In this work, the author report on the perovskite solar cell structure. They systematically simulated the operation mechanism of the device including the effect of the absorber graded bandgap. What is more, a detailed comparison of their device with a conventional device was also performed. Overall, I believe this is a very interesting work, the finding is new, and all the theoretical analysis was nicely carried out. This paper can be accepted for publication after addressing some issues.

Comments on abstract, title, references

the aim of this paper is clear. ●The abstract describes well the work. ● 1D Numerical simulation is performed. ● The title is relevant. ● The references are relevant and recent.

Comments on introduction/background

● The research question is clearly outlined. ● The research question is justified given what is already known about the topic. But, In order to improve the finding further discussion about experimental processing is required.

Comments on methodology

●The process of subject selection is clear. ● The study methods' validity is clear. ● There is enough detail to replicate the study.

Comments on data and results

The data presented in an appropriate way ● Titles and rows labeled correctly and clearly. ● Categories grouped appropriately ● The author's findings are practically meaningful where a carful simulation study is performed. The effect of graded bandgap on device absorption is illustrated. Comparisons between the proposed and the primary device demonstrate that the proposed device outperforms the conventional in terms of short circuit current.

● In this study, the author only theoretically investigated the effect of bandgap engineering on the device figures of merits in terms of short circuit current and open-circuit voltage, however, the band alignment between perovskite absorber material and both ETL and HTL will be affected by changing the bandgap. In order to be realistic, I propose as perspective an investigation on the effect of graded bandgap profile on the device's electrical performance. In addition, It is important for the future work that the author shows how the electric field in both interfaces perovskite/ETL and HTL/perovskite is affected by the bandgap profile of the absorber.

Comments on discussion and conclusions

●The results discussed and well interpreted. ● The conclusions answer the aims of the study ● The conclusions supported by results. ● The study has opportunities to inform future research.