Organic Semiconducting Polymers in Photonic Devices: From Fundamental Properties to Emerging Applications

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The authors of the manuscript “Organic Semiconducting Polymers in Photonic Devices: From Fundamental Properties to Emerging Applications” have explored, in their review, the wide area of organic semiconductors dealing with photonic applications. Literature background and basic info are given, illustrating and clarifying which are the goals which the research in this field is aimed to. Even if may reviews about organic semiconductors are present, they show a discussion about a few examples and the working principles of these semiconductors are often not given; instead, in this review, optical properties and non-linear phenomena associated to polymer organic semiconductors. After this brief description of principles and properties underlying these materials, the focus shifts to a rapid digression. Examples discussed in the manuscript are appropriate. Finally, applications of the materials are examined as components of passive and active components. Emerging applications are considered too. Conclusions are consistent with the info given by the authors and the references are appropriate. This review is not a comprehensive one, but gives the basic principles about the polymer organic semiconductors and their applications in the photonic devices. It could be considered like an introductory review to the topic. Some minor issues are present and for this reason my overall recommendation is to “accept after minor revisions”.

///COMMENTS///

Abstract: I don’t think that this is a “comprehensive” review (see also lines 180-183). This is a well-made review giving interesting hints but a comprehensive review about polymer organic semiconductor should be longer than this one and discussing in details many and many examples, processes, applications. Instead, many points are briefly mentioned or discusses. Obviously, it is very difficult to make a review that is at the same time profoundly detailed and discussing many topics.

Lines 180-186. A brief introduction to conjugated polymers could be useful to schematically introduce the concept and not introducing it abruptly. Then, classes of conjugated polymers can be described.

Line 251: a table reporting the main categories of polymer organic semiconductors could be useful

Author Response

The authors are thankful for the valuable review.

Reviewer: Lines 180-186. A brief introduction to conjugated polymers could be useful to schematically introduce the concept and not introducing it abruptly. Then, classes of conjugated polymers can be described.

Authors: Thank you for your kind suggestion. The introduction part of the Material section was revised to follow your recommendation. Please see lines 181-205

 

Reviewer: Line 251: a table reporting the main categories of polymer organic semiconductors could be useful

Authors: We added an additional table (see line 478) and we believe that these two tables will guide the reader along the material processing and applications.

 

At the end, we are very grateful for the review with constructive comments improving the manuscript level. 

Reviewer 2 Report

Comments and Suggestions for Authors

The review report can be found in the attached file.

Comments for author File: Comments.pdf

Author Response

Revewier: The review discusses well-known and extensively studied polymers without offering any novel insights. While the authors mention that the band gap should be approximately 2 eV for photovoltaic applications—an aspect that has already been thoroughly researched—they do not address charge carrier mobility resistance or polymer morphology. Given that polymers tend to be amorphous, which hinders charge carrier hopping between polymer chains, the authors should explore this aspect in greater depth and consider new techniques to mitigate these challenges.

Authors: Our review specifically focuses on photonic applications of organic semiconductors where optical properties (absorption, emission, nonlinear effects) are the primary interest rather than charge transport mechanisms. The manuscript emphasises unique optical characteristics and photonic device applications, including both passive and active components, with particular attention to emerging areas like neuromorphic and quantum photonics. While we acknowledge the relationship between morphology and optical performance, an in-depth discussion of charge transport falls outside the scope of this photonics-focused review.

 

Reviewer: The authors do not address the thermal stability of the polymers, many of which cannot withstand the temperatures required for photovoltaic device fabrication, leading to degradation and loss of properties. Even in cases where polymers can endure these conditions, their lifespan remains limited due to environmental factors that accelerate degradation, coupled with low efficiency despite their cost-effectiveness. The authors should explore this issue in greater detail.
The solubility of these materials is a critical factor, as most are insoluble, which limits certain device fabrication techniques such as spin coating, as well as characterization methods like UV and NMR spectroscopy. The authors should address this issue, particularly since, for insoluble polymers, UV measurements must be performed on solid-state deposits to determine the optical band gap. It is also advisable for them to discuss electrochemical techniques for both device construction and characterization, including the formation of thin-film deposits and the determination of frontier orbitals (HOMO and LUMO). Additionally, they should consider the electrochemical band gap, which often differs slightly from the optical band gap due to charge and mass transport phenomena inherent to electrochemical methods.

