Low-Temperature CVD-Grown Graphene Thin Films as Transparent Electrode for Organic Photovoltaics
, Natalie P. Holmes 1,3, Mohsen Ameri 4, Krishna Feron 1, Mahir N. Thameel 5, Matthew G. Barr 1, Adam Fahy 1, John Holdsworth 1, Warwick Belcher 1, Paul Dastoor 1,* and Xiaojing Zhou 1,*
Round 1
Reviewer 1 Report
In this study, optimisations in the synthesis of highly transparent graphene layers prepared at low temperature were presented. The manuscript needs significant improvement before it can be published in Coatings.
- Gap of knowledge and novelty of study are very unclear, please improve the introduction part of manuscript significantly. Many articles in this area been published recently. Please review!
- Results and discussion of manuscript need to be improved significantly and supported by recently published articles.
- Several testing and characterisations (e.g., AFM, SEM, XPS, TEM, XRD etc.) have been mentioned in the manuscript however, the results have not been included. Please include all the results and discuss accordingly.
- The latest cited reference in the manuscript is 2016-2017. The author must review all the recently published articles from 2017 to 2022 in this area and include the relevant papers in the manuscript.
Author Response
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Author Response.pdf
Reviewer 2 Report
The measurement results obtained in the study titled "Low-Temperature CVD-Grown Graphene as Transparent Electrode for Organic Photovoltaics" can be published in your journal. however, some measurements do not show the units obtained from the measurement. For example, the unit of resistance in figure 2.
Author Response
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Reviewer 3 Report
The article “Low-Temperature CVD-Grown Graphene as Transparent Electrode for Organic Photovoltaics” was submitted by Zhou and others to the coatings journal. The article claims novelty with good results. However, I have some comments and suggestions that need to be answered.
For a better comparison, it is recommended to draw the table comprising the results of this work and the previously published graphene-CVD-based electrodes in OPVs. Currently, it is quite difficult to comprehend the novelty of the proposed work.
The authors mentioned that the work function is important in achieving the high performance of OPVs. For that, they also performed a UPS analysis. However, there is no clear discussion and information provided related to UPS measurements. Please further elaborate. Also, it is suggested to include the energy level diagram of the OPVs.
For a transparent conducting electrode (TCE), the transmittance of electrodes reported in this work is quite low (Figure 2a). What is the author’s opinion on this?
The authors performed the AFM measurement on the silicon substrate. Is there any specific reason for this? For the OPVs, it was better to compare the surface roughness of glass/ITO electrodes and graphene-based electrodes. I believe this analysis must be included because when we talk about TCEs of OPVs, the transparency and surface morphology is crucial.
What will be the significance of this study related to OPVs under indoor lighting conditions? For a good TCE, it is very imporatnt to perform under different lighting conditions. I will suggest studying and including the recent important work (https://doi.org/10.1016/j.jpowsour.2021.230782; https://doi.org/10.1016/j.apsusc.2021.150852; https://doi.org/10.1016/j.tsf.2020.138006;).
Can the authors please provide the integrated JSC values in order to find the discrepancies in measured and actual JSC values? Also, please include series and shunt resistances values in Table 2.
I believe figures can be improved because most of the figures do not look technical with inconsistent axis, fonts, legends, etc.
There are many typos, spacing, and syntax errors throughout the article. For example, lines # 36, 70, 71, 77, 136, 147, 268, 456 etc..,. Also, there should be consistency in using some terminologies such as minutes, min, hours, hrs, mL-1, ml-1, Ω/sq., etc., Similarly, what is the difference between J and JSC? Please resolve all the linguistic errors in the article.
Author Response
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Author Response File: Author Response.pdf
Reviewer 4 Report
Review on “Low-Temperature CVD-Grown Graphene as Transparent Electrode for Organic Photovoltaics” by Alaa Y. Ali , Natalie P. Holmes , Mohsen Ameri , Krishna Feron , Mahir N. Thameel , Matt Barr , Adam Fahy , John Holdsworth , Warwick Belcher , Paul Dastoor and Xiaojing Zhou, submitted to “Coating” [MDPI]
The authors present a low-temperature scheme for the growth of graphene-like layer on Cu foil, which is subsequently transferred to a test organic photovoltaic (OPV) solar cell. The graphene-like layer replaces the (standard) transparent indium tin oxide (ITO). Two OPV cells, the “graphene”-based and ITO-based are compared. The “graphene”-device is still far from the performance of the ITO-device, which the authors relate to defects in the transferred graphene layer.
Comments :
(1) My first comment is about nomenclature. The authors use “graphene” / “graphene film” to describe their material all along the manuscript, while the authors estimate the thickness of the material to be more than 10 layer thick (line #196).
→ “Graphene” may thus appear misleading and should be replaced by “multilayered graphene” in all the manuscript.
→ what does (n GL~2) means line #172 ? If we understand it as 2 graphene monolayers, it contradicts line #196.
