Skip to Content

Thin-Film Solar with High Efficiency

Solexant is printing inorganic solar cells with nanomaterials.
November 19, 2009

Solar cells made from cheap nanocrystal-based inks have the potential to be as efficient as the conventional inorganic cells currently used in solar panels, but can be printed less expensively. Solexant, a company in San Jose, CA, is currently manufacturing solar cells to test the technology. In order to compete with other thin-film solar companies, Solexant is banking on simpler, cheaper printing processes and materials, as well as lower initial capital costs to build its plants. The company expects to sell modules for $1 per watt, with efficiencies above 10 percent.

Nanocrystal solar: The solar cells at top were made on a roll-to-roll printer from an ink consisting of the rod-shaped inorganic semiconducting nanocrystals shown below. The cells were printed on a flexible metal foil and will be topped with a glass plate.

The company has licensed methods for growing nanocrystals and making them into inks from Paul Alivisatos, professor of nanotechnology at the University of California, Berkeley and interim director of the Lawrence Berkeley National Laboratory. (Alivisatos is on Solexant’s board of directors.) Alivisatos says the advantage of these materials is their potential to combine low cost with high performance. Solar cells made from crystalline silicon are efficient at converting sunlight into electricity, but they’re expensive to manufacture. To bring down the cost, companies have been developing thin-film solar cells from semiconductors that don’t match crystalline silicon’s performance but are much less expensive to make.

Solexant’s goal is to make cheap thin-film solar cells with relatively high efficiencies. It would not disclose what the nanoparticle inks are made of, but the company says they are suspensions of rod-shaped, semiconducting nanocrystals that are four nanometers in diameter and 20 to 30 nanometers long. The Solexant cells are printed on a metal foil as the substrate. Nanocrystal films are simple to print but have poor electrical properties. Electrons tend to get trapped between the small particles. “The trick with these cells is how to deposit the materials on the fly in a way that makes a very conductive surface,” which in turn ensures decent light-to-electricity conversion, says Alivisatos. Solexant begins with nanocrystals because they’re easier to print, and heats them as they’re printed, causing them to fuse together into larger, high-quality microcrystals that don’t have as many places for electrons to lose their way.

The remaining parts of the solar cell, including the electrical contacts and a light-absorbing layer, are also printed on the flexible metal films. This process allows Solexant to print very large areas. When complete, the cells are cut and then topped with a rigid piece of glass.

Making the entire cell using a roll-to-roll process gives the company an advantage over other thin-film photovoltaic companies that print on glass, which is heavier and limited to smaller areas, says Solexant CEO Damoder Reddy. “The cost benefit is dramatic, allowing us to produce cells for 50 cents a watt,” he says. First Solar, a thin-film company that uses vacuum deposition to print its cells onto glass, has manufacturing costs of 85 cents per watt. Nanosolar, another company making nanocrystal solar cells, uses a different semiconductor that requires chemical reactions to take place during printing, which increases the complexity and expense of the process. “We print a preformed semiconductor,” which eliminates such steps, says Reddy.

Solexant has raised $22.5 million in venture funding to build its two-megawatt pilot plant, and is seeking $40 million more over the next year to build a 100-megawatt facility. Solar startups typically seek about $250 million in capital to build such a plant, says Reddy.

The company’s first product, which Reddy says will sell for $1 per watt next year, will contain a single layer of the nanocrystals. The company is currently developing other types of nanocrystals that are more responsive to different bands of the solar spectrum in the hopes of boosting its cells’ efficiency. “Ultimately we want to make a multilayer, broad-spectrum cell,” says Reddy.

Keep Reading

Most Popular

open sourcing language models concept
open sourcing language models concept

Meta has built a massive new language AI—and it’s giving it away for free

Facebook’s parent company is inviting researchers to pore over and pick apart the flaws in its version of GPT-3

transplant surgery
transplant surgery

The gene-edited pig heart given to a dying patient was infected with a pig virus

The first transplant of a genetically-modified pig heart into a human may have ended prematurely because of a well-known—and avoidable—risk.

Muhammad bin Salman funds anti-aging research
Muhammad bin Salman funds anti-aging research

Saudi Arabia plans to spend $1 billion a year discovering treatments to slow aging

The oil kingdom fears that its population is aging at an accelerated rate and hopes to test drugs to reverse the problem. First up might be the diabetes drug metformin.

Yann LeCun
Yann LeCun

Yann LeCun has a bold new vision for the future of AI

One of the godfathers of deep learning pulls together old ideas to sketch out a fresh path for AI, but raises as many questions as he answers.

Stay connected

Illustration by Rose WongIllustration by Rose Wong

Get the latest updates from
MIT Technology Review

Discover special offers, top stories, upcoming events, and more.

Thank you for submitting your email!

Explore more newsletters

It looks like something went wrong.

We’re having trouble saving your preferences. Try refreshing this page and updating them one more time. If you continue to get this message, reach out to us at customer-service@technologyreview.com with a list of newsletters you’d like to receive.