In the photovoltaic industry both the reduction of the silicon material thickness and the increase of the solar cells efficiency are critical topics for optimizing cost reduction. This work presents an innovative and industrially applicable Si-based passivation layer deposited by PECVD, with high passivation quality for the un-doped p-type rear surface of PERC solar cells. Avoiding an extra thermal oxidation step, the PERC process as presented as follows, might be completely feasible for industrial applications. We achieved efficiencies of 19% on monocrystalline p-type Cz-Si and above 17.2% on multicrystalline p-type wafers. The processing of the wafers is developed at a standard industrial level, and no special equipment or processing was required for achieving this efficiencies.

1. HIGH EFFICIENCY INDUSTRIAL PERC SOLAR CELLS
WITH ALL PECVD-BASED REAR SURFACE PASSIVATION
E. Urrejola 1(a), R. Petres 1, J. Glatz-Reichenbach 1, K. Peter 1, H. Plagwitz 2, G. Schubert 2
1
International Solar Energy Research Center - ISC Konstanz, Rudolf-Diesel-Straße 15, D-78467 Konstanz, Germany
2 Sunways AG, Macairestraße 3-5, D-78467 Konstanz, Germany.
(a) Author for correspondence: urrejola.elias@gmail.com
ABSTRACT
In the photovoltaic industry both the reduction of the silicon material thickness and the increase of the solar cells efficiency are critical topics
for optimizing cost reduction. This work presents an innovative and industrially applicable Si-based passivation layer deposited by PECVD,
with high passivation quality for the un-doped p-type rear surface of PERC solar cells. Avoiding an extra thermal oxidation step, the PERC
process as presented as follows, might be completely feasible for industrial applications. We achieved efficiencies of 19% on
monocrystalline p-type Cz-Si and above 17.2% on multicrystalline p-type wafers. The processing of the wafers is developed at a standard
industrial level, and no special equipment or processing was required for achieving this efficiencies.
REFERENCES
[1] G. Beaucarne, et al., 21st EUPVSEC, Dresden,
pp. 554-559 (2006).
[2] S. Dauwe, Lutz Mittelstädt, A. Metz, and R. Hezel,
Progress in Photovoltaics 10, 271 (2002).
[3] E. Urrejola, K. Peter, H. Plagwitz, and G. Schubert,
Journal of Applied Physics 107, 124516 (2010).
[4] E. Urrejola, K. Peter, H. Plagwitz, and G. Schubert,
Applied Physics Letters 98, 153508 (2011).
[5] E. Urrejola, K. Peter, H. Plagwitz, and G. Schubert,
Energy Procedia 8, 331 (2011).
[6] E. Urrejola, K. Peter, H. Plagwitz, and G. Schubert,
Journal of Applied Physics (2011) to be published.
RESULTS: PERC cells compared to Al-BSF
1) I-V:
mc-Si material: JSC + 0.6 [mA/cm2], VOC + 2.3 [mV], η + 0.2 [%]
Cz-Si material: JSC + 1.9 [mA/cm2], VOC + 5.7 [mV], η + 0.9 [%]
A gain in FF is not yet visible due to the series resistance losses normally
found in PERC cells (void formations as shown in Fig. 2).
2) Implied Voc (QSSPC):
655 [mV] for mc-Si cells and 695 [mV] for Cz-Si cells: high passivation quality
3) Spectral Response:
The dielectric rear side shows better passivation quality compared to the
Al-BSF, as visible in the long wavelength regime (infrared response).
CONCLUSIONS
• Simple low-cost industrial process for the fabrication of industrial
rear passivated solar cells
• High efficiency on Cz-Si up to 19 % and 17.2 % on mc-Si for large
area (15.6 x 15.6 cm2) wafers.
• Accessible for industry lines at minimal investments.
• Further optimization of the front side emitter and metallization
needed.
• The formation of voids in the local Al-Si contacts has been partially
avoided by sintering the cells illuminated side down (see Ref. [6])
16.9 / 17.278.9 / 79.3623.6 / 625.134.4 / 34.6mc-Si
18.0 / 18.579.7 / 79.9631.3 / 631.935.8 / 36.0CZ-Si
Al-BSF
17.1 / 17.278.1 / 78.3625.9 / 626.735.0 / 35.2mc-Si
18.9 / 19.079.0 / 79.1637.0 / 637.537.7 / 37.8CZ-Si
i-PERC
η[%]
Avg./best
FF [%]
Avg./best
Voc [mV]
avg./best
Jsc [mA/cm2]
avg./best
SubstrateDevice
Spectral Response
19 % Cz-Si PERC vs. Al-BSF Reference
Table I: I-V Results PERC cells vs. Al-BSF.
The authors gratefully acknowledge the financial support by
the German Federal Ministry of Education and Research
under contract no. 03SSF0335I.
Fig. 1.
i-PERC
device.
The rear side pattern
(geometry and spacing)
used, has been optimized
for best solar cell perfor-
mance. However, void
formation instead of an
Al-Si eutectic is normally
found, increasing series
resistance losses [3-5].
The voids can be partially
avoided by sintering the
cells illuminated side
down [6].
Fig. 2. Al-Si junction [5].
EXPERIMENTAL PART
Both sides are
passivated using an
industrially accessible
standard PECVD device.
The rear side passivation
layer has been optimized
for un-doped polished p-
Si surfaces and presents
high applicability and
reproducibility for PERC
solar cell structures.
MOTIVATION
A promising concept is the incorporation of a dielectric layer at the rear surface
of the thinner wafers, increasing the solar cell efficiency of the standard Al
back-surface-field (BSF) device [1].
Figure 1 shows the PERC structure. Both the front side textured emitter and
the rear side polished surface are passivated using an industrial PECVD
reactor. The contacts are performed by screen printing industrial accessible
metal pastes at the front and rear. The BSF is locally formed in the dielectric
windows.