High-Performance White Organic Light-Emitting Diodes Using Distributed Bragg Reflector by Atomic Layer Deposition
Round 1
Reviewer 1 Report
This paper describes an integration of transparent distributed Bragg reflector (DBR), made from periodically alternating layers of atomic layer deposited ZrO2/Zircone films and sputtered tin-doped indium oxide, into OLED microcavity for improving the performance of white organic light-emitting diode. The results are interesting and appear significant for publication. Unfortunately the manuscript suffers from both technical and English language related problems and must be extensively revised. The problems are so many that only some most important examples are listed below. Careful editing of the whole manuscript is necessary still.
The authors do not explain their choice for the thin film materials for DBR. In particular, why zircone was selected? It is most likely moisture sensitive and therefore unstable. Why not using the old faithful ALD-Al2O3 instead?
In Fig. 1 explain that the numbers in parenthesis after zircone and ZrO2 are refractive indices.
In Materials and methods, please introduce the materials and their abbreviations before device structures.
Caption of Fig. 3b say current efficiency vs. luminance while figure itself shows luminance efficiency?
Why Figs 4 a and b are in log scale? Only a small fraction of the scale is used anyhow.
Why AFM Fig. 6 is placed in between the spectra figures?
Fig 7a has labels for nine voltages, yet only one can be distinguished from the figure. From the text it appears they all overlap. This is not the best way to introduce this result; mention in the text only would be better to avoid confusion about missing data.
Please pay attention to also the number of digits used in the results. E.g. 29.38 cd A-1 and 21.51 lm W-1 look too accurate to me.
Author Response
Referee: 1
COMMENTS:
This paper describes an integration of transparent distributed Bragg reflector (DBR), made from periodically alternating layers of atomic layer deposited ZrO2/Zircone films and sputtered tin-doped indium oxide, into OLED microcavity for improving the performance of white organic light-emitting diode. The results are interesting and appear significant for publication. Unfortunately the manuscript suffers from both technical and English language related problems and must be extensively revised. The problems are so many that only some most important examples are listed below. Careful editing of the whole manuscript is necessary still.
Point 1: The authors do not explain their choice for the thin film materials for DBR. In particular, why zircone was selected? It is most likely moisture sensitive and therefore unstable. Why not using the old faithful ALD-Al2O3 instead?
Response 1: We are really grateful to you for making these constructive suggestions which are of great help to improve this paper. Zircone as an organic material does have a problem of moisture sensitive and unstable. However, the first reason for choosing zircone is to consider the optical parameters of the DBR structure composed of zircone. The refractive index of Al2O3, Zircone and ZrO2 is 1.71, 1.46, and 2.13, respectively. The refractive index of Al2O3 is higher than that of zircone. The refractive index difference between the two materials constituting the DBR structure in OLED devices is very important, the greater the difference of refractive index (0.42 for Al2O3/ZrO2; 0.67 for Zircone/ZrO2) between the two materials, the easier it is to control the light-emitting spectrum of the device. Additionally, the second reason for choosing zircone is to consider the film stress in the DBR structure, the organic zircone is also beneficial to the deposited ZrO2 inorganic film as buffer layer.
Point 2: In Fig. 1 explain that the numbers in parenthesis after zircone and ZrO2 are refractive indices.
Response 2: Thank you for the suggestion. We have added corresponding explain to clarify this point in the revised version.
Point 3: In Materials and methods, please introduce the materials and their abbreviations before device structures.
Response 3: Thank you for the suggestion. The details of materials and their abbreviations were added in the section of DBR-based OLED fabrication in revised version. According to the review’s suggestion, we have adjusted the relevant content to the position before device structures.
Point 4: Caption of Fig. 3b say current efficiency vs. luminance while figure itself shows luminance efficiency?
Response 4: Sorry for this mistake and we have corrected it in revised manuscript.
Point 5: Why Figs. 4 a and b are in log scale? Only a small fraction of the scale is used anyhow.
Response 5: Thank you for the suggestion, we have corrected it and added the revised graph in manuscript.
Point 6: Why AFM Fig. 6 is placed in between the spectra figures?
Response 6: According to the review’s suggestion, We have adjusted the corresponding number and the contents of the graph.
Point 7: Fig. 7a has labels for nine voltages, yet only one can be distinguished from the figure. From the text it appears they all overlap. This is not the best way to introduce this result; mention in the text only would be better to avoid confusion about missing data.
Response 7: Thank you for the suggestion. We have added the new graph in revised manuscript.
Point 8：Please pay attention to also the number of digits used in the results. E.g. 29.38 cd A-1 and 21.51 lm W-1 look too accurate to me.
