Stability Study of Silicon Heterojunction Solar Cells Fabricated with Gallium‐ and Boron‐Doped Silicon Wafers

• Published in: Solar RRL 2021-09, Vol.5 (9), p.n/a
• Main Authors: Vicari Stefani, Bruno, Kim, Moonyong, Wright, Matthew, Soeriyadi, Anastasia, Andronikov, Dmitriy, Nyapshaev, Ilya, Abolmasov, Sergey, Emtsev, Konstantin, Abramov, Alexey, Hallam, Brett
• Format: Article
• Language: English
• Subjects: boron–oxygen; degradation; gallium; heterojunctions; hydrogenation; silicon; stability
• ISSN: 2367-198X; 2367-198X
• DOI: 10.1002/solr.202100406

Herein, a comparison of industrial silicon heterojunction (SHJ) solar cells formed using p‐type (boron‐ or gallium‐doped) Czochralski‐grown silicon (Cz‐Si) wafers is provided. Standard n‐type SHJ solar cells are also fabricated as a reference. Boron‐doped SHJ solar cells are heavily susceptible to boron–oxygen light‐induced degradation (BO‐LID), with an open‐circuit voltage (VOC) reduction of 100 mV in some cells with starting VOC of >720 mV. While an advanced hydrogenation process (AHP) is sufficient to completely stabilize BO‐LID in some cells, resulting in stable VOC of 724 mV, the impact in reducing BO‐LID is variable. This suggests that an AHP alone may not be a reliable method of reducing BO‐LID in industrial SHJ solar cells. In contrast, SHJ solar cells formed using gallium‐doped wafers exhibit VOC > 730 mV and show no degradation during light‐soaking. Yet, the same AHP treatment for gallium‐doped SHJ cells results in a 0.4%abs increase in the conversion efficiency to 22.6% (VOC of 734 mV). The conversion efficiency of the gallium‐doped SHJ solar cells is still lower than the n‐type reference cells, which is largely due to a reduced fill factor (FF). Further work is required to overcome this FF limitation to facilitate high‐efficiency gallium‐doped SHJ solar cells. Herein, silicon heterojunction solar cells fabricated with gallium, boron, and phosphorus‐doped silicon wafers are demonstrated. Boron‐doped cells are heavily susceptible to boron–oxygen light‐induced degradation, with a VOC loss of 100 mV. An advanced hydrogenation process developed to stabilise boron–oxygen defects is applied to boron‐ and gallium‐doped cells, resulting in peak stable efficiencies of 20.9% and 22.6%.