1. In2Se3 Nanowire Growth and
Physical Characterization for
Photovoltaic Use
Anna Dubovitskaya
North Carolina School of Science and Mathematics

2. Introduction: Why Nanowires?
The interest in the use of nanowires for photovoltaic cells
stems from their unique properties:
• Higher efficiencies due to increased absorption
• Higher tolerance for defects
• Shorter diffusion lengths, which reduce trapping or recombination
of photoexcited charge carriers
• Nanowires of the same high crystalline quality and excellent charge
transport as bulk/thin films can be made at a lower cost
• Better resistance to photodegradation compared to existing
photovoltaics.

3. Goals and Hypothesis
The objective for this project was to grow In2Se3 nanowires
and document the parameter ranges for optimal growth.
Hypothesis: there exist nanowire growth parameters that
produce ideal or near-ideal nanowires suitable for further
characterization.

4. Method: Growing Nanowires
We used the vapor-liquid-solid (VLS) method:
1. supersaturate a substrate with vaporized In2Se3 powder
2. Gold catalyzes the growth
3. Solid deposition results in nanowire growth
The following diagram shows this process with silicon nanowires:
Garnett et al. Nanowire Solar Cells

5. Method: Growing Nanowires
The ideal temperature and atomic percentage parameter for nanowire
growth can be approximated using a binary phase diagram, where the
shaded area represents ideal silicon nanowire growth:
Garnett et al. Nanowire Solar Cells

6. Procedure
The nanowires were grown using In2Se3 powder (mixed with
graphite in some experiments)
1. Silicon substrates cleaned using RCA-1
2. Poly-l-lysine solution, left for 10 minutes (positive surface)
3. Rinsed with deionized water and dried.
4. Nanoparticles (10-50nm) placed on wafer
5. Horizontal tube furnace
• Temperature
• Pressure
• Ratio
6. Analyzed with SEM and EDX

7. Procedure: Horizontal Tube Furnace
The growth of the nanowires occurred in a horizontal tube furnace:
• A controlled atmosphere:
• Evacuate the tube furnace to 1x10-3 torr
• Backfill with Argon to the growth pressure
• gas flow is controlled with a mass flow controller,
• constant pressure is maintained by a throttle valve connected to a
capacitance manometer.

8. Best Results
Figures 3&4: Domain sectioning [Same as
Figure 2]
Figure 1: Graphite addition.
Figure 2: The first instance
There is clear forest-like axial
of uniform, nonradial
growth, with some branched
nanowire growth seen in
growth as well [Powder
the project [Powder
Temperature 900°C; Substrate
Temperature 900°C;
Temperature 528.7-165.9°C;
Substrate Temperature
Pressure 0.85 Torr; Flow Rate
650-400°C; Pressure 1.50
60 SCCM; Time 4 Hours]
Torr; Flow Rate 50 SCCM;
Time 0.5 Hours]

9. Best Results
Figure 6: Same substrate as Figure 5, but
a different temperature zone. The
growth direction is more random and
the domains seen in Figures 3&4 are
absent [Same as Figure 2]
Figure 5: This is the best result, with
crystalline growth and uniform
dimensionality [Powder Temperature
900°C; Substrate Temperature 650-400°C;
Pressure 1.50 Torr; Flow Rate 50 SCCM;
Time 0.5 Hours]

10. Best Results: EDX
The previous results showed SEM images of the best results. For figure
5, the EDX analysis graph is below:
This shows In:Se ratios of around 1:1 or 3:4

11. Conclusions
It was found that the ideal parameters include:
• Pressure: 1.0~1.5 torr
• Flow rate: 27~40 SCCM
• higher flow rates can impede the pressure, placing a limit on it
due to the pump’s inability to deal with the flow rate of the
incoming gas
• Substrate Temperature: 640°C
• manipulation of the Furnace Distance vs Temperature graph.
• Powder Temperature: 825°C
• Gold Particle Diameter : 50nm
• double coating.

12. Conclusions: Observations
The following additional observations were made:
• Graphite addition does not have as much impact as first thought
with regard to NW growth
• Figure 5, the most ideal out of the 6 figures, had nanowire diameter
ranges from 45-55nm using 50nm gold nanoparticle catalysts
• Ordered nanowires (the opposite of the sectioning effect in Figure 4)
may be better for light trapping
• EDX results for Figures 2-6 showed no leftover presence of gold
nanoparticles, which may indicate non-VLS growth
• High powder temperatures result in increased uncontrollable
deposition (2D growth) as well as deposition before the start of the
attempt
• Using gold particles that are spatially far apart or small in size results
in greater 2D excess deposition

13. Future Work
Having physically characterized the In2Se3 nanowires, the
next step will be to optically characterize them.
Since these nanowires were made with the intention of
use in photovoltaic solar cells, their optical properties are
crucial in determining their usefulness and maximum
efficiency.
In particular, we want to test the time it takes for
recombination of electron-hole pairs, and the absorption
efficiency of In2Se3 nanowires.

14. Acknowledgements
Dr. Jonathan Bennett
Department of Physics
North Carolina School of Science and Mathematics
Dr. Todd Roberts
Chancellor
North Carolina School of Science and Math
Dr. Marvin Wu,
Department of Physics
North Carolina Central University
Funding provided by: NCSSM Foundation Summer Physical
Science Research Program, National Science
Foundation, National Aeronautics and Space
Administration