Not one to plan his life, José María Miranda arrived at the Institute of Materials Science in Seville after spending a “revealing” year in a research group in Germany. It was a whim of fate that he ended up choosing a group specialising in non-linear optics, as he was also interested in geophysics. Doubts soon arose, but over time he discovered that research was an excellent opportunity to continue learning and all that uncertainty dissipated. Today he is preparing his doctoral thesis in the ‘Multifunctional Optical Materials’ group.
You are the first signatory of the ‘Article of the Month’ for April. What implications does your study have for science?
It is a contribution to the energy model based on the design and optimisation of an optoelectronic device, specifically, a bifacial dye solar cell, into which optical disorder has been introduced. The aim is to improve the efficiency of that cell by increasing the absorption of light. It is important to note that, given the bifacial nature of the cell, the device works on both sides, thus minimising the problems arising from the movement of the sun throughout the day.
Could you describe the function of the dye in solar cells?
In this type of cell, the photosensitive element is a dye, N719, capable of generating electrons when receiving solar radiation. The problem is that not all photons of light are absorbed in the same way throughout the visible spectrum; for example, in the red colour zone, the absorbance decreases significantly. On the other hand, another function of the dye is aesthetic, since the cells can be manufactured in different colours and included in infrastructures of various kinds without losing visual harmony.
How was this problem you refer to solved?
Mainly, by introducing spherical particles with a high refractive index into the cells, specifically titanium dioxide. The inclusion of these particles was done in a disorderly manner. Disorder means that there is no preferential direction of illumination and the improvement in cell functioning is significant, regardless of which side the light falls on.
What hypothesis did you start from?
There are previous works on this type of cells and their properties, since their manufacturing process is cheap and has been optimized over time. First of all, I have to say that we are aware that we cannot compete with silicon photovoltaic technology, but it is also true that dye solar cells can be used where silicon technology does not reach or, today, it is not known how to use it.
Returning to the subject of the question, we started from a theory that had been successfully demonstrated previously, which involved the inclusion of high refractive index light scattering centers within the photoanode of the cell. This implies the increase of the optical path of the light and the residence time of the photons within the electrode. The longer the photons remain there, the more likely they are to interact with the dye molecules and can be absorbed more efficiently.
What is the difference between the previous works and yours?
In the previous contributions, everything was focused on devices that had amorphous particles introduced. We have introduced titanium dioxide nanospheres, which produce a phenomenon called Mie scattering or Mie scattering. In a sphere, there is not the same probability of light scattering at all angles, since forward scattering prevails. This fact is relevant, since in this way we can control the propagation of light within the active layer of our cell through parameters such as the size of the spheres and the filling fraction.
Applying these premises, we achieve an improvement in the efficiency of the device that reaches up to 25% in front illumination, and 33% in rear illumination. By dividing the rear efficiency by the front efficiency, a maximum ratio of around 80% is obtained, one of the highest that has been achieved for dye cells with conventional materials and with a basic architecture.
Let’s focus a little more on you. How long have you been doing research at the ICMS?
I have been here since the beginning of 2014, and since 2015 with an FPU scholarship, so I hope to stay three more years, until I finish my thesis.
Why did you get involved in this world?
Actually, I have always had a wide range of tastes. As a child I already said that I wanted to be a musician and an inventor, so studying Physics was like fostering that kind of curiosity I had for inventiveness. It is true that at the time I was not at all sure what career to choose, but it was my mother who finally convinced me to enroll in Physics.
Regarding research, I was not very clear about what the routine of a researcher was either, however, when I finished my degree, I began a master’s degree at the University of Münster, Germany, and that was a revelation for me. I began to work in a group specialized in nonlinear optics and I realized that research was a very nice way to learn.
What obstacles have you encountered in your career?
There are always obstacles when working and it is necessary to accept them in order to cope with the day to day. Experimental work is nice, but also hard; you can spend a lot of time and nothing works.
Another obstacle, and this one is rather personal, is the self-demand that we researchers often impose on ourselves. Being in prolific and high-projection groups has a price. You never want your group to limp because of you and, even if you receive help and there is no apparent external pressure, sometimes, internal pressures can overcome external pressures. Some people take this as a motivation, but it can be difficult to manage.
Do you have any future projects in sight?
I never plan anything, because life is unpredictable. Until now, my career as a researcher has been a succession of opportunities that have come when I least expected it, and it is better that way. I can say that right now I am quite comfortable with what I do here and my main objective is to finish the thesis.
What would you highlight about cicCartuja as a center?
Mainly, the wide range of research topics it hosts, since it has three completely different institutes. Another virtue that I would highlight about this center is that the scientific staff is very motivated and this helps a lot to advance.
How do you see the current situation for researchers in Spain?
Things are very bad and we don’t know where we will end up settling. If you want to continue in your research career and, precisely, what you want to study is in a Spanish group, it is very difficult to be sure that you will succeed. In a certain way, they force you to find a way to live outside your country.
If it were in your hands, what would you do to improve this situation?
It is a very complicated question to answer, but I am clear that the range of research topics must be expanded so that more people can access it. Another point that I would encourage is the one related to collaboration agreements with companies.
What advice would you give to someone who wants to be a researcher?
I would tell them that, although there are times when things do not go as expected, you have to be patient, since it can be fun and enriching when everything goes well; in that case you fully enjoy it. Another aspect to keep in mind is that it is essential to separate personal life from professional life, especially in those moments when nothing fits. Since there are no fixed hours, it can interfere with your leisure time, but it can never absorb it.
Bibliographic reference:
J. M. Miranda-Muñoz, S. Carretero-Palacios, A. Jiménez-Solano, Y. Li, G. Lozano, H. Míguez. Efficient bifacial dye-sensitized solar cells through disorder by design. Journal of Materials Chemistry A 2016, Vol. 10, 1953-1961. DOI: 10.1039/c5ta10091g