Review Reports - CH3NH3PbBr3 Perovskite Single-Crystal X-Ray Photon-Counting Detection Based on Multi-Layer Electrodes

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This study investigates multilayer electrodes (Au, Au/Ti, and Au/Pt/Ti) for MAPbBr₃ perovskite single crystals used as X-ray photon counting detector. Among the configurations, Au/Pt/Ti exhibits Ohmic contact, the lowest dark current (107 nA·m⁻² at -50 V), and negligible contact potential difference, as confirmed by Kelvin force microscopy. Using a ⁵⁹·⁵ keV monochromatic X-ray source (²⁴¹Am), the Au/Pt/Ti-based detector demonstrates effective photon counting and imaging capabilities.

However, there are some issues need to be discussed.

The mechanism analysis is insufficient. The author observed no significant contact potential difference between Au/Pt/Ti and MAPbBr₃ using KFM, which explains the Ohmic behavior. However, the specific roles of the Pt and Ti layers in aligning the interface energy levels were not further analyzed. To provide a more specific explanation, an analysis of devices containing only Pt or only Ti layers should be added.
The paper mentioned that Ti serves as an adhesion layer and Pt functions as an isolating layer, but no evidence was provided. Either experimental proof or relevant citations should be added.
Similar multilayer electrode structures have been previously reported in perovskite devices. The authors should more clearly elucidate the unique aspects of the electrode design in this work, such as whether the specific mechanism of the Pt layer in suppressing ion migration and interfacial reactions is superior to existing research.

In summary, I would like to recommend the publication of this work after major revisions.

Author Response

However, there are some issues need to be discussed.

Reply:

Dear reviewer 1

Thank you for your important comments which help us improve our manuscript a lot. We have carefully read your comment, following is the point-to-point response.

Best wishes

Xin

Q1: The mechanism analysis is insufficient. The author observed no significant contact potential difference between Au/Pt/Ti and MAPbBr₃ using KFM, which explains the Ohmic behavior. However, the specific roles of the Pt and Ti layers in aligning the interface energy levels were not further analyzed. To provide a more specific explanation, an analysis of devices containing only Pt or only Ti layers should be added.

Reply:

Thank you for your important comments

For “To provide a more specific explanation”

For the Ti/MAPbBr₃ single crystal interface, Wenqing Zhang and co-author have demonstrated that Ti−N bonds formed at the interface of Ti/MAPbBr₃ single crystal effectively inhibit the electrochemical reaction and ultimately improve the operating stability under a high electric field.[29] However, Ti electrode was easily oxidized in air. Besides, Ti/Au electrode would cause significant inter-layer diffusion between Au and Ti, which could lead to device degradation. Thus, inserting 20 nm thickness Pt layer could effectively prevent Ti segregation.[33]

For “an analysis of devices containing only Pt or only Ti layers should be added.”

We have tried to deposit only Pt and Ti on MAPbBr₃ single crystal. Following I-V characterization was added as supporting information Figure S4

Following is added in the manuscript:

“For MAPbBr₃ single crystals with only Ti and Pt, the I-V characterization was shown in Figure S4.”

Following is added in the supporting information:

Figure S4: I-V characterization results of MAPbBr₃ single crystal with only Ti and Pt electrodes.

Q2: The paper mentioned that Ti serves as an adhesion layer and Pt functions as an isolating layer, but no evidence was provided. Either experimental proof or relevant citations should be added.

Reply: We are grateful to your important comment.

For the “Ti serves as an adhesion layer”, this has been demonstrated by Wenqing Zhang and co-authors in published paper entitled of “High-Performance and Stable Perovskite X‑ray Detection and Imaging Based on a Ti Cathode. ACS Appl. Mater. Interfaces 2024, 16, 12844−12852 ” We have added following explanation in the manuscript:

“For the Ti/MAPbBr₃ single crystal interface, Wenqing Zhang and co-author have demonstrated that Ti−N bonds formed at the interface of Ti/MAPbBr3 single crystal effectively inhibit the electrochemical reaction and ultimately improve the operating stability under a high electric field.[29] However, Ti electrode was easily oxidized in air. ”

For the “Pt functions as an isolating layer”. Following is added in the manuscript:

“Besides, Ti/Au electrode would cause significant inter-layer diffusion between Au and Ti, which could lead to device degradation. Thus, inserting 20 nm thickness Pt layer could effectively prevent Ti segregation.[33]”

Q3: Similar multilayer electrode structures have been previously reported in perovskite devices. The authors should more clearly elucidate the unique aspects of the electrode design in this work, such as whether the specific mechanism of the Pt layer in suppressing ion migration and interfacial reactions is superior to existing research.

