A breakthrough for p-type heterojunction cell performance?


From pv magazine Global

A group of scientists from the University of New South Wales (UNSW) in Australia and Russian heterojunction solar module producer Hevel Solar has developed a novel hydrogenation process that is claimed to have the potential to improve the stabilized efficiency of p-type heterojunction (SHJ) solar cell based on gallium-doped silicon wafers.

The solar industry usually applies n-type phosphorusdoped Czochralskigrown silicon (CzSi) wafers in the production of SHJ cells, as these ensure no susceptibility to the boron-oxygen light-induced degradation (B-O LID) that is typical for p-type boron-doped wafers and severely affects SHJ cell performance over time.

N-type wafers offer greater stability, but they are currently more expensive to produce than p-type wafers, which are the mainstream solution for the manufacturing of PERC cells. This means that using p-type wafers may potentially lead to a further cost reduction for the heterojunction technology, as wafer costs still represent 40% of a cell’s total cost.

In order to compete with n-type devices, however, p-type heterojunction cells will have to show improved performance. 

“The same advanced hydrogenation techniques (AHTs) we use in mass production for solving LID and LeTID in p-type PERC solar cells can be used in p-type SHJ solar cells to solve B-O LID when using boron-doped p-type Cz wafers,” research co-author, Brett Hallam, told pv magazine. Even though the gallium-doped and n-type SHJ solar cells were stable in this work and didn’t need the process to improve stability, “we have shown that these same processes can improve the efficiency of gallium-doped and n-type SHJ solar cells by 0.4-0.7% absolute.”

The research group said that the expiration of Shin Etsu‘s gallium doping patent (US6815605B1) has encouraged the solar industry to adopt p-type gallium-doped Cz-Si wafers, which it describes as a potential mainstream solution for the SHJ segment for the next decade. (Read more.)

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