Parasitic Absorption in Polycrystalline Si-layers for Carrier-selective Front Junctions

In this work, we develop SiOx/poly‐Si carrier‐selective contacts grown by low‐pressure chemical vapor deposition and boron or phosphorus doped by ion implantation. We investigate their passivation properties on symmetric structures while varying the thickness of poly‐Si in a wide range (20‐250 nm). Dose and energy of implantation as well as temperature and time of annealing were optimized, achieving implied open‐circuit voltage well above 700 mV for electron‐selective contacts regardless the poly‐Si layer thickness. In case of hole‐selective contacts, the passivation quality decreases by thinning the poly‐Si layer. For both poly‐Si doping types, forming gas annealing helps to augment the passivation quality. The optimized doped poly‐Si layers are then implemented in c‐Si solar cells featuring SiO2/poly‐Si contacts with different polarities on both front and rear sides in a lean manufacturing process free from transparent conductive oxide (TCO). At cell level, open‐circuit voltage degrades when thinner p‐type poly‐Si layer is employed, while a consistent gain in short circuit current is measured when front poly‐Si thickness is thinned down from 250 to 35 nm (up to +4 mA/cm2). We circumvent this limitation by decoupling front and rear layer thickness obtaining, on one hand, reasonably high current (JSC‐EQE = 38.2 mA/cm2) and, on the other hand, relatively high VOC of approximately 690 mV. The best TCO‐free device using Ti‐seeded Cu‐plated front contact exhibits a fill factor of 75.2% and conversion efficiency of 19.6%.

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“…This means that the chemical passivation is excellent in all the three samples. A similar trend has been observed in literature …”

Section: Resultsmentioning

confidence: 99%

“…A similar trend has been observed in literature. 33,63 A similar study is performed on B-implanted poly-Si CSPC on flat substrate. Table 2 shows τ eff , J 0 , and iV OC in as-annealed condition and after FGA treatment for the case of 250-nm-thick poly-Si layer.…”

Section: C-si Surface Passivation By Poly-si Selective Contactsmentioning

confidence: 99%

Implantation‐based passivating contacts for crystalline silicon front/rear contacted solar cells

Limodio

Yang

Groot

et al. 2020

Progress in Photovoltaics

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“…We use the contact resistivity values measured in Rienacker et al The generation profile is simulated by Sunrays with the measured layer thicknesses as input parameter. The optical properties of poly‐Si are taken from Reiter et al Table lists the input parameters for the three analyzed solar cells.…”

Section: Methodsmentioning

confidence: 99%

26.1%‐efficient POLO‐IBC cells: Quantification of electrical and optical loss mechanisms

Hollemann

Haase

Schäfer

et al. 2019

Progress in Photovoltaics

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We present experimental results for interdigitated back contacted (IBC) solar cells with passivating POLO contacts for both polarities with a nominal intrinsic poly‐Si region between them. We reach efficiencies of 26.1% and 24.9% on a 1.3 Ω cm and 80 Ω cm p‐type FZ wafer and 24.6% on a 2 Ω cm n‐type Cz wafer, respectively. The initially measured implied efficiency potentials of the cells after passivating the surfaces are very similar, namely, 26.8%, 26.8%, and 26.4%, respectively. We attribute the difference between the efficiency potential and the final current‐voltage measurement to degradation, perimeter, and series and shunt resistance losses, which we quantify by lifetime measurements. With these measurements in combination with a finite element simulation, we determine the surface recombination velocity in the nominal intrinsic poly‐Si region to be in the range from 13 to 21 cm s−1. Using the same approach, we analyze the increase of the front surface recombination velocity during cell processing from 2 to 10 cm s−1 for the 1.3 Ω cm and from 0.5 to 2.3 cm s−1 for the 80 Ω cm. This leads to the fact that cells fabricated on lowly doped bulk material are more vulnerable to a process‐induced degradation of the surface passivation quality. We further determine the theoretical limits of the cells by firstly idealizing the recombination (28% for 1.3 Ω cm and 28.2% for 80 Ω cm) and secondly also idealizing the optics of the solar cells (29.4% and 29.5%).

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“…[6] Over a wide range of the spectrum doped poly-Si has a lower absorption coefficient than doped a-Si:H, implying a significantly lower absorption loss in a poly-Si layer than in an a-Si:H layer with the same thickness. [7,8,9] For a 15 nm thick, doped poly-Si layer, for example, the parasitic absorption induces a loss in the short circuit current density of 0.75 mA/cm 2 . For a doped a-Si:H layer with the same thickness, the corresponding loss is 3 mA/cm 2 .…”

Section: Introductionmentioning

confidence: 99%

“…For a doped a-Si:H layer with the same thickness, the corresponding loss is 3 mA/cm 2 . [7] However, less than 20 nm thin poly-Si layers have sheet resistances above 1000 Ω/sq. [10] A highly conductive and transparent This is the post-print version of paper published in: IEEE JPV (Volume: 9 , Issue: 1 , Jan. 2019), doi: 10.1109/JPHOTOV.2018.2878337 2 layer on top of the poly-Si could help to ensure the required lateral conductivity for the transport of charge carriers towards the metallization grid on the front side.…”

Section: Introductionmentioning

confidence: 99%

High Temperature Annealing of ZnO:Al on Passivating POLO Junctions: Impact on Transparency, Conductivity, Junction Passivation, and Interface Stability

Wietler

Min

Reiter

et al. 2019

IEEE J. Photovoltaics

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We investigate the enhancement in transparency and conductivity of aluminum doped zinc oxide (ZnO:Al) layers upon high-temperature annealing and its impact on contact resistance as well as on passivation properties of carrier selective junctions based on doped polycrystalline Si on a passivating silicon oxide (POLO). The temperature stability of these junctions allows annealing of the ZnO:Al/POLO combination up to 600 °C. We prepare ZnO:Al films by DC magnetron sputtering at room temperature. We determine complex refractive index of ZnO:Al in dependence of post-deposition annealing (PDA) temperature by spectroscopic ellipsometry. High-temperature annealing improves the conductivity and reduces the absorption within ZnO:Al. The optical losses in a ZnO:Al/POLO stack are rather limited by the poly-Si layer than by the ZnO:Al. The sheet resistance improves from roughly 20000 /sq for 80 nm thick as-deposited ZnO:Al films to 72 /sq after fast firing at 600 °C. At the same time PDA cures the damage induced in the POLO junctions during ZnO:Al deposition. After PDA with AlxOy capping layers, the passivation quality even surpasses the initial level. A transmsission electron microscopy analysis of the interface between the ZnO:Al and the underlying poly-Si reveals the formation of a silicon oxide like interfacial layer after PDA at 400 °C. This interfacial layer causes Manuscript a high contact resistivity of the metal/ZnO:Al/POLO-junction and could limit the thermal budget for cell processing. Our results indicate that after successful process adjustment, ZnO:Al could substitute In-based transparent conductive oxides on POLO cells for cost reasons and also enable a high efficiency potential.

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Parasitic Absorption in Polycrystalline Si-layers for Carrier-selective Front Junctions

Cited by 85 publications

References 8 publications

Implantation‐based passivating contacts for crystalline silicon front/rear contacted solar cells

Implantation‐based passivating contacts for crystalline silicon front/rear contacted solar cells

26.1%‐efficient POLO‐IBC cells: Quantification of electrical and optical loss mechanisms

High Temperature Annealing of ZnO:Al on Passivating POLO Junctions: Impact on Transparency, Conductivity, Junction Passivation, and Interface Stability

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