Temperature Effect of Nano-Structure Rebuilding on Removal of DWS mc-Si Marks by Ag/Cu MACE Process and Solar Cell
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2020-09-18 |
| Journal | Energies |
| Authors | Tian Pu, Honglie Shen, Chaofan Zheng, Yajun Xu, Ye Jiang |
| Institutions | Nanjing University of Aeronautics and Astronautics |
| Citations | 6 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research presents a novel, temperature-controlled texturing method for Diamond-Wire Sawn multi-crystalline Silicon (DWS mc-Si) wafers, overcoming the limitations imposed by surface saw marks and amorphous layers.
- Core Problem Solved: Traditional acid texturing fails on DWS mc-Si due to surface damage (saw marks and amorphous silicon); this new method effectively removes these defects while creating anti-reflection structures.
- Dual-Step Process: The technique utilizes Metal-Assisted Chemical Etching (MACE) with a Cu/Ag dual-element catalyst to form initial nanopores, followed by a critical Nano-Structure Rebuilding (NSR) post-treatment.
- Temperature Control: The NSR treatment temperature is the primary control mechanism, dictating the size of the resulting inverted pyramid structures and the overall surface reflectance.
- Optimal Performance: The highest solar cell efficiency achieved was 19.77% (0.54% absolute improvement over the standard baseline), obtained using NSR treatment at 50 °C.
- Optimal Structure: The 50 °C NSR process yielded uniform inverted pyramids with an edge length of 600 nm, providing the best balance between light trapping and minimizing surface recombination.
- Industrial Relevance: The process is demonstrated to be effective for saw-mark removal and texturing simultaneously, making it highly suitable for mass production of high-efficiency DWS mc-Si solar cells.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Peak Solar Cell Efficiency (Eff) | 19.77 | % | Optimized NSR-50 °C cell |
| Short Circuit Current (Isc) | 9.132 | A | Optimized NSR-50 °C cell |
| Open Circuit Voltage (Voc) | 662 | mV | Optimized NSR-50 °C cell |
| Fill Factor (FF) | 80.39 | % | Optimized NSR-50 °C cell |
| Baseline Standard Cell Efficiency | 19.23 | % | Standard acid-textured cell |
| Optimal NSR Treatment Temperature | 50 | °C | Yields 600 nm pyramids |
| Optimal Pyramid Edge Length | 600 | nm | Structure yielding 19.77% efficiency |
| Average Reflectance (400-900 nm) | 16.50 | % | Optimized NSR-50 °C sample |
| Lowest Reflectance (As-etched) | 6.23 | % | After MACE, before NSR treatment |
| Wafer Type | P-Type mc-Si | N/A | DWS substrate |
| Wafer Thickness | 180 ± 10 | ”m | Initial wafer specification |
| MACE Etchant Concentration (HF) | 5.8 | M | Hydrofluoric acid |
| MACE Catalyst Concentration (AgNO3) | 0.06 | mM | Silver nitrate co-catalyst |
Key Methodologies
Section titled âKey MethodologiesâThe process involves a two-step wet chemical treatment: MACE for initial texturing and NSR for structure refinement and defect removal.
-
Initial MACE Etching (180 s):
- Purpose: Form initial nanopore structures and initiate etching through the amorphous layer.
- Solution: Mixed solution of 5.8 M HF and 0.6 M H2O2.
- Catalysts: Dual elements 2.4 mM Cu(NO3)2 and 0.06 mM AgNO3. Silver (Ag) is used in small dosage to accelerate the etching rate of Copper (Cu) at room temperature.
- Result: Rough surface with nanopores and grooves (average reflectance 6.23%).
-
Metal Particle Removal (180 s):
- Solution: Ammonia and H2O2 mixed solution.
-
Nano-Structure Rebuilding (NSR) Treatment (360 s):
- Purpose: Anisotropic etching to convert nanopores into regular inverted pyramids and eliminate saw marks.
- Solution: 2.52 M H2O2 and 0.42 M NaF.
