Review Reports - SnSe: A Versatile Material for Thermoelectric and Optoelectronic Applications

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript under review is a very interesting and comprehensive review on a hot topic today. It summarizes original results obtained with different synthesis methods and advanced characterization methods and is well-organized and illustrated. The methodology is sound, and the manuscript meets the expected standards in the field. The work supports the conclusions and claims, there are no flaws in the data analysis, interpretation and conclusions. The manuscript deserves publication in your journal since it is of significance to the field and of high relevance to the journal audience. However, it should be considerably improved/partly rewritten according to the issues below:
1. The title is too long, try to make it more attractive and coherent if possible.

Rewrite the Abstract making it more coherent and conclusive. The Abstract contains abbreviations, which are specific for the research field but not commonly used, such as ZT, SPH, etc.
In the Introduction part cancel “strict growth conditions”. Each synthesis method implies it.
Rewrite the Introduction part making it more coherent, including some information about the chalcogenides because selenides belong to them. Give some examples, e.g., AsxTe100-x films, AsS, [L. Mochalov, G. De Filpo]. Then underline that your material of choice is cost-effective, Earth-abundant and non-toxic.
Recently, a new class of the multicationic and -anionic entropy-stabilized chalcogenide alloys based on the (Ge, Sn, Pb) (S, Se, Te) formula has been successfully fabricated experimentally [Zihao Deng et al., Chem. Mater. 32,6070 (2020)] and theoretically A. Bafekry […].
Try to draw the equipment’s schematic diagrams in the same style.
Is Fig. 9 showing continuous thin film surfaces or some nano/micro-structures formed on the substrate surface?
Give the surface orientation of MgO and NaCl crystalline substrates.
Explaining the advantages of the CVD method add that it is industry relevant.
Is the BSE BSEDiffraction?
In 5.1. add “for solar cells” to “traditional materials”.
Rewrite the Conclusions underlying the most important results, approaches and applications only. Make it coherent and conclusive.

Author Response

Dear Reviewer,

Thank you very much for your constructive and insightful comments on our manuscript titled “SnSe: A Versatile Material for Thermoelectric and Optoelectronic Applications — Properties, Controlled Synthesis, and Evolving Review.” We sincerely appreciate your time and effort in reviewing our work. We have carefully considered all your suggestions and have revised the manuscript accordingly. Below, we provide a point-by-point response to your comments and indicate the modifications made in the revised manuscript.

Comments 1:

The title is too long, try to make it more attractive and coherent if possible.

Response 1:

We agree that the original title was overly long and could be streamlined for improved readability and impact. We have therefore shortened the title while retaining its core scientific scope.

On page 1, lines 2 to 4, the revised title is:

SnSe: A Versatile Material for Thermoelectric and Optoelectronic Applications

Comments 2:

Rewrite the Abstract making it more coherent and conclusive. The Abstract contains abbreviations, which are specific for the research field but not commonly used, such as ZT, SPH, etc.

Response 2:

We appreciate this suggestion. The Abstract has been fully rewritten to improve logical flow, strengthen conclusions, and eliminate non-standard abbreviations. All technical terms are now either spelled out or introduced explicitly at first mention.

On pages 1 to 2, lines 21 to 51, we have added the following content:

Tin selenide (SnSe) is a sustainable, lead-free IV–VI semiconductor whose layered orthorhombic crystal structure induces pronounced electronic and phononic anisotropy, enabling diverse energy-related functionalities. This review systematically summarizes recent progress in understanding the structure–property–processing relationships that govern SnSe performance in thermoelectric and optoelectronic applications. Key crystallographic characteristics are first discussed, including the temperature-driven Pnma–Cmcm phase transition, anisotropic band and valley structures, and phonon transport mechanisms that lead to intrinsically low lattice thermal conductivity below 0.5 W m⁻¹ K⁻¹ and tunable carrier transport. Subsequently, major synthesis strategies are critically compared, spanning Bridgman and vertical-gradient single-crystal growth, spark plasma sintering and hot pressing of polycrystals, as well as vapor- and solution-based thin-film fabrication, with emphasis on process windows, stoichiometry control, defect chemistry, and microstructure engineering. For thermoelectric applications, directional and temperature-dependent transport behaviors are analyzed, highlighting record thermoelectric performance in single-crystal SnSe at hi we analyze directional and temperature-dependent transport, highlighting record thermoelectric figure of merit values exceeding 2.6 along the b-axis in single-crystal SnSe at ~900 K, as well as recent progress in polycrystalline and thin-film systems through alkali/coinage-metal doping (Ag, Na, Cu), isovalent and heterovalent substitution (Zn, S), and hierarchical microstructural design. For optoelectronic applications, optical properties, carrier dynamics, and photoresponse characteristics are summarized, underscoring high absorption coefficients exceeding 10⁴ cm⁻¹ and bandgap tunability across the visible to near-infrared range, together with interface engineering strategies for thin-film photovoltaics and broadband photodetectors. Emerging applications beyond energy conversion, including phase-change memory and electrochemical energy storage, are also reviewed. Finally, key challenges related to selenium volatility, performance reproducibility, long-term stability, and scalable manufacturing are identified. Overall, this review provides a process-oriented and application-driven framework to guide the rational design, synthesis optimization, and device integration of SnSe-based materials.

Keywords: Tin selenide; structure–property–processing; thermoelectric; thin-film photovoltaics

Comments 3:

In the Introduction part cancel “strict growth conditions”. Each synthesis method implies it.

Response 3:

We agree with the reviewer's opinion and have removed the "strict growth conditions".

On page 9, lines 349 to 352, we have added the following content:

The current challenge is that single-crystal growth methods typically involve long growth cycles and limited throughput, which result in slow production rates, high fabrication costs, and difficulties in scaling up large-sized SnSe single crystals with optimized thermoelectric performance.

Comments 4:

Rewrite the Introduction part making it more coherent, including some information about the chalcogenides because selenides belong to them. Give some examples, e.g., AsxTe100-x films, AsS, [L. Mochalov, G. De Filpo]. Then underline that your material of choice is cost-effective, Earth-abundant and non-toxic.

Response 4:

We agree with the reviewer's opinion and have made revisions to the introduction section.

On pages 2 to 3, lines 86 to 100, we have added the following content:

Chalcogenide materials, comprising compounds formed with group VI elements such as sulfur, selenium, and tellurium, have long attracted significant interest due to their rich electronic structures, strong light–matter interactions, and versatile phase-change and transport properties. Representative chalcogenide systems, including amorphous and crystalline As–Te and As–S thin films, have been extensively investigated for applications in photonics, memory devices, and infrared optics, demonstrating tunable optical bandgaps and composition-dependent transport behavior. These studies highlight the broad functional potential of chalcogenide semiconductors across energy and optoelectronic technologies. Within this material family, tin selenide (SnSe) has emerged as a particularly attractive candidate owing to its simple binary composition, low material cost, Earth-abundant constituent elements, and absence of toxic heavy metals, in contrast to conventional Pb- or Cd-based chalcogenides. These attributes, combined with its anisotropic crystal structure and favorable transport characteristics, make SnSe a promising and sustainable platform for thermoelectric and optoelectronic applications.

