Heavily doped polysilicon-contact solar cells

Lindholm, F.A.; Neugroschel, A.; Arienzo, M.; Iles, P. A.

doi:10.1109/edl.1985.26155

Cited by 60 publications

(14 citation statements)

References 5 publications

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“…Doped polycrystalline silicon on silicon oxide (poly-Si/SiO x ) passivating contacts utilize the ultrathin oxide layers to passivate the dangling bonds at the c-Si/SiO x interface − while effectively controlling the carrier population as a consequence of the dopants in the poly-Si films and the diffused regions in the c-Si substrate − and the diffused regions in the c-Si substrate . To further improve the chemical passivation of SiO x , hydrogenation treatment is commonly applied.…”

Section: Introductionmentioning

confidence: 99%

Optimum Hydrogen Injection in Phosphorus-Doped Polysilicon Passivating Contacts

Kang

Sio

Stückelberger

et al. 2021

ACS Appl. Mater. Interfaces

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It has previously been shown that ex situ phosphorus-doped polycrystalline silicon on silicon oxide (poly-Si/SiO x ) passivating contacts can suffer a pronounced surface passivation degradation when subjected to a firing treatment at 800 °C or above. The degradation behavior depends strongly on the processing conditions, such as the dielectric coating layers and the firing temperature. The current work further studies the firing stability of poly-Si contacts and proposes a mechanism for the observed behavior based on the role of hydrogen. Secondary ion mass spectrometry is applied to measure the hydrogen concentration in the poly-Si/SiO x structures after firing at different temperatures and after removing hydrogen by an anneal in nitrogen. While it is known that a certain amount of hydrogen around the interfacial SiO x can be beneficial for passivation, surprisingly, we found that the excess amount of hydrogen can deteriorate the poly-Si passivation and increase the recombination current density parameter J 0. The presence of excess hydrogen is evident in selected poly-Si samples fired with silicon nitride (SiN x ), where the injection of additional hydrogen to the SiO x interlayer leads to further degradation in the J 0, while removing hydrogen fully recovers the surface passivation. In addition, the proposed model explains the dependence of firing stability on the crystallite properties and the doping profile, which determine the effective diffusivity of hydrogen upon firing and hence the amount of hydrogen around the interfacial SiO x after firing.

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Section: Introductionmentioning

confidence: 99%

Optimum Hydrogen Injection in Phosphorus-Doped Polysilicon Passivating Contacts

Kang

Sio

Stückelberger

et al. 2021

ACS Appl. Mater. Interfaces

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“…As already pointed out by Lindholm et al [5], this selective blocking effect would analogously be beneficial for solar cell applications. In solar cells, it is crucial to minimize the current J 0e of majority carriers from the base injected into the emitter, where they become minority carriers and recombine either in the emitter or at the emitter surface.…”

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confidence: 82%

A Simple Model Describing the Symmetric <formula formulatype="inline"><tex Notation="TeX">$I\hbox{--}V$</tex></formula> Characteristics of <formula formulatype="inline"><tex Notation="TeX">$\hbox{p}$</tex></formula> Polycrystalline Si/ <formula formulatype="inline"><tex Notation="TeX">$\hbox{n}$</tex></formula> Monocrystalline Si, and <formula formulatype="inline"> <tex Notation="TeX">$\hbox{n}$</tex></formula>

Peibst

Römer

Hofmann

et al. 2014

IEEE J. Photovoltaics

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We present an analytical model for the current transport in polycrystalline (poly)Si/interfacial oxide/monocrystalline (c)-Si base junctions, which consistently describes the symmetrical behavior of an n + poly-Si emitter/p c-Si base and p + poly-Si emitter/n c-Si base configuration. Our model is focused on a regime within which the current transport is possibly dominated by a flow through oxide pinholes rather than by tunneling. For an emitter region assumed to form underneath the interfacial oxide by diffusion of dopants from the poly-Si into the c-Si, we calculate the minority charge carrier distribution and the resistance implied for majority charge carriers. With reasonable parameters, our model simultaneously reproduces the experimentally observed low emitter saturation current densities and low junction resistances values. Our model provides a plausible explanation for the high current gain observed in p-n-p and n-p-n bipolar transistors featuring a poly-Si emitter. In principle, the obtained correlation between recombination current and series resistance is analogous to the situation in a base region of a solar cell with local rear contacts. Thus, a poly-Si/c-Si junction can be explained within the framework of a classical p-n junction picture for a passivated, locally contacted emitter.

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“…Solar energy is one of the most promising technologies for meeting the world’s ever-growing energy demands, and silicon solar cells currently dominate the photovoltaics (PV) industry at 96% market share . Record high efficiencies in Si PV have been reported using passivating contacts based on polycrystalline silicon on silicon oxide (poly-Si/SiO x ) (26.1%) , and hydrogenated amorphous silicon (a-Si:H) in silicon heterojunction (SHJ) cells (26.6%), , applied to high lifetime, n-Cz monocrystalline wafers. Poly-Si/SiO x contacts chemically passivate the crystalline silicon (c-Si) surface with an ultrathin ∼1.4–2.2 nm layer of SiO x . − This oxide layer is either thin enough to allow for quantum mechanical tunneling − and/or has nanoscale pinholes through which charge carriers can transport from the bulk c-Si into the heavily doped poly-Si contacts. ,,− …”

Section: Introductionmentioning

confidence: 99%

Trap-Assisted Dopant Compensation Prevents Shunting in Poly-Si Passivating Interdigitated Back Contact Silicon Solar Cells

Hartenstein

Stetson

Nemeth

et al. 2021

ACS Appl. Energy Mater.

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Using a trap-assisted compensation model, we explain why polycrystalline Si (poly-Si) passivating contacts are able to achieve low leakage current between the doped fingers of interdigitated back contact (IBC) monocrystalline Si solar cells despite mixing of boron and phosphorus dopants in the isolation region. The fill factor of IBC solar cells is strongly affected by the electrical isolation region between n- and p-type fingers, as this region is critical in minimizing shunting losses. During fabrication of monocrystalline Si solar cells with poly-Si passivating contacts, the intrinsic poly-Si isolation region inevitably gets contaminated with both p- and n-type dopants. Using dopant profiles measured with time-of-flight secondary ion mass spectrometry and scanning probe measurements of the isolation region, we demonstrate that despite the dopant spreading during cell processing, a well-compensated region between the doped fingers exists that prevents shunting. The trap-assisted dopant compensation mechanism significantly widens the compensated region to tens of microns, where the residual dopant densities are below the trap density. This enables a high-resistivity region, resulting in low shunt current. Using one-dimensional (1-D) finite element diode simulations, we identify the design parameters and experimental conditions under which a sufficiently resistive region can form. Our measurements of 2-D local resistivity and work function maps across the isolation region using scanning spreading resistance microscopy and Kelvin probe force microscopy demonstrate the existence of a highly resistive, wide compensated region and confirm our proposed compensation mechanism. For our structures, this region is ∼25 μm in width within a ∼150 μm wide finger isolation region with nearly 3 orders of magnitude higher resistivity than the regions dominated by a single type of dopant.

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Heavily doped polysilicon-contact solar cells

Cited by 60 publications

References 5 publications

Optimum Hydrogen Injection in Phosphorus-Doped Polysilicon Passivating Contacts

Optimum Hydrogen Injection in Phosphorus-Doped Polysilicon Passivating Contacts

Trap-Assisted Dopant Compensation Prevents Shunting in Poly-Si Passivating Interdigitated Back Contact Silicon Solar Cells

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