Reply:We are grateful to your important comment.

We have added more information about previously reported in perovskite devices.

Following is added in the manuscript:

“In previous reports, multi-layer electrodes including MoOx/Cu/Ag/MoOx, IZrO/IZO, AZO/Au/AZO, AZO/Cu/Ag/AZO and MoOX/Cr/Al were used as low resistivity and high transmittance electrodes applied in solar cell.[29-33] However, these electrodes are not stable under high bias when contact with MAPbBr₃ single crystal.”

In summary, I would like to recommend the publication of this work after major revisions.

Reply: Thank you very much.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This paper examines various electrodes in combination with a CH₃NH₃PbBr₃ single crystal for the detection and imaging of monochromatic X-ray photons with an energy of 59.5 keV. Multilayer electrodes comprising Au, Au/Ti, and Au/Pt/Ti were studied. Using the current-voltage characteristic, it was found that the Au/Pt/Ti electrode exhibited superior performance. The results obtained in this paper are useful for designing electrodes in optoelectronic devices based on lead halide perovskites.

Questions and comments:

- in lines 57, 90, 227, 247, 258, 262, 277, 280, 283, 286, and 298, the subscript should be corrected;

- in Section 2, the purity of the reagents is not specified;

- the sentence in lines 150-151 needs to be rephrased for greater clarity;

Author Response

This paper examines various electrodes in combination with a CH3NH3PbBr3 single crystal for the detection and imaging of monochromatic X-ray photons with an energy of 59.5 keV. Multilayer electrodes comprising Au, Au/Ti, and Au/Pt/Ti were studied. Using the current-voltage characteristic, it was found that the Au/Pt/Ti electrode exhibited superior performance. The results obtained in this paper are useful for designing electrodes in optoelectronic devices based on lead halide perovskites.

Reply:

Dear reviewer 2

Thank you for your important comments which help us improve our manuscript a lot. We are very sorry for these mistakes and we have corrected these mistakes follow your comments. Following is our point-to-point response.

Best wishes

Xin

Questions and comments:

- in lines 57, 90, 227, 247, 258, 262, 277, 280, 283, 286, and 298, the subscript should be corrected;

Reply:

Thank you for your careful review, we are sorry for these mistakes and we have corrected these subscript. Following is modified in the manuscript:

Line 57 “These attributes have enabled MAPbBr₃ single crystals based X-ray ”

Line 90 “Lead bromide (PbBr₂; 99%)”

Line 227 “MAPbBr₃ single crystals for ”

Line 247 “Crystallization of CsPbBr₃ single”

Line 258 ”Perovskite CsPbBr₃ Single Crystal Detector ”

Line 262 “High speed growth of MAPbBr₃ single ”

Line 277 “Stability of the MAPbBr₃ Single Crystal”

Line 280 “of Detector-Grade Cd_0.9Zn_0.1Te Crystals ”

Line 283 “CH₃NH₃PbBr₃ perovskite single crystal”

Line 286 “ Resolution in Perovskite CsPbBr₃ Detectors ”

Line 298 “Spectrometer-Grade CsPbBr₃ Gamma-ray Detectors. ”

- in Section 2, the purity of the reagents is not specified;

Reply:Thank you for your careful review, we are sorry for these mistakes and we have corrected these subscript. Following is modified in the manuscript:

“(MABr, 99%), were purchased from Sigma Aldrich, USA. Dimethyl sulfoxide (DMSO, 99.9%) and dimethylformamide (DMF, 99.9%) ”

- the sentence in lines 150-151 needs to be rephrased for greater clarity;

Reply:Thank you for your careful review, we have rephrased these sentence in the manuscript. Following is changed:

“ Owing to the low and stable dark current, the Au/Pt/Ti multilayer device was used to detect 59.5 keV photons. As shown in Figure 1g, a clear potential pulse induced by a 59.5 keV photon can be observed. In contrast, for the Au/Ti multilayer device and the Au-only device, the noise levels were too high to discriminate the useful signal (Figure S3). The response to alpha particles is presented in Figure S4.

