In-Situ Piezoelectric Effect for Augmenting Performance of Self-Powered ZnO-Based Photodetector

Round 1

Reviewer 1 Report

In this article, authors present exciting results on the ZnO:PVDF composite based UV photodetector. The article is very well written, authors have thoroughly investigated the materials properties, morphology and realized a solution processed photodetectors on flexible substrates. Excellent results in terms of detectivity, On/Off ratios and rise/fall times, and it is further supported by the reproducibility/stability data.  Results are additionally supported by

comparative evidence of the performance and explanation of the mechanisms. The article will be a good reference for researchers working on the topic. Reviewer recommends the publication of the article with some minor comments.

1.      The ITO has a higher work function, for a good electron extraction/injection contact, have authors considered to use some other low work function transparent electrodes? If it improves the charge collection better?

2.       Although author have presented the stability data for 1000 second, the organic components of the device particularly TFB and PEDOT:PSS are not suitable for the long term stability under continuous UV radiation exposure, as well area of moisture sensitive environments. Please comment on that.

Author Response

Dear reviewer,

Firstly, we are grateful to you for giving us valuable comments. We would like to respond point-to-point to your questions below

• The ITO has a higher work function, for a good electron extraction/injection contact, have authors considered to use some other low work function transparent electrodes? If it improves the charge collection better?

(Response) We are thankful for the suggestion of reviewer. For extracting electrons, there are some electrodes that have suitable work functions such as ITO (WF ≈ 4.62 eV), Ag nanowire (WF ≈ 4.5 eV), and FTO (WF ≈ 4.4 eV). We agree with the reviewer that a lower work function can extract effectively generated electrons.

However, in this work, we focused on fabricating a potential active layer ZnO@β-PVDF for UVA detection. Therefore, we fixed a bottom electrode by using a commercial ITO-coated polyethylene terephthalate (PET) substrate. As we can see in the band energy diagram (in Figure 3d), the conduction band of ZnO (≈ 3.44 eV) is matching well with the work function of the ITO electrode so that the generated electrons in depletion region can be fastly driven to the ITO electrode.

• Although author have presented the stability data for 1000 second, the organic components of the device particularly TFB and PEDOT:PSS are not suitable for the long term stability under continuous UV radiation exposure, as well area of moisture sensitive environments. Please comment on that.

(Response) We agree with reviewer that there is a possibility of photodegradation of TFB and PEDOT:PSS as long-term exposure to UV light. As we know, the photodegradation of organic components mainly comes from photooxidation in the presence of oxygen and moisture. Briefly, when organic polymer exposes to UV light, the photoexcited electrons and holes in the polymer can react with oxygen or moisture to form radicals. Then, these radicals would break down the bonds in polymer chains. Fortunately, when we utilized these polymers in an appropriate energy band diagram where photoexcited electrons and holes in TFB and PEDOT:PSS can easily transfer to the electrodes and make a close circuit, the photoexcited electrons, and holes would not remain in the polymer layers for a long time to form the radicals. Therefore, it may be the reason for the high stability of the device under long-term exposure to UV light. A recent paper that also used the TFB and PEDOT:PSS in an appropriate band diagram for long-time stability (up to several hours) is represented (Adv. Optical Mater. 2022, 10, 2101404, https://doi.org/10.1002/adom.202101404).

We hope our response will satisfy you. We thank you in advance for your consideration.

Sincerely yours

Professor Chung Wung Bark / Department of Electrical Engineering, Gachon University, Korea

Office: 82-31-750-5351 FAX: 82-31-750-8833 e-mail: [email protected]

Reviewer 2 Report

The paper reports on important results and is in most aspects written clearly. My only criticism is raised by the lack of abbreviation explanations (e.g. PVDF). These have to be "deciphered". 

English is ok.

Author Response

Dear reviewer,

Firstly, we are grateful you for giving us valuable comment to enhance the quality of our manuscript. We would like to respond point-to-point to your questions below

Comment: The paper reports on important results and is in most aspects written clearly. My only criticism is raised by the lack of abbreviation explanations (e.g. PVDF). These have to be "deciphered". 

(Response) We appreciate the recommendation of the reviewer. The abbreviations were defined and highlighted in tracking mode in the revised manuscript.

We hope our response will satisfy you. We thank you in advance for your consideration.

Sincerely yours

Professor Chung Wung Bark / Department of Electrical Engineering, Gachon University, Korea

Office: 82-31-750-5351 FAX: 82-31-750-8833 e-mail: [email protected]

Reviewer 3 Report

Manuscript #: coatings-2381451

Manuscript title: In-Situ Piezoelectric Effect for Augmenting Performance of 2 Self-Powered ZnO-Based Photodetector

Comments:

The authors describe the fabrication and characteristics of self-powered ZnO-based UV photodetectors. The manuscript is well written and the presenting data are clear. There are some recommendations.

1. Can the authors add the sample name on Fig. 1c ?

2. Can the authors add all three samples data on Fig. S1 for a clear comparison?

3. Is there “unit” at X & Y axes on Fig. 4c and Fig. 6c?

4. In Fig. 5a, what does “RW” stand for? RW means reverse bias (RV) based on FW (forward bias)?

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 4 Report

In-Situ Piezoelectric Effect for Augmenting Performance of Self-Powered ZnO-Based Photodetector is very interesting paper. Some improvement are required.

Line 10; PVDF (please to write the full name)

Line 10:  ZnO nanoparticles as fillers (what is size and form of nanoparticles)

Line 93, 94: ZnO NPs were prepared through hydrolysis and condensation of ZA using KOH in  a methanol solution at low temperature (please to add a value of the low temperarture)

Line 95: A clear solution was  obtained by stirring the mixture for 30 min. (please to add a stirring rate)

Line 140: Figure 2a presents the X-ray diffraction (XRD) patterns of ZnO nanoparticles (NPs). Can you give an information about form and size of the nanoparticles (SEM-EDS analysis?)

Line 165, 166: The scanning electron microscopy (SEM) image showed the surface morphology of  the ZnO@β-PVDF thin film (Figure 3a). ZnO NPs can form tight and extremely close contacts to form a dense and continuous layer. Unfortunately from Figure 3a, we can not obtain any information about size and form of particles. Do you have TEM-analysis of ZnO Nanoparticles? Are you sure that you prepared nanosized particles.

Author Response

Please see the attachment

Author Response File: Author Response.pdf