1.
R Peibst; F Haase; B Min; C Hollemann; T Brendemühl; K Bothe; R Brendel
In: Progress in Photovoltaics: Research and Applications, Bd. 31, Ausg. 4, S. 327-340, 2023.
@article{Peibst2023,
title = {On the chances and challenges of combining electron-collecting nPOLO and hole-collecting Al-p+ contacts in highly efficient p-type c-Si solar cells},
author = {R Peibst and F Haase and B Min and C Hollemann and T Brendemühl and K Bothe and R Brendel},
doi = {10.1002/pip.3545},
year = {2023},
date = {2023-04-01},
urldate = {2022-02-21},
journal = {Progress in Photovoltaics: Research and Applications},
volume = {31},
issue = {4},
pages = {327-340},
abstract = {ISFH is following a distinct cell development roadmap, which comprises—as a short-term concept—the combination of an n-type doped electron-collecting poly-Si on oxide (POLO) junction with an Al-alloyed p+ junction for hole collection. This combination can be integrated either in front- and back-contacted back junction cells (POLO-BJ) or in interdigitated back-contacted cells (POLO-IBC). Here, we present recent progress with these two cell concepts. We report on a certified M2-sized 22.9% efficient POLO-BJ cell with a temperature coefficient TCη of only −(0.3 ± 0.02) %rel/K and a certified 23.7% (4 cm2 d.a.) efficient POLO-IBC cell. We discuss various specific conceptual aspects of this technology and present a simulation-based sensitivity analysis for quantities related to the quality of the hole-collecting alloyed Al-p+ junction which are subject to continuous improvement and thus hard to predict exactly. We report that the measured pseudo fill factor values decrease more due to metallization than would be expected from recombination in the metallized regions with an ideality factor of one only. The gap to pseudo fill factor values that are theoretically achievable at the respective open-circuit voltages is 1.1%abs (Ga-doped wafer) for POLO-IBC and 1.4%abs (B-doped wafer) to 2%abs (Ga-doped wafer) for POLO-BJ. With an embedded blocking layer for Ag crystallites in the poly-Si, we present a concept to reduce this gap.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
ISFH is following a distinct cell development roadmap, which comprises—as a short-term concept—the combination of an n-type doped electron-collecting poly-Si on oxide (POLO) junction with an Al-alloyed p+ junction for hole collection. This combination can be integrated either in front- and back-contacted back junction cells (POLO-BJ) or in interdigitated back-contacted cells (POLO-IBC). Here, we present recent progress with these two cell concepts. We report on a certified M2-sized 22.9% efficient POLO-BJ cell with a temperature coefficient TCη of only −(0.3 ± 0.02) %rel/K and a certified 23.7% (4 cm2 d.a.) efficient POLO-IBC cell. We discuss various specific conceptual aspects of this technology and present a simulation-based sensitivity analysis for quantities related to the quality of the hole-collecting alloyed Al-p+ junction which are subject to continuous improvement and thus hard to predict exactly. We report that the measured pseudo fill factor values decrease more due to metallization than would be expected from recombination in the metallized regions with an ideality factor of one only. The gap to pseudo fill factor values that are theoretically achievable at the respective open-circuit voltages is 1.1%abs (Ga-doped wafer) for POLO-IBC and 1.4%abs (B-doped wafer) to 2%abs (Ga-doped wafer) for POLO-BJ. With an embedded blocking layer for Ag crystallites in the poly-Si, we present a concept to reduce this gap.
2.
C Hollemann; M Rienäcker; A Soeriyadi; C Madumelu; F Haase; J Krügener; B Hallam; R Brendel; R Peibst
Firing stability of tube furnace-annealed n-type poly-Si on oxide junctions Artikel
In: Progress in Photovoltaics: Research and Applications, Bd. 30, Nr. 1, S. 49-64, 2022.
@article{Hollemann2022,
title = {Firing stability of tube furnace-annealed n-type poly-Si on oxide junctions},
author = {C Hollemann and M Rienäcker and A Soeriyadi and C Madumelu and F Haase and J Krügener and B Hallam and R Brendel and R Peibst},
doi = {10.1002/pip.3459},
year = {2022},
date = {2022-01-01},
journal = {Progress in Photovoltaics: Research and Applications},
volume = {30},
number = {1},
pages = {49-64},
abstract = {Stability of the passivation quality of poly-Si on oxide junctions against the conventional mainstream high-temperature screen-print firing processes is highly desirable and also expected since the poly-Si on oxide preparation occurs at higher temperatures and for longer durations than firing. We measure recombination current densities (J0) and interface state densities (Dit) of symmetrical samples with n-type poly-Si contacts before and after firing. Samples without a capping dielectric layer show a significant deterioration of the passivation quality during firing. The Dit values are (3 ± 0.2) × 1011 and (8 ± 2) × 1011 eV/cm2 when fired at 620°C and 900°C, respectively. The activation energy in an Arrhenius fit of Dit versus the firing temperature is 0.30 ± 0.03 eV. This indicates that thermally induced desorption of hydrogen from SiH bonds at the poly-Si/SiOx interface is not the root cause of depassivation. Postfiring annealing at 425°C can improve the passivation again. Samples with SiNx capping layers show an increase in J0 up to about 100 fA/cm2 by firing, which can be attributed to blistering and is not reversed by annealing at 425°C. On the other hand, blistering does not occur in poly-Si samples capped with AlOx layers or AlOx/SiNy stacks, and J0 values of 2–5 fA/cm2 can be achieved after firing. Those findings suggest that a combination of two effects might be the root cause of the increase in J0 and Dit: thermal stress at the SiOz interface during firing and blistering. Blistering is presumed to occur when the hydrogen concentration in the capping layers exceeds a certain level.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Stability of the passivation quality of poly-Si on oxide junctions against the conventional mainstream high-temperature screen-print firing processes is highly desirable and also expected since the poly-Si on oxide preparation occurs at higher temperatures and for longer durations than firing. We measure recombination current densities (J0) and interface state densities (Dit) of symmetrical samples with n-type poly-Si contacts before and after firing. Samples without a capping dielectric layer show a significant deterioration of the passivation quality during firing. The Dit values are (3 ± 0.2) × 1011 and (8 ± 2) × 1011 eV/cm2 when fired at 620°C and 900°C, respectively. The activation energy in an Arrhenius fit of Dit versus the firing temperature is 0.30 ± 0.03 eV. This indicates that thermally induced desorption of hydrogen from SiH bonds at the poly-Si/SiOx interface is not the root cause of depassivation. Postfiring annealing at 425°C can improve the passivation again. Samples with SiNx capping layers show an increase in J0 up to about 100 fA/cm2 by firing, which can be attributed to blistering and is not reversed by annealing at 425°C. On the other hand, blistering does not occur in poly-Si samples capped with AlOx layers or AlOx/SiNy stacks, and J0 values of 2–5 fA/cm2 can be achieved after firing. Those findings suggest that a combination of two effects might be the root cause of the increase in J0 and Dit: thermal stress at the SiOz interface during firing and blistering. Blistering is presumed to occur when the hydrogen concentration in the capping layers exceeds a certain level.
