dr Juan Pablo Prieto

I want to use science to solve real problems – interview with dr Juan Pablo Prieto, Printing Process Engineer at Saule Technologies

How did your adventure with perovskites begin?

I am from Argentina, but I moved to Spain with my family when I was very young. I have lived there for half of my life. I decided to study Physics and I did my Ph.D. in Nanoscience and Nanotechnology at the University of Valencia, in the field of molecular spintronics. After I finished my Ph.D, the opportunity to work at Saule Technologies appeared. I knew the project and I was really interested in joining it. That is why I did not hesitate for a moment. I wanted to move from the academic research into the private company activity. I felt that Saule Technologies could really have an impact on the society while doing science. Working here allows me to follow my passion, which is science and at the same time be closer to reality, which in the academic environment is sometimes more difficult.

What is your role in the company?

I am a Printing Process Engineer and together with my colleagues we are optimizing the process of fabrication of fully printed perovskite solar cells based on inkjet printing. We start from the ink preparation and characterization of its properties such as viscosity and surface tension. Theis information tells us, if this ink can be correctly used in our printers.


Once we have the correct ink formulation, we apply it on our substrate, onto which the solar cell will be fabricated. We analyze the parameters such as morphology and crystallographic properties of the active layers. Finally, the device performance is measured and related to the fabrication conditions. Thus, we can run many printings every day in order to collect enough data for correcting and designing the proper printing process of the perovskite solar cells.


The idea is to come out of the laboratory at the end of the day with at least one conclusion and getting closer, step by step, to our goal. Currently, we are moving from small modules to large-scale cells, working on transferring the optimized printing process to our production line.

Several years ago solar energy was almost unknown, but now the technologies of generating electricity from solar energy are widely used. What is the future of solar technologies?

When I think about energy I think about the plants, which have been transferring solar energy into their own energy for millions of years. The energy is there, we can also collect it and use it. Photovoltaic technologies are one of the best alternatives to fossil fuels, but I believe that it is possible to make a big change in the model of transferring this energy. In my opinion, the timing for a new technology in this field, such as perovskite photovoltaics, could not be better.


The most often used solar solutions are based on silicon, but these panels are rigid and commonly expensive. Our team is trying to push the limits of perovskite technology towards new functionalities of solar cells. Saule Technologies’ cells will be flexible, light and semi-transparent allowing to use them in many applications. They can be integrated with buildings, clothing as also, because of the low weight, used in space, where every gram is of great importance. Soon we could cover hundreds of kilometers of our planet, including building facades, cars and electronic devices with perovskite solar cells. This gives us the possibility to be independent energetically and have a huge positive impact on the health of our planet. This is for me even more important than the economy aspect of developing this technology.

And how do perovskites perform? Are they stable and efficient?

In terms of efficiency, the perovskite solar cells can compete with the traditional silicon solar cells. In terms of stability, it’s true that there are challenges that we have to deal with, but this technology is developing very fast and every day new improvements appear, such as more stable perovskite formulations. When we combine them with a proper encapsulation of the cell, this technology can be a great and universal solution.

You mentioned ecology. What about the impact of perovskite cells on the environment? Are they eco-friendly?

Many scientists analyze the impact of these materials on the environment, but this topic has not yet been fully researched. Perovskite cells contain lead, but its content is marginal. The final impact depends on the encapsulation of the cells and administration of the recycling process after their lifetime. Proper processes can minimize the impact of lead on the environment.


We have to be also aware that many modern technologies use or emit materials, which are not 100% eco-friendly. This concerns the fuel of our cars, silicon solar panels and many other electronic devices. The goal of each technology is to minimize its impact on the environment by i.e. proper recycling process accompanied by a good encapsulation system strategy.

Are there any major breakthroughs in the field?

The breakthroughs are the new formulations of perovskites, which make them more robust and efficient. Another one is the possibility to combine perovskites with silicon cells for making tandems. This approach allows to increase the efficiency even more by pushing the limits of both technologies as a wider part of the solar spectra can be used for producing energy.