Furthermore, five ²⁴¹Am radioactive sources were used as five point-like X-ray sources. A 1mmthick Al₂O₃ ceramic sheet was placed to filter out alpha particles, allowing only 59.5 keV photons to pass through, as illustrated in Figure 1h. By analyzing the count rate (counts per second) of the Au/Pt/Ti multilayer device at different positions, we successfully obtained an Xray photon counting image.

The five ²⁴¹Am radioactive sources emit only approximately 1000 59.5keV photons per second, resulting in a photon injection rate of just 100 cm⁻² s⁻¹. According to the formula Dair=φ×(μenρ)×E, where Dair is the dose rate, φ is the photon injection rate, E is the energy of each photon and μenρ is the mass energy absorption coefficient, which is 0.0303 cm2g-1 for air.[32], the calculated dose rate is only 0.03 nGy s⁻¹. This value is far below the lowest detectable dose rate of typical energyintegrating Xray detectors.”

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

This paper investigates the differences among three types of electrodes used in MAPbBr₃ for photon-counting X-ray and γ-ray detection. The concept of a multilayer electrode is interesting and demonstrates promising performance when combined with MAPbBr₃. However, the authors are encouraged to address the following points.

The photon-counting demonstration at 59.5 keV is interesting; however, the manuscript would benefit from reporting standard photon-counting figures of merit, particularly the energy resolution (FWHM) and a clearer discussion of the rise time (~2.9 ± 0.2 μs), in comparison with other established heavy‑element photon‑counting detectors, such as CZT.
Regarding long-term stability, the experimental conditions for the measurements shown in Fig. 4(c) and Fig. 4(d) are not clearly specified. In particular, the radiation dose or dose rate under which these measurements were performed should be clarified.
Another important property is spatial resolution. The demonstrated resolution is relatively poor (approximately 2 mm) for many imaging applications. The authors are encouraged to discuss the minimum achievable spatial resolution expected for the proposed detector structure and the factors limiting it.

Author Response

Reviewer 3:

Reply:

Dear reviewer 3

Thank you for your important comments which help us improve our manuscript a lot. Following is our point-to-point response.

Best wishes

Xin

The photon-counting demonstration at 59.5 keV is interesting; however, the manuscript would benefit from reporting standard photon-counting figures of merit, particularly the energy resolution (FWHM) and a clearer discussion of the rise time (~2.9 ± 0.2 μs), in comparison with other established heavyelement photoncounting detectors, such as CZT.

Reply: We are grateful to your important comment. We have added following information in the manuscript:

“The rise time here is not as good as CZT-based photon-counting detectors (about 100 ns). Higher voltage bias should be applied on the device, which could drift these charges with faster speed. “

Regarding long-term stability, the experimental conditions for the measurements shown in Fig. 4(c) and Fig. 4(d) are not clearly specified. In particular, the radiation dose or dose rate under which these measurements were performed should be clarified.

Reply: We are grateful to your important comment. We have added following information in the manuscript:

“the dose rate was only about 0.03 nGy s⁻¹, demonstrating the not bad counting stability. The Au/Pt/Ti device was also very stable. As shown in Figure 4c, the dark current after 6 months (107 nA) maintained almost the same dark current after 3 months (106 nA) stored in ambient. And the long-term irradiation stability was investigated in Figure S7.”

Another important property is spatial resolution. The demonstrated resolution is relatively poor (approximately 2 mm) for many imaging applications. The authors are encouraged to discuss the minimum achievable spatial resolution expected for the proposed detector structure and the factors limiting it.

Reply: We are grateful to your important comment. For commercial X-ray photo-counting detectors applied in CT (NAEOTOM Alpha, SIEMENS), the size of each pixel is about 300 μm. Here, the spatial resolution was limited by the area of the electrodes.

We have added following information in the manuscript:

“Here, the spatial resolution was limited by the area of the electrodes.

