U of T researchers develop nanoscale solar cells

TORONTO—Researchers from the University of Toronto (U of T), King Abdullah University of Science & Technology (KAUST) and Pennsylvania State University (Penn State) have developed a nanoscale semiconductor that captures light and turns it into electricity.

Because of their small scale, the dots can be sprayed onto flexible surfaces, including plastics. This enables the production of solar cells that are less expensive than the existing silicon-based version.

“We figured out how to shrink the wrappers that encapsulate quantum dots down to the smallest imaginable size, a mere layer of atoms,” says states Professor Ted Sargent, corresponding author on the work and holder of the Canada Research Chair in Nanotechnology at U of T.

In this area of research, it has been a challenge to uncover the balance between convenience and performance. The ideal design is one that tightly packs the quantum dots together. The greater the distance between dots, the lower the efficiency.

Until now, quantum dots have been capped with organic molecules that separate the nanoparticles by a nanometer. On the nanoscale, that is a lengthy distance for electrons to travel.

To solve this problem, the researchers used inorganic ligands, (sub-nanometer-sized atoms) that bind to the surfaces of the dots and take up less space. Combining close packing and charge trap elimination allowed the electrons to move rapidly and smoothly through the solar cells, thus providing record efficiency.

“We wrapped a single layer of atoms around each particle. This allowed us to pack well-passivated quantum dots into a dense solid,” says Dr. Jiang Tang, author of the paper who conducted the research while a post-doctoral fellow in The Edward S. Rogers Department of Electrical & Computer Engineering at U of T.

“Our team at Penn State proved that we could remove charge traps, locations where electrons get stuck, while still packing the quantum dots closely together,” says professor John Asbury of Penn State, a co-author of the work.

Professor Aram Amassian of KAUST in Saudi Arabia says the team used visualization methods with sub-nanometer resolution and accuracy to investigate the structure and composition of the passivated quantum dots.

The team’s quantum dots had the highest electrical currents and the highest overall power conversion efficiency ever seen in colloidal-quantum-dots (CQD) solar cells. The performance results were certified by an external laboratory, Newport, which is accredited by the US National Renewable Energy Laboratory.

A technology licensing agreement has been signed by U of T and KAUST and brokered by MaRS Innovations (MI), which will enable the global commercialization of this new technology.