 

Authors: 

Thank you for your additional comments regarding thermal stability, solubility challenges, and characterization methods for organic semiconductors. We appreciate these valuable insights.
In response to your feedback, we have added a new subsection (4.1) titled "Fabrication Approaches for Polymer Photonic Devices" that directly addresses these important considerations. This section discusses both solvent-based and solvent-free processing methods, with particular attention to solubility limitations of many conjugated polymers. We explicitly note how extended π-conjugation can significantly reduce solubility in common solvents or render certain polymers completely insoluble, and how these challenges have driven the development of alternative processing strategies.
The subsection also covers thermal properties of polymers in the context of thermal nanoimprint lithography, hot embossing, and other thermal processing techniques. Additionally, we discuss post-processing methods including thermal annealing that can enhance both optical and electronic properties of the fabricated structures.
While our review remains focused on photonic rather than photovoltaic applications, we believe these additions address the key materials processing challenges that are relevant to the photonic devices discussed throughout the manuscript.

 

Reviewer: Additionally, updating the references would significantly improve the manuscript's relevance and depth.

Authors: Thank you for your suggestion regarding updating references. We appreciate your attention to the currency of cited literature. While we have included many recent works, we have deliberately maintained some older references where they represent seminal contributions or original discoveries that established fundamental concepts in the field. These foundational works provide important historical context and acknowledge the pioneering researchers whose contributions laid the groundwork for current developments. Nevertheless, we have ensured that discussions of emerging applications and recent advances are supported by up-to-date references, with many citations from the last five years, particularly in sections covering neuromorphic photonics, quantum systems, and bio-integrated devices.

Reviewer 3 Report

Comments and Suggestions for Authors

This review article focuses on organic semiconductors for photonic applications as active and passive components.  

The manuscript needs to be revised, and the following main points need to be carefully addressed before it can be considered for publication:

1. First, the added value of this review article among the large literature in the field should be clearly addressed in the
2. Noteworthy, for sake of completeness, in the introduction, the discussion should be extended by providing an overview also on other challenging systems for advanced photonic devices, such as engineered semiconductor nanostructures for high-performance nanodevices, as reported in the following relevant papers [https://doi.org/10.1515/nanoph-2019-0156; https://doi.org/10.1063/1.3578189] which are worth mentioning. This will allow to compare the benefits and performances of different systems (inorganic nanowire structures compared with polymeric nanofibers), justifying the choice to focus on organic semiconductor materials, for better understand the importance of this article.
3. Section “2. Fundamentals principles” seems too elementary; it seems more suitable for a thesis chapter than for a scientific paper. Although a brief overview of the concept is allowed, it is necessary to shorten this section and present/critically comment on the remaining part in more depth. Even within this section, as far as nonlinear optical effects are concerned (from line 132 onwards), each of them should be described and discussed more thoroughly.
4. In the overall paper the carrier transport appears to be of crucial importance for the presented devices; it should be reported that a peculiar method to experimentally investigate the electrical properties, is by using electron beam induced current measurements, as reported in this remarkable article which deserves to be mentioned [https://doi.org/10.1021/nl502995q].
5. Scheme 1, although it is a schematic, should be recalled as Fig.2 and, consequently, all the figures renamed accordingly. The caption of Fig.2 at the beginning should, then reporting the following description: “Schematic of molecular structure …”.
6. An important aspect of the studied structures is related to their preparation methods. Therefore, at least a short paragraph should be inserted and, possibly, the chemical reactions involved should be reported.
7. Furthermore, there should be a discussion on the control, reproducibility in the realization of the polymer, and on the stability over time under different conditions of use.
8. Furthermore, Table 1 should include a further last column reporting the number of the reference from which the data reported in each row is taken.
9. I would like to point out that throughout the article only 2 schematics (Fig.1 and Scheme 1), 2 figures from the literature (Fig.2 and 3) and a table (Table 1) are reported. Therefore, it is suggested that the authors expand the scientific discussion with the description of further peculiar aspects and related examples.
10. The phrase "this comprehensive review" is used several times in the article, as well as in the abstract. Since the paper focuses on a few specific aspects and it is limited in the number of examples that are discussed in depth, it is suggested to avoid the term "comprehensive" which in any case seems unsuitable.
11. On line 580, some data (name of funder/grant number), if any, is missing.

