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Dopants for Enhanced Performance of Tin-Based Perovskite Solar Cells—A Short Review

Coatings 2021, 11(9), 1045; https://doi.org/10.3390/coatings11091045

by Hairui Liu¹, Zuhong Zhang¹, Feng Yang^2,*, Jien Yang¹, Andrews Nirmala Grace³, Junming Li^4,*, Sapana Tripathi⁵ and Sagar M. Jain^6,*

Reviewer 1: Anonymous

Reviewer 2:

Guy Schmerber

Reviewer 3: Anonymous

Coatings 2021, 11(9), 1045; https://doi.org/10.3390/coatings11091045

Submission received: 4 August 2021 / Revised: 23 August 2021 / Accepted: 27 August 2021 / Published: 30 August 2021

(This article belongs to the Special Issue Advanced Perovskite Films for Photovoltaic Application)

Round 1

Reviewer 1 Report

This work is interesting, and the results are meaningful and important. However, I have a few specific concerns regarding this work:

How to check the homogeneous deposition of dopants in perovskite materials?
What are the important features of low-dimensional perovskite materials and how are they distinct (structure, stability and energetics) from other low-dimensional materials such as graphene?
How to get rid of the energy level mismatch and defects generation at the interface of perovskite solar cells?
Can the authors explain the role/effect of pre-existing defects in the dopants?

Author Response

This work is interesting, and the results are meaningful and important. However, I have a few specific concerns regarding this work:

How to check the homogeneous deposition of dopants in perovskite materials?

Reply: Thanks for your suggestion, first, the precursor solution will be stirred well after adding dopants, and the dopants we choose are all soluble in the precursor solvent, as long as the stirring time is sufficient, the dopants can be mixed uniformly. Then we will Later, we will use scanning electron microscope, X-ray diffractometer to detect a random sample, as long as it is different from the sample without doping, it can be considered that the dopant is uniformly added to the perovskite material.

What are the important features of low-dimensional perovskite materials and how are they distinct (structure, stability and energetics) from other low-dimensional materials such as graphene?

Reply: Thanks for your suggestion, the two-dimensional perovskite material is an RP phase perovskite, and the perovskite layer is a sandwich structure surrounded by organic long-chain molecules. The sandwich structure is stacked to form a bulk material, and the layers are combined by van der Waals force. This material is different from conventional two-dimensional materials. Conventional two-dimensional materials only exhibit quantum confinement effects when they are thinned to a few atomic layers and are called two-dimensional materials. The two-dimensional perovskite material is different. Due to the long-chain molecular group separating the perovskite layer, a natural quantum well structure is formed. Even in the bulk phase, it still has a quantum effect, and its quantum effect has a relatively large number of layers. Weak correlation, but strongly depends on the thickness of the perovskite in each layer, that is, the number of orders, denoted by n. n represents the number of perovskite layers contained in each layer. The larger the n, the closer to the three-dimensional perovskite. As n increases, the quantum effect gradually disappears. When n is large, it is called quasi-two dimensional perovskite, but the specific value is inconclusive. Due to the long-chain organic molecular groups, it has relatively better stability than three-dimensional perovskites

How to get rid of the energy level mismatch and defects generation at the interface of perovskite solar cells?

Reply: Thanks for your suggestion, For the mismatch of energy levels, we can add some materials with suitable band gaps to the interface, or we can add some additives to change the energy level position of the original material. There have been many studies aimed at these problems. Interface modification materials can also reduce interface defects and at the same time reduce non-radiative recombination, such as passivation of defects through chemical bonds formed by atoms or groups between materials and enhance charge transfer.

Can the authors explain the role/effect of pre-existing defects in the dopants?

Reply: Thanks for your suggestion, the materials we choose are divided into organic and inorganic materials. The biggest problem among them is the problem of organic matter. First, organic matter is easy to aggregate. If we spin-coating passivation materials, there may be a phenomenon of material aggregation. At this time, we will pass Ultrasound or choose some solvents that are not easy to cause aggregation to solve these problems. Secondly, some organic materials will appear to be insulated, and we will minimize the impact of some defects in the material itself on our perovskite materials or corresponding devices through a small amount of doping.

Please refer to attachment

Author Response File: Author Response.pdf

Reviewer 2 Report

This review article presents and discusses on Current trend and future prospect of dopants in Tin-based Perovskite Solar Cells by H. Liu et al.

Unfortunately, I must say that the paper in its present form is not publishable, there are too many gaps. This study lacks originality in its presentation. This is a good summary of articles to start this topic but it ends there for me. There is not enough openness to the future for solar cells based on FASnI₃ (FA=CN₂H₅) tin-based perovskite type.

What is more disturbing in this manuscript is a cruel lack of crystallographic data which is the basic engine of the journal.

Supplementary remarks:

1) It was better to rewrite the manuscript title. The future prospect side of dopants in tin-based perovskite solar cells is not at all appropriate.

