How to (Not) Make a Perovskite Solar Panel: A Step-by-Step Process

Round 1

Reviewer 1 Report

Reviewer comments:

In this work, the authors present a nice overview of the fabrication of perovskite solar modules (PSMs), based on the existing knowledge and know-how from the smaller lab scale perovskite solar cells (PSCs) devices. Meanwhile they emphasize on the importance of materials selection towards maximizing efficiency and stability over realistic operation conditions. While most of the reported challenges are known to the scientific community, the paper is well written and provides a pleasant and simplified guide on how difficult is to make or (not) make an efficient PSM. I really believe that the paper deserves publication. However, in order to be considered for publication in Processes (MDPI), the authors are strongly encouraged to address the points listed below (major revisions) that are critical for strengthening the paper.

Suggested revisions and recommendations:

1. Page 2, line 49: Number 2 needs to be superscript.

2. Page 3, Section 3.2: The authors are kindly asked to provide and comment on the XRDs of the coated perovskites. It will be interesting to discuss how and if the XRD from the thin side (400 nm) vary when compared to the thicker side (600 nm) of the panel.

3. Page 4, lines 128-130: The authors claim that they employed PTAA polymer as HTL layer due to several reasons. However, these reasons are not mentioned. Please provide them briefly for the reader. More importantly, it is stated that the usage of PTAA has been optimized on one of their previous studies. However, many other authors have previously reported on the advantages of PTAA polymer as HTL in terms of morphology, and carrier transport (E. Serpetzoglou et al. ACS Appl. Mater. Interfaces 9, 43910, 2017 and C. Bi et al. Nat. Commun. 6, 7747, 2015). The authors need to provide these references for the reader.

4. Page 5, Section 3.4: In Table 2 the authors summarize the reasons for the employed materials. For PTAA they state that the main reason is the thermal stability. Did the authors noticed any changes in the perovskite quality when PTAA was employed, when compared to other HTL options?

5. Page 8, Figure 3: I really liked the Figure, especially Figure 3a.

6. Page 11, Section 5: Maybe it would be better to present the performance plots in the discussion part (Section 4), along with the corresponding text on how close to the stability aim of the study were the results.

Author Response

We kindly thank the reviewer for the time spent on revising the work, we will answer reviewer's doubts using a point-by-point method, as follows:

Reviewer comments: In this work, the authors present a nice overview of the fabrication of perovskite solar modules (PSMs), based on the existing knowledge and know-how from the smaller lab scale perovskite solar cells (PSCs) devices. Meanwhile they emphasize on the importance of materials selection towards maximizing efficiency and stability over realistic operation conditions. While most of the reported challenges are known to the scientific community, the paper is well written and provides a pleasant and simplified guide on how difficult is to make or (not) make an efficient PSM. I really believe that the paper deserves publication. However, in order to be considered for publication in Processes (MDPI), the authors are strongly encouraged to address the points listed below (major revisions) that are critical for strengthening the paper.

We thank the reviewer for the kind words, we hope that we will address the questions in order to improve the quality of the paper.

Suggested revisions and recommendations: Page 2, line 49: Number 2 needs to be superscript.

Thanks for checking this, we replace the number and put it as a superscript.

Page 3, Section 3.2: The authors are kindly asked to provide and comment on the XRDs of the coated perovskites. It will be interesting to discuss how and if the XRD from the thin side (400 nm) vary when compared to the thicker side (600 nm) of the panel.

Thanks for the valuable question. To be honest, these modules were fabricated in November 2020, with relative humidity conditions from 20 to 30%. In September in Rome, Italy, unfortunately, the fabrication conditions can't reach relative humidity lower than 50%. Making a new perovskite deposition will not be comparable to what we have fabricated in the past. However, your question is totally understandable and good to ask. An example of perovskite "alpha-phase deposition" has been proven in our previous work (https://doi.org/10.1021/acsami.0c18920), where in Figure 5e and in Figure S4 the uniformity of the perovskite film is reached by Infrared Annealing and the use of GO-K as an interlayer, on a dimension of 50x70mm². We apply the same strategy in this work, with the use of Infrared Annealing and without GO-K, since the architecture, in this case, is inverted and GO-K behaves more as an electron-attracting interlayer. By that time we made some SEM images on a different part of the module and included them in Figure 1, we hope that those images will be sufficient to justify the quality of the perovskite, even though the thickness varies from 400 to 600nm. To make it more clear on the fabrication conditions, we had the relative humidity in the caption of Figure 1.

