Title:
Self-Aligned Self-Doping Selective Emitter for Screen-Printed Silicon Solar Cells
Self-Aligned Self-Doping Selective Emitter for Screen-Printed Silicon Solar Cells
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Author(s)
Rohatgi, Ajeet
Hilali, Mohamed M.
Meier, D. L.
Ebong, Abasifreke
Honsberg, Christiana
Carroll, A. F.
Hacke, P.
Hilali, Mohamed M.
Meier, D. L.
Ebong, Abasifreke
Honsberg, Christiana
Carroll, A. F.
Hacke, P.
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Abstract
A self-aligned selective emitter for screen-printed solar cells is described in which phosphorus dopant is incorporated into a silver paste and diffused into the silicon. This produces an ohmic contact on 70-100 Ω/ emitter due to the doping of silicon underneath the Ag grid. Alloying is performed in a belt furnace at 900 degrees C for 2 min, above the Ag-Si eutectic temperature of 835 degrees C. SIMS analysis showed a surface doping concentration of 1x10(21) cm(-3) for a fritless paste (Dupont PV167) and 2x10(19) cm(-3) for the fritted paste (PV 168). Sheet resistance due to self-doping alone was quite high 121 Ω/ and 700 Ω/ for the PV167 and PV168 pastes, respectively. Therefore, a light diffusion is required underneath the Ag to achieve good ohmic contact. Fritted paste was successfully fired through the SiN(x) AR
coating producing a reasonable ohmic contact to the n+ layers doped up to 100 Ω/ sheet resistance. PC1D model calculations revealed that a selective emitter induced performance enhancement is a function of base resistivity, front and back-surface recombination velocities, and bulk lifetime. For example, if the front-surface recombination velocity (FSRV) is very high (>100,000 cm/s), then the selective emitter under-performs the conventional 40 Ω/
homogeneous emitter cell. However, if the FSRV is 10000 cm/s the selective emitter gives a 0.6% (absolute) increase in cell efficiency. Selective emitter cells fabricated with 70-80 Ω/ sheet resistance between the gridlines produced approximately 16% and 15% efficient cells on float-zone and cast multicrystalline Si materials. Series resistance of 0.75 Ω-cm(2) and a fill factor of ~0.76 were achieved. Selective emitter cells were about 0.3% (absolute) more efficient than the conventional cells with 45 Ω/ homogeneous emitter. Cell analysis revealed that a reduced FSRV could
result in greater improvement.
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Date Issued
2001-10
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Proceedings