Characterization of screen printed and fire-through contacts on LPCVD based passivating contacts in monoPoly™ solar cells

Padhamnath, Pradeep; Buatis, Jammaal Kitz; Khanna, Anuradha; Nampalli, Nitin; Nandakumar, Naomi; Shanmugam, Vinodh; Aberle, Armin G.; Duttagupta, Shubham

doi:10.1016/j.solener.2020.03.087

Cited by 30 publications

(22 citation statements)

References 25 publications

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“…[ 3,4 ] However, forming metal contacts on TOPCon is still a challenge that requires further investigation and improvements. Some commonly reported concerns pertaining to the conventional screen‐printed metallization on TOPCon are 1) higher specific contact resistivity (1.5–10 Ω cm) on thick (>150 nm) poly‐Si passivated contacts [ 5 ] and 2) increase of metal‐induced recombination with decreasing thickness of poly‐Si due to the metal spiking through the poly‐Si and coming in contact with the bulk c‐Si. [ 6 ]…”

Section: Introductionmentioning

confidence: 99%

Laser Ablation and Ni/Cu Plating Approach for Tunnel Oxide Passivated Contacts Solar Cells with Variate Polysilicon Layer Thickness: Gains and Possibilities in Comparison to Screen Printing

Arya

Steinhauser

Gruebel

et al. 2020

Physica Status Solidi (a)

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Recombination of photo-generated charge carriers at metalsemiconductor junctions is a strong limiting factor in achieving high efficiencies for conventional c-Si solar cells [e.g., aluminum back scatter field, passivated emitter rear contact (PERC), etc.]. [1-3] This can be reduced by squeezing the metallized area fraction, but that results in an increase of fill-factor (FF) loses. A novel approach developed at Fraunhofer ISE, namely, tunnel oxide passivated contacts (TOPCon), attempts to counter this effect by implementing passivating contact structures to drastically reduce metal-semiconductor junction recombination. [1,2,4] Passivated contact layers, such as TOPCon, constitute an ultrathin (1-2 nm) silicon oxide (SiO x) layer grown over the bulk c-Si, which is further deposited upon with a highly doped poly-Si layer and finally capped with SiN x. Together they provide excellent passivation, enabling high implied open circuit voltage (iV oc) [2] and carrier selectivity. [2,4] Furthermore, the depletion zone field generated due to high doping of poly-Si also contributes to the passivation effect. Passivating contacts are, therefore, considered to be the next major technological upgrade in the solar cell technology. [3,4] However, forming metal contacts on TOPCon is still a challenge that requires further investigation and improvements. Some commonly reported concerns pertaining to the conventional screen-printed metallization on TOPCon are 1) higher specific contact resistivity (1.5-10 Ω cm) on thick (>150 nm) poly-Si passivated contacts [5] and 2) increase of metal-induced recombination with decreasing thickness of poly-Si due to the metal spiking through the poly-Si and coming in contact with the bulk c-Si. [6] Spiking of the metal paste through the poly-Si layer drastically increases the J 0,met (recombination current at metal-silicon junction) due to poor shielding of recombination at metal contacts, resulting in a low open circuit voltage (V oc). [6] To prevent the penetration of fire-through metal pastes all the way through to the c-Si substrate, it becomes necessary either to keep the thickness of poly-Si above 120 nm or use low temperature metallization techniques. [7-10] However, a thicker poly-Si layer has two serious drawbacks-increased parasitic absorption and higher cost of ownership (COO). Parasitic absorption inflates with increasing poly-Si thickness, resulting in the loss of short circuit current (J sc), [6,11,12] whereas the COO calculations reveal a jump of around 75% if the poly-Si thickness is increased from 50 to 200 nm. [13] Hence, to keep the parasitic absorption and the cost

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Section: Introductionmentioning

confidence: 99%

Laser Ablation and Ni/Cu Plating Approach for Tunnel Oxide Passivated Contacts Solar Cells with Variate Polysilicon Layer Thickness: Gains and Possibilities in Comparison to Screen Printing

Arya

Steinhauser

Gruebel

et al. 2020

Physica Status Solidi (a)

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“…The main findings are in good agreement with other early investigations from our side [ 24 ] and other authors. [ 7,15,28–31 ] The comparison of both pastes for the same polysilicon thickness reveals that paste C forms a lower ohmic contact than paste F at T set = 840 °C firing, but at T set = 870 °C, the opposite holds true.…”