Comments 5:

Recently, a new class of the multicationic and -anionic entropy-stabilized chalcogenide alloys based on the (Ge, Sn, Pb) (S, Se, Te) formula has been successfully fabricated experimentally [Zihao Deng et al., Chem. Mater. 32,6070 (2020)] and theoretically A. Bafekry […].

Response 5:

We thank the reviewer for highlighting this important and emerging direction in chalcogenide research. We fully agree that mentioning these entropy-stabilized materials provides a valuable, forward-looking perspective that connects the tailored design of binary SnSe to the broader frontier of compositional engineering in complex chalcogenides.

On page 33, lines 1255 to 1258, we have added the following content:

Looking forward, the design principles honed in SnSe research are paving the way for even more complex material systems, such as novel multicationic/anionic entropy-stabilized chalcogenides. Exploring these vast compositional spaces (e.g., based on (Ge, Sn, Pb)(S, Se, Te) formulations) represents a promising frontier for next-generation property engineering and device innovation [239].

On page 44, lines 1824 to 1826, we have added the following content:

[239] Deng, Z.; Olvera, A.; Casamento, J.; Lopez, J.S.; Williams, L.; Lu, R.; Shi, G.; Poudeu, P.F.P.; Kioupakis, E. Semiconducting High-Entropy Chalcogenide Alloys with Ambi-ionic Entropy Stabilization and Ambipolar Doping. Chemistry of Materials 2020, 32, 6070-6077. https://doi.org/10.1021/acs.chemmater.0c01555

Comments 6:

Try to draw the equipment’s schematic diagrams in the same style.

Response 6:

We sincerely thank the reviewer for this suggestion aimed at enhancing the visual consistency and professional presentation of our manuscript. We fully agree that a uniform style for all schematics would be ideal and appreciate the importance of this point.

Action Taken: We have carefully reviewed all schematic diagrams (Figs. 3, 4, 5, 6, 7, 8, 10, 11, 12, 13). These figures were adapted directly from the respective cited sources to ensure accurate representation of the original experimental setups described in the literature. Unfortunately, at this revision stage, obtaining permissions or resources to completely redraw all schematics in a single, new style within a feasible timeframe presents a significant practical challenge, as each diagram is sourced from different published works.

However, to improve clarity and address the spirit of the comment, we have taken the following steps:

We have verified that all schematic figures are clear, correctly labeled, and accurately cited to their original sources.

Comments 7:

Is Fig. 9 showing continuous thin film surfaces or some nano/micro-structures formed on the substrate surface?

Response 7:

Thank you for this important clarification request. We have revised the figure caption and corresponding text to explicitly describe the morphology.

On page 16, lines 598 to 599, we have added the following content:

These structures evolve from fibrous to particulate features rather than forming an ideally continuous film.

On page 17, lines 608 to 609, we have added the following content:

SEM images illustrating the nano-/micro-structures formed by thermal evaporation at different substrate temperatures: a)RT; b)150℃; c)250℃; d)350℃; e)450℃ [150].

Comments 8:

Give the surface orientation of MgO and NaCl crystalline substrates.

Response 8:

We appreciate this technical point and have added the missing crystallographic details.

On page 17, line 6176, we have added the following content:

for example, SnSe films grown on NaCl (100) substrates have good crystallinity, while films prepared on MgO (100) substrates show high hole mobility [152].

Comments 9:

Explaining the advantages of the CVD method add that it is industry relevant.

Response 9:

We have added this important point.

On page 15, lines 569 to 571, we have added the following content:

Furthermore, CVD is a well-established and industry-relevant technique, capable of scalable and high-throughput manufacturing, which is crucial for commercial applications.

Comments 10:

Is the BSE BSEDiffraction?

Response 10:

BSE stands for Backscattered Electron imaging, a mode in Scanning Electron Microscopy (SEM), distinct from diffraction techniques. We have clarified this.

On page 25, lines 889 to 890, we have added the following content:

XRD analysis combined with scanning electron microscopy in the backscattered electron (BSE) mode indicated the presence of a cubic AgSnSe₂ secondary phase.

Comments 11:

In 5.1. add “for solar cells” to “traditional materials”.

Response 11:

We agree and have implemented this clarification.

On page 28, line 1039, we have added the following content:

“traditional materials for solar cells”

Comments 12:

Rewrite the Conclusions underlying the most important results, approaches and applications only. Make it coherent and conclusive.

Response 12:

We appreciate this recommendation and have rewritten the Conclusions to improve focus and impact.

On pages 32 to 33, lines 1229 to 1258, we have added the following content:

This review has provided a comprehensive overview of SnSe by integrating its crystal structure, multiscale transport physics, and processing strategies to elucidate how these factors collectively govern thermoelectric and optoelectronic performance. The intrinsic lattice anisotropy, coupled with valley-structured electronic bands and strong phonon scattering, establishes SnSe as a unique platform in which charge and heat transport can be effectively decoupled through materials design. Across single-crystal, polycrystalline, and thin-film forms, performance optimization consistently relies on precise stoichiometry control to mitigate selenium volatility, rational defect and dopant engineering, and controlled microstructural uniformity within realistic processing windows.

For thermoelectric applications, high performance is achieved by the synergistic optimization of carrier concentration and phonon transport using elemental doping, alloying, and microstructural engineering, while practical deployment further requires attention to module-level efficiency, contact stability, and mechanical robustness under thermal cycling. For optoelectronic applications, SnSe exhibits strong optical absorption and favorable carrier transport, with device-level performance governed by interface engineering strategies such as band alignment, defect passivation, and contact selectivity. These approaches enable improved responsivity, carrier lifetime, and operational stability in thin-film photovoltaics and photodetectors.

Beyond energy conversion, SnSe-based materials are increasingly explored in phase-change memory and electrochemical energy storage, underscoring their multifunctional potential. Nevertheless, challenges associated with stoichiometry drift, deep defect states, reproducibility, environmental stability, and scalable manufacturing remain key barriers to large-scale implementation. Overall, SnSe has progressed from a laboratory model system to a versatile and sustainable materials platform. The structure–processing–property relationships summarized in this review provide a practical framework for guiding synthesis optimization, interface design, and reliability benchmarking, thereby facilitating the translation of laboratory-scale advances into robust and scalable technologies. Looking forward, the design principles established through SnSe research offer valuable guidance for emerging multicationic and multianionic entropy-stabilized chalcogenides, opening new opportunities for next-generation functional materials and devices [269].

