Temperature Effect of Nano-Structure Rebuilding on Removal of DWS mc-Si Marks by Ag/Cu MACE Process and Solar Cell

At a Glance

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

Technical Documentation & Analysis: Advanced Surface Texturing via MACE-NSR

Executive Summary

This research demonstrates a highly effective, industrially scalable method for preparing diamond-wire sawn multi-crystalline silicon (DWS mc-Si) wafers, overcoming traditional texturing challenges associated with saw marks and amorphous layers.

Problem Solved: Traditional acid texturing fails on DWS mc-Si due to surface damage (saw marks, amorphous silicon). The MACE-NSR process successfully eliminates these defects.
Core Methodology: A two-step process involving Metal Assisted Chemical Etching (MACE) using a Cu/Ag dual catalyst system, followed by Nano-Structure Rebuilding (NSR) treatment.
Optimal Structure: The NSR treatment at 50 °C for 360 s created uniform inverted pyramid structures with an edge length of 600 nm.
Performance Achievement: This optimized structure yielded a solar cell conversion efficiency of 19.77%, surpassing the standard cell efficiency (19.23%) by 0.54%.
Optical Performance: The optimal wafer achieved an average reflectance of 16.50% across the critical 400-900 nm wavelength range.
Material Relevance: The success hinges on precise control over nanoscale surface morphology and chemical processing, skills directly transferable to advanced diamond substrate preparation for high-power and quantum applications.

Technical Specifications

The following hard data points were extracted from the research, highlighting the optimized parameters and resulting performance metrics.

Parameter	Value	Unit	Context
Substrate Type	P-Type DWS mc-Si	N/A	Wafer thickness 180 ± 10 µm
Resistivity	1-3	Ω·cm	Wafer material specification
Optimal NSR Temperature	50	°C	Yielded highest efficiency
Optimal NSR Time	360	s	Yielded highest efficiency
Highest Efficiency (Eff)	19.77	%	Achieved with NSR-50 °C
Short Circuit Current (Isc)	9.132	A	Highest Isc value (NSR-50 °C)
Open Circuit Voltage (Voc)	662	mV	Highest Voc value (NSR-50 °C)
Optimal Reflectance (Average)	16.50	%	400-900 nm range (NSR-50 °C)
Inverted Pyramid Edge Length	600	nm	Optimal structure size (NSR-50 °C)
MACE Etching Time	180	s	Cu/Ag co-assisted etching step

Key Methodologies

The novel texturing process relies on two distinct chemical etching steps to achieve the desired inverted pyramid morphology and defect removal.

MACE Etching (Nanopore Formation):
- Duration: 180 s.
- Solution Composition: Mixed solution of 5.8 M HF (Hydrofluoric Acid) and 0.6 M H₂O₂ (Hydrogen Peroxide).
- Catalysts: 2.4 mM Cu(NO₃)₂ and 0.06 mM AgNO₃ (Copper and Silver dual elements).
- Result: Formation of nanopore structures and groove-like features, achieving low initial reflectance (< 6.23%).
Metal Particle Removal:
- Duration: 180 s.
- Solution: Ammonia and H₂O₂ mixed solution.
- Purpose: Removal of residual metal particles (Cu/Ag) from the wafer surface.
Nano-Structure Rebuilding (NSR) Treatment:
- Duration: 360 s.
- Solution Composition: 2.52 M H₂O₂ and 0.42 M NaF.
- Mechanism: Anisotropic etching mechanism, preferentially etching <100> orientation faster than <111> orientation.
- Temperature Dependence: Temperature was the critical factor controlling pyramid size and reflectance:
  - 30 °C: Square pores (100-150 nm edge length).
  - 50 °C (Optimal): Regular inverted pyramids (600 nm edge length), saw marks eliminated.
  - 60 °C: Interconnected, larger pyramids (> 900 nm edge length), resulting in higher reflectance (20.46%).
Solar Cell Fabrication:
- Steps: Phosphorus diffusion, Phosphosilicate Glass (PSG) removal, edge isolation, Anti-Reflection (AR) coating, printing, and firing.

6CCVD Solutions & Capabilities

The research highlights the critical need for precise surface engineering and controlled chemical processing to maximize device performance. While this study focused on silicon PV, 6CCVD specializes in high-purity MPCVD diamond, which is essential for next-generation high-power electronics, quantum sensing, and advanced optical systems—all applications demanding similar, or even stricter, surface control and material customization.

Applicable Materials for Advanced Research

6CCVD offers materials that enable research requiring extreme surface quality, high thermal conductivity, and electrochemical stability, directly supporting projects that utilize MACE-like processes or require advanced surface preparation.

6CCVD Material	Relevance to Research Extension	Key Features
Boron-Doped Diamond (BDD)	Excellent electrode material for electrochemical etching (like MACE) and high-power applications. Can be textured or polished to specific roughness.	High conductivity, extreme chemical inertness, wide electrochemical window.
Optical Grade Single Crystal Diamond (SCD)	Required for high-power optics or quantum applications where surface defects (like saw marks) must be eliminated to achieve Ra < 1 nm.	Ultra-low defect density, superior thermal management, exceptional transparency.
Polycrystalline Diamond (PCD) Substrates	Ideal for large-area heat spreading or high-frequency electronics requiring custom metalization schemes.	Custom dimensions up to 125 mm, high thermal conductivity (up to 2000 W/mK).

Customization Potential for Surface Engineering

The paper required precise control over surface morphology (600 nm inverted pyramids) and subsequent metal contact deposition. 6CCVD’s in-house capabilities ensure that researchers can obtain diamond substrates tailored exactly to their experimental needs.

Custom Dimensions: While the paper used 156.75 mm² wafers, 6CCVD provides custom plates and wafers in both SCD (up to 10x10 mm) and PCD (up to 125 mm diameter), ensuring compatibility with industrial scaling efforts.
Surface Finish: The ability to eliminate saw marks is analogous to the need for ultra-smooth surfaces in diamond. 6CCVD guarantees polishing down to Ra < 1 nm for SCD and Ra < 5 nm for inch-size PCD, critical for minimizing surface recombination and maximizing optical performance.
Integrated Metalization: The solar cell fabrication required phosphorus diffusion and contact printing. 6CCVD offers internal metalization services, including the deposition of common contact layers (Au, Pt, Pd, Ti, W, Cu), allowing researchers to receive ready-to-use substrates with pre-patterned contacts for subsequent device integration.

Engineering Support

The successful optimization of the NSR process required systematic analysis of temperature effects on morphology and efficiency. 6CCVD’s in-house PhD team provides expert consultation on material selection and surface preparation techniques for projects involving:

High-Precision Surface Modification: Assisting with material selection for projects requiring nanoscale texturing, etching, or specific crystallographic orientation control (e.g., for NV center creation in SCD).
Thermal Management Integration: Designing diamond heat spreaders for high-efficiency devices (like the mono PERC cells mentioned in the paper’s future work section) to manage the heat generated by high current densities (Isc up to 9.132 A).
Electrochemical Applications: Providing optimized BDD substrates for advanced electrochemical sensing or etching processes, leveraging BDD’s stability in harsh chemical environments (like HF/H₂O₂ mixtures).

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

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

Original Source

DOI: https://doi.org/10.3390/en13184890

References

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