An Alternative to Chlorobenzene as a Hole Transport Materials Solvent for High-Performance Perovskite Solar Cells
Round 1
Reviewer 1 Report
Comments and Suggestions for Authors
Fabrication of perovskite solar cells is the subject of great research attention owing to their potential commercialization. Many researchers are working on the development of PSCs through the design of device architectures, nanostructures, synthesis methods, and modified chemical compositions. But one of crucial effects namely solvent effect on the thin-film morphology and charge transport in PSCs still remains unstudied, The authors have made the attempt to fill in this gap.
In the paper under review some properties of solar cells obtained using Spiro-OMeTAD in chlorobenzene and TOP-HTM-α2 in dichloromethane are described. The results concerning the last one are new and interesting for the researchers. But from my point of view it is not enough to mention only that upon substitution of CB on DCM. I would like to see more discussion of the effects observed and at least the attempts to answer on the next questions (some attempts have been made but I would like to see them more clearly):
1. Which kinds of solvents can be used instead of chlorobenzene? What are the general requirements to these solvents?
2. Why dichloromethane has been chosen? Either some screening of solvents took place and DCM was the best one?
3. What is the mechanism of solvent effect on thin-film properties?
4. Why for different compounds studied different solvents results in improved properties (TOP-HTM-α2 was confirmed to be the best condition when dissolved with DCM, while Spiro-OMeTAD was confirmed to be the best condition when dissolved with CB)?
Author Response
Please see the attachment.
Author Response File: 
Author Response.docx
Reviewer 2 Report
Comments and Suggestions for Authors
Reviewers comments:
The authors present perovskite solar cells fabricated in n-i-p architecture with a novel HTL. The work presents two interesting aspects related to solar cell processing. The results can also be of commercial importance. However, there are plenty of problems with the manuscript.
The primary concern with the manuscript is that except for the IV curves which illustrates a proof of concept there is almost no scientific substance in the paper. I would like to point out a few concerns in the manuscript.
1) Even when we look at the IV curves we find that the authors have not provided any rigid solar cell statistics to support their observations. The way the results are presented gives any reader the impression that this could be a one off result which happens very often in perovskite solar cell processing. I strongly recommend the authors to provide convincing statistics in the form of box plots and tables with averages and standard deviations.
2) This work is all about a new HTL to replace Spiro which is fine but the molecule itself appears to be complex and less known. As the manuscript develops, it becomes a two part story with an emphasis being put on solvent selection as well. When the authors could criticize CB being used as a solvent for the HTL they somehow still use it as an antisolvent for perovskite fabrication which is counter intuitive. Therefore, it is better for the manuscript if they put the emphasis on HTL alone and bring in the usage of DCM as an additional plus point which boosts the PCE.
3) The arguments to support the novel HTL Alpha 2 are very weak. The ideal characteristics of a HTL would be: good hole conductivity/mobility which requires good charge extraction, high transparency, low reflectivity and economic feasibility. However, in this work none of these properties have been elaborated. It is well known that spiro along with it’s additives prove to be a cost escalating factor in the processing of PSC’s. Such aspects can be highlighted with relevant statistics to strengthen the argument.
4) There are no details about the perovskite precursor and the composition of the perovskite. For triple cation perovskites the authors are obligated to describe all the details involved in the preparation of the precursor and the final composition of the perovskite they targeted along with appropriate references. For example like (FA)0.83(Cs)0.05(MA)0.12PbI2.75Br0.25.
5) Space charge limited current (SCLC) is not an ideal characterization to support a charge transporting layer. In the case of PSC’s everyone calculates a defect density based on the trap filled voltage. This routine was not even carried out in this work. When the defect density is characteristic of the perovskite, how the use of a HTL can mitigate or worsen this number? Can this be explained?
6) Another problem with SCLC is that they have carried out the measurements on hole selective devices. I believe the authors had the impression that when an optimized perovskite precursor is used on any surface it will generate the same perovskite. The combination PEDOT/PVK is the not the same as SnO2/PVK electronically and ionically. Therefore, this experimental design needs to be changed. Rather continue the measurements on electron selective devices fabricated on SnO2 to make a meaningful comparison. Personally I urge the authors to read a few papers that point out the basic flaws with SCLC and be careful when they repeat the analysis.
Comments on the Quality of English Language
The language can be imrpoved.
Author Response
Please see the attachment.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
Comments and Suggestions for Authors
The authors have significantly improved the manuscript according to reviewers' comments. I can recommend this paper for the publication.
Reviewer 2 Report
Comments and Suggestions for Authors
The authors have re arranged the paper in a very neat manner. All the concerns that I had raised during the first revision have been adequately addressed. I have no issues with the paper and I recommend this for acceptance.
