Researchers achieved another milestone in the development of fully transparent, efficient solar cells with the development of a transparent electrode that can be used to boost efficiency in tandem solar-cell arrangements, they said.

A team of researchers at Penn State University developed the ultrathin metal electrode for semi-transparent perovskite solar cells, which then can be coupled with traditional silicon cells to boost the performance of both devices, they said.

The invention is a key advancement toward the broad-scale installation of tandem solar cells not only in traditional applications but also in windows in residential homes and offices to create more sustainable forms of energy delivery, something researchers have been working toward for years.

“This is a big step--we finally succeeded in making efficient, semitransparent solar cells,” observed Kai Wang, assistant research professor of materials science and engineering at Penn State and a collaborator on the research.

Optimizing Gold

Key to the invention is a new way to make an ultrathin gold film—which historically has shown promise as a transparent electrode in perovskite solar cells—more conductive, researchers explained. In previous research, scientists struggled to create a uniform later of the material for the electrode, resulting in poor conductivity, they said.

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“Normally, if you grow a thin layer of something like gold, the nanoparticles will couple together and gather like small islands,” explained Dong Yang, assistant research professor of materials science and engineering at Penn State, in a press statement.

To solve this problem, researchers used chromium as a base layer, which enabled the gold to form on top in a continuous, ultrathin layer without previous conductive deficiencies, he said.

 “Chromium has a large surface energy that provides a good place for the gold to grow on top of, and it actually allows the gold to form a continuous thin film,” Yang explained.

Promising Results

Though most solar cells currently used are made from silicon, scientists have been exploring the use of perovskite materials—a broad class of crystalline materials

—as a way to push the limits of current technology by pairing them with traditional cells to create more efficient tandem devices.

Perovskite solar cells themselves comprise five layers, and previous materials tested as transparent electrodes damaged or degraded layers of the cells, researchers noted. Using the combination gold-chromium electrodes shown stability and efficiency over time in lab tests, they said.

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Specifically, the perovskite solar cell that the team developed achieved 19.8 percent efficiency, which researchers said is a record for a semitransparent cell. Combined with a traditional solar cell, the tandem device achieved 28.3 percent efficiency, which is 5 percent more efficiency than a silicon cell on its own, researchers reported in a paper in the journal Nano Energy.

A 5 percent improvement in efficiency is significant, representing about 50 watts more sunlight for every square meter of solar cell material, researchers said. In solar farms with thousands of modules, this can add up to a substantial amount of electricity, they said.

Researchers said their technology demonstrates that tandem perovskite-silicon cells can be used not only in traditional solar-farm arrays but that the introduction of a new transparent component furthers their application for uses in sustainable buildings and other applications.

“This breakthrough in the design of tandem cell architecture based on a transparent electrode offers an efficient route toward the transition to perovskite and tandem solar cells,” Yang said in a press statement

Elizabeth Montalbano is a freelance writer who has written about technology and culture for more than 20 years. She has lived and worked as a professional journalist in Phoenix, San Francisco, and New York City. In her free time, she enjoys surfing, traveling, music, yoga, and cooking. She currently resides in a village on the southwest coast of Portugal.