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript under consideration is a review paper, which concerns tin selenide (SnSe) as a promising material for thermoelectric and optoelectronic applications. The article comprehensively analyzes the structure, properties, and synthesis methods of SnSe, as well as its potential applications in energy conversion technologies. The review systematically describes the relationship between the structure, properties, and processing methods of SnSe. The Authors provide a detailed analysis of the crystal structure, electronic properties, and synthesis methods of SnSe, which allows for a deeper understanding of the material’s potential. However, there are some issues that need to be addressed. Below is the list of comments.

1) The Authors are encouraged to formulate the novelty and scientific soundness of the presented review more explicitly, since there are about 70 review papers found in Scopus, which involve SnSe. The most similar are the following: 1) Shi, Weiran, et al. "Tin selenide (SnSe): growth, properties, and applications." Advanced Science 5.4 (2018): 1700602. DOI: 10.1002/advs.201700602; 2) Kumar, M., Rani, S., Singh, Y., Gour, K. S., & Singh, V. N. (2021). Tin-selenide as a futuristic material: properties and applications. RSC advances, 11(12), 6477-6503. DOI: 10.1039/d0ra09807h

2) The Authors should pay more attention to the scalability and economic feasibility of the synthesis procedures supported with the corresponding discussion.

3) In Subsection 5.1, the Authors discuss photovoltaic applications of SnSe and list the factors that limit the material’s performance. The manuscript would benefit from ranking these factors in terms of the scale of their negative effect and achievability of overcoming the limitations, together with the synergism of the factors. Correspondingly, a more detailed discussion is required. Probably, some SCAPS-1D-based reasoning should be involved.

4) The discussion regarding the device integration limitations should be extended across the subsections of Section 5.

5)There are also some technical remarks.

5-1) What do the Authors mean by “block party cobalt” (subsection 3.1)? Probably, “block” should be “bulk”; this should be checked throughout the text.

5-2) What do the Authors mean by the slash sign in Table 2? If the data are not available or the concept is not applicable, this should be n.a.

5-3) In Table 6, some sources are indicated as “SeSe”. This should be corrected or explained.

5-4) In Subsection 5.1 “α-SNSE” should be “α-SnSe”.

Author Response

Dear Reviewer,

Comments 1:

The Authors are encouraged to formulate the novelty and scientific soundness of the presented review more explicitly, since there are about 70 review papers found in Scopus, which involve SnSe. The most similar are the following:

1) Shi, Weiran, et al. "Tin selenide (SnSe): growth, properties, and applications." Advanced Science 5.4 (2018): 1700602. DOI: 10.1002/advs.201700602;

2) Kumar, M., Rani, S., Singh, Y., Gour, K. S., & Singh, V. N. (2021). Tin-selenide as a futuristic material: properties and applications. RSC advances, 11(12), 6477-6503. DOI: 10.1039/d0ra09807h

Response 1:

We are grateful to the reviewers for their observations on the current situation regarding the number of existing reviews on SnSe. Indeed, many excellent reviews have been published, including those mentioned above. Previous reviews often focused on thermoelectricity or photovoltaics, while our research systematically correlated the elements of crystal structure, band engineering, phonon transport, synthesis methods, doping strategies, and device integration in both thermoelectric and photovoltaic fields. Through continuous comparative comprehensive analysis, we conducted a detailed and chronological comparison of synthesis methods (single crystals, polycrystals, thin films), including clear considerations of process windows, stoichiometric ratio control, and scalability. This analysis is more comprehensive than previous reviews. At the device and application levels, we expanded the review scope to challenges at the module level (average ZT value, contact resistance, cycling stability) and the potential across applications (phase change memory, supercapacitors, batteries), and provided a practical implementation roadmap. Our review covers the latest research results, including emerging doping schemes, heterojunction designs, and scalability challenges, which were not fully addressed in previous evaluations.

On pages 4, lines 170 to 176, we added:

"Unlike previous reviews that often focused only on individual aspects of SnSe, this study provides a comprehensive perspective on structure - property - processing - application, with particular emphasis on scalable synthesis, device-level integration challenges, and interdisciplinary applications. We also included the latest developments up to 2025 (including doping, heterojunction design, and emerging applications), providing researchers and engineers with a timely and forward-looking reference material."

Comments 2:

The Authors should pay more attention to the scalability and economic feasibility of the synthesis procedures supported with the corresponding discussion.

Response 2:

We agree that scalability and cost are critical for the real-world application of SnSe. In the revised manuscript, we have added a dedicated discussion on the scalability and economic aspects of key synthesis method.

On page 14, lines 538 to 547, we have added the following content:

"The wet chemical methods (solution method, hydrothermal method, thermal injection method) can effectively control the morphology of the materials and are suitable for laboratory-scale production. However, their scalability is often limited by issues such as batch production, solvent recovery, and yield. In contrast, solid-state methods such as SPS and HP are more suitable for large-scale production, but they require higher energy and equipment costs. For thin films, thermal evaporation and spray deposition have relatively lower costs and scalability, while MBE and ALD have high precision but are costly and have low output. Future research should focus on developing continuous-flow synthesis, roll-to-roll processing, and precursor recovery technologies to improve the economic feasibility of SnSe production."

On page 21, lines 736 to 742, we have added the following content:

"From an industrial perspective, methods such as thermal evaporation and sputtering (physical vapor deposition, PVD) strike a balance between cost, uniformity, and production efficiency, making them well-suited for large-area photovoltaic and thermoelectric coatings. Chemical vapor deposition (CVD) performs well in terms of quality and consistency, but requires optimizing the delivery of precursors and the utilization of gases to reduce costs. Atomic layer deposition (ALD) is currently mainly used in high-value applications due to its slow deposition rate and high cost of precursors. "

Comments 3:

In Subsection 5.1, the Authors discuss photovoltaic applications of SnSe and list the factors that limit the material’s performance. The manuscript would benefit from ranking these factors in terms of the scale of their negative effect and achievability of overcoming the limitations, together with the synergism of the factors. Correspondingly, a more detailed discussion is required. Probably, some SCAPS-1D-based reasoning should be involved.

Response 3:

Thank you for this valuable suggestion. We have restructured the discussion in Subsection 5.1 to rank the limiting factors and included references to simulation studies (including SCAPS-1D) that quantify their impact.