Author Response

Reviewer: 1. First, the added value of this review article among the large literature in the field should be clearly addressed in the

Authors: Thank you for emphasising the importance of clearly stating our review's added value. We have completely revised the abstract to address this concern. The new abstract now explicitly highlights the distinctive contribution of our work – focusing on organic semiconductors as a specialised subset of polymer materials with unique combined electronic-optical functionality that enables capabilities impossible with conventional insulating polymers. 

 

Reviewer: 2. Noteworthy, for sake of completeness, in the introduction, the discussion should be extended by providing an overview also on other challenging systems for advanced photonic devices, such as engineered semiconductor nanostructures for high-performance nanodevices, as reported in the following relevant papers [https://doi.org/10.1515/nanoph-2019-0156; https://doi.org/10.1063/1.3578189] which are worth mentioning. This will allow to compare the benefits and performances of different systems (inorganic nanowire structures compared with polymeric nanofibers), justifying the choice to focus on organic semiconductor materials, for better understand the importance of this article.

Authors: Thank you for suggesting additional context regarding inorganic semiconductor nanostructures. While we acknowledge the value of comparing organic semiconductors with inorganic counterparts, we have deliberately kept our focus narrow to maintain the review's clarity and depth on polymer-based systems. A comprehensive comparison with inorganic nanowire structures would significantly expand the scope and potentially dilute our targeted analysis of organic semiconductor materials in photonic applications. The introduction does briefly mention traditional inorganic materials as context, which we believe provides sufficient framing without diverting from our core focus. We appreciate your suggestion and will consider a comparative analysis for future work.

 

Reviewer: 3. Section “2. Fundamentals principles” seems too elementary; it seems more suitable for a thesis chapter than for a scientific paper. Although a brief overview of the concept is allowed, it is necessary to shorten this section and present/critically comment on the remaining part in more depth. Even within this section, as far as nonlinear optical effects are concerned (from line 132 onwards), each of them should be described and discussed more thoroughly.

Authors: Thank you for your thoughtful comments regarding Section 2. We understand your concern that this section might appear elementary. Our intention was to provide sufficient background for readers who may be approaching organic semiconductors from adjacent fields such as photonics or materials science and may not be familiar with their fundamental properties. This inclusivity aligns with the interdisciplinary nature of the field.
Regarding the nonlinear optical effects discussion, we appreciate your suggestion for more thorough treatment. While we recognise the value this would add, we made a deliberate choice to maintain balance across the review's scope. Given our primary focus on materials systems and device applications, expanding the nonlinear effects discussion would either require significant additional length or would necessitate reducing other critical sections. We believe the current treatment provides a sufficient foundation for understanding the subsequent device discussions while maintaining an appropriate scope for a review article.

 

Reviewer: 4. In the overall paper the carrier transport appears to be of crucial importance for the presented devices; it should be reported that a peculiar method to experimentally investigate the electrical properties, is by using electron beam induced current measurements, as reported in this remarkable article which deserves to be mentioned [https://doi.org/10.1021/nl502995q].

Authors: Thank you for suggesting the inclusion of electron beam induced current (EBIC) measurements as a characterization technique. While EBIC has indeed proven valuable for investigating carrier transport in many semiconductor systems, particularly inorganic materials like the Ga/GaAs structures referenced, we have intentionally limited our discussion of such characterization methods for several reasons.
First, electron beam techniques present significant challenges when applied to organic semiconductors due to the radiation sensitivity of these materials. Polymer systems often experience degradation under electron beam exposure, which can alter the very properties being measured and potentially lead to misleading results.
Second, as mentioned in our previous response, our review maintains a deliberate focus on the optical properties and photonic applications of organic semiconductors rather than their electronic transport characteristics. While we acknowledge the interconnection between optical performance and carrier transport, a detailed discussion of transport characterization methods would extend beyond our intended scope. We appreciate your suggestion and recognize the value of EBIC for semiconductor characterization in appropriate material systems.

