Surface Passivation of Organic-Inorganic Hybrid Perovskites with Methylhydrazine Iodide for Enhanced Photovoltaic Device Performance

Round 1

Reviewer 1 Report

Hu et. al reported the application of hydrophobic methylhydrazine  iodide molecule as a surface passivating agent for the n-i-p type perovskite solar cell. They showed improvements in both PCE  and device stabilities of the un-encapsualted solar cells. The results are presented clearly backed up by experimental results. This manuscript is acceptable for publication as is format.

If any thing the authors wishes to add, is the rationality in choosing the MHYI and a comparative performance discussion between MYHI used in this work versus PFPEAI, PESAI, Pydrinium iodide etc.. used in other works. 

A generic picture to look for in a surface passivating agent based on the comparative discussion would enhance the quality of this work further.

Author Response

Response: Thank you very much for the suggestion. In the manuscript, we have added comparative device performance plots for the post-treatment of different ammonium salts (PEAI [1], PyI [2], NMAI [3], pFPEAI [4], oFPEAI [5], mFPEAI [5]) as suggested by the reviewer, as shown in Figure S6. In addition, we have revised our supporting information manuscript on page 3 according to the comment. The additions in the main text on page 7 are as follows: Our results demonstrate promising performance based on the comprehensive data we collected from devices treated with various ammonium salts (Figure S6, Supporting Information). Furthermore, the MHy cation and the FA cation are similar in structure and have a similar ionic radius (2.62 Å for MHy⁺, 2.47 Å for FA⁺) [6]. This is the reason why we chose this molecule.

Author Response File: Author Response.pdf

Reviewer 2 Report

Hu et al. shown a passivation strategy to step up efficiency on perovskite.

I am ok go ahead with publication after minor revision:

- please in the introduction you might introduce some work to let reader understand better, like https://iopscience.iop.org/article/10.1088/2515-7639/acc893/meta

-  please comment on the stability, why you are not getting better results

- please comment on the perovskite structure, and precise composition of the precursors and methods in grams.

Author Response

Response: We thank the reviewer for the constructive comment. We have added the following section on page 1 of the main text to help the reader understand better. ‘Additionally, it is believed that achieving long-term stability, minimizing or eliminating the use of toxic solvents, and preventing lead leakage are among the most difficult parts of commercialization [11–15].’

 

- please comment on the stability, why you are not getting better results

Response: Thanks for the reviewer’s comment. In this manuscript, we use MHyI to passivate defect-rich perovskite surfaces and reduce non-radiative recombination. Also, MHyI can interact with PbI₂ to some extent, and the XRD plots (Figure 1c) show a certain decrease in the peak of PbI₂, which contributes to the long-term stability of the device [11]. According to the results in Figures 4d and 4f, the long-term stability and maximum power point (MPP) tracking stability of the device are moderately enhanced by MHyI passivation. We attribute the improved device stability to reduced PbI₂ and surface defects. Based on the reported literature [2], we consider this to be a normal level for the long-term stability performance of the device in Figure 4f. As for the MPP test, the passivated devices only maintained 57% of their original efficiency after 200 hours of continuous light immersion. We attribute the unsatisfactory result to two primary factors. Firstly, during device operation, the additive tBP in Spiro-OMeTAD evaporates spontaneously, creating voids in the perovskite films. This, in turn, leads to the accumulation of LiTFSI, ultimately resulting in device degradation [12]. Secondly, we have found that our two-step process produces a higher residual amount of lead iodide. This can be decomposed into metallic lead and iodine under illumination [11,13], leading to decreased device performance.

In summary, achieving good MPP results requires two key steps. Firstly, it is important to use a more stable HTL, such as undoped P3HT and doped PTAA [14]. Secondly, it is crucial to take steps to reduce the adverse effects of lead iodide on the overall durability of the devices. By following these steps, optimal MPP results can be achieved.

 

- please comment on the perovskite structure, and precise composition of the precursors and methods in grams.

Response: Thanks for the reviewer’s comment. In this manuscript, we have used the regular device structure of Glass/FTO/SnO₂/(FAPbI₃)_1-x(MAPbBr₃)_x/MHyI/Spiro-OMeTAD/Au. (FTO: F-doped Tin Oxide; Spiro-OMeTAD: 2,2’,7,7’-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9’-spirobifluorene). The perovskite light-absorbing layer was prepared using a two-step spin-coating method containing two vials of precursor solutions, lead iodide (a 1.45 M solution of PbI₂ (DMF/DMSO, v: v = 9:1)) and organic ammonium salt (FAI: MABr: MACl = 75 mg:7.5 mg:9 mg in 1 mL IPA), respectively. FAI is used to form the main component of FAPbI₃-based perovskite, which can obtain a high device efficiency. MABr is used for the doping of MA cation and Br anion to suppress the spontaneous α-to-δ phase transition of the FAPbI₃-based perovskite [15]. Adjusting the MACl content to obtain perovskite films with large grains [16,17]. The above composition ratios have been optimized from the literature [18] and are suitable for our laboratory. The one-step method enables the precursor solution composition to be designed precisely according to the specific chemical formula of the perovskite to be obtained. Unlike the one-step method, in the second step of the two-step process, FAI and MABr enter the film in a competing relationship, so the exact chemical formula of the perovskite cannot be determined directly and accurately. It has been reported that Cl escapes after annealing and that there is no residual Cl in the final perovskite film [16,17]. So we generally use (FAPbI₃)_1-x(MAPbBr₃)_x [1] to denote the chemical formula of the perovskite processed by the two-step method.

Author Response File: Author Response.pdf

Reviewer 3 Report

 

The manuscript "Surface Passivation of Organic-Inorganic Hybrid Perovskites with Methylhydrazine Iodide for Enhanced Photovoltaic Device Performance" demonstrated a facile post-treatment strategy utilizing methylhydrazine iodide (MHyI) to passivate the surface of the perovskite film to improve performance in perovskite solar cells.

The topic may be of interest to a broad audience of scientists working in the field of the production and characterization of perovskite solar devices and the study aims to integrate knowledge into an important application such as passivating defects in the perovskite film and successfully suppressing carrier non-radiative 20 recombination.

The manuscript is clear, and the study is well conducted and sufficiently clearly described. The results obtained are at the state of art and well supported from characterization measurements. The study is suitable for the purpose of this journal. I recommend that you accept this contribution as it stands, checking only for text editing and minor spell checking.

Author Response

Response: Thank you very much for the positive comments and constructive suggestions. We also appreciate the reviewer for spending time to review our manuscript. We have revised the manuscript according to reviewer’s comments.

 

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Author Response File: Author Response.pdf