Engineering of TiO₂ or ZnO—Graphene Oxide Nanoheterojunctions for Hybrid Solar Cells Devices

Round 1

Reviewer 1 Report

Dear Editor!

The manuscript «Engineering of TiO₂ or ZnO-Graphene Oxide Nanoheterojunctions for Hybrid Solar Cells Devices» submitted for consideration by Photonics report on the electrical characterization of two types of solar cells devices: FTO/(PAH/GO)_x/TiO₂/Al and FTO/(PAH/GO)_x/ZnO/Al. In general, the manuscript contains interesting results, which are useful for practice. However, part of the manuscript contains the results of the work [27] previously published by the authors. In the abstract, methodology section 2, discussion section 3 and conclusions authors present as one of the results of the manuscript the characterization of samples by UV-VIS absorbance spectra. In fact, these results have already been previously published by authors in the work [27]. In this regard, I recommend that authors exclude duplication of results and focus in this manuscript on principally new data.

In addition, it is not clear from the text of the manuscript, from what thinking the number of PAH/GO bilayers was chosen to be 20 for the study of environment conditions influence. This needs to be clearly explained.

In view of the above, I think the changes in the text concerning the mentioned above questions will improve the quality of manuscript and recommend the major revision.

Author Response

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Reviewer 2 Report

This paper deals with the role of (PAH/GO)_X bilayer for their TiO₂ and ZnO based solar cell device structures. The novelty of this work seems relatively high but cannot be said it is impactful since no photo J-V performance has not been shown. Moreover, no band alignment analysis work has been shown. Since the PAH/GO insertion is the main selling point of the work, providing relevant energy level match with other layers seems essential. For the case of TiO₂ based device, for instance, numerous articles showing band alignment analysis were published, including 10.1021/acsami.6b01246, 10.1021/jp5107313. References for the ZnO also easily can be found. In addition, the followings should be addressed upon resubmission:

1. Line 37 - This is not correct considering the fact that c-Si is one of the most widely used PV materials, and its cost per watt is way lower than other commercially available thin-film materials. The Ga-based device has a different story. Ga is the essential raw material for LED products, and this leads to instability in the supply chain. Authors should claim the advantage of this thin film based PV technology instead of claiming the disadvantage of the crystalline PV materials. For instance, simplified process steps.
2. Line 231 - More detail analysis can be provided. According to the SEM images, it seems that the rough FTO surface has been flattened out by thick bilayers, not by aggregation of the TiO2. It would be advantageous if the SEM of the FTO surface is provided as reference.
3. Line 239 - It is tough to identify the scale bar in Fig. 2 and 3 as well.
4. Line 338 - It is not clear to me how these samples were stored between the measurements. Also, it is not shown how long time has passed after each measurement.

Author Response

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Reviewer 3 Report

I have carefully checked the manuscript entitled: Engineering of TiO2 or ZnO - Graphene Oxide Nanoheterojunctions for Hybrid Solar cells Devices by Duarte Carreira, Paulo Ribeiro, Maria Raposo and Susana Sério. In my opinion, the manuscript describes in a good way the different alternatives to assembly the heterojunctions between a organic component/GO with different kind of oxides in order to observe the carrier transport capability through a device. 

In order to improve the quality of the article, authors must emphasize what are the differences between this work and the actual state of the art, due to there is not clarity along the main text. In addition, Authors could delete the context related with the fossil fuels and concentrate in the different modifications that diverse research groups have carried out in order to see the interactions in a heterostructure based composite.

Author Response

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Round 2

Reviewer 1 Report

The authors answered all questions and eliminated all inaccuracies.

Author Response

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Reviewer 2 Report

The manuscript has been improved significantly after the authors have addressed the reviewers' comments thoroughly. However, I am not convinced of part of the responses, particularly, the following points:

1. According to the authors' response #1, they claimed that band alignment could not be done due to a lack of experimental facilities, such as XPS or UPS. This is understandable; however, not all reports demonstrate the band alignment based on their own XPS measurement data. The primary purpose of this alignment is to bring a brief map for understanding the carrier pathway across the device. I believe there are enough reliable data sets for drawing the dedicated band alignment figure for this device.
2. Regarding the sample storage, it sounds to me that the samples have been stored in the desiccator in ordinary order, for instance, with silica-gel. I would suggest putting this detail measure for moisture control as well.

Author Response

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