Guiding the way to improved solar cell performance

Bilayer solar cell based on the organic semiconductor copper(I) thiocyanate (CuSCN) provides a new platform for exciton diffusion studies.
Credit: © 2020 KAUST

Understanding how particles travel through a device is vital for improving the efficiency of solar cells. Researchers from KAUST, working with an international team of scientists, have now developed a set of design guidelines for enhancing the performance of molecular materials.

When a packet of light, or photon, is absorbed by a semiconductor, it generates a pair of particles known as an exciton. An electron is one part of this pair; the other is its positively charged equivalent, called a hole. Excitons are electrically neutral, so it is impossible to set them in motion by applying an electric field. Instead the excitons “hop” by a random motion or diffusion. The dissociation of the excitons into charges is necessary to create a current but is highly improbable in an organic semiconductor.

“So typically, we need to blend two semiconductors, a so-called electron donor and an electron acceptor, to efficiently generate free charges,” explains Yuliar Firdaus. “The donor and acceptor materials penetrate into one another; maximizing the exciton diffusion length– the distance the exciton can travel before recombining and being lost– is crucial for optimizing the organic solar cell’s performance.

Many previous organic solar cells were made by blending a polymer with molecules, known as fullerenes. But more recently, replacing the fullerene with other organic materials such as nonfullerene small molecules produced impressive improvements in device efficiency.

Firdaus and colleagues combined measurements of the photocurrent with ultrafast spectroscopy to calculate the diffusion length of a wide variety of nonfullerene molecules. They observed very long exciton diffusion lengths, in the range of 20 to 47 nanometers–an improvement on the 5 to 10 nanometer range characteristic of fullerenes.

To better understand this improvement, the team compared data describing the crystallographic structure of the molecules with quantum chemical calculations. In this way they could identify key relationships between the chemical structure of the molecule and the diffusion length. With these connections established, the scientists developed a set of rules to aid in the synthesis of improved materials and, ultimately, help the design of organic photovoltaic devices with improved conversion efficiency.

“Next, we plan to investigate how film processing processes might affect the exciton transfer rate of the existing small-molecule acceptors,” says Firdaus. “We are also interested in translating the molecular design rules to synthesize new acceptor materials with better performance.”

Media Contact

Michael Cusack
King Abdullah University of Science & Technology (KAUST)

All news from this category: Materials Sciences

Materials management deals with the research, development, manufacturing and processing of raw and industrial materials. Key aspects here are biological and medical issues, which play an increasingly important role in this field.

innovations-report offers in-depth articles related to the development and application of materials and the structure and properties of new materials.

Back to the Homepage

Comments (0)

Write comment

Latest posts

Seawater as an electrical cable !?

Wireless power transfers in the ocean For drones that can be stationed underwater for the adoption of ICT in mariculture. Associate professor Masaya Tamura, Kousuke Murai (who has completed the…

Rare quadruple-helix DNA found in living human cells with glowing probes

New probes allow scientists to see four-stranded DNA interacting with molecules inside living human cells, unravelling its role in cellular processes. DNA usually forms the classic double helix shape of…

A rift in the retina may help repair the optic nerve

In experiments in mouse tissues and human cells, Johns Hopkins Medicine researchers say they have found that removing a membrane that lines the back of the eye may improve the…

Partners & Sponsors

By continuing to use the site, you agree to the use of cookies. more information

The cookie settings on this website are set to "allow cookies" to give you the best browsing experience possible. If you continue to use this website without changing your cookie settings or you click "Accept" below then you are consenting to this.