Foam-like 3D Graphene as a Charge Transport Modifier in Zinc Oxide Electron Transport Material in Perovskite Solar Cells
and Rajan Jose 5,6,*Round 1
Reviewer 1 Report
In this work，ZnO was embed in foam-like 3D graphene for electrode material of a Perovskite Solar Cell. the3D graphene can play a role of charge collector media and maintain stereo frame. Comparing to TiO2, ZnO has similar band structure and higher charge mobility, while higher charge recombination rate. So the result obtained by the work can give some guidance for future study.
1 I suggest the authors give a scheme to depict the film preparation process.
2 The XRD spectrum should be modified to XRD pattern.
3 The figures for calculating band gap energies should be revised, the intersection should be on the X-axis. Why the band gap pf ZnO is so large (3.8), generally, the band gaps are around 3.0-3.2 eV.
4 The image resolution of Figure 7 should be modified.
5 The author say“The size of semicircles followed the order of 0.25 < 0.50 < 0.75 < 1.00 < control ZnO, which indicate that the 3DG can reduce the internal resistance and improves the charge transport. ” But the result of ZnO (black line) has the smallest radius.
6 It is known that graphene aerogel has been widely studied in recent years. Please give the distinction between the foam-like 3D graphene and graphene aerogel?
Author Response
In this work，ZnO was embed in foam-like 3D graphene for electrode material of a Perovskite Solar Cell. The 3D graphene can play a role of charge collector media and maintain stereo frame. Comparing to TiO2, ZnO has similar band structure and higher charge mobility, while higher charge recombination rate. So the result obtained by the work can give some guidance for future study.
Response: Many thanks for your time and critically reviewing the manuscript. Your comments are indeed helpful to improve the quality of the manuscript.
- I suggest the authors give a scheme to depict the film preparation process.
Response: The schematic representation for 3DG- ZnO nanoparticles preparation is included in the revised version (Figure 1a).
- The XRD spectrum should be modified to XRD pattern.
Response: The XRD spectrum replaced with XRD pattern in the revised manuscript.
3. The figures for calculating band gap energies should be revised, the intersection should be on the X-axis. Why the band gap pf ZnO is so large (3.8), generally, the band gaps are around 3.0-3.2 eV.
Response: Thank you for your note. As you would notice from the figure, the extrapolation from the straight linear portion does not significantly change the intercept. Further, as you pointed out, we too have reported the band gap of pure ZnO as 3.23 eV. Regarding the shifts in values with 3DG, there could be two sources: (i) enhanced scattering and (ii) carbon doping. We have clarified this issue in the manuscript, which read as:
“The obtained band gap for the 3DG modified ZnO is 3.8 eV compared to the pristine ZnO at 3.23 eV. This enlarged band gap of ZnO-3DG is expected to result from the enhanced scattering of corresponding films as well as carbon doping within the ZnO photoanode. This band gap increment implies the decrease in particle size of ZnO-3DG, which is similar to the report by Zubair et al.[62]”
4. The image resolution of Figure 7 should be modified.
Response: The resolution of the Figure 7 has an improved form in the revised manuscript.
5. The author say, “The size of semicircles followed the order of 0.25 < 0.50 < 0.75 < 1.00 < control ZnO, which indicate that the 3DG can reduce the internal resistance and improves the charge transport.” But the result of ZnO (black line) has the smallest radius.
Response: Many thanks pointing out this error; this was in fact a typo and has been corrected in the manuscript, which read as “The size of semicircles followed the order of 0.25 > 0.50 > 0.75 > 1.00 > control ZnO, which indicate that the 3DG can reduce the internal resistance and improves the charge transport.”
6. It is known that graphene aerogel has been widely studied in recent years. Please give the distinction between the foam-like 3D graphene and graphene aerogel?
Response: Graphene aerogels exhibit enhanced mechanical properties with a very low density as low that show outstanding resilience can fully recover after more than 90% compression. The detail is included in the introduction of the revised manuscript.
Reviewer 2 Report
This manuscript reports foam-like 3D graphene/zinc oxide electron transport layers for high performance Perovskite Solar Cells. Transition metal oxides such as TiO2 and ZnO are the most prominent candidates as an ETL, because of their high electron mobility. In particular solution-processed zinc oxide films can be introduce as an ETL involving “optical spacers” that increase the absorption of light. Although ZnO has been studied for decades in communities researching solar cells, it is still necessary to improve long-term stability and processibility of ZnO interlayers. Therefore, this work might be of interest for publication if the authors can clarify the following questions:
- I suggest the authors to provide a schematic diagram explaining device structure.
- In Figure 5, the band gap energies for ZnO (control) should be presented and explained. In addition, the bandgap of ZnO-3DG-1.00 seems not to be 3.8 eV.
- In figure 1, 2b,3 and 6, the concentration of 3DG should be explained.
- The result of light absorption (figure 7a and b) should be discussed in detail. Why the reflectance of film increases as the 3DG content increases? It seems that the light absorption efficiencies of films significantly influence on the device performance.
- The origin of improved open circuit voltage should be discussed in the text. It would be helpful to indicate energy level diagram. [Adv. Energy Mater. 2011, 1, 690–698]
- In table 1, the series and sheet resistance of devices should be calculated, and their effect on the device performance should be discussed.
Author Response
This manuscript reports foam-like 3D graphene/zinc oxide electron transport layers for high performance Perovskite Solar Cells. Transition metal oxides such as TiO2 and ZnO are the most prominent candidates as an ETL, because of their high electron mobility. In particular solution-processed zinc oxide films can be introduce as an ETL involving “optical spacers” that increase the absorption of light. Although ZnO has been studied for decades in communities researching solar cells, it is still necessary to improve long-term stability and processibility of ZnO interlayers. Therefore, this work might be of interest for publication if the authors can clarify the following questions:
Response: Thank you so much for critically reviewing the manuscript.
- I suggest the authors to provide a schematic diagram explaining device structure.
Response: The schematic is included in the revised manuscript.
- In Figure 5, the band gap energies for ZnO (control) should be presented and explained. In addition, the bandgap of ZnO-3DG-1.00 seems not to be 3.8 eV.
Response: Pure ZnO has a standard energy band gap around 3.2 eV. Figure 5 is updated in the revised manuscript.
- In figure 1, 2b,3 and 6, the concentration of 3DG should be explained.
Response: The concentration of the 3DG is included in the mentioned Figures.
- The result of light absorption (figure 7a and b) should be discussed in detail. Why the reflectance of film increases as the 3DG content increases? It seems that the light absorption efficiencies of films significantly influence on the device performance.
Response: The relevant discussion included on page 15 in the revised manuscript.
- The origin of improved open circuit voltage should be discussed in the text. It would be helpful to indicate energy level diagram. [Adv. Energy Mater. 2011, 1, 690–698]
Response: The discussion oof improve open circuit voltage and energy band diagram (Figure 1b) included in the revised manuscript. In the cited reference, Akinori Saeki and coworkers investigate the correlation between organic photovoltaic cells and dynamics of transient photoconductivity by flash-photolysis time-resolved microwave conductivity. Blend ratios, annealing, impurities, and degradation effects in bulk heterojunction films consisting of P3HT and PCBM are examined, demonstrating a facile screening method to survey the potential of optoelectronic materials.
- In table 1, the series and sheet resistance of devices should be calculated, and their effect on the device performance should be discussed.
Response: The series and sheet resistance of the devices have already calculated in Table 2 and its effect on the devices have discussed in the manuscript.
Round 2
Reviewer 2 Report
After careful revision and mention all comments, I think this manuscript is ready to publish.
