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Results for “nanopinholes”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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5 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

High-Performance Passivating Contacts for Si PV Based on Engineered, Doped Nanopinholes through Dielectric Layers

We present a novel, industrially relevant method to fabricate high-performance poly-Si passivating contacts for Si PV. Passivating contacts based on SiOx/poly-Si layer stacks have been implemented in record-efficiency homojunction Si solar cells. In this technology, the carrier transport through a surface-passivating SiOx is enabled either by quantum-tunneling or nanopinholes. The doped poly-Si layer provides charge-carrier selectivity. Previously, the ISFH research group demonstrated a record 26.1% efficient Si homojunction cell, where transport pinholes in ~2 nm SiOx were produced by thermal breakdown at > 1000 degrees C, which is hard to control and is surface morphology-dependent. At room temperature, our new process uses electroless plating of Ag nanoparticles, followed by metal-assisted chemical etching. Nanogalvanic corrosion yields < 20 nm-wide nanopinholes in an insulating > 2 nm SiOx layer. The nanopinholes are filled by a heavily doped a-Si:H overlayer. We drive in the dopants into the Si wafer with subsequent high-temperature annealing. Preferential incorporation of dopants at pinhole locations results in nanoscale p+/n or n+/n junctions near the wafer interface. Each heavily-doped nanoscale pinhole junction collects and transports photogenerated carriers to the cell metal contacts. The density of the engineered nanopinholes can be tuned over a wide range which is critical for optimization of device performance. The same nanogalvanic corrosion principles can be applied to produce doped transport pinholes in well-passivating thick dielectric SiOx/SiNy stacks. Importantly, our process does not rely on thermal breakdown of the dielectric layers and can be applied to textured wafers resulting in Si solar cells with > 20% conversion efficiency.

dielectric layer↗
DOE OSTI2025

Nanopinhole-Enabled, Hole-Selective Poly-Si/SioxNy Passivating Contacts on Textured c-Si for Si Solar Cells

The next-generation silicon photovoltaics will be based on passivating electron- and hole-selective contacts with both very low interface recombination and contact resistivities. While the emerging mainstream TOPCon technology has developed excellent electron-selective poly-Si/tunneling SiOx contacts, hole-selective contacts, especially on textured surfaces, have remained a significant challenge. This contribution introduces novel high-performance hole selective poly-Si contacts on pyramid-textured Si, enabled by electrochemically produced hole transport nanopinholes in a 10 nm oxynitride passivating dielectric stack capped by p+ poly-Si. The highly passivating oxynitride layer is produced via atomic intermixing of O and N atoms in the initial SiOx/SiNy layer stack upon thermal annealing. Carrier transport is governed by nanopinhole density and size are tuned by Ag nanoparticle electrodeposition and surface attachment chemistries. This results in passivating hole contact resistivities in the m..omega..-cm2 range, while preserving interface recombination current prefactor around 5 fA/cm2.

14 SOLAR ENERGY↗
DOE OSTI2025

Self‐Assembled Monolayer Templating for Engineered Nanopinholes in Passivated Contact Solar Cells

We present a novel self-assembled monolayer (SAM)-based technique to make nanopinhole-enabled passivated contacts on silicon solar cells by tuning the SAM coverage area and etch selectivity. We deposit trimethyl-silyl Si(CH 3 ) 3 groups using hexamethyldisilazane (HMDS) as the precursor over passivating dielectric layers and their stacks (SiO 2 , SiN x , SiO 2 /SiN x ) and interrupt the HMDS attachment chemistry shortly before a full monolayer is formed on its surface. Subsequent etching in dilute HF produces pinholes through the dielectric layers due to the higher etch resistance of the SAM to HF etching. The pinhole areal density (10 4 –10 8 /cm 2 ) and size (10–1000 nm) can be tuned both by duration of HMDS attachment and HF etch time. Pinholes were characterized by atomic force microscopy, tetramethylammonium hydroxide (TMAH) selective etch, and Ag decoration by electroless plating. Polysilicon (poly-Si) passivated contacts enabled by pinholes were formed by subsequent deposition of doped amorphous silicon (a-Si:H) followed by thermal crystallization and dopant drive-in. At optimal areal pinhole density ≈10 7 /cm 2 , contacts exhibit both passivation and carrier transport via pinholes as evidenced by electron beam induced current, transmission line measurements, and carrier lifetime measurements. Solar cells based with these pinhole contacts show V oc = 723 mV and FF = 80.3%. The remaining SAM layer does not affect device performance.

14 SOLAR ENERGY↗
DOE OSTI2023

Nanopinhole Passivating Contact Si Solar Cells Fabricated with Metal-Assisted Chemical Etching

Monocrystalline Si (c-Si) solar cells with passivating contacts based on doped polycrystalline Si (poly-Si) on ≈2.0 nm silicon oxide (SiO x ) require >1000 °C thermal processing to create conducting pinholes in the SiO x layer. However, this high thermal budget can induce bulk defects in the Czochralski c-Si wafers used as the cell absorber layer. We demonstrate that pinholes can instead be created using metal-assisted chemical etching on planar or textured morphologies, at room temperature. This wet process creates up to 200 nm wide conducting pinholes that are directly observed with transmission electron and atomic force microscopies. High-performance hole-selective poly-Si/SiN y /SiO x and electron-selective poly-Si/SiO x passivating contacts are fabricated and implemented in laboratory-scale solar cells. This process development significantly broadens the range of passivation layer materials, their thicknesses, and surface morphologies, which enables the design of poly-Si contacts with superior passivating quality.

14 SOLAR ENERGY↗