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Friday, 21 Sep 2018

UCLA researchers develop perovskite-CIGS tandem solar cell with 22.4 percent power conversion efficiency

The two layers are joined by a nanoscale interface that the UCLA researchers designed, the interface helps give the device higher voltage, which increases the amount of power it can export

UCLA | Perovskite–CIGS tandem solar cell - with record 22.4 percent power conversion efficiency

30 Aug 2018 | Editor

Materials scientists from the UCLA Samueli School of Engineering have developed a highly efficient thin-film perovskite-CIGS solar cells that generates more energy from sunlight than typical solar panels, thanks to its tandem design.

These devices are made by spraying a thin layer of perovskite — an inexpensive compound of lead and iodine that has been shown to be very efficient at capturing energy from sunlight — onto a commercially available CIGS (copper, indium, gallium and selenide) solar cell.

The research team's solar cell has a power conversion efficiency of 22.4 percent, a record in power conversion efficiency for a perovskite–CIGS tandem solar cell.

The performance was confirmed in independent tests at the U.S. Department of Energy's National Renewable Energy Laboratory. (The previous record, set in 2015 by a group at IBM’s Thomas J. Watson Research Center, was 10.9 percent.)

The UCLA device’s efficiency rate is similar to that of the poly-silicon solar cells that currently dominate the photovoltaics market.

According to the announcement the cell's CIGS base layer, which is about 2 microns thick, absorbs sunlight and generates energy at a rate of 18.7 percent efficiency on its own, but adding the 1 micron-thick perovskite layer improves its efficiency.

The two layers are joined by a nanoscale interface that the UCLA researchers designed; the interface helps give the device higher voltage, which increases the amount of power it can export.

The entire assembly sits on a 2 mm thick glass substrate.

"With our tandem solar cell design, we’re drawing energy from two distinct parts of the solar spectrum over the same device area."


"The technique of spraying on a layer of perovskite could be easily and inexpensively incorporated into existing solar-cell manufacturing processes."


"Devices using the two-layer design could eventually approach 30 percent power conversion efficiency. This will be the research group’s next goal."


"This increases the amount of energy generated from sunlight compared to the CIGS layer alone."


"Our technology boosted the existing CIGS solar cell performance by nearly 20 percent from its original performance,” Yang said. “That means a 20 percent reduction in energy costs."


Professor Yang Yang, UCLA's Carol and Lawrence E. Tannas Jr. Professor of Materials Science

The study’s lead authors are Qifeng Han, a visiting research associate in Yang’s laboratory, and Yao-Tsung Hsieh and Lei Meng, who both recently earned their doctorates at UCLA. The study’s other authors are members of Yang’s research group and researchers from Solar Frontier Corp.’s Atsugi Research Center in Japan.

The research was supported by the National Science Foundation and the Air Force Office of Scientific Research. Yang and his research group have been working on tandem solar cells for several years and their accomplishments include developing transparent tandem solar cells that could be used in windows.

High-performance perovskite/Cu(In,Ga)Se2 monolithic tandem solar cells

Qifeng Han | Yao-Tsung Hsieh | Lei Meng | Jyh-Lih Wu | Pengyu Sun | En-Ping Yao | Sheng-Yung Chang | Sang-Hoon Bae | Takuya Kato | Veronica Bermudez | Yang Yang

  • Department of Materials Science and Engineering, University of California–Los Angeles, Los Angeles, CA 90095, USA.
  • Atsugi Research Center, Solar Frontier K.K., Atsugi, Kanagawa 243-0206, Japan.

Science 31 Aug 2018: | Vol. 361, Issue 6405, pp. 904-908 | DOI: 10.1126/science.aat5055

Perovskite/CIGS tandem cells

Tandem solar cells can boost efficiency by using more of the available solar spectrum. Han et al. fabricated a two-terminal tandem cell with an inorganicorganic hybrid perovskite top layer and a Cu(In,Ga)Se2 (CIGS) bottom layer. Control of the roughness of the CIGS surface and the use of a heavily doped organic hole transport layer were crucial to achieve a 22.4% power conversion efficiency. The unencapsulated tandem cells maintained almost 90% of their efficiency after 500 hours of operation under ambient conditions.

Abstract

The combination of hybrid perovskite and Cu(In,Ga)Se2 (CIGS) has the potential for realizing high-efficiency thin-film tandem solar cells because of the complementary tunable bandgaps and excellent photovoltaic properties of these materials. In tandem solar device architectures, the interconnecting layer plays a critical role in determining the overall cell performance, requiring both an effective electrical connection and high optical transparency. We used nanoscale interface engineering of the CIGS surface and a heavily doped poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) hole transport layer between the subcells that preserves open-circuit voltage and enhances both the fill factor and short-circuit current. A monolithic perovskite/CIGS tandem solar cell achieved a 22.43% efficiency, and unencapsulated devices under ambient conditions maintained 88% of their initial efficiency after 500 hours of aging under continuous 1-sun illumination.

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