2) For stabilization the tin-based perovskite solar cells, this leads to the need to dope with inorganic or organic materials, as was the case for lead-based perovskite solar cells. At the end of the discussion, you need to come up with new ideas for prospective materials that can significantly improve the long-term stability of these tin-based perovskite solar cells.

3) In the Additives section, it is better to write 2.1 Inorganic Materials. 2.2. Organic Materials. It makes more sense.

4) You mention the ionic radius of Pb²⁺ is 119 pm and that of Sn²⁺ is 110 pm (page 2, line 56). The ionic radius of Sn²⁺ is 118 pm.

See Shanon, R. D Revised effective Ionic radii and systematic studies of interatomie distances in halides and chaleogenides. Acta Cryst. A32, 751 (1976).

5) Sb is very often associated (it is true that antimony is Sb³⁺ with an ionic radius of 90 pm) as a dopant for Sn-based materials. Would this dopant be possible or even conceivable for the stabilization of tin-based perovskite solar cells ?

Author Response

This review article presents and discusses on Current trend and future prospect of dopants in Tin-based Perovskite Solar Cells by H. Liu et al.

Reply: Thanks for your suggestion, in general, our article is a summary of some current tin-based perovskite solar cells. Because the depth of the problem is not enough, we can only make some simple summary, and now tin-based perovskite solar cells is still the oxidation of Sn²⁺, we have not yet been able to think of a study that can completely solve the stability of tin-based perovskites. We can only put forward some of our simple opinions in the conclusion. Hope you can agree with us.

What is more disturbing in this manuscript is a cruel lack of crystallographic data which is the basic engine of the journal.

Reply: Thanks for your suggestion, the purpose of this article is not to introduce the crystal structure of tin-based perovskites, but to briefly summarize some of the work that everyone is currently doing to stabilize tin-based perovskites. I hope readers will be inspired by this article. For example, doping, transforming two-dimensional into three-dimensional perovskite and other means to stabilize tin-based perovskite solar cells. Hope you can agree with us.

Supplementary remarks:

1) It was better to rewrite the manuscript title. The future prospect side of dopants in tin-based perovskite solar cells is not at all appropriate.

Reply: Thanks for your suggestion, we have rewritten the manuscript title.

Reply: Thanks for your suggestion, our current work is hoping to briefly summarize the work of some tin-based perovskite solar cells. When reading this article, readers can find out which work has been done well, which work has not been done well, which needs to be improved, and which can be referred to. This is the purpose of this article. Hope you can agree with us.

3) In the Additives section, it is better to write 2.1 Inorganic Materials. 2.2. Organic Materials. It makes more sense.

Reply: Thanks for your suggestion, we also think this suggestion is good, so we have corrected the title a bit.

4) You mention the ionic radius of Pb²⁺ is 119 pm and that of Sn²⁺ is 110 pm (page 2, line 56). The ionic radius of Sn²⁺ is 118 pm.

See Shanon, R. D Revised effective Ionic radii and systematic studies of interatomie distances in halides and chaleogenides. Acta Cryst. A32, 751 (1976).

Reply: Thanks for your suggestion, we think your reference is very meaningful, we have revised the wrong description of the atomic radius.

Reply: Thanks for your suggestion, although Sb and Sn will be the most combined in other fields, such as Sn-Sb alloys, in tin-based perovskite solar cells, the biggest problem of tin-based perovskite is the oxidation of Sn²⁺. If this problem can be solved, the development of tin-based perovskite solar cells will take a big step forward. And our focus is not on the issue of substitution. The ionic radius of Pb²⁺ and Sn²⁺ are very close. We believe that substitution is not a problem, but because Pb is not an environmentally friendly metal, we focused on tin-based perovskites. If Sb can resist the oxidation of Sn²⁺, we think it is still useful for stabilizing the stability of tin-based perovskites. If not, the effect should not be great.

Author Response File: Author Response.pdf

Reviewer 3 Report

The text is publishable, but after major revision.

The work should be compared within the literature in terms of experimental methodologies, results or even simulated results. Because the presented discussion is like a sum of various researchers work with a sentence. This is needed to place this work in perspective with other work in the field and provide more credibility to the manuscript.
Line 18, skyrocket (??), Stop using such fascinating words. Are these type of words relevant to the presented subject?
Line 20, Authors should mention who are the potential candidates? How could authors directly and simply write to be a noble prize nomination?
Line 23, these (?), Are they lead based perovskite solar cells (?). Please check rectify the error.
Line 47-58, no reference citation. Line 48, is there any investment report from the later mentioned companies, if so please cite. Line 51, if there is any proper report on the environmental concern of lead, cite the report.
To enrich the introduction section, the following published papers related to Sn based solar cells with different treatment methods and obtained results can be cited in line 59:

https://doi.org/10.3390/coatings7020034, https://doi.org/10.1039/D1RA04470B, https://doi.org/10.1016/j.apsusc.2021.150152, https://doi.org/10.1109/PVSC.2016.7749627, https://doi.org/10.3390/coatings11070754, https://doi.org/10.1007/s42341-021-00311-6, https://doi.org/10.4229/EUPVSEC20162016-1BV.6.40, https://doi.org/10.1016/j.molstruc.2021.130631

