Low Surface Recombination Velocity by Low-Absorption Silicon Nitride on c-Si

We demonstrate that nearly stoichiometric amorphous silicon nitride (SiN x ) can exhibit excellent surface passivation on both p - and n -type c-Si, as well as low absorption at short wavelengths. The key process to obtain such a SiN x is the optimized deposition pressure. The effective carrier life...

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Bibliographic Details
Published in:IEEE journal of photovoltaics 2013-01, Vol.3 (1), p.554-559
Main Authors: Yimao Wan, McIntosh, K. R., Thomson, A. F., Cuevas, A.
Format: Article
Language:English
Subjects:
Absorption
amorphous materials
charge carrier lifetime
Optical surface waves
Passivation
Photovoltaic cells
Silicon
Temperature measurement
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Summary:We demonstrate that nearly stoichiometric amorphous silicon nitride (SiN x ) can exhibit excellent surface passivation on both p - and n -type c-Si, as well as low absorption at short wavelengths. The key process to obtain such a SiN x is the optimized deposition pressure. The effective carrier lifetimes of these samples exceed the commonly accepted intrinsic upper limit over a wide range of excess carrier densities. We achieve a low S eff,UL of 1.6 cm/s on 0.85-Ω·cm p -type and immeasurably low S eff,UL on 0.47-Ω·cm n -type silicon passivated by the SiN x deposited at 290°C. Capacitance-voltage ( C - V ) measurements reveal that this SiN x has a density of interface states of 3.0 × 10 11 eV -1 cm -2 at midgap and an insulator charge of 5.6 × 10 11 cm -2 . By comparing the measured injection-dependent S eff,UL with calculated S eff,UL by an extended Shockley-Read-Hall (SRH) model, we conclude that either Defect A or B (or both) observed by Schmidt is likely to dominate the surface recombination at our Si-SiN x interface. In addition to the outstanding surface passivation, this SiN x has a low absorption coefficient at short wavelengths. Compared with Si-rich SiN x of an equivalent passivation, the optimized SiN x would enhance the photogenerated current density by more than 0.66 mA/cm 2 or 1.40 mA/cm 2 for solar cells encapsulated in glass/ethylene-vinyl acetate or operating in air, respectively. The SiN x described here is ideally suited for high-efficiency solar cells, which require good surface passivation and low absorption from their front surface coatings.
ISSN:2156-3381
2156-3403
DOI:10.1109/JPHOTOV.2012.2215014