The aim of this research, carried out over the past three years and still under way, is to seek less costly, more flexible and more efficient materials when converting solar energy into electricity, heat or other type of energy. To this end, the researchers studied fundamental physical processes occurring in an artificial device made up of organic molecules. The molecules chosen participate in the processes of natural photosynthesis, and thus the device can absorb light efficiently.
It is generally thought that photosynthesis and photovoltaic artificial devices and the conversion of lght to electricity occur in femtosecond time scales (a femtosecond is a thousand billionth of a second) and involves an incoherent process of electron transfer. However, the work published in the Nature Communications journal identifies that the process of generating an electric current induced by the light absorbed has quantum coherence, i.e. is a stable and robust process lasting 25 femtoseconds in which losses do not occur.
Moreover, the results indicate that this process is mediated by the vibrations of a linker or connector. “First solar energy is absorbed. Later, pairs of charge carriers are generated and, when these pairs separate, an electric current is obtained”, explained Angel Rubio. It is with this last state that the UPV/EHU has been involved. “We identify the microscopic component that dictates the separation of charge after the light has been absorbed, and which gives rise to the creation of the electric current. This component is what unites the light-absorbing molecule (porphyrin) with that which receives the electron (fullerene). Knowing the mechanism causing this separation, the system can be optimized and controlled. In fact, we are now looking to how to enhance and characterise the interface, in such a way that devices can be designed, which are efficient and long lasting; in short, that they be sustainable”, explained Professor Rubio.
Researchers from Modena (Italy), Oldenburg and Berln (Germany) have undertaken the experimental part of this research and the theoretical part was developed by the UPV/EHU NanoBio Spectroscopy team, led by Professor Rubio, in collaboration with the European infrastructure for Theoretical Spectroscopy (ETSF), the UPV/EHU Department of Physics of Materials, the CSIC-UPV/EHU Center for the Physics of Materials and the Donostia International Physics Center (DIPC).