3.
M Rienäcker; Y Larionova; J Krügener; S Wolter; R Brendel; R Peibst
Rear Side Dielectrics on Interdigitating p+-(i)-n+ Back-Contact Solar Cells – Hydrogenation vs. Charge Effects Proceedings Article
In: WIP, (Hrsg.): Proceedings of the 38th European Photovoltaic Solar Energy Conference and Exhibition, S. 154-157, Online Event, 2021, ISBN: 3-936338-78-7.
@inproceedings{Rienäcker2021c,
title = {Rear Side Dielectrics on Interdigitating p+-(i)-n+ Back-Contact Solar Cells – Hydrogenation vs. Charge Effects},
author = {M Rienäcker and Y Larionova and J Krügener and S Wolter and R Brendel and R Peibst},
editor = {WIP},
doi = {10.4229/EUPVSEC20212021-2BO.12.2},
isbn = {3-936338-78-7},
year = {2021},
date = {2021-11-16},
booktitle = {Proceedings of the 38th European Photovoltaic Solar Energy Conference and Exhibition},
pages = {154-157},
address = {Online Event},
abstract = {Polysilicon-on-oxide (POLO) passivating contacts and interdigitated back-contact (IBC) cell technologies have recently attracted a lot of interest as candidates for the implementation in the next generation of solar cells. An IBC cell with POLO junctions for both polarities – a POLO²-IBC cell – has to electrically isolate the highly defective p+ and n+ poly-Si regions on the rear side of the cell to avoid parasitic recombination. Inserting an initially undoped, intrinsic (i) region between the p+ and n+ poly-Si regions was demonstrated to successfully prevent the parasitic recombination in the transition region of ISFH’s 26.1%- efficient POLO²-IBC cell. In order to further improve the conversion efficiency towards 27%, we apply hydrogen-donating dielectric layer stacks to the p+-(i)-n+ POLO interdigitating rear side to enhance the passivation quality of the POLO junctions. We indeed show a significant improvement of POLO junctions on symmetrical full-area homogenously doped reference samples, but when we apply a hydrogen-donating layer stack on the p+-(i)-n+ POLO interdigitating rear side, we observe a strong degradation in the performance of the POLO²-IBC cell. We attribute this to the formation of a conductive channel between the p+ and n+ poly-Si regions due to the strong negative charge density of the hydrogen-donating layer stack.},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
Polysilicon-on-oxide (POLO) passivating contacts and interdigitated back-contact (IBC) cell technologies have recently attracted a lot of interest as candidates for the implementation in the next generation of solar cells. An IBC cell with POLO junctions for both polarities – a POLO²-IBC cell – has to electrically isolate the highly defective p+ and n+ poly-Si regions on the rear side of the cell to avoid parasitic recombination. Inserting an initially undoped, intrinsic (i) region between the p+ and n+ poly-Si regions was demonstrated to successfully prevent the parasitic recombination in the transition region of ISFH’s 26.1%- efficient POLO²-IBC cell. In order to further improve the conversion efficiency towards 27%, we apply hydrogen-donating dielectric layer stacks to the p+-(i)-n+ POLO interdigitating rear side to enhance the passivation quality of the POLO junctions. We indeed show a significant improvement of POLO junctions on symmetrical full-area homogenously doped reference samples, but when we apply a hydrogen-donating layer stack on the p+-(i)-n+ POLO interdigitating rear side, we observe a strong degradation in the performance of the POLO²-IBC cell. We attribute this to the formation of a conductive channel between the p+ and n+ poly-Si regions due to the strong negative charge density of the hydrogen-donating layer stack.
4.
C Hollemann; N Folchert; S P Harvey; P Stradins; D L Young; C Lima Salles Souza; M Rienäcker; F Haase; R Brendel; R Peibst
In: Solar Energy Materials and Solar Cells, Bd. 231, S. 111297, 2021, ISSN: 0927-0248.
