Flexible Triboelectric Sensor for Physical Motion Monitoring, which now provides a more robust background on the subject matter.

We hope these amendments address the concerns raised adequately, and we appreciate the thorough scrutiny which has undoubtedly improved the quality of our work. Thank you for your invaluable input.

Reviewer 3 Report (New Reviewer)

Comments and Suggestions for Authors

The paper presents a simple chemical vapor etching method for the fabrication of grooved Si surface. Solar cells based on Si with grooved surface exhibited improved performance in comparison with unetched Si. These results are intriguing and have the potential to attract wide attention. However, before it can be accepted for publication, there are some issues that need to be addressed:

1. The authors emphasize the importance of proper temperature control for achieving high-quality grooved Si surface on page 3, but no comparative experiments were carried out to demonstrate this claim. It would be beneficial to include such experiments to support the statement.

2. Figure 2a and 5a appear to be unnecessary because figure 1b already provides the necessary information.

3. In equation (1), “e” should be the depth of the grooves, and “i” and “j” should be subscripts.

4. SEM images should be provided to illustrate the accuracy of equation (1).

5. Did the width of the grooves affect the etching rate?

6. Figure 6b may be misleading to readers. The electrodes are in fact not only in the grooves, but also expanded out of the grooves as can be seen in Figure 7b. It is necessary to redraw figure 6b to accurately represent the electrode configuration.

Author Response

Reply to the reviewer 3

We are immensely grateful for your insightful feedback, which has significantly contributed to improving the quality and clarity of our manuscript. Your thorough review and constructive remarks are highly appreciated.

 

A1: The volume of the free acid container portion located between the acid solution surface and the substrate is saturated with acid vapors at a certain temperature. Acid vapor may exceed the limit corresponding to saturation as the temperature increases. As a result, it forms a mist, resulting in the formation of tiny drops on the container walls and, in particular, the Si substrate, preventing the formation of uniform grooves. In order to help prevent the vapor from condensing on the silicon surface throughout the engraving process, the temperatures of the acid solution and the silicon substrate were carefully controlled and kept at 30°C and 45°C, respectively. Details were added in the revised paper

A2: Figure 2a and 5a were deleted from the revised paper

A3: Equation (1) was corrected in the revised paper

A4: SEM images were added in revised paper to illustrate the accuracy of equation (1).

A5: No, the width of the grooves does not affect the etching rate, because the vapor pressure is uniform across the entire silicon surface

A6: Figure 6 has been redrawn in the revised paper.

We hope these amendments address the concerns raised adequately, and we appreciate the thorough scrutiny which has undoubtedly improved the quality of our work. Thank you for your invaluable input.

 

Round 2

Reviewer 2 Report (New Reviewer)

Comments and Suggestions for Authors

Paper can be published as it is.

Comments on the Quality of English Language

Please have a native speaker proof read the article.

Author Response

Dear Reviewer,

Thank you.

The paper was proofread and edited by Dr. Jim Newall. The certificate is attached. 

All questions have been answered in round 1

Thank you for recommending our manuscript for publication. Your previous comments were instrumental in guiding the refinement of our work. By addressing those concerns, we genuinely believe our article has significantly improved in clarity and depth. It now aligns better with the quality standards of the journal.

We deeply appreciate your time and the constructive feedback you provided throughout the review process. Your insights were invaluable, and we are grateful for the opportunity to enhance our contribution to the scientific community under your guidance.

Prof. M.Ben Rabha

Author Response File: Author Response.pdf

Reviewer 3 Report (New Reviewer)

Comments and Suggestions for Authors

I recommend the publication of the paper.

Author Response

Dear Reviewer,

Thank you for recommending our manuscript for publication. Your previous comments were instrumental in guiding the refinement of our work. By addressing those concerns, we genuinely believe our article has significantly improved in clarity and depth. It now aligns better with the quality standards of the journal.

We deeply appreciate your time and the constructive feedback you provided throughout the review process. Your insights were invaluable, and we are grateful for the opportunity to enhance our contribution to the scientific community under your guidance.

Pro.M.Ben Rabha

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

In the article “Fabrication and Characterization of Silicon Surface Grooving by CV-Etching Technique for Interdigitated Front Contact Solar Cells”, the authors report provides significant findings regarding the use of chemical vapor etching methods to create cross-metal contacts in solar cells. The paper clearly introduces the background, methods, and results of the research, highlighting its potential for improving solar cell efficiency. However, for the consideration of publication, the following suggestions should be addressed:

(1)  The schematic in Figure 1a is quite blurry and unclear. The authors should consider further improvements.

(2)  I didn't see AFM and TEM results! These data are important for the characterization of silicon surface.

(3)  The lack of XPS data in the analysis results makes it difficult to understand the valence state or bonding situation of the thin film atoms in a deeper way.

(4)  The XRD data of the samples after surface treatment have not been provided, which is a fundamental analytical result that should be included.

 

(5)  The extent of the benefits of this surface treatment on solar cells is not clearly evident from both the abstract and the conclusion. It seems that there is a lack of preliminary data to validate the effectiveness of the treatment.

 

Author Response

Reviewer #2:

In the article “Fabrication and Characterization of Silicon Surface Grooving by CV-Etching Technique for Interdigitated Front Contact Solar Cells”, the authors report provides significant findings regarding the use of chemical vapor etching methods to create cross-metal contacts in solar cells. The paper clearly introduces the background, methods, and results of the research, highlighting its potential for improving solar cell efficiency. However, for the consideration of publication, the following suggestions should be addressed:

(1)  The schematic in Figure 1a is quite blurry and unclear. The authors should consider further improvements.

(2)  I didn't see AFM and TEM results! These data are important for the characterization of silicon surface.

