- Email: [email protected]
R&D pilot line production of multi-crystalline Si solar cells exceeding cell efficiencies of 18%
Available online at www.sciencedirect.com
Energy Procedia 8 (2011) 313–317
SiliconPV: 17-20 April 2011, Freiburg, Germany
R&D pilot line production of multi-crystalline Si solar cells exceeding cell efficiencies of 18 % P. Engelhart*, J. Wendt, A. Schulze, C. Klenke, A. Mohr, K. Petter, F. Stenzel, S. Hörnlein, M. Kauert, M. Junghänel, B. Barkenfelt, S. Schmidt, D. Rychtarik, M. Fischer, J.W. Müller, P. Wawer Q-Cells SE, Sonnenallee 17-21, 06766 Bitterfeld-Wolfen, Germany
Abstract In this paper we report on a pilot production of multi-crystalline p-type Si cells in the Reiner-Lemoine Research Center at Q-Cells SE. The cells are double-side contacted and feature a lowly doped emitter, a fineline-printed Ag grid in combination with plating as front metallisation and a dielectric passivated rear with local contacts. Using upgraded metallurgical grade (UMG) and Poly Si we report on median cell efficiencies >18 % over a whole brick and independently conformed top efficiencies of up to 18.35 % (UMG) and 18.45 % (Poly) on large cell areas (243 cm2). Furthermore, with a module efficiency of 17.84% on 1.5 m2 we report on a new world record on multi-crystalline large area modules (60 cells). To our knowledge, these are the highest efficiencies on cell level based on UMG Si and on multi-crystalline modules reported so far.
© 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of SiliconPV 2011. © 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of SiliconPV 2011. Keywords: Si solar cell; module; UMG Si; high-efficiency; a
1. Introduction Record cell efficiencies above 20 % based on multi-crystalline (mc) Si wafers have been reached on an aperture area (ap) of 1 cm2 [1]. On larger cell area (218 cm2) remarkable 19.3 % were reached by Mitsubishi Electric Corp [2]. The non-availability of crystallographic surface texturing of mc wafers is
* Corresponding author. Tel.: +49 (0)3494669952146; fax: +49 (0)3494669954001. E-mail address: [email protected]
1876–6102 © 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of SiliconPV 2011. doi:10.1016/j.egypro.2011.06.142
314
P. Engelhart et al. / Energy Procedia 8 (2011) 313–317
circumvented by the so-called “honeycomb” texture for these cells [1,2]. Recently SCHOTT Solar AG published results of rear side passivated mc cells using a standard isotropic texture with cell efficiencies above 18 % [3] and the current record efficiency (ap) of 17.55 % on module level [2]. We report in this work on a pilot production of > 18 % double-side contacted mc cells with dielectric passivated front and rear side fabricated at our Research Center (see Figure 1). We present results with this cell concept using mc Si material based on 100% UMG feedstock and poly feedstock respectively. Our pilot production serves as a development platform to transfer our next generation cell concept into production and to monitor single processes on a high efficiency level. We link our cell development close to our module technology by finishing the processed cells into larger area modules. This enables an efficient technological development for maximum output power on module level. 2. Experimental 2.1. Cell design In our Research Center we established a pilot production of high-efficiency p-type Si solar cells. The weekly production cycle amounts to a few hundred cells in order to provide statistically relevant information and to represent material characteristics like inhomogeneities over an ingot. SiNx passivation layer and ARC
n+ emitter
Front side metallisation
p- type silicon
Rear side passivation layer
Point contacts Rear side metallisation
Fig. 1. Schematic cross-section of the the solar cell design with passivated front and rear (not to scale)