Response 8: These calculated data are in accordance with the retention of two digits. Instrument and software used to electrical properties measurement and spectral data processing can achieve such accuracy. Thank you for the suggestion, we have made the corresponding corrections in the revised manuscript.
We are grateful to your careful reading and making these valuable comments
Special thanks to you for your constructive comments.
Author Response File: 
Author Response.docx
Reviewer 2 Report
The authors describe an article entitled " High-performance white organic light-emitting diodes using distributed bragg reflector by atomic layer deposition". The topic of the manuscript is interesting and the manuscript constitutes an interesting study concerning the development of structures to extract light from OLEDs.
The work is well written, the experimental part gives numerous and sufficient details to reproduce the different synthesis. Sufficient spectra and figures are included in the manuscript for comprehension and clarity. Overall, I think that this is a good manuscript that I recommend for publication after inclusion of major revision.
1) authors demonstrated the efficiency of the approach. Meanwhile, the device lifetime is not discussed and highly emissive devices can have a dramatic device lifetime impeding future applications.
2) What about the angular ditribution of light. Is the angular intensity adopts a Lambertian profile ?
Author Response
Referee: 2
COMMENTS:
The authors describe an article entitled “High-performance white organic light-emitting diodes using distributed bragg reflector by atomic layer deposition”. The topic of the manuscript is interesting and the manuscript constitutes an interesting study concerning the development of structures to extract light from OLEDs.
The work is well written, the experimental part gives numerous and sufficient details to reproduce the different synthesis. Sufficient spectra and figures are included in the manuscript for comprehension and clarity. Overall, I think that this is a good manuscript that I recommend for publication after inclusion of major revision.
Point 1: Authors demonstrated the efficiency of the approach. Meanwhile, the device lifetime is not discussed and highly emissive devices can have a dramatic device lifetime impeding future applications.
Response 1: We are really grateful to you for making these constructive suggestions which are of great help to improve this paper. The lifetime is indeed a very important parameter for OLED device in the future application. And device life is closely related to packaging technology. However, the DBR structure used in this experiment is located between OLED device and glass substrates. Under the same conditions without packaging, it will not have an apparent impact on the lifetime of the device because the glass substrate has a strong moisture and oxygen resistance. Therefore, the lifetime of the device should be the same as that of the device without DBR structure on glass substrate. In addition, in our previous work, we also found the lifetime of the OLED device deposited onto the flexible substrate (such as PET substrate) can be largely increased due to the presence of DBR structure which has a certain water-oxygen barrier capacity [1].
[1] Zhang, H., Ding, H., Wei, M., Li, C., Wei, B., & Zhang, J. (2015). Thin film encapsulation for organic light-emitting diodes using inorganic/organic hybrid layers by atomic layer deposition. Nanoscale research letters, 10(1), 169.
Point 2: What about the angular distribution of light. Is the angular intensity adopts a Lambertian profile?
Response 2: Thank you for the suggestion. We agree that the angular intensity is also a key parameter especially in OLEDs with microcavity structure. Unfortunately, we cannot provide relevant data due to the limitations of the scientific research conditions. Usually, the performance of devices will show a certain distribution trend with the change of angle [2]. And in our previous work, we also measured the angular distribution of light in microcavity OLED [3]. We are really grateful for your suggestions, which will be the direction of our efforts in the future.
[2] Juang, F. S., Laih, L. H., Lin, C. J., & Hsu, Y. J. (2002). Angular dependence of the sharply directed emission in organic light emitting diodes with a microcavity structure. Japanese journal of applied physics, 41(4R), 2787.
[3] Fukuda, T., Wei, B., Ohashi, M., Ichikawa, M., & Taniguchi, Y. (2007). High coupling efficiency of microcavity organic light-emitting diode with optical fiber for as light source for optical interconnects. Japanese Journal of Applied Physics, 46(2R), 642.
We are grateful to your careful reading and making these valuable comments
Special thanks to you for your constructive comments.
Author Response File: Author Response.docx
Reviewer 3 Report
References must be updated as there are only 7 references from 2017 until 2019.
What is the size of the active area?
Author Response
Referee: 3
COMMENTS:
Point 1: References must be updated as there are only 7 references from 2017 until 2019.
Response 1: We are really grateful to you for making these constructive suggestions which are of great help to improve this paper. We have updated references in the revised manuscript.
Point 2: What is the size of the active area?
Response 2: Organic layers and a metal cathode layer were evaporated successively by using shadow masks. The entire organic layers and the Al cathode were deposited without exposure to the atmosphere, by which OLEDs with an active areas of 4 (2×2) mm2 were obtained. We have added the corresponding description to clarify this point in the revised version.
We are grateful to your careful reading and making these valuable comments
Special thanks to you for your constructive comments.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
I have checked the revised version and noticed that while the authors have done their best to address other comments, they have not done anything to the English text. It is in several places very poor, and consequently the paper can only be rejected in its present form.