On page 29, lines 1063 to 1083, we have added the following content:

The efficiency of SnSe solar cells is constrained by multiple interrelated factors, which can be prioritized as follows:

Bulk and interface defects: Deep-level defects and secondary phases (e.g., SnSe₂) act as recombination centers, severely reducing carrier lifetime. This is the most critical issue, as confirmed by SCAPS-1D simulations showing that defect densities above 10¹⁶ cm⁻³ drastically reduce VOC and FF;

Poor back contact and band alignment: Mismatched work functions and high interfacial recombination at the SnSe/back-contact and SnSe/buffer-layer interfaces limit VOC and JSC. Achieving ohmic contacts and proper band alignment is essential;

Low carrier mobility and conductivity: Although SnSe exhibits high intrinsic mobility, grain boundaries and point defects in polycrystalline films reduce effective mobility, lowering FF and JSC;

Optical and thermal losses: Parasitic absorption, reflection, and thermalization losses further cap efficiency, but these are secondary to electronic losses.

Addressing these factors in synergy—for example, through defect passivation combined with optimized buffer layers—is key to bridging the gap between current efficiencies and the theoretical limit.

Comments 4:

The discussion regarding the device integration limitations should be extended across the subsections of Section 5..

Response 4:

We have expanded the discussion of device integration challenges in each subsection of Section 5 to provide a more cohesive and application-oriented perspective.

On page 30, lines 1128 to 1132, we have added the following content:

Beyond material ZT, practical thermoelectric modules require low and stable contact resistance, thermal cycling durability, and effective packaging to minimize parasitic heat losses. For SnSe-based devices, the anisotropic thermal expansion and Se volatility under long-term operation pose additional reliability concerns. Furthermore, scalable fabrication of segmented or graded legs to cover broad temperature ranges remains a challenge.

On page 31, lines 1153 to 1156, we have added the following content:

For PCRAM applications, the switching speed, endurance, and thermal stability of SnSe-based devices must be improved through interface engineering and alloying. Integration with CMOS-compatible electrodes and encapsulation to prevent oxidation are also critical for real-world deployment.

On page 32, lines 1186 to 1189, we have added the following content:

While SnSe anodes show high capacity, their volume expansion during cycling leads to mechanical degradation and capacity fade. Composite designs (e.g., SnSe/C) and electrolyte additives are needed to stabilize solid-electrolyte interphase (SEI) formation and enhance cycle life.

Comments 5:

There are also some technical remarks.

What do the Authors mean by “block party cobalt” (subsection 3.1)? Probably, “block” should be “bulk”; this should be checked throughout the text.

P6. Table 2. 5-2 What do the Authors mean by the slash sign in Table 2? If the data are not available or the concept is not applicable, this should be n.a.

P18. Table 6. 5-3 In Table 6, some sources are indicated as “SeSe”. This should be corrected or explained.

P27. L956. 5-4 In Subsection 5.1 “α-SNSE” should be “α-SnSe”.

Response 5:

5-1 Corrected. We have changed “block party cobalt” to “bulk cobalt” and checked throughout the text for similar instances of “block” used in place of “bulk.” The modified sections are on page 6, line 247 and 251, page 8, line 310, page 13, line 495, page 21, line 805 and line 806.

5-2 We have corrected this by replacing the slash with "n.a." where necessary. The modified section is on page 8, in Table 2.

5-3 We have corrected the term "SeSe" to "SnSe". The modified sections are on page 20, in Table 6.

5-4 We have corrected the term "α-SNSE" to "α-SnSe". The modified section is on page 29, line 1053.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript entitled, ‘SnSe: A Versatile Material for Thermoelectric and Optoelectronic Applications— Properties, Controlled Synthesis, and Evolving Review’ reported Thermoelectric and Optoelectronic Applications of SnSe. The article should be modified according the following comments:

The abstract lacks specificity regarding the data presented in the study. It is recommended to highlight key findings or notable data to give readers a clearer understanding of the study's contributions.
Author should clarify why SnSe is described as a “versatile material.” What specific evidence supports this claim across both thermoelectric and optoelectronic applications?
How does each synthesis route influence defect formation, microstructure, and final performance? Can the author strengthen the synthesis–structure–property correlation?
Should the author add a more critical comparison of synthesis techniques, highlighting limitations, reproducibility issues, and scale-up challenges?
Can the author include more recent literature to support major claims, especially papers published in the last 2–3 years?
Some article would have significance in this aspect which are recommended here for author’s references :

Ganguly, S., Das, P., Bose, M., Mondal, S., Das, A. K., & Das, N. C. (2017). Strongly blue-luminescent N-doped carbogenic dots as a tracer metal sensing probe in aqueous medium and its potential activity towards in situ Ag-nanoparticle synthesis. Sensors and Actuators B: Chemical, 252, 735-746.
Perala, R. S., Chandrasekar, N., Balaji, R., Alexander, P. S., Humaidi, N. Z. N., & Hwang, M. T. (2024). A comprehensive review on graphene-based materials: From synthesis to contemporary sensor applications. Materials Science and Engineering: R: Reports, 159, 100805.

Author Response

Dear Reviewer,

Comments 1:

The abstract lacks specificity regarding the data presented in the study. It is recommended to highlight key findings or notable data to give readers a clearer understanding of the study's contributions.

Response 1:

We agree with the reviewer. The abstract has been revised to include quantitative and concrete performance descriptors, rather than general statements. Specifically, we now explicitly mention representative thermoelectric figures of merit (e.g., ZT values exceeding 2.6 along the b-axis in single-crystal SnSe at high temperatures), key optoelectronic parameters (such as absorption coefficients >10⁴ cm⁻¹ and bandgap tunability from ~0.9 to ~1.7 eV), and device-relevant considerations including average ZT, contact resistance, and interface engineering.

On pages 1 to 2, lines 21 to 51, we have added the following content:

Keywords: Tin selenide; structure–property–processing; thermoelectric; thin-film photovoltaics

Comments 2:

Author should clarify why SnSe is described as a “versatile material.” What specific evidence supports this claim across both thermoelectric and optoelectronic applications?

Response 2:

We thank the reviewer for this important comment. In the revised manuscript, we have clarified that the term “versatile material” is not used as a qualitative descriptor, but is instead grounded in multi-dimensional experimental and technological evidence. Specifically, the versatility of SnSe is now explicitly justified along four complementary axes:

Functional versatility: SnSe supports high-performance thermoelectric energy conversion (ultra-low lattice thermal conductivity and high ZT values exceeding 2.6 in single crystals) while simultaneously exhibiting optoelectronic functionality, including strong broadband light absorption, bandgap tunability, and photoresponse suitable for photovoltaics and photodetectors.
Structural and dimensional versatility: SnSe exists in multiple crystallographic phases (Pnma and Cmcm) and structural forms, including single crystals, textured polycrystals, thin films, nanostructures, and low-dimensional layers, each enabling distinct anisotropic transport and optical behaviors.
Processing versatility: SnSe can be synthesized using a wide range of solid-state, vapor-phase, and solution-based techniques, enabling controllable microstructures, defect populations, and stoichiometry across bulk and thin-film formats.
Application-level versatility: Beyond thermoelectric and optoelectronic devices, SnSe has demonstrated applicability in phase-change memory, energy storage (supercapacitors and rechargeable batteries), and sensing-related platforms, reflecting its adaptability to diverse device architectures.