(3)  The lack of XPS data in the analysis results makes it difficult to understand the valence state or bonding situation of the thin film atoms in a deeper way.

(4)  The XRD data of the samples after surface treatment have not been provided, which is a fundamental analytical result that should be included.

(5)  The extent of the benefits of this surface treatment on solar cells is not clearly evident from both the abstract and the conclusion. It seems that there is a lack of preliminary data to validate the effectiveness of the treatment.

Response: We appreciate your suggestion and the whole paper were revised according to your remarks. The entire manuscript has undergone a comprehensive proofreading and revision, with the revised parts highlighted in red and violet font

1-  Figure 1a was improved in revised paper

2- I agree with the referee, AFM and TEM results are important for the characterization of silicon surface. but the SEM is the suitable characterization in our case to clarify the surface groove before and after metallic contacts

3- This is true and I agree with you on this point, but unfortunately we do not have XPS in Tunisia and this analysis requires traveling outside the country, which is difficult in light of the current situation. I will endeavor to conduct XPS analysis in my future work

4- More information’s were added in the revised paper

“In fact, we did not treat the surface because the silicon surface exposed to solar radiation was not treated, but we compared two solar cells before and after buried metal contact. That is, the first cell show in figure 6a with the metal contact form is on the surface, while the second cell show in figure 6b has the buried metal contact form is on the depth, as shows in figure 6.

Figure 6. Solar cells before and after buried contact (a) simple metal contact form is on the surface and (b) buried metal contact form is on the depth  was added in revised paper

The buried contact solar cell is that the metal is buried in the formed groove inside the silicon solar cell.

Solar cells with buried metal contacts (Figure 6b) improve charge carrier extraction by providing larger contact surfaces and reducing the distance traveled by the carriers compared to the simple contact model (Figure 6a) with small contact surfaces and a large distance traveled by the carriers. In photovoltaic cells, carriers generated by incident light need to travel across a large distance within the semiconductor material to reach the metal contacts. If there is significant recombination along this path, it can reduce the overall efficiency of the solar cell, when carriers have to travel over a large distance within the semiconductor and encounter small contact surfaces, there's a higher probability of recombination events occurring, Thus, a solar cell with buried metal contact (Figure 6b) increases the collection area, reduces contact resistance, and has a low probability of recombination, resulting in improved solar cell efficiency.”

. 5- In the revised paper, the benefits of surface grooves on solar cells are explained in both the abstract and conclusion, which are as follows

- A simple, low-cost chemical vapor technique was used

 - The formation of a thick, porous layer of powder that can be easily dissolved in water to create grooves on mc-Si wafers using a high-quality anti-acid mask

-Multicrystalline silicon solar cells fabrication with interdigitated front contacts

 -Internal quantum efficiency characterization

Based on the present results a comprehensive approach is needed in the future to achieve the desired improvements in internal quantum efficiency and overall cell efficiency

 

Yours Sincerely

 

Prof. Mohamed Ben Rabha

 

Reviewer 2 Report

Comments and Suggestions for Authors

The authors claim to present a study of the chemical vapor etching to generate grooves in Si wafers.  I fail to see the novelty in this work. The study is extremely if not completely similar to the article published by the authors earlier this year (DOI: 10.3390/cryst13030425 ), where they also compared a groove Si cell using their technique to a reference Si solar cell.

The authors being the paper by comparing to other grooving techniques and then proceed to describe their technique without saying what the advantage of their technique is compared to other techniques used currently. The only sentence came in page 6 saying "One significant advantage of this new technology is the ability to produce low-cost grooves on mc-silicon. " without any information as to why the authors believe their technique is cheaper than other technologies. Then the authors proceed to compare to a ref mc-Si solar cell in figure 6 with no grooves (presumably since it was not describe adequately) instead of comparing to a cell with grooves done with other techniques to asses the viability of their technique.

They also state in line 319 "Additionally, the finger-like structures of interdigitated front contacts minimize shadowing effects, allowing more incident light to reach the surface of the cell." I fail to see how adding additional metal to the front reduces shadowing. In fact if there was reduced shadowing the benefits in the IQE will show up in all wavelengths not just the short wavelengths, what the front interdigitated contact allows is to reduce the diffusion length necessary for collection, and hence increases short wavelength collection, not reduce shadowing. 

The entire article is full of repetitive sentences and statements.  In fact figure 1 b is repeated in Figure 2 and figure 5, and comes from the previous papers from the same authors. As one example of the repetitiveness in the article in line 92 the authors state "This process allows for the precise formation of grooves, channels, or other desired structures, which contributes to the fabrication of high-quality solar cells. This technique is crucial in the fabrication of various semiconductor devices because it enables the formation of specific patterns and structures that enhance the performance of these devices.", then proceed to say the same statement in the next paragraph "These patterned grooves are the desired outcome of the etching process, which can be used for various applications, including in the fabrication of solar cells with interdigitated contacts [18] or other semiconductor devices. "  The entire article is full of repetitive sentences like this. For this reason this should not be published and needs to be re-written. 

Author Response

Manuscript ID: sustainability-2586251
We thank you for giving us the opportunity to revise our manuscript, and
we sincerely thank you for your thoughtful and helpful comments. we
have made careful modifications and revisions on the original manuscript.
The changed sentences have been marked as red color in the revised
version. We hope that the revised paper will meet your standard.
Yours Sincerely

We appreciate your feedback regarding the need for a comprehensive proofread throughout our manuscript and re-written . Ensuring the quality of language, grammar, and overall readability is crucial, and we take your comment seriously. We have thoroughly reviewed and proofread the entire manuscript to minimise the language, grammar, and overall readability issues and it was re-written. If still more corrections are required, we are ready to do more correction and we believe that it can be performed during the production even.
Prof. Mohamed Ben Rabha

Author Response File: Author Response.pdf