Page 4, lines 128-130: The authors claim that they employed PTAA polymer as HTL layer for several reasons. However, these reasons are not mentioned. Please provide them briefly for the reader. More importantly, it is stated that the usage of PTAA has been optimized in one of their previous studies. However, many other authors have previously reported on the advantages of PTAA polymer as HTL in terms of morphology, and carrier transport (E. Serpetzoglou et al. ACS Appl. Mater. Interfaces 9, 43910, 2017 and C. Bi et al. Nat. Commun. 6, 7747, 2015). The authors need to provide these references for the reader.

Thanks for the comment. We add the suggested reference and wrote the sentence: "we decided to use PTAA for several reasons: it requires low-temperature annealing (100°C) and it’s solution processable with non-hazaourd solvents, such as Anisole.

Page 5, Section 3.4: In Table 2 the authors summarize the reasons for the employed materials. For PTAA they state that the main reason is the thermal stability. Did the authors noticed any changes in the perovskite quality when PTAA was employed, when compared to other HTL options?

Thanks for the comment. The aim of the work was based on defining a guideline to make (or not make) a perovskite solar panel. We didn't compare the quality of the perovskite layer using different HTLs in this work, however, we are working on replacing PTAA by using NiOx as a more compact and homogenous layer to employ for large areas above 15x15cm2. Another recent work we have done was to replace PTAA with carbazole-based HTLs, such as BPT-1 and BPT-2, as shown in the following paper "https://doi.org/10.1002/eem2.12455". As shown in that work, on Figure 6b, T90 for PTAA-based device was 902 hours, telling us that indeed the system is stable under thermal stress.

Page 8, Figure 3: I really liked the Figure, especially Figure 3a.

Thanks for the positive comment, we believe that a personal touch makes the paper closer to the reader.

Page 11, Section 5: Maybe it would be better to present the performance plots in the discussion part (Section 4), along with the corresponding text on how close to the stability aim of the study were the results.

Many thanks for the comment, performance plot has been moved to section 4, as suggested.

Author Response File: Author Response.pdf

Reviewer 2 Report

I think this paper doesn’t mention scientific parts of perovskite solar cells, just a report on a large area modules.

I think some technical parameters should be discussed as a paper.

Author Response

We kindly thank the reviewer for the time spent on revising the work, we will answer the reviewer's doubts using a point-by-point method, as follows:

I think this paper doesn’t mention scientific parts of perovskite solar cells, just a report on a large area modules.

Thanks for the comment, however, the aim of this work is to provide a guideline for researchers and people working in the perovskite field, on the state of art of perovskite solar modules, not on cells, and specifically on how to (or not to) connect them, we honestly don't think that solar cells should be described in details. To make things clear, we had a sentence in the introduction part, as follows: "Our aim is to guide the reader on the processes needed to build a Perovskite Solar Panel, a fabrication procedure totally different from Perovskite Solar Cells, in which other techniques and optimizations are used, focusing more on the scientific part of the technology rather than the engineering issues and how to address limits.".

I think some technical parameters should be discussed as a paper.

Thanks for the comment, we had technical fabrication deposition in the experimental part of the work, as follows: "

Perovskite Preparation. PbI₂ (1 M), CsI (0.1 M), and FAI (with a weight ratio of FAI:PbI₂-CsI 1:20) were dissolved in DMF (0.876 mL) and DMSO (86 μL); FAI and FABr (0.4 M mL−1), with FABr molar fractions of 20 mol % was dissolved in IPA. The final perovskite precursor ratio is the following: Cs0.1FA0.9Pb(I0.94Br0.06)3.

 

Module Fabrication. Perovskite Solar Modules with an active area of 201 cm² are realized on fluorine-doped tin oxide (FTO) conductive glass (Pilkington, 8 Ω□⁻¹) patterned through a raster scanning laser. The P1 process, designing 16 series connected cells, was performed for the module layout using the same parameters (λ = 355 nm, Nd:YVO4 pulsed at 80 kHz, fluence = 648mJ cm⁻²). The patterned substrates are cleaned in an ultrasonic bath, by subsequent washing in a detergent with deionized water, acetone, and 2-propanol (10 min for each step). The patterned substrates have been set initially at 20×30 cm² for to facilitate the optimization of the ptaa and perovskite layer by a semi automatized blade-slot die coater with 3 different drying step methods (fan, hot gas air, and IRA), called “Charon” designed by Cicci Research srl, and subsequentially cutted with a 20x20cm². the deposition is carried out in ambient air.