 

Reviewer: 5. Scheme 1, although it is a schematic, should be recalled as Fig.2 and, consequently, all the figures renamed accordingly. The caption of Fig.2 at the beginning should, then reporting the following description: “Schematic of molecular structure …”.

Authors: We will follow all recommendations of the Editors regarding the manuscript modification to follow the journal rules.

 

Reviewer: 6. An important aspect of the studied structures is related to their preparation methods. Therefore, at least a short paragraph should be inserted and, possibly, the chemical reactions involved should be reported.

Authors: Thank you for highlighting the importance of preparation methods for these structures. We fully agree that fabrication approaches are critical to understanding the implementation of organic semiconductors in photonic devices. In direct response to your comment, we have added a new subchapter (Section 4.1: "Fabrication Approaches for Polymer Photonic Devices") that addresses this important aspect. This new section provides a comprehensive overview of both solvent-based and solvent-free processing methods, with particular attention to the challenges posed by solubility limitations of many conjugated polymers. The section also includes a detailed table (Table 1) summarizing various fabrication techniques, their key features, resolution capabilities, applications, and compatible materials. We believe this addition significantly enhances the practical value of the review by connecting material properties with fabrication considerations. Thank you for this constructive suggestion that has improved the manuscript.

 

Reviewer: 7. Furthermore, there should be a discussion on the control, reproducibility in the realization of the polymer, and on the stability over time under different conditions of use.

Authors: Thank you for suggesting a discussion on control, reproducibility, and long-term stability of polymers under various conditions. While we acknowledge the importance of these aspects for practical implementation, we have made a deliberate choice to limit our scope to focus primarily on the optical properties and photonic applications of organic semiconductors. A comprehensive treatment of long-term stability would necessitate substantial additional content on degradation mechanisms, environmental factors, encapsulation strategies, and accelerated aging studies—topics that would extend significantly beyond our current focus and available space. We do touch briefly on stability considerations in the context of specific materials and devices throughout the manuscript, but a dedicated in-depth analysis of these aspects would be better suited to a separate review specifically focused on stability and reliability considerations in organic semiconductor devices.

 

Reviewer: 8. Furthermore, Table 1 should include a further last column reporting the number of the reference from which the data reported in each row is taken.

Authors: The table weas modified according to your comment.

 

Reviewer: 9. I would like to point out that throughout the article only 2 schematics (Fig.1 and Scheme 1), 2 figures from the literature (Fig.2 and 3) and a table (Table 1) are reported. Therefore, it is suggested that the authors expand the scientific discussion with the description of further peculiar aspects and related examples.

Authors: Thank you for your observation regarding the visual elements in our manuscript. We appreciate your suggestion to include additional figures to enhance the scientific discussion. We would like to note that in addition to the elements you mentioned (Fig. 1, Scheme 1, Fig. 2, Fig. 3, and Table 1), we have also included Table 2, which provides a comprehensive overview of passive and active photonic devices based on organic semiconductors. The two tables serve different but complementary purposes - Table 1 summarizes fabrication techniques with their key features and applications, while Table 2 categorizes device types by their material families and functions. Together with the figures and scheme, we believe these elements provide substantial visual support for the concepts discussed. Nevertheless, we understand the value of additional visual representations and will consider incorporating more illustrative examples in future work to further strengthen the presentation of key concepts.

 

Reviewer: 10. The phrase "this comprehensive review" is used several times in the article, as well as in the abstract. Since the paper focuses on a few specific aspects and it is limited in the number of examples that are discussed in depth, it is suggested to avoid the term "comprehensive" which in any case seems unsuitable.

Authors: Thank you for highlighting our repeated use of the term "comprehensive" throughout the manuscript. We agree that this characterisation could potentially set expectations that exceed the scope of any single review. In response to your feedback, we have carefully revised the text to remove this descriptor throughout the manuscript, including in the abstract. We have replaced it with more precise language that better reflects the specific focus and boundaries of our review. This modification helps present our work more accurately and avoids overstating its breadth.

 

Reviewer: 11. On line 580, some data (name of funder/grant number), if any, is missing.

Authors: Thank you for your sharp-eyed review. The funding was mentioned in the acknowledgement section. The revised manuscript is corrected.

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

No comments