This document discusses using rapid laser scanning to texture surfaces for applications such as solar cells and military equipment. It demonstrates that laser scanning allows for high flexibility and precision compared to other texturing methods. The document investigates different laser parameters and their effects on texturing mechanisms and performance. Optimal parameters were identified that enhanced light trapping for solar cells through crystalline structures and enabled stealth and thermal functions for military applications.

1. Surface Texturing by rapid scanning of
pulsed laser beam
Di Liu, Matthew Quigley
Advisor: Dr. David Hwang
Annual Student Research Poster
Symposium, May 10, 2013
Department of Mechanical
Engineering
College of Engineering and
Applied Sciences (CEAS)
Surface texturing in micro/nanoscale plays an important role in many application fields
including enhanced light trapping in solar cell, surface anti-icing by super hydrophobicity in
wind turbine and airplane wings, and enhanced convective and radiative heat transfer from
surface. In this study, we demonstrate high flexibility and control precision offered by the
pulsed laser scanning method. Compared with conventional laser-based approach,
nanosecond laser scanning method we tested corresponds to a highly cost-effective and
uniform means for the texturing of arbitrary sample area and shape. Relevant texturing
mechanisms are explained based on advanced characterization by scanning electron
microscope and Raman spectroscopy.
Acknowledgement
Summary
• Rapid laser scanning enabled superior textured surfaces for solar & military applications.
• Detailed texturing mechanisms were investigated in relation to target device performance.
• For solar cell, light trapping was greatly enhanced with optimal crystalline structures.
• For military applications, desired stealth and thermo-fluidic functions were enabled.
*. The research is supported by Yuco optics corp. (Bohemia, NY) through SPIR program, and Advanced Energy
Research and Technology Center (Stony Brook, NY).
*. SEM characterization was performed at the Center for Functional Nanomaterials, Brookhaven National
Laboratory supported by US Department of Energy.
New Approach : Rapid scanning of pulsed laser beam
Conventional surface texturing techniques
By D. Neuhaus et al. (2007)By D. Yong Wu et al. (2007)
By L. Dobrzaǹski et al. (2008) By SiOnyx
Ti c-Si c-Si c-Si
Chemical Wet Etching
• Limited flexibility as
crystalline plane
dictates
Laser Ablative Texturing
• Loose structural: issues
on carrier transport and
limit in current extraction
Ultrafast Laser Texturing
• High laser cost, lack of
arbitrary scale
uniformity
Mechanical Roughing
• Quality limited due
to friction with
abrasive particles
Experimental setup
Effect of laser parameters : 3 representative regimes
Ablation dominant
• Excellent light trapping
• Structural issues
Melting dominant
• Excellent light trapping
• Favorable structures
Mild melting
• Insufficient light trapping
• Low textures
Spectral reflectance data show Performance
of Black Si depending on laser parameters
Silicon surface texturing for enhanced light trapping
Si surface morphology results comparison
*Different optical properties are achieved by different surface texture structures
*Brown Silicon is formed and dominated by ablative phase change
*Shorter wavelength gives smaller scale of spikes and shallower affected depth
Brown Si Black Si
λ=355nm
Super black metal surface texturing by laser scanning
Black Cu SEM image
http://en.wikipedia.org/wiki/F-117_Nighthawk
http://thegundeck.blogspot.com/2011/01/how-
much-for-pentagon.html
Black Silicon for advanced Si solar cells
• Laser-based texturing
• High flexibility and control precision
Light trapping enhancement
Stealth function : minimal reflection
of UV, visible and IR illumination
Enforcing Pool
boiling for improved
heat transfer by
phase change
http://www.81.net/hangkongdongtai/04262301
92013_3.html
http://isnps.unm.edu/research/facilities/
IR image
Cu
Blackbody-like
Thermal Emission
Key Advantages
• Size independent uniformity
• Precision texture control：
active control of unit features
dictated by local melting and
thermo-capillary effect
• Simultaneous annealing for
improved carrier diffusion
• Cost-effective laser solution
Photograph
image
SEM image
• Ablation dominant regime is
superior in light trapping but with
low crystalline quality
• Melting dominant regime show
good light trapping and excellent
crystalline quality
Improved heat transfer and control of
phase change (cooling, anti-freezing)
Transient behavior during laser process
Necessary
ablation
for spikes
formation
Secondary annealing for efficient current extraction
On Laser focus
Off Laser focus
Laser focal position effects on secondary annealing
Extended
laser
beam for
annealing
Cross section Raman
spectroscopy
Anti icing texturing
Non-textured Textured
http://www.gao.pitt.edu/antiicing.html
522cm-1
(Single crystal Si peak)
Black Si
λ=532nm
Raman shift /cm-1
Efficient Current
Extraction
*Good Crystallinity
*Minimal stress
Focused on military and defense applications
Black Cu
Colorized Steel
Reflect specific wavelength