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

This paper demonstrates that introducing multi-layer **Au/Pt/Ti electrodes** in CH₃NH₃PbBr₃ (MAPbBr₃) single-crystal detectors improves metal–semiconductor contact, significantly reducing dark current and noise compared to conventional electrodes. As a result, the optimized device enables stable low-dose 59.5 keV X-ray photon-counting detection and basic imaging, highlighting the importance of electrode engineering in perovskite radiation detectors. These are some comments from my side:
1. The paper lacks a quantitative benchmark against existing MAPbBr₃ or CsPbBr₃ photon-counting detectors.
2. The crystallization process (65–85 °C) is relatively broad. Specify temperature ramp rate, growth time, and reproducibility.
3. Improve your literature review by adding new works in other applications of perovskite materials, such as DOI: 10.1021/acsami.5c21545.
4. The PTFE filter pore size is listed as 30 μm, which seems unusually large. Confirm whether this is correct.
5. The claim of Ohmic contact is based only on linear I–V curves. Provide temp-dependent I–V.
6. Is Pt acting as a diffusion barrier or modifying the interface dipole?
7. Dark current density is reported, but device area normalization is unclear. Explicitly define the active area.
8. Long-term stability is shown for 3–6 months, but:
Were devices stored in ambient or inert conditions in the long-term stability test? Was the humidity controlled?
9. Include irradiation stability tests.

Comments on the Quality of English Language

Dear editor,

In my opinion, this paper needs revision before being considered for publication.

Best,

Author Response

Reviewer 4:

Reply:

Dear reviewer 4

Best wishes

Xin

The paper lacks a quantitative benchmark against existing MAPbBr₃ or CsPbBr₃ photon-counting detectors.

Reply: Thank you for your wonderful comments. We have added following in the manuscript:

“These attributes have enabled MAPbBr3 single crystals based X-ray detectors to achieve impressive sensitivity and lowest detection limits, positioning them as viable alternatives to conventional materials such as amorphous selenium, cadmium zinc telluride, and silicon.[17-20] In previous work, CsPbBr₃ single crystal was used as high flux X-ray photon counting detectors with count rate of 263 kcps.[9] Further, MAPbI₃ single crystal was applied in X-ray photon counting detectors with the extrmely low noise-equivalent dose of 90 pGyair.[5]”

The crystallization process (65–85 °C) is relatively broad. Specify temperature ramp rate, growth time, and reproducibility.

Reply: Thank you for your wonderful comments.

“which was placed on a programmable heating station (IKA-RET control-visc) and the growth temperature is 65 to 85 ℃ with rate of 1℃h^-1.”

Improve your literature review by adding new works in other applications of perovskite materials, such as DOI: 10.1021/acsami.5c21545.

Reply:Thank you for your wonderful comments.

We have cited more important papers. Following is added in the manuscript:

“In recent years, lead halide perovskites have garnered significant attention as promising candidates for X-ray detection, owing to their exceptional optoelectronic properties, including high atomic numbers, large mobility-lifetime (μτ) products, and low-cost solution-processability.[11-14]”

The PTFE filter pore size is listed as 30 μm, which seems unusually large. Confirm whether this is correct.

Reply: Thank you for your careful comment, we have corrected this mistake. Following is modified in the manuscript:

“The solutions were filtered through a PTFE filter with a 0.22 μm pore size”

The claim of Ohmic contact is based only on linear I–V curves. Provide temp-dependent I–V.

Reply:Thank you for your wonderful comment. We have added the temp-dependent I-V in Supporting information Figure S3.

Following is added in the manuscript:

“And the I-V characterization with different temperature was shown in Figure S3.”

Following is added in the supporting information:

Figure S3. Temp-dependent I-V characterization of Au/Pt/Ti device.

Is Pt acting as a diffusion barrier or modifying the interface dipole?

Reply:Thank you for your wonderful comment. Yes, Pt acted as a diffusion barrier to prevent the Ti/Au inter-diffuision. Following is added in the manuscript:

Dark current density is reported, but device area normalization is unclear. Explicitly define the active area.

Reply:Thank you for your wonderful comment. We have defined the active area in the manuscript as following:

“the thickness of three type of electrodes was 200 nm and the area of the active area was 25 mm²”

Long-term stability is shown for 3–6 months, but:
Were devices stored in ambient or inert conditions in the long-term stability test? Was the humidity controlled?

Reply:Thank you for your wonderful comment. The devices were stored in ambient. Following is added in the manuscript:

“As shown in Figure 4c, the dark current after 6 months (107 nA) maintained almost the same dark current after 3 months (106 nA) stored in ambient”

Include irradiation stability tests.

Reply: Thank you for your wonderful comment. We have added the irradiation stability tests in Supporting information Figure S7.

Following is added in the manuscript:

“And the long-term irradiation stability was investigated in Figure S7”

Following is added in the supporting information:

Figure S7: X-ray irradiation stability.

Author Response File: Author Response.pdf