Nature Energy: organic solar cells made from non-toxic solvents

A new process for the preparation of organic solar cells using environmentally friendly solvents has been developed thanks to extensive international research, in which scientists from the Institute of Macromolecular Chemistry also participated. The results of the joint effort were recently published in the prestigious scientific journal Nature Energy.

One of the major scientific topics in recent years has been the development of technologies for more sustainable energy production and storage. Among the most promising sustainable energy solutions today are solar cells made from organic molecules or polymers. However, despite their advantages (they are usually thin, lightweight and flexible), most organic cells developed so far have a low power conversion efficiency (PCE). Although researchers have succeeded in recent years in developing solar cells with a PCE above 18 %, they have not done so without toxic, low boiling point solvents such as chloroform.

An international research team has recently presented a new process for preparing organic solar cells using environmentally friendly solvents in the prestigious journal Nature Energy. The scientists have succeeded in preparing organic solar cells with efficiencies exceeding 17 % without using solvents that are harmful to humans and the environment.

Scientists from six institutions and four countries were involved in researching this new generation of solar cells: Soochow University (China), Linköping University (Sweden), the Czech Academy of Sciences (Czech Republic), the Ulsan National Institute of Science and Technology (Korea), Chongqing University (China) and the Chinese Academy of Sciences (China). In particular, the long-term collaboration between the Department of NMR Spectroscopy (IMC CAS) and the Department of Physics, Chemistry and Biology (IFM) of Linköping University (Sweden) was crucial for the new study. "We have been collaborating with our colleagues from Sweden on research and development in the field of solar cells for the last few years. Our knowledge and measurement capabilities with our NMR instruments are an indispensable part of the research goals," describes Dr. Sabina Abbrent and Dr. Libor Kobera from the Department of NMR Spectroscopy (IMC CAS).

The international team of scientists analysed the prepared material very comprehensively. "An extensive structural study was carried out using a wide portfolio of analytical methods such as NMR, FTIR, 2D GIWAX, TGA, MALDI-TOF and UV-VIS. The material properties were characterized using electrical quantities (J-V characterization), electroluminescence measurements, CV and LBIC analyses, while the long-term stability of the prepared materials was also tested," describes Dr. Jiří Brus, Head of the Department of NMR Spectroscopy.

The aim of the researchers from the IMC (Dr. Libor Kobera, Dr. Sabina Abbrent, Dr. Jiří Brus) was to describe the structure of the new organic solar cells at molecular to atomic resolution by means of a detailed analysis and to reveal the structural effects that induce an increase in the conversion of solar radiation into electrical energy. To do this, they used one of the key methods for studying the structure of matter at the atomic level: high-resolution nuclear magnetic resonance (NMR). The scientists at the IMC have been conducting the research over the past year, carrying out a series of sophisticated and time-consuming experiments.

The key properties exhibited by the newly developed material (processability without the use of halogenated solvents, enabling the production of a uniform module with a large surface area, without annealing, at high efficiency and excellent stability) are among the essential requirements for the industrial development of organic solar cells. The researchers' findings could thus help to develop commercially viable organic solar cells with high PCE values using environmentally friendly solvents in the future.

Mechanismus vzájemného působení a krystalizace molekul v systému typu host-hostitel vyvinutého pro pokročilé environmentálně přátelské organické solární články, kde klíčovou roli hrají amfifilní oligo(ethylenglykolové) řetězce, které vedou k posílení mezimolekulárních pi-pi interakcí a následnému zvýšení účinnosti konverze energie. (Převzato z Nature Energy. 6, 2021, s 1045-1053)

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