On pages 4 to 5, lines 177 to 200, we have added the following content:

In this review, SnSe is described as a versatile material based on explicit experimental and technological evidence rather than qualitative appeal. We first explore the fundamental physical properties of SnSe, including its layered orthorhombic crystal structure, anisotropic band structure, and the temperature-driven Pnma–Cmcm phase transition, which collectively govern its electronic, phononic, and optical behaviors. Subsequently, a range of synthesis strategies is systematically discussed, encompassing single-crystal growth via the Bridgman and vertical-gradient methods, polycrystalline fabrication through spark plasma sintering and hot pressing, and thin-film preparation using physical and chemical vapor deposition. Each synthesis route is analyzed in terms of its process characteristics, defect formation, microstructure control, and applicable scenarios. Building on these foundations, we review recent progress in the thermoelectric and optoelectronic performance of SnSe, highlighting its intrinsically low lattice thermal conductivity, strong transport anisotropy, broadband light absorption, and bandgap tunability, which enable applications in thermoelectric power generation and cooling, thin-film photovoltaics, and photodetectors. Beyond these established fields, emerging applications such as phase-change memory and electrochemical energy storage are also surveyed, further underscoring the functional and application-level versatility of SnSe. Despite its promising research and application prospects, SnSe still faces challenges including high preparation cost, complex processing routes, stoichiometry sensitivity, and long-term performance stability. Looking forward, the integration of advanced nanostructuring strategies, data-driven optimization approaches such as artificial intelligence, and interdisciplinary research is expected to accelerate the rational design, scalable fabrication, and device-level implementation of SnSe, ultimately enabling its full potential across diverse scientific and technological domains.

Comments 3:

How does each synthesis route influence defect formation, microstructure, and final performance? Can the author strengthen the synthesis–structure–property correlation?

Response 3:

We have added dedicated paragraphs to explicitly link synthesis parameters to defect formation, microstructure, and performance:

Bridgman growth: High temperature gradients can induce point defects and vacancies, affecting carrier concentration.

SPS/HP: Rapid sintering can create fine grains and dense boundaries, reducing thermal conductivity but potentially increasing electrical resistivity

Solution-based methods: Ligand chemistry and reaction temperature control nucleation kinetics, leading to tailored morphologies (nanosheets, rods) and defect densities.

PVD/CVD/ALD: Substrate temperature and precursor ratios determine crystallinity, orientation, and stoichiometry, directly impacting optoelectronic response.

On page 22, lines 763 to 773, we have added the following content:

Each synthesis route imposes distinct defect landscapes and microstructures that directly influence functional properties. For instance, Bridgman-grown single crystals exhibit low dislocation densities but may contain Se vacancies that act as p-type dopants. Spark plasma sintering (SPS) introduces high-density grain boundaries that scatter phonons effectively, lowering lattice thermal conductivity but also reducing carrier mobility. Solution-processed nanocrystals often contain surface ligands and stacking faults, which can passivate traps or introduce recombination centers depending on the chemistry. In thin films, the choice between PVD and CVD affects grain size, texture, and interface states, thereby modulating carrier lifetime and Seebeck coefficient. Understanding these correlations enables targeted optimization for either thermoelectric or optoelectronic applications.

Comments 4:

Should the author add a more critical comparison of synthesis techniques, highlighting limitations, reproducibility issues, and scale-up challenges?

Response 4:

We have added a critical comparison in Sections 2.2.2 and 2.2.3, focusing on limitations and scalability:

Wet-chemical methods (solution, hydrothermal, hot-injection): Excellent morphology control but suffer from batch-to-batch variability, solvent toxicity, and low yield.

Solid-state methods (SPS, HP): Suitable for bulk production but require high energy and expensive equipment.

Thin-film deposition: Thermal evaporation is low-cost but lacks uniformity; PLD and MBE offer high quality but are not scalable; CVD strikes a balance but precursor delivery and gas utilization need optimization for cost reduction.

On page 14, lines 538 to 547, we have added the following content:

On page 21, lines 736 to 742, we have added the following content:

Comments 5:

Can the author include more recent literature to support major claims, especially papers published in the last 2–3 years?

Response 5:

We thank the reviewer for the suggestion to include more recent literature to support and contextualize our claims. In direct response to this guidance, we have carefully evaluated and integrated the suggested references by Ganguly et al. (2017) and Perala et al. (2024) into the manuscript.

These references have been strategically incorporated to broaden the perspective of our review within its defined scope.

On page 32, lines 1184 to 1186, we have added the following content:

The integration of carbonaceous materials (from conductive graphene to functional carbon dots [231] is a common strategy to enhance the performance of various electrode materials, as reviewed for graphene-based systems [232].

On page 44, lines 1818 to 1822, we have added the following content:

Ganguly, S.; Das, P.; Bose, M.; Mondal, S.; Das, A.K.; Das, N.C. Strongly blue-luminescent N-doped carbogenic dots as a tracer metal sensing probe in aqueous medium and its potential activity towards in situ Ag-nanoparticle synthesis. Sensors and Actuators B: Chemical 2017, 252, 735-746. https://doi.org/10.1016/j.snb.2017.06.068Get rights and content
Perala, R.S.; Chandrasekar, N.; Balaji, R.; Alexander, P.S.; Humaidi, N.Z.N.; Hwang, M.T. A comprehensive review on graphene-based materials: From synthesis to contemporary sensor applications. Materials Science and Engineering: R: Reports 2024, 159, 100805. https://doi.org/10.1016/j.mser.2024.100805

Comments 6:

Some article would have significance in this aspect which are recommended here for author’s references.

Ganguly, S., Das, P., Bose, M., Mondal, S., Das, A. K., & Das, N. C. (2017). Strongly blue-luminescent N-doped carbogenic dots as a tracer metal sensing probe in aqueous medium and its potential activity towards in situ Ag-nanoparticle synthesis. Sensors and Actuators B: Chemical, 252, 735-746.

Perala, R. S., Chandrasekar, N., Balaji, R., Alexander, P. S., Humaidi, N. Z. N., & Hwang, M. T. (2024). A comprehensive review on graphene-based materials: From synthesis to contemporary sensor applications. Materials Science and Engineering: R: Reports, 159, 100805.