- Temperature Dependence:
- 30 °C: Nanopores enlarge, forming small squares (100-150 nm edge length).
- 40 °C: Pyramidal orientation (<111>) starts appearing at the bottom of shallow pores.
- 50 °C (Optimal): Square pores nearly disappear, forming regular inverted pyramids (600 nm edge length). Saw marks are almost eliminated.
- 60 °C: Pyramids interconnect, surface becomes flatter, and edge length exceeds 900 nm (reflectance increases to 20.46%).
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Solar Cell Fabrication: Standard screen-printed sequence: Phosphorus diffusion, Phosphosilicate Glass (PSG) removal, edge isolation, Anti-Reflection (AR) coating, printing, and firing.
Commercial Applications
Section titled âCommercial ApplicationsâThis technology provides a critical enabling step for the mass production of high-efficiency solar cells utilizing cost-effective DWS wafers.
- Photovoltaic (PV) Industry: Directly applicable to the manufacturing of multi-crystalline silicon solar cells, offering a necessary upgrade path from older MWSS technology.
- DWS Wafer Integration: Facilitates the commercial adoption of diamond-wire sawing by providing a robust texturing solution that handles the inherent surface damage (saw marks and amorphous layers).
- Efficiency Improvement: Enables DWS mc-Si cells to achieve conversion efficiencies (19.77%) competitive with standard cells, improving the overall cost-per-watt metric.
- Surface Engineering: The NSR process is a specialized surface treatment for defect removal and controlled nanostructure formation, potentially adaptable for other semiconductor surface passivation requirements.
- Advanced Cell Architectures: The inverted pyramid structure is beneficial for light trapping, and the methodology could be transferred to mono-crystalline PERC processes to reduce surface recombination at pyramid cusps.
View Original Abstract
The absence of an effective texturing technique for diamond-wire sawn multi-crystalline silicon (DWS mc-Si) solar cells has hindered commercial upgrading from traditional multi-wire slurry sawn silicon (MWSS mc-Si) solar cells. In this work, we present a novel method for the removal of diamond-wire-sawn marks in a multi-crystalline silicon wafer based on metal assisted chemical etching process with Cu/Ag dual elements and nano-structure rebuilding (NSR) treatment to make a uniform inverted pyramid textured structure. The temperature effect of NSR solution was systematically analyzed. It was found that the size of the inverted pyramid structure and the reflectance became larger with the increase of the NSR treatment temperature. Furthermore, the prepared unique inverted pyramid structure not only benefited light trapping, but also effectively removed the saw-marks of the wafer at the same time. The highest efficiency of 19.77% was obtained in solar cells with an inverted pyramid structure (edge length of 600 nm) fabricated by NSR treatment at 50 °C for 360 s, while its average reflectance was 16.50% at a 400-900 nm wavelength range.
Tech Support
Section titled âTech SupportâOriginal Source
Section titled âOriginal SourceâReferences
Section titled âReferencesâ- 2005 - Multicrystalline silicon for solar cells [Crossref]
- 2018 - Solar cell efficiency tables (version 52) [Crossref]
- 2010 - Characterization of polycrystalline silicon wafers for solar cells sliced with novel fixed-abrasive wire [Crossref]
- 2012 - Textural development of SiC and diamond wire sawed sc-silicon wafer [Crossref]
- 2004 - Fixed abrasive diamond wire saw slicing of single-crystal silicon carbide wafers [Crossref]
- 2014 - Comparison of diamond wire cut and silicon carbide slurry processed silicon wafer surfaces after acidic texturisation [Crossref]
- 2005 - Etch stop of silicon surface induced by tribo-nanolithography [Crossref]
- 2019 - Cylindrically focused nonablative femtosecond laser processing of long-range uniform periodic surface structures with tunable diffraction efficiency [Crossref]
- 2010 - Anti-reflecting and photonic nanostructures [Crossref]
- 2018 - Formation mechanism of inverted pyramid from sub-micro to micro scale on c-Si surface by metal assisted chemical etching temperature [Crossref]