Section: Resultsmentioning

confidence: 99%

Progress in p‐type Tunnel Oxide‐Passivated Contact Solar Cells with Screen‐Printed Contacts

et al. 2021

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Herein, an update on the work on high‐efficiency p‐type solar cells with p‐type‐passivating rear contacts formed by low‐pressure chemical vapor deposition and screen‐printed contacts is given. It is shown that thin polysilicon layers enable a high level of surface passivation but do show increased contact resistivity and especially contact recombination. Commercially available pastes and dependence of contact resistivity and contact recombination on polylayer thickness and firing set temperature are investigated. For 240 nm‐thick poly‐Si layers, the values down to 4 mΩ cm2 and 60 fA cm−2 are observed. For the presented process sequence, improved hydrogenation as one possibility to increase the passivation quality of the passivating contact structure is identified. Implementing all findings into a final solar cell, a maximum total area conversion efficiency of 21.2% is reported.

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“…[2,3] In this way, losses from recombination are suppressed, and excellent recombination current density values below 5 and below 10 fA cm À2 can be achieved, with implied open-circuit voltage (iV oc ) values greater than 730 and 720 mV for the n-and p-type polysilicon, respectively. [4][5][6][7][8][9] Excellent results have been obtained when thick polysilicon layers (%200 nm) are utilized in the passivating stacks, with values of 1-2 mΩ cm 2 for the contact resistivity and 250-20 fA cm À2 for metal-polysilicon recombination current density. [8][9][10][11][12][13] However, excellent passivation and contact properties with thick polysilicon layers come at the expense of absorption losses incurring in the polysilicon layer.…”

Section: Introductionmentioning

confidence: 99%

“…[4][5][6][7][8][9] Excellent results have been obtained when thick polysilicon layers (%200 nm) are utilized in the passivating stacks, with values of 1-2 mΩ cm 2 for the contact resistivity and 250-20 fA cm À2 for metal-polysilicon recombination current density. [8][9][10][11][12][13] However, excellent passivation and contact properties with thick polysilicon layers come at the expense of absorption losses incurring in the polysilicon layer. Passivation and contact properties for polysilicon/SiO x layer stacks with textured silicon substrates were presented by Ciftpinar et al [10] In that work, low-pressure chemical vapor deposition (LPCVD)-based polysilicon layers doped with POCl 3 diffusion (ex situ doping) were used with a thin thermal oxide.…”

Section: Introductionmentioning

confidence: 99%

Influence of Silicon Substrate Surface Finish on the Screen‐Printed Silver Metallization of Polysilicon‐Based Passivating Contacts

Chaudhary

Hoß

Lossen

et al. 2022

Physica Status Solidi (a)

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Passivated contact based on a thin interfacial oxide and a highly doped polysilicon layer has emerged as the next evolutionary step to increase the efficiencies of industrial silicon solar cells. To take maximum advantage from this layer stack, it is vital to limit the losses at the metal polysilicon interface, which can be quantified as metal polysilicon recombination current density (J 0met) and contact resistivity. In cell concepts, wherein a large variety of silicon substrate surface finish can be obtained, it is essential to know how the surface finish affects the J 0met and contact resistivity. Herein, commercially available fire through silver paste and the metal‐polysilicon recombination current densities and contact resistivity are used for three different silicon substrate surface finishes, namely: planar or saw damage etched (SDE), chemically polished in acidic solution and alkaline pyramidal textured. Contact resistivity values below 3 mΩ cm2 with J 0met in order of the recombination current density of the doped region (J 0pass) are obtained for samples with planar surface for both 150 and 200 nm n+ polysilicon layer thicknesses. The results presented in this work show that the samples with flat substrate morphology outperform the samples with textured surfaces.

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Characterization of screen printed and fire-through contacts on LPCVD based passivating contacts in monoPoly™ solar cells

Cited by 30 publications

References 25 publications

Laser Ablation and Ni/Cu Plating Approach for Tunnel Oxide Passivated Contacts Solar Cells with Variate Polysilicon Layer Thickness: Gains and Possibilities in Comparison to Screen Printing

Laser Ablation and Ni/Cu Plating Approach for Tunnel Oxide Passivated Contacts Solar Cells with Variate Polysilicon Layer Thickness: Gains and Possibilities in Comparison to Screen Printing

Progress in p‐type Tunnel Oxide‐Passivated Contact Solar Cells with Screen‐Printed Contacts

Influence of Silicon Substrate Surface Finish on the Screen‐Printed Silver Metallization of Polysilicon‐Based Passivating Contacts

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