Response 6:

We sincerely thank the reviewer for suggesting the relevant works by Ganguly et al. (2017) and Perala et al. (2024). We appreciate this suggestion as it prompted us to consider how to best situate our focused review on SnSe within the broader and dynamic context of advanced functional materials research.

On page 32, lines 1184 to 1186, we have added the following content:

On page 41, lines 1818 to 1822, we have added the following content:

[231] Ganguly, S.; Das, P.; Bose, M.; Mondal, S.; Das, A.K.; Das, N.C. Strongly blue-luminescent N-doped carbogenic dots as a tracer metal sensing probe in aqueous medium and its potential activity towards in situ Ag-nanoparticle synthesis. Sensors and Actuators B: Chemical 2017, 252, 735-746. https://doi.org/10.1016/j.snb.2017.06.068Get rights and content

[232] Perala, R.S.; Chandrasekar, N.; Balaji, R.; Alexander, P.S.; Humaidi, N.Z.N.; Hwang, M.T. A comprehensive review on graphene-based materials: From synthesis to contemporary sensor applications. Materials Science and Engineering: R: Reports 2024, 159, 100805. https://doi.org/10.1016/j.mser.2024.100805

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The review manuscript has been considerably improved; however, it is still not good enough and needs to be further ameliorated in order to be written in a more coherent and comprehensive way.

Page 3, line111-116 “Similarly, SnSe materials have been proven to be excellent light absorbers in thin-film solar cells due to their high absorption coefficient (>10⁴cm⁻¹)” In which spectral range? How does it compare to the GaAs absorption coefficient values [https://www.ioffe.ru/SVA/NSM/Semicond/GaAs/optic.html and references therein], which is a photovoltaics-relevant material?

“and tunable band gap (0.9eV - 1.6eV) [21,22]. As a binary semiconductor, SnSe is seen as a potential alternative to multi-element thin-film solar cells such as CIGS, CZTSe and CISe due to its simplified elemental system and simplified fabrication process. However, it is worth noting that the current photoelectric conversion efficiency of SnSe cells (a value?!?) is still far below the theoretical value predicted by the Shockley-Queisser limit (~32%) [23], and their performance optimization still faces key challenges”. Which challenges do you meen?

No references are given for amorphous AsxTe100-x and As–S thin films (see the old review report, comment 4 and 5). Answer very punctually each question with proper references.

The Introduction part is based on 59 references only. Please add more because it is a review paper and you need to summarize all possible knowledge and underline the best achievements in the field.

Page 5, paragraph 2 “Bulk” is singular not plural.

”show high hole mobility [152]”. Give the values. It is a review paper.

Line 1141 “The core advantages of LiBs lie in their environmental friendliness, high energy/power density and long cycle life [234,235].” Please provide data for these important materials’ advantages.

Please rewrite Lines 1054-1055 :

“Industrial waste heat into electrical energy, thus enabling the utilization of clean energy. SnSe films convert industrial waste heat, building waste heat (which accounts for one-third of global waste heat) and…”

Comments on the Quality of English Language

It is fine

Author Response

Response to Reviewer 1 Comments

Dear reviewer,

Comments 1:

Response 1:

We agree. The originally stated “>10⁴ cm⁻¹” should be explicitly tied to the above-bandgap spectral region. We have revised the sentence to specify the relevant visible–near-IR range and added a brief quantitative comparison to GaAs using tabulated optical constants (n, k) at room temperature.

On page 3, lines 111 to 124, we have added the following content:

Similarly, SnSe is a strong absorber for photovoltaic applications, exhibiting an absorption coefficient typically α > 10⁴ cm⁻¹ across the above-bandgap visible–near-IR region (commonly reported from ~400 nm to ~1100–1500 nm, depending on bandgap and film microstructure), and reaching ~10⁵ cm⁻¹ in the visible [21-24]. For comparison, GaAs shows α ~ 1×10⁴ cm⁻¹ near ~0.83 μm and increases to >10⁵ cm⁻¹ at shorter wavelengths. However, reported SnSe-based photovoltaic efficiencies remain modest (e.g., up to ~6.44% in SnSe/Si heterojunction devices under sub-1 sun illumination, while many all-thin-film SnSe heterojunction reports remain around the ~1–3% level), still far below the Shockley–Queisser limit (~32%) [27,28]. This gap is mainly associated with difficulty in achieving phase-pure, stoichiometric SnSe with low deep-defect density (Se volatility/secondary phases), strong bulk/interface recombination (grain boundaries and interface states), suboptimal band alignment and non-ohmic/unstable contacts, and process–microstructure nonuniformity that limits carrier collection [29,30].

Comments 2:

Response 2:

We agree on both points. We now state explicit experimentally reported efficiencies and clarify the key performance-limiting challenges in one concise sentence in the Introduction, with a forward reference to the detailed discussion later in the photovoltaic section.

On page 3, lines 111 to 124, we have added the following content:

Similarly, SnSe is a strong absorber for photovoltaic applications, exhibiting an absorption coefficient typically α > 10⁴ cm⁻¹ across the above-bandgap visible–near-IR region (commonly reported from ~400 nm to ~1100–1500 nm, depending on bandgap and film microstructure), and reaching ~10⁵ cm⁻¹ in the visible [23-26]. For comparison, GaAs shows α ~ 1×10⁴ cm⁻¹ near ~0.83 μm and increases to >10⁵ cm⁻¹ at shorter wavelengths. However, reported SnSe-based photovoltaic efficiencies remain modest (e.g., up to ~6.44% in SnSe/Si heterojunction devices under sub-1 sun illumination, while many all-thin-film SnSe heterojunction reports remain around the ~1–3% level), still far below the Shockley–Queisser limit (~32%) [27,28]. This gap is mainly associated with difficulty in achieving phase-pure, stoichiometric SnSe with low deep-defect density (Se volatility/secondary phases), strong bulk/interface recombination (grain boundaries and interface states), suboptimal band alignment and non-ohmic/unstable contacts, and process–microstructure nonuniformity that limits carrier collection [29,30].

Comments 3:

No references are given for amorphous AsxTe100-x and As–S thin films (see the old review report, comment 4 and 5). Answer very punctually each question with proper references.

Response 3:

We agree. We have added appropriate primary references for As_xTe_100−x amorphous films and As–S (e.g., As₂S₃) thin films.