@article{Hollemann2021c,
title = {Changes in hydrogen concentration and defect state density at the poly-Si/SiOx/c-Si interface due to firing},
author = {C Hollemann and N Folchert and S P Harvey and P Stradins and D L Young and C Lima Salles Souza and M Rienäcker and F Haase and R Brendel and R Peibst},
doi = {10.1016/j.solmat.2021.111297},
issn = {0927-0248},
year = {2021},
date = {2021-10-01},
journal = {Solar Energy Materials and Solar Cells},
volume = {231},
pages = {111297},
abstract = {We determined the density of defect states of poly-Si/SiOx/c-Si junctions featuring a wet chemical interfacial oxide from lifetime measurements using the MarcoPOLO model to calculate recombination and contact resistance in poly-Si/SiOx/c-Si-junctions. In samples that did not receive any hydrogen treatment, the Dit,cSi is about 2 × 1012 cm−2 eV⁻1 before firing and rises to 3–7 × 1012 cm⁻2 eV⁻1 during firing at measured peak temperatures between 620 °C and 863 °C. To address the question of why AlOx/SiNy stacks in contrast to pure SiNy layers for hydrogenation during firing provides better passivation quality, we have measured the hydrogen concentrations at the poly-Si/SiOx/c-Si interface as a function of AlOx layer thickness and compared these to J0 and calculated Dit,c-Si values. We observe an increase of the hydrogen concentration at the SiOx/c-Si interface upon firing as a function of the firing temperature that exceeds the defect concentrations at the interface several times. However, the AlOx layer thickness appears to cause an increase in hydrogen concentration at the SiOx/c-Si interface in these samples rather than exhibiting a hydrogen blocking property.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We determined the density of defect states of poly-Si/SiOx/c-Si junctions featuring a wet chemical interfacial oxide from lifetime measurements using the MarcoPOLO model to calculate recombination and contact resistance in poly-Si/SiOx/c-Si-junctions. In samples that did not receive any hydrogen treatment, the Dit,cSi is about 2 × 1012 cm−2 eV⁻1 before firing and rises to 3–7 × 1012 cm⁻2 eV⁻1 during firing at measured peak temperatures between 620 °C and 863 °C. To address the question of why AlOx/SiNy stacks in contrast to pure SiNy layers for hydrogenation during firing provides better passivation quality, we have measured the hydrogen concentrations at the poly-Si/SiOx/c-Si interface as a function of AlOx layer thickness and compared these to J0 and calculated Dit,c-Si values. We observe an increase of the hydrogen concentration at the SiOx/c-Si interface upon firing as a function of the firing temperature that exceeds the defect concentrations at the interface several times. However, the AlOx layer thickness appears to cause an increase in hydrogen concentration at the SiOx/c-Si interface in these samples rather than exhibiting a hydrogen blocking property.
5.
F Haase; B Min; C Hollemann; J Krügener; R Brendel; R Peibst
In: Progress in Photovoltaics: Research and Applications, Bd. 29, Nr. 5, S. 516-523, 2021.
@article{Haase2021,
title = {Fully screen-printed silicon solar cells with local Al-p+ and n-type POLO interdigitated back contacts with a VOC of 716 mV and an efficiency of 23%},
author = {F Haase and B Min and C Hollemann and J Krügener and R Brendel and R Peibst},
doi = {10.1002/pip.3399},
year = {2021},
date = {2021-05-01},
journal = {Progress in Photovoltaics: Research and Applications},
volume = {29},
number = {5},
pages = {516-523},
abstract = {We demonstrate the fabrication of a fully screen-printed p-type silicon solar cell with local hole-collecting Al-alloyed (Al-p+) contacts with a record open circuit voltage of 716 mV. The solar cell is fabricated by using almost the same process equipment as PERC cells. One of the dominant recombination losses in PERC cells is the recombination in the passivated and in the contacted emitter regions that so far limit the open circuit voltage to values below 700 mV. We eliminate these loss channels by substituting the P-diffused emitter by a passivating n-type poly-Silicon on Oxide (nPOLO) contact. We place this contact on the rear side because of its otherwise strong parasitic absorption. The Al-p+ contacts are also located at the rear side to avoid front-side shading. This results in a POLO-IBC cell structure. The efficiency of the best cell so far is 23.0% with a designated area of 4 cm2 fabricated on a M2-sized wafer. Scanning electron microscopy reveals an Al-p+ thickness of less than 3.3 μm and only a few 100 nm at the contact ends, which is less than the 5 μm typically for optimized Al-p+ contacts. A comparison of measured and simulated current-voltage curves over a variation of the contact fraction extracts a high saturation current density of the Al-p+ contact of J0-Al -p+ = 2,250 fA cm−2 for the current screen-print conditions and Al-paste causing an absolute efficiency loss of 0.5%abs. The recombination at the AlOx/SiNy surface and the shunt resistance limits the cell by 0.6%abs each.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We demonstrate the fabrication of a fully screen-printed p-type silicon solar cell with local hole-collecting Al-alloyed (Al-p+) contacts with a record open circuit voltage of 716 mV. The solar cell is fabricated by using almost the same process equipment as PERC cells. One of the dominant recombination losses in PERC cells is the recombination in the passivated and in the contacted emitter regions that so far limit the open circuit voltage to values below 700 mV. We eliminate these loss channels by substituting the P-diffused emitter by a passivating n-type poly-Silicon on Oxide (nPOLO) contact. We place this contact on the rear side because of its otherwise strong parasitic absorption. The Al-p+ contacts are also located at the rear side to avoid front-side shading. This results in a POLO-IBC cell structure. The efficiency of the best cell so far is 23.0% with a designated area of 4 cm2 fabricated on a M2-sized wafer. Scanning electron microscopy reveals an Al-p+ thickness of less than 3.3 μm and only a few 100 nm at the contact ends, which is less than the 5 μm typically for optimized Al-p+ contacts. A comparison of measured and simulated current-voltage curves over a variation of the contact fraction extracts a high saturation current density of the Al-p+ contact of J0-Al -p+ = 2,250 fA cm−2 for the current screen-print conditions and Al-paste causing an absolute efficiency loss of 0.5%abs. The recombination at the AlOx/SiNy surface and the shunt resistance limits the cell by 0.6%abs each.
6.
R Peibst
Towards 28 %-Efficient Si Single Junction Solar Cells with Better Passivating POLO Junctions Vortrag
Online Event, 22.04.2021, (SiliconPV 2021 - 11th International Conference on Silicon Photovoltaics).
@misc{Peibst2021,
title = {Towards 28 %-Efficient Si Single Junction Solar Cells with Better Passivating POLO Junctions},
author = {R Peibst},
year = {2021},
date = {2021-04-22},
address = {Online Event},
note = {SiliconPV 2021 - 11th International Conference on Silicon Photovoltaics},
keywords = {},
pubstate = {published},
tppubtype = {presentation}
}
7.
