Research Progress on Transparent Conductive Properties of SnO₂ Thin Films

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript topic is relevant to the field of optoelectronics, particularly given the industry's shift toward Indium-free Transparent Conductive Oxides (TCOs). However, in its current state, the manuscript functions more as a "catalogue of summaries" rather than a critical scientific review. It lists results paper-by-paper without sufficiently synthesizing the data to explain why certain methods yield better results or analyzing the underlying physical mechanisms (such as scattering mechanisms) in depth. Furthermore, there are significant typographical errors regarding units and symbols that must be corrected.

Major Comments

1. The current structure (Sections 4.1 and 4.2) reads largely as a list of abstracts: "Author X did Y and achieved Z." A high-quality review must compare and contrast findings.

• • My suggestion: Instead of listing papers chronologically or by author, group the discussion by physical phenomena. For example, when discussing doping (Sb, F, Ta), compare the efficiency of these dopants across different methods. Why does Sb-doping yield different mobility limits in Spray Pyrolysis compared to Magnetron Sputtering?
  • My suggestion: Section 5 ("The Influence of different preparation methods...") is the most important section but is currently too brief. The authors should expand this to discuss the trade-offs between grain boundary scattering (dominant in chemical methods) vs. ionized impurity scattering (dominant in high-quality physical films).

2. Section 3 lists basic equations (Tauc plot, Haacke FOM, conductivity) but lacks a discussion on the physics of conduction in SnO₂.

• • The manuscript mentions the Burstein-Moss effect in passing (Section 4.2.1), but it is not explained in the theory section.
  • There is no discussion on the specific scattering mechanisms limiting mobility in SnO₂ (grain boundary vs. ionized impurity vs. lattice vibration). This is fundamental to understanding why the reported mobilities vary so much between ALD and Sol-Gel methods.

3. Treatment of p-type vs. n-type: SnO₂ is intrinsically n-type. The review mentions a study on p-type ZNTO (Ref [22] in the text), but fails to highlight that achieving p-type conductivity in SnO₂ is a major, controversial challenge in the field. The review should explicitly separate the discussion of standard n-type TCOs and the emerging/difficult field of p-type SnO₂, rather than mixing them without context.

4. Figures and Data Visualization:

• • Figure Quality: Most figures (Fig 2, 3, 4, etc.) appear to be direct reproductions from cited papers. While cited, a review paper benefits significantly from new, composite plots generated by the authors. For example, a plot gathering data points (Resistivity vs. Process Temperature) from all 50+ cited papers would be much more valuable than reproducing Figure 2 from a single study.
  • Figure 12: The caption mentions "pure SnO₂ and ATO" but the X-axis is "Sb doping concentration." The distinction is confusing; at 0% doping, it is pure. Please clarify.

5. Typos and Unit Errors: There are pervasive errors in the representation of units, likely due to formatting issues. For instance, Sheet resistance is frequently written as "Ω/□" or "Ω/sq". It should be standardized. In all cases, check the units and ensure consistency.

Minor Comments

1. Abstract: The sentence "It also prospects the application prospects..." is tautological and grammatically incorrect. Please rewrite for better flow (e.g., "It also forecasts the application potential...").
2. Introduction: Table 1 comparison is useful, but the cost comparison is missing. Since the introduction emphasizes "Indium-free" to reduce cost, a column comparing the relative raw material costs of In, Sn, Zn, and Ti would strengthen the argument.
3. Section 4.1.2 (PLD): The manuscript states PLD has a "defect density of 10¹⁵ cm^-3". This is a very strong claim for an oxide thin film. Please verify if this refers to bulk crystals or thin films, as thin films usually have higher defect densities.
4. Formatting: The Tables (2, 3, 4, 5, 6, 7) contain a column for "Year." This is unnecessary in a scientific review table; the citation number is sufficient. I suggest removing the "Year" column to make space for more technical data (e.g., process temperature or thickness).
5. Missing Key Studies: While the review focuses on 2020-2025, it should briefly acknowledge the "champion" historical values for SnO₂ (e.g., F-doped SnO₂ by Gordon et al.) to provide a baseline for how much progress has actually been made in the last 5 years.
6. References: Please ensure all references are formatted consistently. Some appear to be incomplete or lack DOI numbers in the final list.

The English must be polished to correct unit errors, and the discussion must delve deeper into the mechanisms of conductivity rather than just reporting values.