There are many different working groups that are developing perovskite cells, but Saule Technologies is the first team that has presented a prototype working in the laboratory and in operating conditions. How were you able to get ahead of the competition?

Saule Technologies, as many other academic groups and companies are working on producing perovskite solar cells with the best efficiency in a controlled environment, like the laboratory. But what makes Saule Technologies special is that our work is focused on developing this technology under real environmental conditions as well. Additionally, other groups are mostly using glass as a substrate for solar cells with small active areas. Our company took the challenge of using flexible polymeric substrates with big active areas in order to respond to the real demands of the market.


Our team has presented a module based on a flexible substrate, being the first one able to charge a smartphone, working outside the laboratory under real environmental conditions. We want to test this technology in the toughest situations. Our aim is to contribute to the science of the perovskite field, at the same time making this technology available for everyone as soon as possible. I believe that this approach, experimenting and pushing the field forward, is something that differentiates us from other working groups.

Big companies are also active in the solar technology sector. Tesla and Solar City recently announced a new product – solar roof tiles. Can perovskites be the next step?

Tesla and SolarCity are taking the already existing technology and adapting it, giving it another shape, which is more aesthetical than the traditional solar panels. This is a smart strategy for an easier and more attractive integration of solar panels into buildings, underlining the potential of solar energy. In my opinion, these proposals will contribute to stimulating the field.


On the other hand we have perovskite cells, which can not only cover roofs, but also windows, they can be integrated with your car or with buses among other applications. We are not two competing companies, but offering complementary solutions, which can bring us closer to our goal – changing the energy sector and making solar energy available for everyone.

Saule Technologies has recently launched its new laboratory. How will this help in your work?

Recently we launched our clean room, where we can manufacture more reliable and efficient devices under controlled conditions of humidity and cleanness. The possibility of controlling environmental variables during our experiments, allows us to get more reproducible and solid results. It is also very well equipped, with advanced R&D printers, evaporators and a long list of instruments for a complete characterization of the layers and the final devices we prepare. In this sense, the clean room can be considered as one of the best equipped optoelectronics laboratories in Europe and should be marked as an important spot in the perovskite photovoltaic field. These work conditions allow us to face the challenges of our project with all the tools we need in order to make good science and develop our production line according to our plans.

You joined the company about a year ago. How did it change during this time?

When I joined Saule Technologies, the company was operating in a totally different place. During the year the company has grown impressively, improving the facilities and the size of our team. Not only did we gain a lot of knowledge about the perovskite photovoltaics, but also the company’s philosophy of working has evolved and adapted making it an extremely interesting environment for a scientist . We are a young company, with a young spirit, but with big expectations. That is why we are not afraid to face the challenges of this field.

You talk about improving the environment and helping the society. Are those your goals as a scientist?

When I started to study nanotechnology I saw some documentaries about how this field can help the society in extreme conditions, for example during disasters and wars in the poorest countries. New technology can give access to energy or clean water and can really change our world. That is what I want to do – create a technology that can make a difference in the society. My goal is to use science to solve real problems. I am glad that I can do that in Saule Technologies, because access to energy is one of those problems.

What is your dream application of perovskites?

I thought about it many times. My dream application is inspired by the recent problems of refugees, people struggling in really bad conditions, without electricity, water or heating systems. This is all happening in the 21st century. To help them and improve their life conditions I would like to see tents with perovskite cells, which can provide electricity and heat. In general I dream of a world in which perovskite solar cells are part of our daily life, taking profit of this huge amount of energy that we receive from the sun, contributing to a real revolution in the energy sector.

You are really engaged in your work. What do you do when you get out of the laboratory?

One of the things I really love to do is to write, it is one of my favorite activities. I really enjoy writing essays and poetry and one of my dreams is to publish my own book. I also feel that when you do science a natural need for art can appear. That is why I write, play the guitar, sing and shoot photographs. For me it is like finding balance in my life.