C Hollemann
Influence of Firing on the Interface State Density of n-Type Poly-Si Passivating Contacts Vortrag
Online Event, 22.04.2021, (SiliconPV 2021 - 11th International Conference on Silicon Photovoltaics).
@misc{Hollemann2021,
title = {Influence of Firing on the Interface State Density of n-Type Poly-Si Passivating Contacts},
author = {C Hollemann},
year = {2021},
date = {2021-04-22},
address = {Online Event},
note = {SiliconPV 2021 - 11th International Conference on Silicon Photovoltaics},
keywords = {},
pubstate = {published},
tppubtype = {presentation}
}
8.
N Folchert
Modelling the Annealing of Poly-Si/SiOx/c-Si Junctions Vortrag
Online Event, 22.04.2021, (SiliconPV 2021 - 11th International Conference on Silicon Photovoltaics).
@misc{Folchert2021b,
title = {Modelling the Annealing of Poly-Si/SiOx/c-Si Junctions},
author = {N Folchert},
year = {2021},
date = {2021-04-22},
address = {Online Event},
note = {SiliconPV 2021 - 11th International Conference on Silicon Photovoltaics},
keywords = {},
pubstate = {published},
tppubtype = {presentation}
}
9.
N Folchert
Easy-to-Apply Contact Resistance Measurements of the Interfacial Oxide in Poly-Si/SiOx/c-Si Junctions – Revisiting the Cox & Strack Formula Vortrag
Online Event, 20.04.2021, (SiliconPV 2021 - 11th International Conference on Silicon Photovoltaics).
@misc{Folchert2021,
title = {Easy-to-Apply Contact Resistance Measurements of the Interfacial Oxide in Poly-Si/SiOx/c-Si Junctions – Revisiting the Cox & Strack Formula},
author = {N Folchert},
year = {2021},
date = {2021-04-20},
address = {Online Event},
note = {SiliconPV 2021 - 11th International Conference on Silicon Photovoltaics},
keywords = {},
pubstate = {published},
tppubtype = {presentation}
}
10.
F Haase
23%-Efficient Screen-Printed IBC Cells on Cz-Grown Silicon with n-Type Poly-Si Passivating Contact and Al-alloyed p-Type Contact Vortrag
Online Event, 19.04.2021, (SiliconPV 2021 - 11th International Conference on Silicon Photovoltaics).
@misc{Haase2021b,
title = {23%-Efficient Screen-Printed IBC Cells on Cz-Grown Silicon with n-Type Poly-Si Passivating Contact and Al-alloyed p-Type Contact},
author = {F Haase},
year = {2021},
date = {2021-04-19},
address = {Online Event},
note = {SiliconPV 2021 - 11th International Conference on Silicon Photovoltaics},
keywords = {},
pubstate = {published},
tppubtype = {presentation}
}
11.
C N Kruse; S Schäfer; F Haase; V Mertens; H Schulte-Huxel; B Lim; B Min; T Dullweber; R Peibst; R Brendel
In: Scientific Reports, Bd. 11, Nr. 1, S. 996, 2021, ISSN: 2045-2322.
@article{Kruse2021,
title = {Simulation-based roadmap for the integration of poly-silicon on oxide contacts into screen-printed crystalline silicon solar cells},
author = {C N Kruse and S Schäfer and F Haase and V Mertens and H Schulte-Huxel and B Lim and B Min and T Dullweber and R Peibst and R Brendel},
doi = {10.1038/s41598-020-79591-6},
issn = {2045-2322},
year = {2021},
date = {2021-01-13},
journal = {Scientific Reports},
volume = {11},
number = {1},
pages = {996},
abstract = {We present a simulation-based study for identifying promising cell structures, which integrate poly-Si on oxide junctions into industrial crystalline silicon solar cells. The simulations use best-case measured input parameters to determine efficiency potentials. We also discuss the main challenges of industrially processing these structures. We find that structures based on p-type wafers in which the phosphorus diffusion is replaced by an n-type poly-Si on oxide junction (POLO) in combination with the conventional screen-printed and fired Al contacts show a high efficiency potential. The efficiency gains in comparsion to the 23.7% efficiency simulated for the PERC reference case are 1.0% for the POLO BJ (back junction) structure and 1.8% for the POLO IBC (interdigitated back contact) structure. The POLO BJ and the POLO IBC cells can be processed with lean process flows, which are built on major steps of the PERC process such as the screen-printed Al contacts and the $$backslashtextAl_backslashtext2 backslashtextO_backslashtext3 /backslashtextSiN $$Al2O3/SiNpassivation. Cell concepts with contacts using poly-Si for both polarities ($$backslashtextPOLO^2$$POLO2-concepts) show an even higher efficiency gain potential of 1.3% for a $$backslashtextPOLO^2$$POLO2BJ cell and 2.2% for a $$backslashtextPOLO^2$$POLO2IBC cell in comparison to PERC. For these structures further research on poly-Si structuring and screen-printing on p-type poly-Si is necessary.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We present a simulation-based study for identifying promising cell structures, which integrate poly-Si on oxide junctions into industrial crystalline silicon solar cells. The simulations use best-case measured input parameters to determine efficiency potentials. We also discuss the main challenges of industrially processing these structures. We find that structures based on p-type wafers in which the phosphorus diffusion is replaced by an n-type poly-Si on oxide junction (POLO) in combination with the conventional screen-printed and fired Al contacts show a high efficiency potential. The efficiency gains in comparsion to the 23.7% efficiency simulated for the PERC reference case are 1.0% for the POLO BJ (back junction) structure and 1.8% for the POLO IBC (interdigitated back contact) structure. The POLO BJ and the POLO IBC cells can be processed with lean process flows, which are built on major steps of the PERC process such as the screen-printed Al contacts and the $$backslashtextAl_backslashtext2 backslashtextO_backslashtext3 /backslashtextSiN $$Al2O3/SiNpassivation. Cell concepts with contacts using poly-Si for both polarities ($$backslashtextPOLO^2$$POLO2-concepts) show an even higher efficiency gain potential of 1.3% for a $$backslashtextPOLO^2$$POLO2BJ cell and 2.2% for a $$backslashtextPOLO^2$$POLO2IBC cell in comparison to PERC. For these structures further research on poly-Si structuring and screen-printing on p-type poly-Si is necessary.