For mc Si cell fabrication standard 156 156 mm2 sized wafers are used with resistivities between 1 – 2 cm “poly Si” (based on Siemens feedstock), and 0.6 – 2 cm “UMG Si” (based on UMG feedstock). We texture the 160 – 180 µm thick wafers using a standard isotropic inline-texturing process and subsequently perform a lowly doped emitter by POCl3 tube-diffusion. We deposit a low-temperature dielectric surface passivation on front (single anti-reflection coating) and rear. Metal contacts are realized by fineline printing and plating on the front and local contacts on the rear. 3. Results and Discussion 3.1. I-V solar cell characteristics Table I shows the efficiency distribution of a pilot run comprising about 300 solar cells based on poly and UMG Si. A median efficiency of 18.2% on poly Si and 18.0% on UMG Si was achieved. Please note that the processed wafers represent the distribution of whole Si bricks. Thus the spread in Table I includes also the defect rich material from the bottom and top of the brick. The difference between poly and UMG
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P. Engelhart et al. / Energy Procedia 8 (2011) 313–317
Si mainly arises due to 0.7 mA/cm2 higher short circuit current density of the poly Si cells with Jsc,median = 36.6 mA/cm2 compared to 35.9 mA/cm2 of the UMG Si cells. This can be attributed to the lower bulk lifetime of the UMG Si wafers. However, the higher net doping of the compensated UMG Si balances the loss in lifetime resulting in similar open circuit voltages of 640 – 645 mV. Furthermore, we observe a fill factor advantage of ~ 1%abs of the UMG Si cells due to the higher net doping which is in particular beneficial for cell designs with a point contacted base.
25
UMG-Si Poly-Si
Ratio [%]
20 15 10 5 0 17,6
17,8
18,0
Efficiency
18,2
18,4
[%]
Fig. 3. Efficiency ratio of solar cells from a pilot solar series (300 cells).
Table I shows the photovoltaic parameters of our top cells (total area 243 cm2) with efficiencies of 18.35% on UMG Si and 18.45% on ploy Si. To our knowledge, this is the highest efficiency reported on UMG Si cells so far. Table 1. Photovoltaic parameters of champion cells out of a pilot production run (total area 243 cm2 measurement). The data are independently confirmed at Fraunhofer ISE
Voc [mV]
Jsc [mA/cm2]
FF [%]
[%]
UMG cell
650
36.5
77.2
18.35
POLY cell
647
36.8
77.4
18.45
3.2. Analysis of UMG Si cells We perform quantum efficiency analyses of UMG cells processed on adjacent wafers in our production line (with Al-BSF, called “standard”) and Research Center to quantify the benefits of our new processes. Figure 2 shows the internal quantum efficiency (IQE) and reflection of both cell types from
316
P. Engelhart et al. / Energy Procedia 8 (2011) 313–317
which we deduce a gain in Jsc due to a less recombinative emitter and less grid shading of 0.5 mA/cm2 each. By numerical modelling we quantify the contribution of the rear to a gain in Jsc of 1.2 mA/cm2 due to the reduced surface recombination and of 1.0 mA/cm2 due to the enhanced light trapping.
Normalized short circuit current Jsc [-]
100
IQE / Reflection [%]
80
60
High-efficiency UMG cell
40
"Standard" UMG cell
20
0
400
600
800
1000
1200
1,0 0,8 0,6 0,4 0,2 0,0
Wavelength [nm]
0
200
400
600
800
1000 2
Illumination intensity [W/m ]
Fig. 2. (a) Internal quantum efficiency (circle symbols) and reflection (square symbols) of a high-efficiency cell compared to a “standard” UMG Si cell; (b) Low illumination performance of a high-efficiency (open symbols) and a “standard” (filled symbols) UMG cell. The measured Jsc values of both cell types show a linear behaviour (straight line).
Considering the energy yield of a PV system the cell/module performance under low irradiation conditions is crucial. We therefore checked our new cell concept by measuring the cell characteristic from 0.1 – 1 suns. Figure 3 shows the short circuit current of a UMG Si cell normalized to Jsc @ 1sun. Our optimized dielectric passivation shows a linear behavior and we observe no reduced current collection probability at low light intensities similar to a Al-BSF rear. 4. New Multi-Crystalline World Record Module We finish our Si solar cells from pilot production into large area modules (60 cells) with conventional layout. Our champion module reaches an output power of 268 W. An independently confirmed measurement at ESTI (European Solar Test Installation) of this module leads to a module efficiency of 17.84 % on an aperture area of 1.5 m2. With this value we report on a new multi-crystalline module world record. Table 1. Photovoltaic parameters of our record module. The data are independently confirmed at ESTI.