(2) My second comment is close to Ethics.
The authors present here a first the optimization of the growth temperature. (400-800°C) of the “multilayer graphene” and second H2 optimization at fixed temperature (600°C) in the supplementary .
The problem is that the Supplementary Info have been published by the same authors in
“Growth of Multi-Layered Graphene Using OrganicSolvent-PMMA Film as the Carbon Source under Low Temperature Conditions” International Journal of Chemical and Materials Engineering, Vol:13, No:2, 2019
[As a side note, please remark here the correct usage of “multilayer graphene” in the 2019 work, see comment(1)]
→ all 3 figures of the current SI are in the main text of 2019, with more info (H2 flow rate) for Fig S1.
Surely the re-use of the exact same figure is a cause of concern, both from ethics and copyright.
→ the work from 2019, although extremely close to the present manuscript is not cited. Why would the authors choose not to cite their own work and yet re-use the graphical material ?
Addressing this point alone warrants a major revision in my opinion.
(3) lines #140-147 “describe” (fragment of sentences) details of XRD and TEM analysis which are not presented in the current manuscript.
(4) Although important in the manuscript narrative, the growth section is relative to the multi-layer graphene growth is minimalist (line#99 102), at the very least duration and pressure should be added, with a schematic (see comment 5).
(5) The complete fabrication process (Cu preparation, multilayer graphene growth, transfer, solar cell fabrication) should be graphically detailed in a separate figure. Currently the information is there but scattered.
(6) It is unclear whether the Raman data (fig1) is collected on as-grown sample or after PMMA-assisted transfer. Please also add the laser wavelength (currently 4 lasers ? #line 138)
(7) Following comment (6), could the authors compare Raman data before/after PMMA-assisted transfer ? How does the transfer affect the layer “quality” (as far as it can be assessed by Raman).
How local measurements compare with large scale Raman maps ? (see also comment 8)
(8) It is unclear how “continuous” and “defective” the multilayer graphene layers are after transfer. The surprising variations of Jsc and Voc with respect to the cell area hints at major spatial inhomogeneity, in the multi-layer graphene itself (i.e. growth issue) or during the OPV cell fabrication (i.e. process issue).
Given such a spread in Jsc and Voc, firm conclusions on any specific causes are unlikely.
(9) Do the ITO cell also change Jsc and Voc with cell area ?
(10) There are no image of any device (ITO or graphene), although several have been fabricated and measured. Not showing any actual graphene-based device (in the main text or SI) is a source of concern for any reviewer.
(11) The conclusion reads:
“The morphology, structural, chemical, and optical properties of graphene films were characterised using AFM, optical microscopy, SEM, XPS and Raman spectroscopy and it was found that multilayer graphene was formed with amorphous carbon present and that the transfer technique resulted in tears, folding and wrinkles in the graphene electrode”
→ no AFM (beside SI which is not the main text), no optical microscopy, no SEM data shown.
→ amorphous carbon is not mentioned anywhere else in the manuscript, except line #201, with no supporting data.
→ “tears, folding and wrinkles” are not shown, which relates to comments (6-8) about the actual quality of the transferred multi-layered graphene.
==> unsupported statements, all requiring proper quantification and discussion.
(12) Generic comment : I am curious how the multi-layered graphene obtained at lower temperature (400°C) behaves as electrode for the OPV. Given the extensive damage seemingly occurring during the transfer process, does the initial “graphene” quality actually matter ?
---------- Conclusion ----
Close call between major revision vs reject/resubmit. Major revision on the benefit of the doubt.
Assessing spatial inhomogeneities is critical before any publication.
Author Response
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Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The manuscript can be accepted in its present form.
Author Response
We thank reviewer 2 for approving our revision.
Reviewer 3 Report
I am not satisfied with the authors answers. The integrated EQE data is quite important to understand the discrepancies in the measured JSC values. Also, as suggested the influence of series and shunt resistance cannot be neglected. In addition, although indoor OPV are not the main consideration of this study. However, to enhance the scope, there must be some studies with relevant discussion in the introduction. So, I believe the authors are not serious about addressing the reviewer comments. In the present form, the article does not meet the current standard of this journal.
Author Response
We thank reviewer 3 for his personal views on how to enhance our manuscript. However, as we have stated that the focus of this manuscript is not to make champion photovoltaic devices, but to identify the spatial inconsistency of the graphene film as the transparent electrode for organic photovoltaic. Whether stating the integrated EQE data or not does not change any conclusion of the manuscript. In addition, we have showed more detailed analysis on the device series resistance and shunt resistance in Figure 6 and 7. For the reviewer’s final point on the indoor OPV, we believe it is beyond the scope of our manuscript, so that we do not need to mention in the introduction.
Reviewer 4 Report
The authors have amended their manuscript and significantly reworked the SI.
I have no major objection for publication.
Author Response
We thank reviewer 4 for the positive comment and approved our revision.