12.
N Folchert; R Peibst; R Brendel
Modeling recombination and contact resistance of poly-Si junctions Artikel
In: Progress in Photovoltaics: Research and Applications, Bd. 28, Nr. 12, S. 1289-1307, 2020.
@article{Folchert2020,
title = {Modeling recombination and contact resistance of poly-Si junctions},
author = {N Folchert and R Peibst and R Brendel},
doi = {10.1002/pip.3327},
year = {2020},
date = {2020-12-01},
journal = {Progress in Photovoltaics: Research and Applications},
volume = {28},
number = {12},
pages = {1289-1307},
abstract = {We present a semi-analytical model for the calculation of the current through and the recombination in carrier-selective junctions consisting of a poly-Si/SiOx/c-Si layer stack. We calculate the recombination parameter J0 and the contact resistance ρC after solving the band-bending-problem on both sides of the interfacial oxide. Comparisons with finite-element simulations show that the current calculation is reliable at all bias conditions except for inversion and that current through pinholes is resolved adequately in the model. The model allows a coherent description of lifetime-, current-voltage- and capacitance-voltage measurements performed on a sample with dominant tunneling. We use our model to investigate the influence of oxide thickness and pinhole density on J0 and ρC of our state-of-the-art poly-silicon-on-oxide (POLO) junctions and demonstrate its usefulness for the optimization of poly-Si based junctions.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We present a semi-analytical model for the calculation of the current through and the recombination in carrier-selective junctions consisting of a poly-Si/SiOx/c-Si layer stack. We calculate the recombination parameter J0 and the contact resistance ρC after solving the band-bending-problem on both sides of the interfacial oxide. Comparisons with finite-element simulations show that the current calculation is reliable at all bias conditions except for inversion and that current through pinholes is resolved adequately in the model. The model allows a coherent description of lifetime-, current-voltage- and capacitance-voltage measurements performed on a sample with dominant tunneling. We use our model to investigate the influence of oxide thickness and pinhole density on J0 and ρC of our state-of-the-art poly-silicon-on-oxide (POLO) junctions and demonstrate its usefulness for the optimization of poly-Si based junctions.
13.
R Peibst; R Brendel; F Haase; C Hollemann; C Kruse; Y Larionova; B Lim; J Krügener; B Min; M Rienäcker
Passivating poly-Si on oxide contacts – from fundamental investigations towards industrial implementation Vortrag
Online Event, 30.11.2020, (2nd International Conference on Photovoltaic Science and Technologies (PVCon2020)).
@misc{Peibst2020b,
title = {Passivating poly-Si on oxide contacts – from fundamental investigations towards industrial implementation},
author = {R Peibst and R Brendel and F Haase and C Hollemann and C Kruse and Y Larionova and B Lim and J Krügener and B Min and M Rienäcker},
year = {2020},
date = {2020-11-30},
address = {Online Event},
note = {2nd International Conference on Photovoltaic Science and Technologies (PVCon2020)},
keywords = {},
pubstate = {published},
tppubtype = {presentation}
}
14.
S Schäfer; A Mercker; V Mertens; T Neubert; A Köhler; L Mettner; R Brendel; R Peibst
Laser-Induced Oxidation of Doped Poly-Si at Room Temperature for Si Solar Cells with Structured Passivated Contacts Vortrag
Online Event, 10.09.2020, (37th European Photovoltaic Solar Energy Conference and Exhibition).
@misc{Schäfer2020,
title = {Laser-Induced Oxidation of Doped Poly-Si at Room Temperature for Si Solar Cells with Structured Passivated Contacts},
author = {S Schäfer and A Mercker and V Mertens and T Neubert and A Köhler and L Mettner and R Brendel and R Peibst},
year = {2020},
date = {2020-09-10},
address = {Online Event},
abstract = {Purpose of the work, scientific approach and innovation: Passivated contacts that use polysilicon on oxide (POLO) show outstanding electrical surface passivation of silicon. However, poly-Si-based junctions have been mainly applied to the rear side of solar cells, either in an IBC architecture [1] or in a front and back side-contacted (FBC) cell [2]. Highly doped poly-Si on the rear side causes less parasitic absorption than on the front side. A possible compromise is to have the POLO contacts only locally under the front metal fingers of an FBC solar cell and spare the interfinger regions. This can be done by localized deposition in the first place, e.g. via shadow masks, or by a three step process with formation of a sacrificial dielectric layer on top of the poly-Si (1), subsequent structuring to form an etching mask (2) and final etching process (3). In this abstract we demonstrate an alternative process where the etching mask is created locally by laser treatment of the poly-Si. Thereby the aforementioned steps (1) and (2) are combined in a single laser process. We show that a local irradiation by UV-ps laser pulses changes the etch resistiveness of the poly-Si in an alkaline solution, which is sufficient to remove the poly- Si in the non-lasered areas. The etch resistiveness increases when additional oxygen gas is introduced to the process chamber. We therefore explain the findings by a laser-induced oxidation of the poly-Si rather than by amorphization of the poly-Si. We demonstrate the process to work on planar as well as textured silicon. The advantage of the lasered etching mask is the reduction of process complexity and process time as compared to ablating the complete interfinger region, which is roughly 98% of the front side.},
note = {37th European Photovoltaic Solar Energy Conference and Exhibition},
keywords = {},
pubstate = {published},
tppubtype = {presentation}
}
Purpose of the work, scientific approach and innovation: Passivated contacts that use polysilicon on oxide (POLO) show outstanding electrical surface passivation of silicon. However, poly-Si-based junctions have been mainly applied to the rear side of solar cells, either in an IBC architecture [1] or in a front and back side-contacted (FBC) cell [2]. Highly doped poly-Si on the rear side causes less parasitic absorption than on the front side. A possible compromise is to have the POLO contacts only locally under the front metal fingers of an FBC solar cell and spare the interfinger regions. This can be done by localized deposition in the first place, e.g. via shadow masks, or by a three step process with formation of a sacrificial dielectric layer on top of the poly-Si (1), subsequent structuring to form an etching mask (2) and final etching process (3). In this abstract we demonstrate an alternative process where the etching mask is created locally by laser treatment of the poly-Si. Thereby the aforementioned steps (1) and (2) are combined in a single laser process. We show that a local irradiation by UV-ps laser pulses changes the etch resistiveness of the poly-Si in an alkaline solution, which is sufficient to remove the poly- Si in the non-lasered areas. The etch resistiveness increases when additional oxygen gas is introduced to the process chamber. We therefore explain the findings by a laser-induced oxidation of the poly-Si rather than by amorphization of the poly-Si. We demonstrate the process to work on planar as well as textured silicon. The advantage of the lasered etching mask is the reduction of process complexity and process time as compared to ablating the complete interfinger region, which is roughly 98% of the front side.