Author Response

Comments1

1. The current structure (Sections 4.1 and 4.2) reads largely as a list of abstracts: "Author X did Y and achieved Z." A high-quality review must compare and contrast findings.

My suggestion: Instead of listing papers chronologically or by author, group the discussion by physical phenomena. For example, when discussing doping (Sb, F, Ta), compare the efficiency of these dopants across different methods. Why does Sb-doping yield different mobility limits in Spray Pyrolysis compared to Magnetron Sputtering?

My suggestion: Section 5 ("The Influence of different preparation methods...") is the most important section but is currently too brief. The authors should expand this to discuss the trade-offs between grain boundary scattering (dominant in chemical methods) vs. ionized impurity scattering (dominant in high-quality physical films).

Response 1:Thank you for pointing this out.Therefore, I have changed the group by physical phenomena such as multiple-structure and doped SnO₂(at page 8-20 ).furthermore,I have enlarged the section 5 to discuss the trade-offs between grain boundary scattering.

Comments 2:

2. Section 3 lists basic equations (Tauc plot, Haacke FOM, conductivity) but lacks a discussion on the physics of conduction in SnO₂.

The manuscript mentions the Burstein-Moss effect in passing (Section 4.2.1), but it is not explained in the theory section.

There is no discussion on the specific scattering mechanisms limiting mobility in SnO₂ (grain boundary vs. ionized impurity vs. lattice vibration). This is fundamental to understanding why the reported mobilities vary so much between ALD and Sol-Gel methods.

Response 2:Thank you for pointing this out.Therefore, I have added a section 3.3 to explain Physical Conduction Mechanism of SnO₂ at page 5.

Comments 3:

3. Treatment of p-type vs. n-type: SnO₂ is intrinsically n-type. The review mentions a study on p-type ZNTO (Ref [22] in the text), but fails to highlight that achieving p-type conductivity in SnO₂ is a major, controversial challenge in the field. The review should explicitly separate the discussion of standard n-type TCOs and the emerging/difficult field of p-type SnO₂, rather than mixing them without context.

Response 3:Thank you for pointing this out.Therefore, I have emphsized that p-SnO₂ is a new and difficult challenge at page 10.

Comments 4:

4. Figures and Data Visualization:

Figure Quality: Most figures (Fig 2, 3, 4, etc.) appear to be direct reproductions from cited papers. While cited, a review paper benefits significantly from new, composite plots generated by the authors. For example, a plot gathering data points (Resistivity vs. Process Temperature) from all 50+ cited papers would be much more valuable than reproducing Figure 2 from a single study.

Figure 12: The caption mentions "pure SnO₂ and ATO" but the X-axis is "Sb doping concentration." The distinction is confusing; at 0% doping, it is pure. Please clarify.

Response 4:Thank you for pointing this out.Therefore, I have collected all of the cited papers in one table at page 21.Furthermore, I remedy the figure 12 at page15.

Comments 5:5. Typos and Unit Errors: There are pervasive errors in the representation of units, likely due to formatting issues. For instance, Sheet resistance is frequently written as "Ω/□" or "Ω/sq". It should be standardized. In all cases, check the units and ensure consistency.

Response 5:Thank you for pointing this out.Therefore, I have checked the typos and unit Errors in the whole paper.

Minor Comments 1:

Abstract: The sentence "It also prospects the application prospects..." is tautological and grammatically incorrect. Please rewrite for better flow (e.g., "It also forecasts the application potential...").

Response 1:Thank you for pointing this out.Therefore, I have changed that sentence to “It also forecasts the application potential of” in the abstract.

Minor Comments 2:

Introduction: Table 1 comparison is useful, but the cost comparison is missing. Since the introduction emphasizes "Indium-free" to reduce cost, a column comparing the relative raw material costs of In, Sn, Zn, and Ti would strengthen the argument.

Response 2:Thank you for pointing this out.Therefore, I have added the cost and row materials of comprision in the table 1 at page2.

Minor Comments 3:

Section 4.1.2 (PLD): The manuscript states PLD has a "defect density of 10¹⁵ cm^-3". This is a very strong claim for an oxide thin film. Please verify if this refers to bulk crystals or thin films, as thin films usually have higher defect densities.

Response 3:Thank you for pointing this out.Therefore, I have changed “10¹⁵ cm⁻³”to “from 10¹⁶ cm^-3 to 10¹⁹ cm^-3”

Minor Comments 4:

Formatting: The Tables (2, 3, 4, 5, 6, 7) contain a column for "Year." This is unnecessary in a scientific review table; the citation number is sufficient. I suggest removing the "Year" column to make space for more technical data (e.g., process temperature or thickness).

