Researchers at the University of Montreal, the Science and Technology Facilities Council, Imperial College London and the University of Cyprus determined how light rays excite the chemical structures of organic solar panels, allowing them to produce charges.
Indeed, until now, scientists did not know exactly what was happening in plastic solar panels, making it difficult to improve their profitability, thereby preventing the widespread use of technology.
“Our findings are of great importance for understanding the fundamental mechanisms at the molecular level, all systems for the conversion of solar energy. We have made great progress toward completion of a quest actively pursued for decades, “says the lead author of the study, Françoise Provencher, the University of Montreal. The findings were published in the Nature Communications.

The researchers examined the fundamental principles underlying reactions that define the operation of devices for converting solar energy into studying the new type of photovoltaic diodes based on an assembly of semiconductor polymer and fullerene derivatives.
Polymers are large molecules made up of a large number of small molecular structures of the same type. They are called “organic” because of atoms which are also in the composition of the molecules necessary for life (carbon, nitrogen, sulfur) are made. A fullerene molecule is a soccer ball shape, composed of carbon atoms. “In these and other similar devices, the absorption of light results in the formation of an electron and a positively charged species. To generate electricity, these two species are separate and the electron must migrate away from the positive charge. If the electron cannot get away fast enough, both positive and negative charges recombine and the process simply does not produce electricity. The overall efficiency of solar devices depends on the number of pairs of charges recombine compared to those who separate, “says Sophia Hayes of the University of Cyprus, the last author of the study.

The team’s work has led to two important conclusions.
“We have used the femtosecond stimulated Raman spectroscopy, says Tony Parker of the Central Laser Facility of the Science and Technology Facilities Council. The femtosecond stimulated Raman spectroscopy is an ultrafast laser technique that provides advanced details on the structural changes chemical bonds during the extremely fast chemical reactions. The laser provides information on the vibration of the molecules when they interact with the laser light pulse. ”
Calculations of great complexity on these vibrations have allowed scientists to confirm the evolution of molecules. First, they discovered that both the electron released from the positive center, rapid molecular rearrangement must reassemble the final products in about 300 femtoseconds (0.0000000000003 s).
A femtosecond is the SI unit of time equal to 10−15 of a second: a femtosecond is to a second what a second is to 3.7 million years. Promptness and speed increase and help maintain the charge separation.
Next, the researchers noted that all relaxation processes and molecular reorganization following the initial charge separation, as observed by the femtosecond stimulated Raman spectroscopy must be extremely small.
“Our findings open the way for further research for understanding the differences between the systems that produce efficient solar cells and systems should have the same efficiency, but do not perform as well. There is no doubt that a better understanding of what works well and less well will design improved ” solar panels, said Carlos Silva, the University of Montreal, senior author of the study.

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