15.
L David; S Hübner; B Min; C Hollemann; T Dippell; P Wohlfart; R Peibst; R Brendel
Fired-Only Passivating Poly-Si on Oxide Contacts with DC-Sputtered In-Situ Phosphorous-Doped Silicon Layers Vortrag
Online Event, 08.09.2020, (37th European Photovoltaic Solar Energy Conference and Exhibition).
@misc{David2020,
title = {Fired-Only Passivating Poly-Si on Oxide Contacts with DC-Sputtered In-Situ Phosphorous-Doped Silicon Layers},
author = {L David and S Hübner and B Min and C Hollemann and T Dippell and P Wohlfart and R Peibst and R Brendel},
year = {2020},
date = {2020-09-08},
address = {Online Event},
abstract = {The PV industry is currently introducing passivating contacts into pilot and mass production lines. A record efficiency of 24.58% was already demonstrated with an n-type industrial solar cell using low pressure vapor deposition (LPCVD) of poly-Si as well as the interfacial oxide [1]. However, the inherent double-sided deposition of LPCVD layers increases process complexity because a subsequent etching step is needed for single-side passivating contacts. Single-side deposition of doped silicon layers using PECVD, APCVD or thermal evaporation is an option for decreasing the complexity. But these CVD techniques use hazardous gases like phosphine for doping and thus require elaborated safety measures. In this work, we report on sputtering with a conventional firing-step as an alternative approach for the fabrication of passivating contacts. It allows single-side deposition at low deposition temperature when compared to LCPVD and PECVD. In addition no hazardous gases are required for doping. We demonstrate contact deposition by direct current (DC) sputtering of a phosphorous-doped silicon target and use a conventional firing step for contact formation used for hightemperature screen-print metallization. We measure an implied open circuit voltage (iVOC) of up to 695 mV with a median of 680 mV for symmetric P-doped poly-Si on oxide (POLO) samples.},
note = {37th European Photovoltaic Solar Energy Conference and Exhibition},
keywords = {},
pubstate = {published},
tppubtype = {presentation}
}
The PV industry is currently introducing passivating contacts into pilot and mass production lines. A record efficiency of 24.58% was already demonstrated with an n-type industrial solar cell using low pressure vapor deposition (LPCVD) of poly-Si as well as the interfacial oxide [1]. However, the inherent double-sided deposition of LPCVD layers increases process complexity because a subsequent etching step is needed for single-side passivating contacts. Single-side deposition of doped silicon layers using PECVD, APCVD or thermal evaporation is an option for decreasing the complexity. But these CVD techniques use hazardous gases like phosphine for doping and thus require elaborated safety measures. In this work, we report on sputtering with a conventional firing-step as an alternative approach for the fabrication of passivating contacts. It allows single-side deposition at low deposition temperature when compared to LCPVD and PECVD. In addition no hazardous gases are required for doping. We demonstrate contact deposition by direct current (DC) sputtering of a phosphorous-doped silicon target and use a conventional firing step for contact formation used for hightemperature screen-print metallization. We measure an implied open circuit voltage (iVOC) of up to 695 mV with a median of 680 mV for symmetric P-doped poly-Si on oxide (POLO) samples.
16.
F Haase; B Min; C Hollemann; J Krügener; R Brendel; R Peibst
Fully Screen-Printed Silicon Solar Cells with Local Al-BSF Base Contact and a Voc of 711 mV Vortrag
Online Event, 07.09.2020, (37th European Photovoltaic Solar Energy Conference and Exhibition).
@misc{Haase2020b,
title = {Fully Screen-Printed Silicon Solar Cells with Local Al-BSF Base Contact and a Voc of 711 mV},
author = {F Haase and B Min and C Hollemann and J Krügener and R Brendel and R Peibst},
year = {2020},
date = {2020-09-07},
address = {Online Event},
abstract = {We investigate the open circuit voltage potential of local aluminum-back surface fields (Al-BSF) on cell level. We implement these contacts in a cell process, which uses almost the same process equipment as PERC cells [1,2]. The most limiting factor in PERC cells is the emitter and emitter contact recombination that typically limits the open circuit voltage to values below 700 mV. We eliminate this losses channel by substituting the P-diffused emitter by a passivating n-type poly-Silicon on Oxide (POLO) contact. We place this contact on the rear side because of its strong free carrier absorption. The Al-BSF contacts are also located at the rear side to avoid front-side shading. Figure 1 shows the resulting POLO-IBC cell structure with interdigitated back contacts that uses Al-BSF for the hole selective contact and n-type POLO for the electron selective contact.},
note = {37th European Photovoltaic Solar Energy Conference and Exhibition},
keywords = {},
pubstate = {published},
tppubtype = {presentation}
}
We investigate the open circuit voltage potential of local aluminum-back surface fields (Al-BSF) on cell level. We implement these contacts in a cell process, which uses almost the same process equipment as PERC cells [1,2]. The most limiting factor in PERC cells is the emitter and emitter contact recombination that typically limits the open circuit voltage to values below 700 mV. We eliminate this losses channel by substituting the P-diffused emitter by a passivating n-type poly-Silicon on Oxide (POLO) contact. We place this contact on the rear side because of its strong free carrier absorption. The Al-BSF contacts are also located at the rear side to avoid front-side shading. Figure 1 shows the resulting POLO-IBC cell structure with interdigitated back contacts that uses Al-BSF for the hole selective contact and n-type POLO for the electron selective contact.
