Highly Stable Inverted CdSe/ZnS-Based Light-Emitting Diodes by Nonvacuum Technique ZTO as the Electron-Transport Layer
, Fawad Saeed 1,†, Ahmad Raza 1, Abida Parveen 1, Ali Asghar 1, Nasrud Din 1, Zhang Chao 2, Jing Chen 1,*, Qasim Khan 1,3,* and Wei Lei 1,*Round 1
Reviewer 1 Report
Authors try to fabricate and examine QD-LED with ZTO as electron transporting layer. there are some issues in the manuscript before accepting.
- in the synthesis part, authors mentioned modified by reported procedure. but they didn't mention what are the modifications was done in this manuscript. need to be include proper synthesis.
- in line 111, authors mentioned 0.2 M (0.225g) was dissolved.... what chemical they used. need to be include.
- authors explained in XRD single peak at 32.5, but if you see in the 2c there is small peak around 67. what is the peak at around 67? is it any starting material or impurity? need explanation.
- need to compare the obtained XRD peaks with standard JCPDS values.
- the External quantum efficiency is depends on optimal thickness of QDs. author didn't mention about what thickness was used.
- in figure 1c, author didn't mention anywhere about PL emission in which state, weather its a solution PL or film PL. need proper explanation in manuscript as well as in figure.
- authors mentioned he PLQY of the QDs in the film state 147 is estimated to be 31%. at what thickness author got 31% PLQY. need explanation.
- in general the PL depend on thickness of QDs. did author measured any PL emission with different thickness of QDs?
- author should also need to include EL spectra of the fabricated device.
Author Response
Response to Reviewer 2 Comments
We appreciate the reviewer for carefully reading the article which helped us to improve and revise the manuscript. We have considered all the suggestions and modified the manuscript accordingly.
Point 1: In the synthesis part, the authors mentioned modified by reported procedure. but they didn't mention what are modifications were done in this manuscript. need to include proper synthesis.
Response 1: We thank the reviewer for the valuable comments. We include the proper synthesis process in the revised manuscript about the CdSe/ZnS QDs after minor modifications (Page no.4; line no 89-99; red color text).
Point 2: in line 111, the authors mentioned 0.2 M (0.225g) was dissolved.... what chemical they used. need to be inclusive.
Response 2: For the synthesis of SnO2, we used 0.2 M (0.225g) of SnCl2 in ethanol and we have mentioned it in the revised manuscript (line no 104; red color text).
Point 3: authors explained in XRD single peak at 32.5, but if you see in the 2c there is a small peak around 67. what is the peak at around 67? is it any starting material or impurity? need explanation.
Response 3: Firstly, we prepare ZnO and SnO2 in ethanol and explained in detail the “experimental section”. For the synthesis of Zinc Tin oxide (ZTO), we mixed these two materials discussed above with an equal molar ratio. Because the ZnO nanoparticles show a peak around 67° (ACS Appl. Electron. Mater. 2020, 2, 2383−2389) as reason shows a small peak at this angle due to the impurity of the materials in (Figure 2c).
Point 4: Need to compare the obtained XRD peaks with standard JCPDS values.
Response 4: To identify the composition of the prepared nanocrystals, an X-ray diffraction (XRD) analysis was performed. The XRD pattern of CdSe-ZnS (Figure 1b) in the revised manuscript represents three main peaks had three main diffraction peaks at 25.36°, 43.02°, and 50.72° corresponding to the (111), (221), and (311) reflection planes respectively, of the cubic structure of CdSe/ZnS (reference card “JCPDS 01-088-2346”). These peaks were broad, indicating the small crystal size of the CdSe/ZnS QD and their nanometric size (Finsy and De Jaeger, 1991).
Point 5: the External quantum efficiency is depending on optimal thickness of QDs. author didn't mention about what thickness was used.
Response 5: The important question raised by the reviewer is appreciated. The thickness of the CdSe/ZnS QDs in the designed structure for that External quantum efficiency is 40 nm and we mentioned it in the revised manuscript. (Line no 191-192; red color text).
Point 6: in figure 1c, author didn't mention anywhere about PL emission in which state, whether it’s a solution PL or film PL. need proper explanation in manuscript as well as in figure.
Response 6: The absorption and PL spectra of the synthesized CdSe/ZnS QDs (in solution) are given in Figure 1c. And we have mentioned in the revised manuscript (line no 136; red color text).
Point 7: authors mentioned the PLQY of the QDs in the film state 147 is estimated to be 31%. at what thickness author got 31% PLQY. need explanation.
Response 7: We thank the reviewer for indicating the mistakes. The calculated PLQY of the CdSe/ZnS QDs in the solution is 80%. Whereas, PLQY of the QDs in film state is estimated to be 31% with a thickness of 40 nm.
Point 8: In general, the PL depend on thickness of QDs. did author measure any PL emission with different thickness of QDs?
