Toshiba tests transparent solar cell layered on silicon cell for 9.5% efficiency

Researchers at Toshiba in Japan have reported an advancement in output and reliability with its layered transparent solar cell/silicon solar cell prototype.

The researchers have reported a transparent cuprous oxide (Cu₂O) solar cell with a conversion efficiency of 9.5%, the highest level yet achieved for a Cu₂O cell. This was realized by enlarging its predecessor, announced in December 2021, and points to the potential for mass production. The new cell is expected to provide a boost for the development of EV that do not require plug-in charging, and to advance other mobility applications, such as high-altitude platform stations, telecom platforms in the stratosphere.

Tandem cells position a solar cell over a standard silicon cell. The cells generate power at different wavelengths, raising areal output, and have great potential to boost the efficiency of solar modules. In addition to Toshiba’s transparent Cu₂O cell, work is being done on two other tandem cell technologies: fabrication with gallium arsenide (GaAs) or other III-V materials; and perovskite crystal thin-films. Production costs for the former range from several hundred- to several thousand-times the cost of a single silicon cell, severely restricting application. The latter cannot yet deliver the necessary reliability and guaranteed output for the 20-years-and-more life of a silicon cell.

Toshiba’s R&D focuses on the advantages of transparent Cu₂O cells: fabrication with naturally abundant materials cuts costs; a hard and strong, and moisture resistant material, all guarantees of reliability; and light transmittance qualities that open the way to high level power generation efficiency.

Toshiba’s painstaking efforts are now bearing fruit. In a research project supported by Japan’s New Energy and Industry Technology Development Organization (NEDO), researchers have pushed the conversion efficiency of the Cu₂O cell to 9.5%, a full 1.1% over the 8.4% reported last year. It was achieved by enlarging the cell and suppressing carrier recombination in the edge of Cu₂O generation layer, which degrades generation efficiency.

“We found that a larger cell size effectively suppresses photocarrier recombination,” explains Kazushige Yamamoto, a Fellow at Toshiba’s Corporate Research & Development Center, and leader of the research team. “Increasing the power generation area from the previous 3x3mm² to 10x3mm² produced a relative reduction in recombination in the edge of cell, and the resulting increase in photocurrent pushed the efficiency to 9.5%.”

Toshiba has estimated that positioning the new Cu₂O solar cell over a 25% efficient silicon cell realizes a Cu₂O-Si tandem cell with a 28.5% efficiency — notably surpassing 26.7%, the highest reported efficiency for any standard silicon cell, and close to 29.1%, the highest reported efficiency for any GaAs cell.

Under test criteria defined by NEDO, Toshiba found that a one-time charge enables the current Cu₂O-Si tandem cell to power an electric vehicle for 37 km, and further improvements in solar cells toward the theoretical maximum efficiency of 42.3% are expected to extend the range to a distance approaching 55 km. These are both recognized as practical distances for short trips without recharging, and would reduce charging frequency for longer trip.

Toshiba targets a practical Cu₂O-Si tandem cell with a 10% efficient Cu₂O cell and an overall efficiency of 30%, and the new cell records solid progress to that goal. Looking to mass production, the company is working to enlarge cell size, and has made a prototype with a power generation area of 40mm² and an efficiency around 8%. The efficiency falloff in the larger cell is due to a less uniform layer and Toshiba continues to refine thin film deposition technology for uniform deposition over a larger area.

News item from Toshiba

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Original Source: https://www.solarpowerworldonline.com/2022/09/toshiba-tests-transparent-solar-cell-layered-on-silicon-cell-for-9-5-efficiency/