Line 81, Jokar et al ( Reference is missing).
Line 100, should be rewritten. The sentence is written as, ……..dimensions, and structure. and also proposes…
Line 116, there is no reference for Cao et al. [?]
Line 122, there is no reference for Tai and co-workers [?]
Line 122, there is no reference for Liao and co-workers [?] Similar errors are throughout the manuscript, so authors are required to check and put the sentence with proper reference citation.
Line 136, 147, no reference for the mentioned text.
While the cited work has been presented in present tense throughout the manuscript. Authors are required to present the cited results in proper publishable format. Proper use of articles and verbs are necessarily required throughout the manuscript.
Figures should be indicated in the same format throughout the text. For example, somewhere it is like .. Fig. 1a, Fig. 1b (format), while in other sentences it is like Fig. e-f.
Line 175, Yu and collaborators proposed 2,2,2-trifluoroethylamine hydrochloride (TFEACl), for what ? Similarly throughout the manuscript, please check and add a proper reason and citation.
Authors have mentioned about the morphology of the films (line 186-187)? Is there any effect of the polycrystalline grain size/orientation in terms of PCE? There are only a few figure related to the analytical characterization of the presented materials. It would be helpful for the readers to understand the quality of the films, so if authors could add few figures in the revised manuscript.
What are the outcomes and suggestions to the readers from the inorganic and organic additives? This should be added at the end of respective section.
Line 228, perovskite. have adjustable…. remove the full stop and check the typos throughout the manuscript.
Line 230, it should be a crystal structure, not crystal diagram. Please check for the proper notation throughout the manuscript.
The conclusion and perspectives section is not proper and has to be totally revised. This section should clearly demonstrate the results by percentage and compare them by data and numbers to show the best scenario. Authors could provide a table with PCE achieved by various cited references. Reviewer didn’t find any perspective look in the section. It is a generic paragraph. And this is not in line with the title of the paper.
Reviewer plausibly believe that the manuscript would be read and checked by all the authors before submitting the revised manuscript.

Author Response

The work should be compared within the literature in terms of experimental methodologies, results or even simulated results. Because the presented discussion is like a sum of various researchers work with a sentence. This is needed to place this work in perspective with other work in the field and provide more credibility to the manuscript.

Reply: Thanks for your suggestion, in general, our article is a summary of some current tin-based perovskite solar cells. Because the depth of the problem is not enough, we can only make some simple summary, and now tin-based perovskite solar cells is still the oxidation of Sn²⁺. As for the comparison and summary, we feel that there are many ways to stabilize tin-based perovskites. We cannot simply say which method is better. It would be too one-sided to describe which method is better. We just want to let readers know what work has been done on tin-based perovskite solar cells. Hope you can agree with us.

Line 18, skyrocket (??), Stop using such fascinating words. Are these type of words relevant to the presented subject?

Reply: Thanks for your suggestion, we also feel this word is not suit, so we have modified it.

Line 20, Authors should mention who are the potential candidates? How could authors directly and simply write to be a noble prize nomination?

Reply: Thanks for your suggestion, we have replaced the original expression.

Line 23, these (?), Are they lead based perovskite solar cells (?). Please check rectify the error.

Reply: Thanks for your suggestion, this sentence means that the degradation of lead-based perovskite solar cells will cause the toxic metal lead to be lost to the environment, which is not friendly to the environment, and environmental issues are now a major issue we are concerned about, so many people are not optimistic about lead-based Perovskite solar cells.

Line 47-58, no reference citation. Line 48, is there any investment report from the later mentioned companies, if so please cite. Line 51, if there is any proper report on the environmental concern of lead, cite the report.

Reply: Thanks for your suggestion, investment reports generally belong to the company's internal secrets. It is difficult for us non-members of their companies to obtain these things, but these companies can easily retrieve them on the Internet when they are engaged in the photovoltaic industry. We have cited a report about the environmental concern of lead. (10.1038/s41467-019-13910-y).

To enrich the introduction section, the following published papers related to Sn based solar cells with different treatment methods and obtained results can be cited in line 59:

https://doi.org/10.3390/coatings7020034,

https://doi.org/10.1109/PVSC.2016.7749627,

https://doi.org/10.4229/EUPVSEC20162016-1BV.6.40

Reply: Thanks for your suggestion, we feel that the above three documents are very complex with our content, so we cited them in the article.

Line 81, Jokar et al (Reference is missing).