Scientists make a new electrical component

In the future, low-carbon societies using Internet of Things (IoT) devices will become commonplace. But to achieve this, we must first realize highly efficient and stable renewable energy sources. Solar cells are considered a promising option, but their electrical contacts suffer from a “trade-off” relationship between surface passivation and conductivity. Recently, Japanese researchers have developed a new type of electrical contact capable of solving this problem.

The newest type of commercial photovoltaic cell (solar cell) uses stacked layers of crystalline silicon (c-Si) and an ultrathin layer of silicon oxide (SiOX) to form an electrical contact. SiOX is used as a “passivating” film, a non-reactive layer that improves device performance, reliability and stability. But this does not mean that simply increasing the thickness of this passivation layer will lead to improved solar cells. SiOX is an electrical insulator and there is a trade-off relationship between passivation and electrical contact conductivity in solar cells.

In a new study published in Nanomaterials applied by ACSa research team led by Assistant Professor Kazuhiro Gotoh and Professor Noritaka Usami of Nagoya University has developed a new SiOX layer that simultaneously allows high passivation and improved conductivity. Dubbed NAnocrystalling Transport path in Ultrathin dielectrics for REinforcing passivating contact (NATURE contact), the new electrical contact consists of three-layer structures made of a layer of silicon nanoparticles sandwiched between two layers of oxygen-rich SiO.X. “You can think of a passivation film as a big wall with doors. In the NATURE contact, the big wall is SiOX layer and gates are silicon nanocrystals,” says Dr. Gotoh.

The conductivity of electrical contact in solar cells depends on the formation of a “carrier pathway” for the transport of electronic charges. The formation of this electrical pathway depends on a high temperature treatment called “annealing”.

Previous research has shown that SiOX contacts which contain silicon nanoparticles as the carrier path can obtain good electrical properties. In the NATURE contact, the annealing process leads to the formation of very small silicon nanocrystals in the passivation layer which are nearly spherical in shape. The diameter of these nanocrystals corresponds to the thickness of the passivation layer. Thus, by controlling the annealing conditions, the diameter and subsequent thickness of the passivation layer can be adjusted.

The research team fabricated NATURE contacts and then subjected them to various annealing conditions. By studying the contacts under a transmission electron microscope, they discovered that silicon nanocrystals formed in the contact at an annealing temperature of 750°C. They also studied the electrical properties of the contact. They saw that compared to existing contacts such as tunnel oxide passivation contact (TOPCon) or polysilicon on oxide (POLO) contacts, the NATURE had comparable contact resistance and “current” values. recombination”, a phenomenon that causes current and voltage losses. in solar cells and decreases their efficiency.

“NATURE contact overcomes the trade-off relationship between shielding ability and conductivity of passivation films. This development will lead to the realization of future building-integrated photovoltaics (BIPV) and vehicle-integrated photovoltaics (VIPV) and help us realize zero-energy buildings and solar cars in future decarbonized societies,” concludes Dr. Gotoh.

The article, “Silicon Nanocrystals Embedded in Nanolayered Silicon Oxide for Crystalline Silicon Solar Cells”, was published in the journal Nanomaterials applied by ACS January 28, 2022 at the DOI: 10.1021/acsanm.1c03355.

Authors:

Ryohei Tsubata*, Kazuhiro Gotoh*, Masashi Matsumi*, Markus Wilde, Tetsuya Inoue*, Yasuyoshi Kurokawa*, Katsuyuki Fukutani and Noritaka Usami*

* Affiliated with Nagoya University

Funding:

This work was financially supported by the Japan Society of the Promotion Science (JSPS) KAKENHI Grant number18H05951, 20K15127, the New Energy and Industrial Technology Development Organization (NEDO) of Japan, 15100646-0, and Grants-in-Aid for Scientific Research on Innovative domains “Hydrogenomics”, JP18H05514 and JP18H05518.

About Nagoya University, Japan

Nagoya University has a history of around 150 years, with its roots in a temporary medical school and hospital established in 1871, and was officially established as Japan’s last imperial university in 1939. Although sizable modest compared to the largest universities in Japan, Nagoya University has been striving for excellence since its founding. Six of Japan’s 18 Nobel Laureates since 2000 have done some or all of their Nobel Prize-winning work at Nagoya University: four in physics – Toshihide Maskawa and Makoto Kobayashi in 2008, and Isamu Akasaki and Hiroshi Amano in 2014; and two in Chemistry – Ryoji Noyori in 2001 and Osamu Shimomura in 2008. In Mathematics, Shigefumi Mori did his Fields Medal winning work at the University. A number of other important discoveries were also made at the University, including Okazaki’s DNA fragments by Reiji and Tsuneko Okazaki in the 1960s; and exhaustion forces by Sho Asakura and Fumio Oosawa in 1954.

Website: https://en.nagoya-u.ac.jp/


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