Aperture area 1.5 m2
Voc [V] 38.9
Jsc [A] 9.04
[%] 17.84
5. Conclusion In the Reiner-Lemoine Research Center at Q-Cells SE we established a pilot production of highefficiency, both side passivated multi-crystalline Si solar cells with the aim to transfer our next generation cell concept into production at maximum speed. With new record efficiencies exceeding 18 % (total area,
P. Engelhart et al. / Energy Procedia 8 (2011) 313–317
large scale) we demonstrate the high-efficiency potential of our cell concept also on cost-effective multicrystalline Si (UMG) wafers. We achieved an independently confirmed cell efficiency of 18.35 % (ta) based on UMG Si, which is to our knowledge the highest value reported so far for this material. Following our strategy to optimize our technology for maximum module output we fabricated a 17.84 % efficient multi-crystalline large area module which represents a new world record.
Acknowledgements This work is supported in frame of the Adaptum project (0904/00109) by EFRE, Sachsen Anhalt and of the Alba II project (0329988C) by BMU and of the HiFy project (1004/00062) by EFRE, Sachsen Anhalt.
References [1] Schulz O, Glunz SW, Willeke GP. Multicrystalline silicon solar cells exceeding 20% efficiency. Prog. Photovolt.: Res. Appl. 2004; 12, p.553-8. [2] Green MA, Emery K, Hishikawa Y, Warta W. Solar cell efficiency tables (version 37). Prog. Photovolt.: Res. Appl. 2011;19,p.84-92. [3] Schmich E, Gassenbauer Y, Ramspeck K, Dressler K, Fiedler M, Hefner W, et al. Industrial multi-crystalline silicon solar cells with dielectric passivated rear side and efficiencies above 18%. Proceedings of the 25th European Photovoltaic Solar Energy Conference and Exhibition 2010. in press.
317
Energy Procedia 8 (2011) 313–317
SiliconPV: 17-20 April 2011, Freiburg, Germany
R&D pilot line production of multi-crystalline Si solar cells exceeding cell efficiencies of 18 % P. Engelhart*, J. Wendt, A. Schulze, C. Klenke, A. Mohr, K. Petter, F. Stenzel, S. Hörnlein, M. Kauert, M. Junghänel, B. Barkenfelt, S. Schmidt, D. Rychtarik, M. Fischer, J.W. Müller, P. Wawer Q-Cells SE, Sonnenallee 17-21, 06766 Bitterfeld-Wolfen, Germany
Abstract In this paper we report on a pilot production of multi-crystalline p-type Si cells in the Reiner-Lemoine Research Center at Q-Cells SE. The cells are double-side contacted and feature a lowly doped emitter, a fineline-printed Ag grid in combination with plating as front metallisation and a dielectric passivated rear with local contacts. Using upgraded metallurgical grade (UMG) and Poly Si we report on median cell efficiencies >18 % over a whole brick and independently conformed top efficiencies of up to 18.35 % (UMG) and 18.45 % (Poly) on large cell areas (243 cm2). Furthermore, with a module efficiency of 17.84% on 1.5 m2 we report on a new world record on multi-crystalline large area modules (60 cells). To our knowledge, these are the highest efficiencies on cell level based on UMG Si and on multi-crystalline modules reported so far.