 

A 10-minute UV-ozone treatment was performed prior to layer processing. A PTAA solution in anisole (5 mg/mL, 300 μL) was injected on one side of the substrate with a syringe forming a uniform meniscus between the substrate and the blade: the deposition was performed air with relative humidity from 20 to 30%, using 100 μm height and 5 mm/ s speed, followed by annealing at 100 °C for 10 min. Subsequently, the samples were exposed to UV-ozone for 10 min and then transferred back for perovskite layer deposition. Perovskite deposition is performed with controlled humidity from 20 to 30% using “Charon”: the plate of the machine was kept constant at 30 °C; in the first step, the blade height was fixed at 100μm and the precursor solution (PbI₂, CsI, and FAI in DMF/DMSO 9:1) was kept stirred at room temperature just before the deposition. Precursor solution (300 μL) was injected on one side of the substrate with a syringe forming a uniform meniscus between the substrate and the blade, then the plate moved at a fixed speed of 10 mm/s; once the substrate crossed the blade system, an air-drying system set at 65 °C was used with a fixed pressure of 125 L min⁻¹. Immediately after the drying step, the substrate was placed back in its starting position. During the second step a precursor solution, made of FAI and FABr in IPA, was kept in a syringe dispensing the slot die; the initial flow rate was adjusted to form a uniform meniscus between the substrate and slot die head placed at 70 μm from the substrate and once the meniscus was formed the flow rate was kept at 500 μL min⁻¹ and the plate moved at a fixed speed of 20 mm/s; once the substrate crossed the slot die system, an air-drying system, set at room temperature with a fixed pressure of 100 L min⁻¹, and a couple of infrared lights were used for 5 s, after that the substrate was placed in a hot plate at 130 °C for 40 min. Infrared lights are composed of 2 emitters of 400 mm length with 2 kW total electrical power. Lamps are composed of infrared quartz with a fast medium wave emitter with peaks in the range of 1.6−2.0 μm and a working emitter temperature at 1462°C. Blade, slot die, and drying apparatuses were placed at a specific distance from each other and were activated and controlled by software during the deposition.

On top of the perovskite layer, 30 nm of C60 as ETL and 8 nm of BCP as a buffer layer were thermally evaporated at a vacuum pressure of 10^-6 mbar. Finally, as the back-contact, 100 nm of Au electrode was deposited on top of the layers by thermal evaporation at 10^-5 mbar. To form interconnects in the module, P2 and P3 were performed (λ = 355 nm, Nd:YVO4 pulsed at 80 kHz, fluence^P2 = 195 mJ cm⁻², fluence^P3 = 206mJ cm⁻²) following a similar procedure reported elsewhere[10].".

Author Response File: Author Response.pdf

Reviewer 3 Report

Castriotta et al. introduced the method to make a perovskite solar panel. This work is of interest for the fields of perovskite solar cells. It is recommended to be accepted by Processes.

 

1.     In the Materials and Methods section, the detailed conditions for preparation of perovskite solutions and films should be provided.

2.     The “CsFa perovskite” should be changed to “CsFA perovskite”.

3.     Better introduced the methods used in the state-of-the-art high-performance perovskite panels.

4.     Better cite a review paper for perovskite solar cells to make it easier for the unprofessional readers to understand, such as Adv. Sci.,2016, 3 (7), 1500324.

Author Response

We kindly thank the reviewer for the time spent on revising the work, we will answer reviewer's doubts using a point-by-point method, as follows:

Castriotta et al. introduced the method to make a perovskite solar panel. This work is of interest for the fields of perovskite solar cells. It is recommended to be accepted by Processes.

Thanks a lot for your comment, we believe that a guideline on how to (or not to) build a perovskite solar panel is useful for all research and industrial perovskite community.

In the Materials and Methods section, the detailed conditions for preparation of perovskite solutions and films should be provided.

Indeed! We add the preparation and fabrication details of all the modules in the material and methods section, such as: "

Perovskite Preparation. PbI₂ (1 M), CsI (0.1 M), and FAI (with a weight ratio of FAI:PbI₂-CsI 1:20) were dissolved in DMF (0.876 mL) and DMSO (86 μL); FAI and FABr (0.4 M mL−1), with FABr molar fractions of 20 mol % was dissolved in IPA. The final perovskite precursor ratio is the following: Cs0.1FA0.9Pb(I0.94Br0.06)3.

