| Work Detail |
An international team of researchers has shown that monolithic perovskite-silicon tandem solar cells do not suffer the same degree of reverse bias degradation typically seen in perovskite single-junction solar cells under partial shading. They explained that the tandem devices are “protected” by the silicon subcell.
Researchers from Princeton University in the United States and King Abdullah University of Science and Technology (KAUST) in Saudi Arabia have tested the reverse bias stability of monolithic perovskite-silicon tandem cells, comparing their performance. with that of single junction perovskite metal halide solar cells, and have found that the tandem device is “protected by the silicon subcell against reverse bias.”
In the article “ Reverse-bias resilience of monolithic perovskite/silicon tandem solar cells ,” recently published in Joule , the scientists point out that the silicon subcell offers a resistance to reverse bias in both long-term reverse voltage bias tests at the single cell level and partial shading tests at the module level.
“We knew that the diode of the silicon solar cell would be considerably higher resistance in reverse bias than that of the perovskite solar cell. “This means that the tandem should inherit the high stability of the silicon solar cell, rather than the poor reverse polarization stability of the perovskite solar cell alone,” Barry P. Brand, co-author of the research, told pv magazine . .
He also explained that typically efforts to improve some aspect of a device, such as reverse bias stability, compromise some other aspect of its operation, such as efficiency. “In this case, thats not the case,” he said. “The silicon-perovskite tandem cell is the most efficient and also improves reverse bias stability. “Thats something really worth mentioning.”
The researchers hope the results will be significant for the commercial prospects of silicon-perovskite solar cells, as they contribute to advantages over other options. “Not only are they more efficient, but they dont suffer from the reverse bias stability problem of a typical perovskite single junction solar cell. These factors decisively influence the commercial prospects of any solar technology,” says Brand.
The team conducted a series of stress tests to compare the reverse bias stability of three encapsulated cell technologies. Specifically, a perovskite single junction cell, fabricated from a triple cation perovskite solution spin-coated on glass, a silicon heterojunction single junction cell fabricated on a Topsil floating zone wafer, and a monolithic solar cell in Perovskite-silicon tandem fabricated using the same deposition conditions and techniques as single junction test cells, except for the layers required for the tandem.
The cells were encapsulated in thermoplastic polyurethane with edge sealing between glass sheets. To mimic reverse bias conditions in a practical scenario, the cells were connected in chains. The partial shading test included an initial 5 min maximum power point tracking (MPPT) with all three cells exposed to 1 sun illumination, followed by full shading of one of the cells and continuation of MPPT for 30 m, followed by an additional 10 min MPPT with all three cells exposed to 1 sun illumination. Next, the team measured the power output across the module and the voltage drop across the shaded cells before, during and after shading.
“Favourable voltage distribution, rather than an overall improvement in breakdown voltage, plays the most important role in the reverse bias protection effect,” the researchers noted.
In conclusion, they noted that the advantages of the tandem cell are its higher efficiency, a well-developed manufacturing process, and the ability to withstand the stress of reverse polarism to maintain stability under partial shading conditions. Regarding the reverse bias resistance of perovskite single junction cells, they noted that further research will be needed in areas such as processing technology and ion blocking barrier layers. |