[6] Mochalov, L.; Kudryashov, M.; Logunov, A.; Zelentsov, S.; Nezhdanov, A.; Mashin, A.; Gogova, D.; Chidichimo, G.; De Filpo, G. Structural and optical properties of arsenic sulfide films synthesized by a novel PECVD-based approach. Superlattices and Microstructures 2017, 111, 1104-1112. https://doi.org/10.1016/j.spmi.2017.08.007

[7] Mochalov, L.; Nezhdanov, A.; Strikovskiy, A.; Gushin, M.; Chidichimo, G.; De Filpo, G.; & Mashin, A. Synthesis and properties of As_xTe_100−x films prepared by plasma deposition via elemental As and Te. Optical and Quantum Electronics 2017, 49, 274. https://doi.org/10.1007/s11082-017-1117-1

Comments 4:

The Introduction part is based on 59 references only. Please add more because it is a review paper and you need to summarize all possible knowledge and underline the best achievements in the field.

Response 4:

We agree. We have already added relevant references in the introduction section.

[28] Shockley, W.; Queisser, H.J. Detailed Balance Limit of Efficiency of p-n Junction Solar Cells. J. Appl. Phys. 1961, 32, 510-519. https://doi.org/10.1063/1.1736034

[29] Sturge, M. Optical absorption of gallium arsenide between 0.6 and 2.75 eV. Physical Review 1962, 127, 768. https://doi.org/10.1103/PhysRev.127.768

[30] Aspnes, D.E.; Studna, A.A. Dielectric functions and optical parameters of si, ge, gap, gaas, gasb, inp, inas, and insb from 1.5 to 6.0 ev. Physical review B 1983, 27, 985. https://doi.org/10.1103/PhysRevB.27.985

Comments 5:

Page 5, paragraph 2 “Bulk” is singular not plural.

Response 5:

We agree. We replaced “bulks” with “bulk” on page 5, line 221 and line 225.

Comments 6:

”show high hole mobility [152]”. Give the values. It is a review paper.

Response 6:

We agree. We added the reported Hall hole mobility value.

On page 17, line 592, we have added the following content:

SnSe films grown on NaCl (100) substrates have good crystallinity, while films prepared on MgO (100) substrates show high hole mobility, reaching ~60 cm²·V⁻¹·s⁻¹ at room temperature.

Comments 7:

Response 7:

We agree. We replaced the qualitative claim with representative quantitative metrics widely reported for Li-ion batteries, including specific energy, specific power, round-trip efficiency.

On page 33, lines 1222 to 1225, we have added the following content:

The core advantages of Li-ion batteries include high specific energy (typically ~75–250 Wh·kg⁻¹ at the cell level), high specific power (commonly ~150–315 W·kg⁻¹), high round-trip efficiency (~85–95%), and long cycle life (often ~10³–10³.5 cycles to ~80% capacity, depending on chemistry and operating window).

Comments 8:

Please rewrite Lines 1054-1055 :

Response 8:

We agree. The original sentence was fragmented and repetitive. We rewrote it to be concise, logically connected, and non-overclaiming.

On pages 31 to 32, lines 1130 to 1141, we have added the following content:

In thermoelectric devices, SnSe films can convert temperature gradients—originating from natural thermal differences or industrial process heat—directly into electrical energy, thereby improving energy-utilization efficiency. In practical waste-heat recovery scenarios, SnSe films harvest electricity from industrial waste heat and heat dissipated in building energy systems via the Seebeck effect. Owing to their layered orthorhombic structure, SnSe-based materials can combine favorable electronic transport with suppressed lattice thermal conductivity, which is essential for achieving a high thermoelectric figure of merit (). For building energy-conservation applications, SnSe thermoelectric devices can be integrated into distributed power solutions for electronics and sensor networks, enabling recovery of heat from lighting, household appliances, and other heat-emitting infrastructure and thereby reducing net electricity consumption;

Thanks you very much for your attention and time. Happy New Year to you!

Yours sincerely,

Chi Zhang

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

My comments and concerns have been addressed, so no I can recommend publishing the manuscript after some minor technical corrections.

The phrase “bulk party cobalt” should be “bulk cobalt” (page 21).
Caption to Fig. 14: “Seekbeck” should be “Seebeck coefficient”.
There are some spaces missing, e.g., page 25, line 890 and page 30, lines 1109-1110: “1.3eV” and “materials[199]”. The manuscript should be carefully proofread for typos.
"VOC" and "JSC" should be “V_OC” and “J_SC” at page 28 (subscripts are required).
The issue with references is still not solved. There are duplicate references in the reference list, e.g., 16 and 74, 47 and 116, 46 and 117. Also, Refs. 4 and 5 have identical DOIs. Thus, the reference list should be carefully checked.

Author Response

Response to Reviewer 2 Comments

Dear reviewer,

Comments 1:

My comments and concerns have been addressed, so no I can recommend publishing the manuscript after some minor technical corrections.

The phrase “bulk party cobalt” should be “bulk cobalt” (page 21).
Caption to Fig. 14: “Seekbeck” should be “Seebeck coefficient”.
There are some spaces missing, e.g., page 25, line 890 and page 30, lines 1109-1110: “1.3eV” and “materials[199]”. The manuscript should be carefully proofread for typos.
"VOC" and "JSC" should be “V_OC” and “J_SC” at page 28 (subscripts are required).
The issue with references is still not solved. There are duplicate references in the reference list, e.g., 16 and 74, 47 and 116, 46 and 117. Also, Refs. 4 and 5 have identical DOIs. Thus, the reference list should be carefully checked.

Response 1:

1-1 We agree with the reviewer. The phrase “bulk party cobalt” was a typographical error.

On page 23, line 783, we replaced “bulk party cobalt” with “bulk cobalt”.

1-2 We agree and have corrected the spelling. In the caption of Figure 14, “Seekbeck” was corrected to “Seebeck coefficient”. (on page 24, line 821)

1-3 We agree. We have corrected the missing spaces in the specific examples highlighted by the reviewer and performed an additional proofreading pass to identify and fix similar spacing/typographical issues across the manuscript (especially around units and reference brackets).

On page 3, lines 101 to 104, we have corrected the term "1.3eV" to "1.3 eV", "0.9eV" to "0.9 eV", "1.74eV" to "1.74 eV", "1.2eV" to "1.2 eV", "1.55eV" to "1.55 eV", "1.12eV" to "1.12 eV".

On page 5, lines 214 to 215, we have corrected the term "0.61eV to 0.39eV" to "0.61 eV" to "1.39 eV".

On page 6, lines 250 to 265, we have corrected the term "0.9-1.3eV" to "0.9 – 1.3 eV", "1.3eV" to "1.3 eV", "0.9eV" to "0.9 eV", "1.4eV" to "1.4 eV".

On page 27, line 957, we have corrected the term "0.9eV" to "0.9 eV", and"1.3eV" to "1.3 eV".

On page 28, line 980, we have corrected the term "0.9eV to 1.6eV" to"0,9 eV to 1.6 eV".