Response 4:Thank you for pointing this out.Therefore, I have deleted “years” to add the thickness, FOM_normand ρ_norm in the table 2 at page21.

Minor Comments 5:

Missing Key Studies: While the review focuses on 2020-2025, it should briefly acknowledge the "champion" historical values for SnO₂ (e.g., F-doped SnO₂ by Gordon et al.) to provide a baseline for how much progress has actually been made in the last 5 years.

Response 5:Thank you for pointing this out.Therefore, I have briefly acknowledged the "champion" historical values at section 4.4.2 at page15.

Minor Comments 6:

References: Please ensure all references are formatted consistently. Some appear to be incomplete or lack DOI numbers in the final list.

Response 6:Thank you for pointing this out.Therefore, I have added all the DOI to reference paper.

Reviewer 2 Report

Comments and Suggestions for Authors

Review of the manuscript Coatings-4051989 for the Authors: This manuscript is a broad, mostly literature-based review of tin dioxide (SnO₂) thin films. The review is timely because SnO₂ is a leading ITO alternative and the paper collects many recent (2020–2025) reports and compares performance ranges. However, the manuscript reads as a descriptive catalogue rather than a critical, synthesis-oriented review: quantitative comparisons are sometimes inconsistent, mechanistic discussion is superficial in places, and a few important topics (stability, standardization of metrics, realistic device benchmarking) are under-developed. Please see the detailed comments below.

1) The review reports many numbers from the literature (in multiple tables) but rarely normalizes them or discusses measurement variability. Different authors report sheet resistance, transmittance, and mobility under widely differing film thicknesses, measurement geometries, annealing histories, and mass loadings; the review should (a) explicitly discuss how these differences limit direct comparison, and (b) where possible present normalized metrics (e.g., FOM vs thickness) or highlight representative best-in-class results with measurement details.

2) Industrial adoption of TCOs hinges on long-term stability (thermal, humidity, mechanical flexing, chemical exposure). While the manuscript briefly mentions stability issues (e.g., ALD films losing mobility in humid environments), there is no dedicated, systematic section comparing durability tests (e.g., 85°C/85% RH, high-temperature annealing, bending cycles, chemical resistance) across the methods and dopants. Add a focused section summarizing stability data and mitigation strategies (passivation layers, encapsulation, compositional tuning).

3) The role of oxygen vacancies, dopant sites (substitutional vs interstitial), and band-filling (Burstein–Moss) are mentioned but not developed quantitatively. For a materials-oriented audience, include schematic band diagrams showing how common dopants (Sb, F, Al, Ta, W, Ag, Zn) affect carrier density and mobility and discuss mechanisms that limit mobility (ionized-impurity scattering vs grain-boundary scattering). Cite representative experimental or computational studies where available.

4) The utility of SnO₂ as a replacement for ITO depends on integrating the TCO into real devices (OPV, OLED, perovskite PV, touch panels). The review rarely reports device-level metrics (device VOC/FF changes with electrode, series resistance impact, device lifetimes). Add a subsection that ties film properties to device performance, and summarize studies that directly compare SnO₂ vs ITO in functioning devices.

5) Tables 2–5 — add columns for film thickness and measurement method. Where possible, list the reference directly in each row (some rows already include refs but add explicit citation). Also note whether transmittance is at 550 nm or an average over 400–700 nm.

6) In the conclusions add explicit, prioritized recommendations for future research (e.g., standardized reporting templates, stability testing under IEC/industry conditions, development of high-mobility low-absorption dopants, scalable ALD/continuous ALD research). The current conclusion gives high-level suggestions but would benefit from specifics.

7) Language and style are mostly ok. Fix minor typographical/format issues (several figure captions refer to percentages without units in text; ensure consistent notation for exponents and SI units).

8) Several references are repeated or formatted inconsistently — tidy the bibliography and ensure DOI entries are included.

This review contains valuable, up-to-date material and useful comparative tables that will benefit the field. However, before acceptance it requires substantive revision to (1) improve critical synthesis (normalize comparisons and discuss measurement variability), (2) add a focused treatment of stability/durability, (3) deepen the mechanistic discussion of doping and defect physics, and (4) make tables and figures more reproducible by including measurement details (thickness, probe method, wavelength). After those changes (and editorial polishing), the manuscript would serve as a strong, practical resource on SnO₂ TCOs. With the mentioned revision this review would be a useful reference for the TCO community. For now my recommendation is major revision.