© 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of SiliconPV 2011. © 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of SiliconPV 2011. Keywords: Si solar cell; module; UMG Si; high-efficiency; a
1. Introduction Record cell efficiencies above 20 % based on multi-crystalline (mc) Si wafers have been reached on an aperture area (ap) of 1 cm2 [1]. On larger cell area (218 cm2) remarkable 19.3 % were reached by Mitsubishi Electric Corp [2]. The non-availability of crystallographic surface texturing of mc wafers is
* Corresponding author. Tel.: +49 (0)3494669952146; fax: +49 (0)3494669954001. E-mail address: [email protected]
1876–6102 © 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of SiliconPV 2011. doi:10.1016/j.egypro.2011.06.142
314
P. Engelhart et al. / Energy Procedia 8 (2011) 313–317
circumvented by the so-called “honeycomb” texture for these cells [1,2]. Recently SCHOTT Solar AG published results of rear side passivated mc cells using a standard isotropic texture with cell efficiencies above 18 % [3] and the current record efficiency (ap) of 17.55 % on module level [2]. We report in this work on a pilot production of > 18 % double-side contacted mc cells with dielectric passivated front and rear side fabricated at our Research Center (see Figure 1). We present results with this cell concept using mc Si material based on 100% UMG feedstock and poly feedstock respectively. Our pilot production serves as a development platform to transfer our next generation cell concept into production and to monitor single processes on a high efficiency level. We link our cell development close to our module technology by finishing the processed cells into larger area modules. This enables an efficient technological development for maximum output power on module level. 2. Experimental 2.1. Cell design In our Research Center we established a pilot production of high-efficiency p-type Si solar cells. The weekly production cycle amounts to a few hundred cells in order to provide statistically relevant information and to represent material characteristics like inhomogeneities over an ingot. SiNx passivation layer and ARC
n+ emitter
Front side metallisation
p- type silicon
Rear side passivation layer
Point contacts Rear side metallisation
Fig. 1. Schematic cross-section of the the solar cell design with passivated front and rear (not to scale)
For mc Si cell fabrication standard 156 156 mm2 sized wafers are used with resistivities between 1 – 2 cm “poly Si” (based on Siemens feedstock), and 0.6 – 2 cm “UMG Si” (based on UMG feedstock). We texture the 160 – 180 µm thick wafers using a standard isotropic inline-texturing process and subsequently perform a lowly doped emitter by POCl3 tube-diffusion. We deposit a low-temperature dielectric surface passivation on front (single anti-reflection coating) and rear. Metal contacts are realized by fineline printing and plating on the front and local contacts on the rear. 3. Results and Discussion 3.1. I-V solar cell characteristics Table I shows the efficiency distribution of a pilot run comprising about 300 solar cells based on poly and UMG Si. A median efficiency of 18.2% on poly Si and 18.0% on UMG Si was achieved. Please note that the processed wafers represent the distribution of whole Si bricks. Thus the spread in Table I includes also the defect rich material from the bottom and top of the brick. The difference between poly and UMG
315
P. Engelhart et al. / Energy Procedia 8 (2011) 313–317
Si mainly arises due to 0.7 mA/cm2 higher short circuit current density of the poly Si cells with Jsc,median = 36.6 mA/cm2 compared to 35.9 mA/cm2 of the UMG Si cells. This can be attributed to the lower bulk lifetime of the UMG Si wafers. However, the higher net doping of the compensated UMG Si balances the loss in lifetime resulting in similar open circuit voltages of 640 – 645 mV. Furthermore, we observe a fill factor advantage of ~ 1%abs of the UMG Si cells due to the higher net doping which is in particular beneficial for cell designs with a point contacted base.
25
UMG-Si Poly-Si
Ratio [%]
20 15 10 5 0 17,6
17,8
18,0
Efficiency
18,2
18,4
[%]
Fig. 3. Efficiency ratio of solar cells from a pilot solar series (300 cells).