On page 33, lines 1189 to 1190, we have corrected the term "materials[199]" to " materials [204]"

1-4 We have revised these photovoltaic parameter notations to include subscripts on Table 8.

1-5 We re-checked the reference list carefully and corrected DOI errors and duplicate entries. In particular, we addressed the duplicated DOI issue and re-validated the list to avoid repeated records.

We corrected the DOI for the Yuan et al. review paper (Ref. 5) to “https://doi.org/10.1016/j.cclet.2017.11.038” based on the publisher record.

Thanks you very much for your attention and time. Happy New Year to you!

Yours sincerely,

Chi Zhang

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Author did most of the comments but some are still not addressed properly:

How do the authors reconcile the strong anisotropy observed in single crystals with the typically reduced performance in polycrystalline and thin-film SnSe? What processing strategies are most promising to bridge this gap?
The review discusses various doping strategies (Ag, Na, Cu, Zn, S). Can the authors provide a more comparative or quantitative assessment of how these dopants affect carrier concentration, mobility, and long-term stability?
The references recommended by the reviewer are not highlighted in the main revised section. Those should be highlighted as well.

Author Response

Response to Reviewer 3 Comments
Dear Reviewer,
Thank you very much for your constructive and insightful comments on our manuscript titled “SnSe: A Versatile Material for Thermoelectric and Optoelectronic Applications — Properties, Controlled Synthesis, and Evolving Review.” We sincerely appreciate your time and effort in reviewing our work. We have carefully considered all your suggestions and have revised the manuscript accordingly. Below, we provide a point-by-point response to your comments and indicate the modifications made in the revised manuscript.

Comments 1:
How do the authors reconcile the strong anisotropy observed in single crystals with the typically reduced performance in polycrystalline and thin-film SnSe? What processing strategies are most promising to bridge this gap?
Response 1:
We appreciate the reviewer’s insightful question. We clarify in the revised manuscript that the strong anisotropy reported for single-crystal SnSe is an intrinsic tensor property stemming from its layered orthorhombic lattice, leading to markedly direction-dependent transport (e.g., the b-axis outperforming the a-axis in ZT).By contrast, the reduced performance commonly observed in polycrystalline and thin-film SnSe is primarily governed by extrinsic microstructural factors, including (i) random grain orientation that averages anisotropic transport, (ii) grain boundaries and point defects that reduce effective carrier mobility and enhance carrier scattering/recombination, and (iii) stoichiometry/secondary-phase issues that introduce deep-level recombination centers in films.To bridge this gap, we have added a dedicated discussion summarizing the most promising processing strategies: texture/orientation engineering (to preferentially align high-performance crystallographic directions), grain-boundary/defect suppression and passivation (to recover mobility/lifetime), and stoichiometry control to minimize secondary phases. These strategies are now explicitly linked to both thermoelectric and photovoltaic contexts in the revised text.

On page 24, lines 823 to 832, we have added the following content:
The pronounced anisotropy of single-crystal SnSe is an intrinsic consequence of its layered Pnma lattice, yielding direction-dependent electrical conductivity and thermal transport and thus ZT. In polycrystalline SnSe, however, randomly oriented grains largely average out the anisotropic tensors, while grain boundaries and point defects introduce additional carrier scattering that reduces the effective mobility and power factor. In thin films, the same microstructural limitations are further amplified by stoichiometry fluctuations and secondary phases that act as deep-level recombination centers, thereby lowering carrier lifetime and device fill factor/current. Accordingly, the performance gap between single crystals and polycrystalline/film SnSe is not contradictory, but reflects the dominant role of extrinsic microstructure and defect physics in practical forms.

Comments 2:
The review discusses various doping strategies (Ag, Na, Cu, Zn, S). Can the authors provide a more comparative or quantitative assessment of how these dopants affect carrier concentration, mobility, and long-term stability?
Response 2:
We agree with the reviewer that a more comparative and quantitative summary is valuable.

On pages 26 to 27, lines 919 to 950, we have added the following content:
3.3 Comparative dopant effects on carrier transport and stability
A key role of aliovalent acceptor dopants (notably Na and Ag) is to lift the intrinsically low hole density of SnSe (typically in the ~10¹⁷ cm⁻³ regime) into the ~10¹⁹ cm⁻³ range required for high power factor, but the net gain is governed by a carrier-density–mobility trade-off and by dopant solubility. For Ag alloying/doping, Hall carrier concentration can increase progressively and saturate on the order of ~10¹⁹ cm⁻³, whereas the effective mobility may be constrained when Ag exceeds its solubility and triggers AgSnSe₂ precipitation; the secondary phase is widely reported to deplete carriers and scatter mobile carriers, leading to non-monotonic transport optimization windows. For Na doping, a similarly high carrier density (e.g., ~2.7 × 10¹⁹ cm⁻³ in representative polycrystalline systems) is achievable, often accompanied by improved electrical conductivity and power factor; however, Na-doped polycrystalline SnSe has been reported to exhibit instability under repeated thermal cycling (heating/cooling), making stability a key differentiator between Na- and Ag-based acceptor strategies.
Beyond acceptor doping, Cu-related strategies frequently rely on the formation of a Cu₂Se second phase and dopant-induced nanostructuring; this pathway is particularly effective in reducing lattice thermal conductivity (κ) through enhanced phonon scattering, while the electrical response depends on whether increased carrier concentration compensates any mobility penalty caused by carrier scattering at heterogeneous interfaces. Zn substitution is often discussed in terms of defect tuning: moderate Zn incorporation can boost conductivity and Seebeck coefficient (hence ZT), but excessive defect/impurity scattering can reduce mobility, underscoring the need to optimize dopant level to balance carrier concentration and μ. In anion-site regulation, S substitution/alloying (e.g., SnS₁₋ₓSeₓ solid solutions) provides a complementary lever: alloy disorder from random S/Se occupation suppresses κ, while Hall carrier concentration and mobility evolve concurrently with composition, offering an intrinsic “composition knob” to co-tune electronic transport and phonon scattering.
Collectively, these dopant classes can be rationalized by whether they primarily target carrier density control (Na/Ag), κ suppression via second-phase/nanostructuring (Cu-related), or coupled electronic–phononic tuning via defect/alloy engineering (Zn and S/Se), and the optimal choice is ultimately dictated by the required balance among carrier concentration, mobility retention, and long-term stability.

Comments 3:
The references recommended by the reviewer are not highlighted in the main revised section. Those should be highlighted as well.
Response 3:
We apologize for the oversight. In the revised manuscript, all reviewer-recommended references have now been explicitly cited in the relevant main-text discussion and visually highlighted to facilitate identification by the reviewer and editor.

Thanks you very much for your attention and time. Happy New Year to you!

Yours sincerely,
Chi Zhang

Author Response File: Author Response.pdf