 

Module Fabrication. Perovskite Solar Modules with an active area of 201 cm² are realized on fluorine-doped tin oxide (FTO) conductive glass (Pilkington, 8 Ω□⁻¹) patterned through a raster scanning laser. The P1 process, designing 16 series connected cells, was performed for the module layout using the same parameters (λ = 355 nm, Nd:YVO4 pulsed at 80 kHz, fluence = 648mJ cm⁻²). The patterned substrates are cleaned in an ultrasonic bath, by subsequent washing in a detergent with deionized water, acetone, and 2-propanol (10 min for each step). The patterned substrates have been set initially at 20×30 cm² for to facilitate the optimization of the ptaa and perovskite layer by a semi automatized blade-slot die coater with 3 different drying step methods (fan, hot gas air, and IRA), called “Charon” designed by Cicci Research srl, and subsequentially cutted with a 20x20cm². the deposition is carried out in ambient air.

 

A 10-minute UV-ozone treatment was performed prior to layer processing. A PTAA solution in anisole (5 mg/mL, 300 μL) was injected on one side of the substrate with a syringe forming a uniform meniscus between the substrate and the blade: the deposition was performed air with relative humidity from 20 to 30%, using 100 μm height and 5 mm/ s speed, followed by annealing at 100 °C for 10 min. Subsequently, the samples were exposed to UV-ozone for 10 min and then transferred back for perovskite layer deposition. Perovskite deposition is performed with controlled humidity from 20 to 30% using “Charon”: the plate of the machine was kept constant at 30 °C; in the first step, the blade height was fixed at 100μm and the precursor solution (PbI₂, CsI, and FAI in DMF/DMSO 9:1) was kept stirred at room temperature just before the deposition. Precursor solution (300 μL) was injected on one side of the substrate with a syringe forming a uniform meniscus between the substrate and the blade, then the plate moved at a fixed speed of 10 mm/s; once the substrate crossed the blade system, an air-drying system set at 65 °C was used with a fixed pressure of 125 L min⁻¹. Immediately after the drying step, the substrate was placed back in its starting position. During the second step a precursor solution, made of FAI and FABr in IPA, was kept in a syringe dispensing the slot die; the initial flow rate was adjusted to form a uniform meniscus between the substrate and slot die head placed at 70 μm from the substrate and once the meniscus was formed the flow rate was kept at 500 μL min⁻¹ and the plate moved at a fixed speed of 20 mm/s; once the substrate crossed the slot die system, an air-drying system, set at room temperature with a fixed pressure of 100 L min⁻¹, and a couple of infrared lights were used for 5 s, after that the substrate was placed in a hot plate at 130 °C for 40 min. Infrared lights are composed of 2 emitters of 400 mm length with 2 kW total electrical power. Lamps are composed of infrared quartz with a fast medium wave emitter with peaks in the range of 1.6−2.0 μm and a working emitter temperature at 1462°C. Blade, slot die, and drying apparatuses were placed at a specific distance from each other and were activated and controlled by software during the deposition.

On top of the perovskite layer, 30 nm of C60 as ETL and 8 nm of BCP as a buffer layer were thermally evaporated at a vacuum pressure of 10^-6 mbar. Finally, as the back-contact, 100 nm of Au electrode was deposited on top of the layers by thermal evaporation at 10^-5 mbar. To form interconnects in the module, P2 and P3 were performed (λ = 355 nm, Nd:YVO4 pulsed at 80 kHz, fluence^P2 = 195 mJ cm⁻², fluence^P3 = 206mJ cm⁻²) following a similar procedure reported elsewhere[10].".

The “CsFa perovskite” should be changed to “CsFA perovskite”.

Thanks for the feedback, we replaced CsFa with CsFA-perovskite.

Better introduced the methods used in the state-of-the-art high-performance perovskite panels.

Thanks for the comment, we integrated this part in the Materials and Methods (see previous answer), the flow of the paper looks more smooth in our opinion.

Better cite a review paper for perovskite solar cells to make it easier for the unprofessional readers to understand, such as Adv. Sci.,2016, 3 (7), 1500324.

Thanks for the comment, we add this reference in the manuscript.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Paper can be accepted in the present form.