Perovskites are the holy grail of photovoltaic technologies. During the conversation we had in January 2021 with Ignacio Mártil de la Plaza, who is a PhD in Physics and Professor of Electronics at the Complutense University of Madrid, this expert in advanced solar cell technologies explained that perovskites have traveled in ten years the same path that silicon took fifty years to travel.
The hegemonic material with which researchers in photovoltaic technologies work is silicon, but as of 2009 this chemical element has been forced to give up part of its role. That year the first study dedicated to a solar cell made with a perovskite was published, and its efficiency at that time was only 3.8%. It is a very low number, and, in addition, the material degraded perceptibly in a few hours.
Since then the landscape has changed a lot. Solar cells that combine silicon and perovskites to form tandem or multijunction structures currently have an efficiency of approximately 30%. Besides, they no longer degrade in hours. They are much more stable than they were when perovskites entered the realm of photovoltaic panels. And, as a tip, they are cheap and easy to make. Even so, there is still a lot of research to be done.
Some metals increase the efficiency of perovskites by 250%
Before going any further, we would like to take a moment to review what perovskites are and why they have so much to contribute to solar cells. The term perovskite is a generic denomination that identifies a family of materials whose crystalline structure is similar to that of a material called calcium titanate. However, the most important thing is that their attractiveness comes from properties that make them optimal from a theoretical point of view for converting solar energy into electrical energy.
There is a property that a semiconductor must have to be optimal, at least in theory, which is known as the energy gap. It is a concept that comes from Quantum Physics and identifies the minimum energy that a material can absorb. For the solar cell that we want to manufacture with this material to be optimal, it must be in the neighborhood of 1.5 electron volts (eV), and there is a family of perovskite materials that have that property.
The chemical elements with which we can manufacture perovskites are very abundant in the earth’s crust
In addition, these materials absorb radiation very well, so very little is needed to absorb the radiation from the Sun. Another point in their favor that we cannot ignore is that the chemical elements with which we can manufacture them are very abundant in the earth’s crust (carbon, nitrogen, hydrogen, lead…). However, and this works against them, the perovskites that work best are those with lead, and it is a highly polluting element.
Usually, when the material obtained is synthesized, it is deposited on a glass substrate, but a group of researchers from the University of Rochester, in New York (United States), led by Professor of Optics Chunlei Guo, has come up with the idea of trying something different. . And it is that instead of depositing the perovskites once they have been synthesized on a glass substrate they have placed them on a sandwich structure which alternately combines layers of metal and layers of a dielectric material.
A quick note: a dielectric is a component with a very low electrical conductivity, and therefore behaves like an insulator. According to their tests, Professor Guo and his collaborators have managed, thanks to this peculiar strategy, to increase the energy conversion efficiency of perovskites by 250%. It is a real barbarity. This parameter describes, in a simple way, the ability with which the conglomerate of perovskites, metal and dielectric transforms solar energy into electrical energy.
Professor Guo and his collaborators have succeeded in increasing the energy conversion efficiency of perovskites by 250%. It’s a real barbarity
There is a lot of promising research being done with perovskites in the field of photovoltaic technologies, and other experiments have yielded very interesting results, but none comes close to that of these researchers. In the article they have published in Nature Photonics they explain in detail the peculiarities of their experiment. It is not essential to read it to assume the magnitude of this finding, but we are interested in not overlooking the fact that the metals used by these researchers to “dope” the perovskites are silver and aluminum oxide. The latter acts as a dielectric. Looks very good. Let’s cross our fingers that this investigation bears fruit.
Cover Image: Kindel Media
More information: Nature Photonics