17.
B Min; A Merkle; T Brendemühl; N Wehmeier; Y Larionova; B Beier; L David; H Schulte-Huxel; T Dullweber; R Peibst; R Brendel
POLO Back Junction: An Elegant Way to Implement Electron-Collecting Passivating Contacts in p-Type Industrial Silicon Solar Cells Vortrag
Online Event, 07.09.2020, (37th European Photovoltaic Solar Energy Conference and Exhibition).
@misc{Min2020,
title = {POLO Back Junction: An Elegant Way to Implement Electron-Collecting Passivating Contacts in p-Type Industrial Silicon Solar Cells},
author = {B Min and A Merkle and T Brendemühl and N Wehmeier and Y Larionova and B Beier and L David and H Schulte-Huxel and T Dullweber and R Peibst and R Brendel},
year = {2020},
date = {2020-09-07},
address = {Online Event},
abstract = {any manufacturers select passivating contacts as the key technology to boost the cell efficiency level of industrial silicon solar cells. For its implementation in mass production, most of them choose n-type solar cells featuring boron emitter at the front side and electron-collecting passivating contacts at the rear side, which is also known as TOPCon structure. However, it is a huge leap for current cell manufacturers to implement this structure in mainstream production, since it requires multiple pieces of new equipment and the change from p-type to n-type wafers. Hence, there is still a need for an alternative concept for the industrialization of passivating contacts which needs only few pieces of equipment to be added to current PERC production lines. In this paper, we present recent progress of our alternative cell concept to implement electroncollecting passivating contacts in mass production of p-type solar cells. Based on the bifacial PERC+ structure, we only replace the POCl3-diffused emitter by an electron-collecting poly-Si on oxide (POLO) contact while all other components are maintained. It is not necessary to pattern the poly-Si layers since the electron-collecting POLO contacts are located at the cell rear side, resulting in a POLO back junction solar cell [1]. Compared to our previous work [2] we improve, among other things, the front side of POLO back junction cells with 5 busbars achieving an efficiency up to 20.5 % and an open-circuit voltage up to 693 mV.},
note = {37th European Photovoltaic Solar Energy Conference and Exhibition},
keywords = {},
pubstate = {published},
tppubtype = {presentation}
}
any manufacturers select passivating contacts as the key technology to boost the cell efficiency level of industrial silicon solar cells. For its implementation in mass production, most of them choose n-type solar cells featuring boron emitter at the front side and electron-collecting passivating contacts at the rear side, which is also known as TOPCon structure. However, it is a huge leap for current cell manufacturers to implement this structure in mainstream production, since it requires multiple pieces of new equipment and the change from p-type to n-type wafers. Hence, there is still a need for an alternative concept for the industrialization of passivating contacts which needs only few pieces of equipment to be added to current PERC production lines. In this paper, we present recent progress of our alternative cell concept to implement electroncollecting passivating contacts in mass production of p-type solar cells. Based on the bifacial PERC+ structure, we only replace the POCl3-diffused emitter by an electron-collecting poly-Si on oxide (POLO) contact while all other components are maintained. It is not necessary to pattern the poly-Si layers since the electron-collecting POLO contacts are located at the cell rear side, resulting in a POLO back junction solar cell [1]. Compared to our previous work [2] we improve, among other things, the front side of POLO back junction cells with 5 busbars achieving an efficiency up to 20.5 % and an open-circuit voltage up to 693 mV.
18.
T Dullweber; M Stöhr; C Kruse; F Haase; M Rudolph; B Beier; P Jäger; V Mertens; R Peibst; R Brendel
In: Solar Energy Materials and Solar Cells, Bd. 212, S. 110586, 2020, ISSN: 0927-0248.
@article{Dullweber2020c,
title = {Evolutionary PERC+ solar cell efficiency projection towards 24% evaluating shadow-mask-deposited poly-Si fingers below the Ag front contact as next improvement step},
author = {T Dullweber and M Stöhr and C Kruse and F Haase and M Rudolph and B Beier and P Jäger and V Mertens and R Peibst and R Brendel},
doi = {10.1016/j.solmat.2020.110586},
issn = {0927-0248},
year = {2020},
date = {2020-08-01},
journal = {Solar Energy Materials and Solar Cells},
volume = {212},
pages = {110586},
abstract = {Monofacial PERC and bifacial PERC + solar cells have become the mainstream solar cell technology exhibiting conversion efficiencies around 22.5% in mass production. We determine a specific saturation current density J0},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Monofacial PERC and bifacial PERC + solar cells have become the mainstream solar cell technology exhibiting conversion efficiencies around 22.5% in mass production. We determine a specific saturation current density J0
19.
C Hollemann; F Haase; J Krugener; R Brendel; R Peibst
Firing stability of n-type poly Si on oxide junctions Vortrag
15.06.2020, (IEEE 47th PVSC Virtual Meeting).