Comments on the Quality of English Language

Language and style are mostly ok. Fix minor typographical/format issues (several figure captions refer to percentages without units in text; ensure consistent notation for exponents and SI units). 

Author Response

Comment 1: The review reports many numbers from the literature (in multiple tables) but rarely normalizes them or discusses measurement variability. Different authors report sheet resistance, transmittance, and mobility under widely differing film thicknesses, measurement geometries, annealing histories, and mass loadings; the review should (a) explicitly discuss how these differences limit direct comparison, and (b) where possible present normalized metrics (e.g., FOM vs thickness) or highlight representative best-in-class results with measurement details.

Response 1:

Thank you for pointing this out.Therefore,I have added a normalized metrics like FOM_norm and ρ_norm at page7.

Comment 2:Industrial adoption of TCOs hinges on long-term stability (thermal, humidity, mechanical flexing, chemical exposure). While the manuscript briefly mentions stability issues (e.g., ALD films losing mobility in humid environments), there is no dedicated, systematic section comparing durability tests (e.g., 85°C/85% RH, high-temperature annealing, bending cycles, chemical resistance) across the methods and dopants. Add a focused section summarizing stability data and mitigation strategies (passivation layers, encapsulation, compositional tuning).

Response 2:

Thank you for pointing this out.Therefore,I have added a section 6.3 to compare the stability of SnO₂ by diffierent methods at page29.

Comment 3:The role of oxygen vacancies, dopant sites (substitutional vs interstitial), and band-filling (Burstein–Moss) are mentioned but not developed quantitatively. For a materials-oriented audience, include schematic band diagrams showing how common dopants (Sb, F, Al, Ta, W, Ag, Zn) affect carrier density and mobility and discuss mechanisms that limit mobility (ionized-impurity scattering vs grain-boundary scattering). Cite representative experimental or computational studies where available.

Response3:

Thank you for pointing this out.Therefore, I have cited a issue to discuss sb doped SnO₂ thin films’ Physical Conduction Mechanism at page5.

Comment 4:The utility of SnO₂ as a replacement for ITO depends on integrating the TCO into real devices (OPV, OLED, perovskite PV, touch panels). The review rarely reports device-level metrics (device VOC/FF changes with electrode, series resistance impact, device lifetimes). Add a subsection that ties film properties to device performance, and summarize studies that directly compare SnO₂ vs ITO in functioning devices.

Response 4:

Thank you for pointing this out.Therefore, I have added a section (6. SnO₂ Transparent Conductive Films in Devices) to summorize the perfomance of devices by SnO₂ and ITO at page 27.

Comment 5:Tables 2–5 — add columns for film thickness and measurement method. Where possible, list the reference directly in each row (some rows already include refs but add explicit citation). Also note whether transmittance is at 550 nm or an average over 400–700 nm.

Response 5:

Thank you for pointing this out.Because I have deleted table 3-5, I leave the table 2  which is summrized about 50 references in one table. Therefore, I have added the citation and transmittance in 550nm or Vis-avg in the table 2.

Comments 6:In the conclusions add explicit, prioritized recommendations for future research (e.g., standardized reporting templates, stability testing under IEC/industry conditions, development of high-mobility low-absorption dopants, scalable ALD/continuous ALD research). The current conclusion gives high-level suggestions but would benefit from specifics.

Response 6:

Thank you for pointing this out.Therefore, I have added explicit, prioritized recommendations for future research in the conclusion at page 31.

Comment 7:Language and style are mostly ok. Fix minor typographical/format issues (several figure captions refer to percentages without units in text; ensure consistent notation for exponents and SI units).

Response 7:

Thank you for pointing this out.Therefore, I have Fixed minor typographical/format issues.

Comments 8:Several references are repeated or formatted inconsistently — tidy the bibliography and ensure DOI entries are included.

Response 8:

Thank you for pointing this out.Therefore, I have added DOI behind the all references.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have successfully addressed the previous concerns; I recommend the manuscript for publication without further changes. 

Reviewer 2 Report

Comments and Suggestions for Authors

Review of the manuscript Coatings-4051989 v2 for the Authors: In the revised version, the authors have substantially improved and expanded the manuscript. As noted previously, this work represents a valuable contribution to the field of transparent conducting oxides (TCOs); therefore, in my opinion, the paper can now be accepted for publication.