Table I shows the photovoltaic parameters of our top cells (total area 243 cm2) with efficiencies of 18.35% on UMG Si and 18.45% on ploy Si. To our knowledge, this is the highest efficiency reported on UMG Si cells so far. Table 1. Photovoltaic parameters of champion cells out of a pilot production run (total area 243 cm2 measurement). The data are independently confirmed at Fraunhofer ISE
Voc [mV]
Jsc [mA/cm2]
FF [%]
[%]
UMG cell
650
36.5
77.2
18.35
POLY cell
647
36.8
77.4
18.45
3.2. Analysis of UMG Si cells We perform quantum efficiency analyses of UMG cells processed on adjacent wafers in our production line (with Al-BSF, called “standard”) and Research Center to quantify the benefits of our new processes. Figure 2 shows the internal quantum efficiency (IQE) and reflection of both cell types from
316
P. Engelhart et al. / Energy Procedia 8 (2011) 313–317
which we deduce a gain in Jsc due to a less recombinative emitter and less grid shading of 0.5 mA/cm2 each. By numerical modelling we quantify the contribution of the rear to a gain in Jsc of 1.2 mA/cm2 due to the reduced surface recombination and of 1.0 mA/cm2 due to the enhanced light trapping.
Normalized short circuit current Jsc [-]
100
IQE / Reflection [%]
80
60
High-efficiency UMG cell
40
"Standard" UMG cell
20
0
400
600
800
1000
1200
1,0 0,8 0,6 0,4 0,2 0,0
Wavelength [nm]
0
200
400
600
800
1000 2
Illumination intensity [W/m ]
Fig. 2. (a) Internal quantum efficiency (circle symbols) and reflection (square symbols) of a high-efficiency cell compared to a “standard” UMG Si cell; (b) Low illumination performance of a high-efficiency (open symbols) and a “standard” (filled symbols) UMG cell. The measured Jsc values of both cell types show a linear behaviour (straight line).
Considering the energy yield of a PV system the cell/module performance under low irradiation conditions is crucial. We therefore checked our new cell concept by measuring the cell characteristic from 0.1 – 1 suns. Figure 3 shows the short circuit current of a UMG Si cell normalized to Jsc @ 1sun. Our optimized dielectric passivation shows a linear behavior and we observe no reduced current collection probability at low light intensities similar to a Al-BSF rear. 4. New Multi-Crystalline World Record Module We finish our Si solar cells from pilot production into large area modules (60 cells) with conventional layout. Our champion module reaches an output power of 268 W. An independently confirmed measurement at ESTI (European Solar Test Installation) of this module leads to a module efficiency of 17.84 % on an aperture area of 1.5 m2. With this value we report on a new multi-crystalline module world record. Table 1. Photovoltaic parameters of our record module. The data are independently confirmed at ESTI.
Aperture area 1.5 m2
Voc [V] 38.9
Jsc [A] 9.04
[%] 17.84
5. Conclusion In the Reiner-Lemoine Research Center at Q-Cells SE we established a pilot production of highefficiency, both side passivated multi-crystalline Si solar cells with the aim to transfer our next generation cell concept into production at maximum speed. With new record efficiencies exceeding 18 % (total area,
P. Engelhart et al. / Energy Procedia 8 (2011) 313–317
large scale) we demonstrate the high-efficiency potential of our cell concept also on cost-effective multicrystalline Si (UMG) wafers. We achieved an independently confirmed cell efficiency of 18.35 % (ta) based on UMG Si, which is to our knowledge the highest value reported so far for this material. Following our strategy to optimize our technology for maximum module output we fabricated a 17.84 % efficient multi-crystalline large area module which represents a new world record.
Acknowledgements This work is supported in frame of the Adaptum project (0904/00109) by EFRE, Sachsen Anhalt and of the Alba II project (0329988C) by BMU and of the HiFy project (1004/00062) by EFRE, Sachsen Anhalt.
References [1] Schulz O, Glunz SW, Willeke GP. Multicrystalline silicon solar cells exceeding 20% efficiency. Prog. Photovolt.: Res. Appl. 2004; 12, p.553-8. [2] Green MA, Emery K, Hishikawa Y, Warta W. Solar cell efficiency tables (version 37). Prog. Photovolt.: Res. Appl. 2011;19,p.84-92. [3] Schmich E, Gassenbauer Y, Ramspeck K, Dressler K, Fiedler M, Hefner W, et al. Industrial multi-crystalline silicon solar cells with dielectric passivated rear side and efficiencies above 18%. Proceedings of the 25th European Photovoltaic Solar Energy Conference and Exhibition 2010. in press.
317