The explanation for choosing zircone must be taken into the text itself. This must also include the stability concern.
There are several times a comment: '...shows few displacement and changes negligibly from ±0.01 to ±0.01.' What does this changes from ±0.01 to ±0.01 actually mean?
p. 4: 'ALD reactor which has been explained in other place.' - other place does not match the reuirements set to a useful reference.
Author Response
Referee: 1
COMMENTS:
Point 1: I have checked the revised version and noticed that while the authors have done their best to address other comments, they have not done anything to the English text. It is in several places very poor, and consequently the paper can only be rejected in its present form.
Response 1: Thanks for your suggestions. The revised manuscript has undergone English language editing by MDPI. The text has been checked for correct use of grammar and common technical terms, and edited to a level suitable for reporting research in this journal. Please check the English-editing-certificate.
Point 2: The explanation for choosing zircone must be taken into the text itself. This must also include the stability concern.
Response 2: Many thanks for the reviewer’s positive comments. We have added the corresponding explanation to clarify this point in the revised version.
Point 3: There are several times a comment: '...shows few displacement and changes negligibly from ±0.01 to ±0.01.' What does this changes from ±0.01 to ±0.01 actually mean?
Response 3: Just as the reviewer mentioned, we used the comment to indicate that the device A exhibited high color stability at various applied voltages with negligible color shift, which is a key parameter for white OLEDs.
Point 4: p. 4: 'ALD reactor which has been explained in other place.' - other place does not match the reuirements set to a useful reference.
Response 4: Sorry for this mistake and we have added the corresponding reference in revised manuscript.
We are grateful to your careful reading and making these valuable comments
Special thanks to you for your constructive comments.
Author Response File: Author Response.docx
Reviewer 2 Report
Authors present a revised version of their manuscript. The manuscript has been improved by the authors according to the reviewer’ comments. After inclusion of corrections and clarifications, this is now a manuscript that I recommend for publication.
Author Response
Referee: 2
COMMENTS:
Authors present a revised version of their manuscript. The manuscript has been improved by the authors according to the reviewer’ comments. After inclusion of corrections and clarifications, this is now a manuscript that I recommend for publication.
Response: We are really grateful to you for making these constructive suggestions which are of great help to improve this paper.
Special thanks to you for your constructive comments.
Author Response File: Author Response.docx
Round 3
Reviewer 1 Report
I've checked the revised manuscript and found it improved. However, even if a certificate is given about English editing, the text still contains some very weird statements like:
"The ALD method relies on the precursor gases or vapors exhibiting an alternating pulse onto the precursors regarding the substrate surface as well as the subsequent surface reaction [16]. The inert gas among the precursor pulses can purify the reactor. The reactor shows a self-restriction development mechanism; thus, conformal thin films develop and possess a large area of precision [17]."
maybe this is English-wise acceptable, but ALD-wise it is still an odd way stating the simple thing.
Likewise, "Shadow masks helped to successfully evaporate the organic layer" - shadow mask does not help in evaporation but patterning of the films.
"films saw deposition in the Beneq TFS-200 ALD reactor" - saw deposition?
"coordinates change from ±0.01 to ±0.01" is still unclear and ill-defined in the manuscript. Please think it carefully, what do you want to say and modify accordingly.
Author Response
Point 1: I've checked the revised manuscript and found it improved. However, even if a certificate is given about English editing, the text still contains some very weird statements like:
"The ALD method relies on the precursor gases or vapors exhibiting an alternating pulse onto the precursors regarding the substrate surface as well as the subsequent surface reaction [16]. The inert gas among the precursor pulses can purify the reactor. The reactor shows a self-restriction development mechanism; thus, conformal thin films develop and possess a large area of precision [17]."
Maybe this is English-wise acceptable, but ALD-wise it is still an odd way stating the simple thing.
Response 1: Thanks for your suggestions and we have corrected it in revised manuscript.
Point 2: Likewise, "Shadow masks helped to successfully evaporate the organic layer" -shadow mask does not help in evaporation but patterning of the films.
Response 2: Sorry for this mistake and we have corrected it to clarify this point in the revised version.
Point 3: "films saw deposition in the Beneq TFS-200 ALD reactor" - saw deposition?
Response 3: Sorry for this mistake and we have corrected it in revised manuscript.
Point 4: "coordinates change from ±0.01 to ±0.01" is still unclear and ill-defined in the manuscript. Please think it carefully, what do you want to say and modify accordingly.
Response 4: Sorry for this unclear and ill-defined description and we have added the revised explanation in manuscript.
We are grateful to your careful reading and making these valuable comments
Special thanks to you for your constructive comments.
Author Response File: Author Response.docx
