Study linked to the Center for Innovation in New Energies (CINE) reveals details of perovskite films with unprecedented precision
Perovskites are a class of materials that have drastically transformed the energy production scenario with their use in photovoltaic cells in recent years, therefore receiving great attention from the scientific community around the world. From the beginning of research in 2009, in just five years, an efficiency of converting solar energy into electrical energy was reached above 20%, a value that continues to grow and, today, is equivalent to that of photovoltaic cells based on solar energy. silicon, which dominate the world market. “Never has a photovoltaic technology grown so much in such a short time, with the advantage of its manufacturing being faster, simpler and cheaper than silicon, for example”, says Ana Flávia Nogueira, professor at the Unicamp Chemistry Institute and coordinator of one of the research divisions of the Center for Innovation in New Energies (CINE), an engineering research center financed by the São Paulo State Research Support Foundation (Fapesp), in partnership with Shell.
Despite advances, important challenges remain for the commercial application of perovskite photovoltaic cells. “Initially, there was a race for efficiency, but now that we have achieved satisfactory rates, the research community in the area is returning a little, seeking to better understand this material, with so much potential and about which there are still many open questions”, says Walnut. In CINE's Dense Energy Carrier Division (DEC), coordinated by the researcher, studies take place on three main fronts: lead-free perovskites, which presents the problem of toxicity; large-scale device production; and, precisely, fundamental studies of the physical chemistry of perovskites. And, with the help of the National Synchrotron Light Laboratory (LNLS), the group has just managed to “see” what no one had seen before: the individual grains in films of two types of organic-inorganic hybrid perovskite (CsFAMA and FAMA). To this end, he used an innovative technique that can now be used in nanoscale mapping and, thus, in the analysis and production of knowledge about a whole set of other films.
“During the preparation of the films, we have the formation of impurities, or other crystalline structures, in a process that is not entirely understood. With the usual x-ray techniques, we can know that these different phases are there, but we cannot map their location”, explains Nogueira. Among these phases – which have the same composition, but different arrangements of atoms –, the researcher describes that there is one that is active, that is, it promotes the photovoltaic effect (called the black phase), and another that is not photoactive, the yellow phase ( yellow phase). “At LNLS, we use Synchrotron radiation in the infrared region, concentrated at the tip of the microscope. With this pioneering use of the so-called nanoinfrared, it is possible to choose exactly the grain we want to analyze and, based on its infrared spectrum, a kind of 'fingerprint', 'signature' of that phase, we can know where it is, in which grain”, he details. “In the future, this understanding could allow, for example, in the synthesis to increase the active phase in perovskite films”, she concludes.
The results of the study were published on October 25 in the journal Science Advances, from the Science group, in the article titled “Nanoscale mapping of chemical composition in organic-inorganic hybrid perovskite films”. The first author is Rodrigo Szostak, whose doctoral research, under the supervision of Ana Flávia Nogueira and co-supervision of Hélio Tolentino and Raul de Oliveira Freitas, both from LNLS, led to the reported results. In addition to them, other postgraduate students linked to the Nanotechnology and Solar Energy Laboratory, coordinated by Nogueira, other LNLS researchers and international partners from Switzerland (EPFL) also signed the publication.
CINEMATOGRAPHY
The New Energy Innovation Center was launched in May 2018, with funding from Fapesp and Shell and a coordination hub based at Unicamp. In addition to Unicamp, the University of São Paulo (USP) and the Institute for Energy and Nuclear Research (Ipen) also lead the center, in collaboration with six other national institutions and 14 from other countries. In addition to the Dense Energy Carrier Division (DEC) focusing on hydrogen generation and CO2 conversion from sunlight, the Center has three other divisions: Advanced Energy Storage (AES), Methane to Products (M2P) and Computational Materials Science and Chemistry (CMSC). Together, the four divisions conduct more than 20 research projects. More information at cine.org.br.