Response 8: The important question raised by the reviewer is appreciated. Yes, of course, PL depends on the thickness of QDs. The thickness in the as-designed QD-LED structure is 40 nm. Also, we measured PL with different thicknesses and found that PL intensity gradually decreases with increasing thickness of the CdSe/ZnS QDs in film state.
Point 9: author should also need to include EL spectra of the fabricated device.
Response 9: We have included the EL spectrum according to the reviewer’s suggestion. The EL spectrum of the device is compared with the PL of the QDs film state (Figure 5d; page no. 7) and the corresponding texts are included in the manuscript (line no. 250-252; red color text).
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Please explain why some device parameters as luminance or current efficiency are below the state of the art for the QD-LED (CdSe/ZnS).
The investigated Quantum Dot LED shows a photoluminescence (PL) peak at 620 nm. Could the authors comment on methods how to obtain also a good blue-green emission?
Several typos reduce the clarity of the paper, as examples:
Rows 17-18, instead ”is critical to achieving which guarantees high efficiency”
recommended “is critical to achieve high efficiency”
Row 30, instead “have attracted a lot of attention to be an active material”
Should be “have attracted a lot of attention as an active material”
Row 41, instead “Usually, invert CdSe/ZnS QD-LED”
Should be “Usually, inverted CdSe/ZnS QD-LED”
Row 134, instead “EDINBURGD (FS5) system”
Should be “EDINBURGH (FS5) system”
Author Response
Response to Reviewer 1 Comments
We thank the reviewer of “electronics” for carefully reading and providing their valuable comments and suggestions to our article. We have revised the manuscript to address the questions raised by reviewer #1, which has improved the quality and scope of the article.
In the following, we have responded to the reviewer’s comments in black color text and our answers to these questions in red text. In addition, some text is added or modified in the manuscript and the figure captions as well, which are marked in red color text for your convenience.
We feel that the manuscript in the revised form is now ready for publication in “electronic” and we also hope that this article will be appealing to the broad range of audiences working in the relevant fields.
Point 1: Please explain why some device parameters as luminance or current efficiency are below the state of art for the QD-LED (CdSe/ZnS).
Response 1: Conventional QD-LEDs have higher luminance or current efficiency than inverted structures. But inverted-structured QD-LEDs (CdSe/ZnS) have been indicated as prospering successors to conventional QD-LEDs. In inverted QD-LEDs, metals that have air stability and high work functions are used as the anode, indium tin oxide (ITO) is generally used as the negative electrode, and metal-oxide thin films (such as ZnO, ZTO, TiO2) are used as the electron injection layers (EILs). These metal oxides have other advantages, like solution-processable, mechanical and electrical durability, transparency in the visible region, and cost-efficient. In inverted based QD-LEDs, charge carrier injection between electrodes is an important issue, because there is an energy difference between ITO and the polymers due to the high work function of ITO, nearly 4.7eV. ZnO and ZTO are commonly used as electron injection layers due to their broad bandgap (E.g., ⁓ 3.5 eV), efficient electron transporting characteristics, and low work function. Moreover, ZnO films can be easily deposited by solution-processable method and are therefore applicable to flexible substrates, which is the future technology of QD-LED displays and light-emitting transistors.
Point 2: The investigated Quantum Dot LED shows a photoluminance (PL) peak at 620 nm. Could the author's comments on methods how to obtain also a good blue-green emission?
Response 2: The photoluminance (PL) peak of red CdSe/ZnS quantum dots shows a peak at 620 nm, and we demonstrated that by changing the particle size of quantum dots (QDs), we obtain a good blue-green emission. If the particle size of the QDs is so small and the bandgap is large, then it shows a PL blue emission at 430 nm. With a slightly larger particle size and a lower bandgap than blue, it shows green emission at 530 nm.
Point 3: Rows 17-18, instead “is critical to achieving which guarantees high efficiency” should be recommended “is critical to achieve high efficiency”
Response 3: We corrected the words as “is critical to achieve high efficiency” and highlighted them on the revised manuscript (rows 18; with red text).
Point 4: Row 30, instead “have attracted a lot of attention to be an active material” should be “have attracted a lot of attention as an active material”
Response 4: We corrected the words as “have attracted a lot of attention as an active material” and highlighted them on the revised manuscript (row 29-30; with red text).
Point 5: Row 41, “Usually, invert CdSe/ZnS QD-LED” should be “Usually, inverted CdSe/ZnS QD-LED”
Response 5: We corrected with the word “Usually, inverted CdSe/ZnS QD-LED” and highlighted it on the revised manuscript (row 39; with red text).
Point 6: Row 134, instead “EDINBURGD (FS5) system” should be “EDINBURGH (FS5) system “
Response 6: Mistakenly we wrote and corrected with the word “EDINBURGH (FS5) system” and highlighted it in the revised manuscript (row 123; with red text).
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
This revised version of the manuscript is recommended for acceptance, as the authors have addressed all the comments satisfactorily.
