Progressing New Methods to Use Light and Reliable Organic Solar Cells for Wearables

June 19, 2020 by Luke James

In the electronics space, organic solar cells may find a range of useful applications, particularly in the development of wearable devices.

Now, scientists at Okayama University have reported what is believed to be the first instance of an electrochemical reaction that produces thienoacenes, useful materials that are used in organic solar cells


Organic Solar Cells

Organic photovoltaic (OPV) solar cells are the latest generation of solar cell technology. They are very strong absorbents of light and are able to harness much higher amounts of sunlight than other cells, making them far more efficient and cost-effective. Other advantages of OPVs include their lightweight profiles and large area coverage, and they are driving the solar energy industry forward as the latest research and development continues to improve sustainability. 

One area where OPVs are set to make great strides is in the field of electronics, particularly the development of novel electronic devices such as wearables. This is because of their status as ideal alternatives to common energy storage enable us to meet our goals for green, inexpensive, and portable energy sources.

Moreover, due to the rapid development of wearable devices and other electronics such as advanced sensors, the need for green power sources that are robust, accessible has become a new challenge that photovoltaic cells, systems, and platforms could overcome. 

More often than not, batteries in these devices are composed of light and robust organic semiconductor molecules. However, synthesizing these molecules involves the use of expensive rare metal catalysts in a complex process that drives up manufacturing costs. This challenge is what the Okayama team set out to solve—and they claim to have done just that with a new, novel reaction system. 


Electrochemical setup for the synthesis of thienoacene derivatives.

The electrochemical setup for the synthesis of thienoacene derivatives. Image credited to Okayama University


A Novel Reaction System

The team’s reaction system was developed to synthesize thienoacene derivatives, important components found in organic semiconductors. Using environmentally friendly organic electrolysis, the team focused on constructing carbon-sulfur (C-S) bonds because “they are… abundant and significant in the field of pharmaceuticals and materials science,” said Professor Seiji Suga.

C-S bonds are usually constructed via transition metal-catalyzed cross-coupling, but this requires the use of rare metal catalysts which makes the reaction expensive.

Instead, the research team focused on a different eco-friendly method called “electrochemical carbon-heteroatom bond formation” which requires relatively mild conditions in contrast to the other method.  "Over the past several years, we were interested in the development of new methods for thienoacene synthesis, acene derivatives that have a good track record in organic electrochemistry, and are attractive candidates for useful organic materials,” added Professor Suga. 


A Successful Synthesis

With a basis for their study, the researchers then find novel electrochemical methods for thienoacene synthesis. They found that the desired C-S bond formation occurred in the presence of a bromide ion which acts as a powerful promoter of the reaction. Using this strategy, the team synthesized types of thienoacene derivatives called "π-expanded thienoacene derivatives." This represents the first time that C-S bond formation for the synthesis of thienoacene derivatives has been carried out successfully. 

The team’s study provides a glimmer of hope that, in future, organic semiconductor molecules can be produced using a cost-effective technique and without expensive metal catalysts.