@misc{Hollemann2020b,
title = {Firing stability of n-type poly Si on oxide junctions},
author = {C Hollemann and F Haase and J Krugener and R Brendel and R Peibst},
year = {2020},
date = {2020-06-15},
abstract = {Passivated contacts by poly-Si on oxide (POLO) junctions yield high passivation qualities after an appropriate annealing process at temperatures between 800°C and 1050°C. In today's typical cell production, a second, high temperature process is applied during ‘firing’. Firing is commonly used together with screen printed contacts in industrial production. Thus, a high stability of the passivation quality against this firing process is highly desirable – and also expected since the previous high-temperature process implies a much higher thermal budget. However, in this work we found a significant decrease in effective lifetimes of up to 75% for n-type POLO samples with thin interfacial oxide at firing temperatures of 620°C to 900°C. This holds without a supply of hydrogen (no capping layers). Experiments with hydrogen-rich dielectric capping layers show, however, that a coating with AlOx as opposed to SiNy, can significantly increase the stability of the passivation. Capacitance-voltage measurements show that the saturation current density correlates to the density of defect states at the SiOx/c-Si interface when varying the firing temperature. Although firing with hydrogen supplying layers seems to be viable, our results may indicate that the chemical configuration of the SiOx/Si interface changes from Si-O to Si-H bonds upon firing. If this hypothesis holds true, possible implications on the long-term stability of the passivation quality should be evaluated.},
note = {IEEE 47th PVSC Virtual Meeting},
keywords = {},
pubstate = {published},
tppubtype = {presentation}
}
Passivated contacts by poly-Si on oxide (POLO) junctions yield high passivation qualities after an appropriate annealing process at temperatures between 800°C and 1050°C. In today's typical cell production, a second, high temperature process is applied during ‘firing’. Firing is commonly used together with screen printed contacts in industrial production. Thus, a high stability of the passivation quality against this firing process is highly desirable – and also expected since the previous high-temperature process implies a much higher thermal budget. However, in this work we found a significant decrease in effective lifetimes of up to 75% for n-type POLO samples with thin interfacial oxide at firing temperatures of 620°C to 900°C. This holds without a supply of hydrogen (no capping layers). Experiments with hydrogen-rich dielectric capping layers show, however, that a coating with AlOx as opposed to SiNy, can significantly increase the stability of the passivation. Capacitance-voltage measurements show that the saturation current density correlates to the density of defect states at the SiOx/c-Si interface when varying the firing temperature. Although firing with hydrogen supplying layers seems to be viable, our results may indicate that the chemical configuration of the SiOx/Si interface changes from Si-O to Si-H bonds upon firing. If this hypothesis holds true, possible implications on the long-term stability of the passivation quality should be evaluated.
20.
R Peibst; C Kruse; S Schäfer; V Mertens; S Bordihn; T Dullweber; F Haase; C Hollemann; B Lim; B Min; R Niepelt; H Schulte-Huxel; R Brendel
For none, one, or two polarities—How do POLO junctions fit best into industrial Si solar cells? Artikel
In: Progress in Photovoltaics: Research and Applications, Bd. 28, Nr. 6, S. 503-516, 2020.
@article{Peibst2020,
title = {For none, one, or two polarities—How do POLO junctions fit best into industrial Si solar cells?},
author = {R Peibst and C Kruse and S Schäfer and V Mertens and S Bordihn and T Dullweber and F Haase and C Hollemann and B Lim and B Min and R Niepelt and H Schulte-Huxel and R Brendel},
doi = {10.1002/pip.3201},
year = {2020},
date = {2020-06-01},
journal = {Progress in Photovoltaics: Research and Applications},
volume = {28},
number = {6},
pages = {503-516},
abstract = {Abstract We present a systematic study on the benefit of the implementation of poly-Si on oxide (POLO) or related junctions into p-type industrial Si solar cells as compared with the benchmark of Passivated Emitter and Rear Cell (PERC). We assess three aspects: (a) the simulated efficiency potential of representative structures with POLO junctions for none (=PERC+), one, and for two polarities; (b) possible lean process flows for their fabrication; and (c) experimental results on major building blocks. Synergistic efficiency gain analysis reveals that the exclusive suppression of the contact recombination for one polarity by POLO only yields moderate efficiency improvements between 0.23%abs and 0.41%abs as compared with PERC+ because of the remaining recombination paths. This problem is solved in a structure that includes POLO junctions for both polarities (POLO2), for whose realization we propose a lean process flow, and for which we experimentally demonstrate the most important building blocks. However, two experimental challenges—alignment tolerances and screen-print metallization of p+ poly-Si—are unsolved so far and reduced the efficiency of the “real” POLO2 cell as compared with an idealized scenario. As an intermediate step, we therefore work on a POLO IBC cell with POLO junctions for one polarity. It avoids the abovementioned challenges of the POLO2 structure, can be realized within a lean process flow, and has an efficiency benefit of 1.59%abs as compared with PERC—because not only contact recombination is suppressed but also the entire phosphorus emitter is replaced by an n+ POLO junction.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Abstract We present a systematic study on the benefit of the implementation of poly-Si on oxide (POLO) or related junctions into p-type industrial Si solar cells as compared with the benchmark of Passivated Emitter and Rear Cell (PERC). We assess three aspects: (a) the simulated efficiency potential of representative structures with POLO junctions for none (=PERC+), one, and for two polarities; (b) possible lean process flows for their fabrication; and (c) experimental results on major building blocks. Synergistic efficiency gain analysis reveals that the exclusive suppression of the contact recombination for one polarity by POLO only yields moderate efficiency improvements between 0.23%abs and 0.41%abs as compared with PERC+ because of the remaining recombination paths. This problem is solved in a structure that includes POLO junctions for both polarities (POLO2), for whose realization we propose a lean process flow, and for which we experimentally demonstrate the most important building blocks. However, two experimental challenges—alignment tolerances and screen-print metallization of p+ poly-Si—are unsolved so far and reduced the efficiency of the “real” POLO2 cell as compared with an idealized scenario. As an intermediate step, we therefore work on a POLO IBC cell with POLO junctions for one polarity. It avoids the abovementioned challenges of the POLO2 structure, can be realized within a lean process flow, and has an efficiency benefit of 1.59%abs as compared with PERC—because not only contact recombination is suppressed but also the entire phosphorus emitter is replaced by an n+ POLO junction.