High‐quality amorphous silicon thin films for tunnel oxide passivating contacts deposited at over 150 nm/min. (26th August 2020)

• Record Type: Journal Article
• Authors: Li, Shenghao; Pomaska, Manuel; Hoß, Jan; Lossen, Jan; Qiu, Kaifu; Hong, Ruijiang; Finger, Friedhelm; Rau, Uwe; Ding, Kaining
• Is Part Of: Progress in photovoltaics. Volume 29:Number 1(2021)
• Page Start: 16
• Page End: 23
• Publication Date: 2020-08-26
• Subjects: blistering -- deposition rate -- HWCVD -- microstructure factor -- oxygen concentration -- passivation -- sheet resistance; Solar cells -- Periodicals; Photovoltaic cells -- Periodicals; Solar power plants -- Periodicals; 621.31245
• DOI: 10.1002/pip.3333
• Languages: English
• ISSNs: 1062-7995

Abstract

Abstract: Hot‐wire chemical vapor deposition was utilized to develop rapidly grown and high‐quality phosphorus‐doped amorphous silicon (a‐Si:H) thin films for poly‐crystalline silicon on tunnel oxide carrier‐selective passivating contacts. Deposition rates higher than 150 nm/min were obtained for the in situ phosphorus‐doped a‐Si:H layers. To optimize the passivating contact performance, material properties such as microstructures as well as hydrogen content were characterized and analyzed for these phosphorus‐doped a‐Si:H films. The results show that a certain microstructure of the films is crucial for the passivation quality and the conductance of passivating contacts. Porous silicon layers were severely oxidized during high‐temperature crystallization, giving rise to very low conductance. The insufficient effective doping concentration in these layers also yields inferior passivation quality due to lack of field‐effect passivation. On the other hand, dense silicon layers are insensitive to oxidation but very sensitive to blistering of the films during the subsequent high‐temperature process steps. By optimizing the deposition parameters, a firing‐stable‐implied open‐circuit voltage of 737 mV and a contact resistivity of 10 mΩ·cm 2 were achieved at a high deposition rate of 100 nm/min while 733 mV and 90 mΩ·cm 2 were achieved at an even higher deposition rate of 150 nm/min. Abstract : The microstructure of a‐Si:H layer is critical for passivating contacts on silicon solar cells. On one hand, the silicon network should be dense enough to prevent the in‐diffusion of oxygen during high temperature annealing, which increases the sheet resistance. On the other hand, the silicon layer should not be too dense that hydrogen cannot effuse out of the layer and blistering occurs.