New research and innovation
In this context, a research group at Dianji University in Hangzhou, China has developed a new technique to achieve significant improvements in the efficiency of thin-film Si-Si solar cells. Their research, published in the Journal of Photonics for Energy (JPE) , represents a major advance in silicon solar cell technology.
The proposed technique improves some key optical and electrical properties, which the team identified as responsible for the difference in conversion efficiency of thick and thin Si-Si solar cells. Using commercial software, they performed optical simulations of various thin cell models. Through further experiments using solar cells, researchers have developed an innovative manufacturing method that offers many advantages over traditional techniques.
Instead of using the silicon alloy cutting method typically used to create thick C-Si layers, the team used the layer transfer method. They used hydrofluoric acid to etch holes in a thick silicon wafer. This porous layer serves as a substrate for growing a 20 µm thick monocrystalline silicon layer, which can be easily removed and transferred to a flexible stainless steel layer.
Performance improved for nanofilms
To improve the optical and electrical performance of thin silicon layers, researchers deposited metal nanofilms on both sides using plasma- enhanced chemical vapor deposition: SiO 2 /SiN x /SiO x and Al 2 O 3 /SiN x /SiO layers. X solar cells with a hierarchical pattern on the front and back sides.
The front SiN x /SiO x and back SiO x /SiN x layers increase the light absorption of the silicon layer at shorter and longer wavelengths, respectively. This improved the short-circuit current density, which is a measure of how many charge carriers a solar cell can generate and collect. Compared to the standard solar cell used as reference, the current density increased from 34.3 mA/ cm2 to 38.2.
Moreover, the SiO 2 and Al 2 O 3 layers provide a high passivation of the surface, reducing the loss of recombination and generated charge carriers. This increases the open circuit voltage, which is a measure of the maximum voltage produced by the solar cell. It increases from 632 mV to 684 mV in the reference cell when using the proposed design. As a result, the solar cell's fill factor, an indicator of how close a solar cell is to its maximum theoretical efficiency, increased from 76.2 percent to 80.8 percent.Simulations and experiments confirmed that the proposed technique improved the conversion efficiency from 16.5% to 21.1%, a significant gain of 4.6% (compared to the reference cell, equivalent to an improvement of about 28%). This brings the efficiency of thin Si-Si solar cells closer to their thicker industrial counterparts, currently reaching 24%.
"Overall, the results of this research provide a new way to produce high-performance thin-crystalline silicon solar cells using significantly less silicon than 20 years," said Leonidas Balilis, associate editor of JPE and professor of condensed matter physics at the university. From Patras. , Greece. - µm, or about one-eighth of the amount required for 160 µm-thick cells in a given plate size.
These advances will help the wider and cheaper adoption of silicon solar technology, thanks to lower costs and expanding solar panel manufacturing capacity.
Reference: Guanglin Ji, Zhen Zhang, Jinshuo Han, Shengji Ma, Yu Zhang, Lu Wang and Wensheng Yan, 12 September 2023, Journal of Energy Photonics .doi: 10.1117/1.JPE.13.035501
