Transcript MRS POster - Tufts University

Wet Chemistry Based Copper Oxide and Zinc Oxide Nanowire
Photovoltaic Cells
S. MacNaughton1, D. F. DeMeo2, Sameer Sonkusale1, Thomas E. Vandervelde2
Nanoscale Integrated Circuits and Sensors Laboratory,
2Renewable Energy and Applied Photonics Laboratory
ECE department, Tufts University, Medford, MA, USA
1
Abstract
Fabrication
Band Structure
Results
Solar cells are a promising, green energy source; however,
cost and efficiency limitations prevent widespread
adoption. We propose a solar cell design that is costeffective both in production and materials. Here, the
junction is made of copper (I) oxide and zinc oxide, which
are oxides of earth-abundant metals. Furthermore, we
utilize a wet chemistry fabrication process, making the
production of such cells inexpensive and easily scalable.
The process involves growing copper nanowires,
depositing zinc, oxidizing, and depositing a top contact,
detailed in the fabrication section. This is a greener
manufacturing method of solar cells where no harmful
compounds or excessive energy is used in fabrication.
Currently results are pending.
Right: Copper
nanowire growth is
successful and
consistant
Band diagram of the
pn junction between
ZnO and CuO
Left: Zinc on copper
nanowires
Right: EDS showing the presence
of both zinc and copper
Nanowire, earth abundant oxide solar cells offer
several advantages over traditional bulk silicon:
Top View
 Inexpensive materials - copper, zinc and their oxides
are earth-abundant and easily refined elements and
molecules.
 Inexpensive fabrication - the electrochemical
fabrication techniques presented here are used
extensively in industry due to their ease of operation
and cost-effectiveness at all scales of production.
 Hot carrier conversion - the nanowire arrangement of
this cell allows for more energy to be harvested from
each photon absorbed.
 Increased absorption - the nanowires create a dark
surface which improves absorption in the cell.
Thermal
oxidation causes
interdiffusion
across the Cu/Zn
boundary.
Therefore ZnO is
directly
electroplated
onto the copper
oxide nanowires.
Zn evaporated
onto CuO
nanowires
Thermalization of hot carrier
Much progress has been made on
developing the process to fabricate these
solar cells.
The largest difficulty is to
overcome short circuiting the layers when
depositing the top contact. As can be seen
we see a diode response before the top
contact layer is applied, however once the
top contact is in place the cell only exhibits a
resistive response.
Future work includes further testing and
fabrication to obtain a working sample.
There is also much work to be done in
optimizing each layer. The ITO transparent
conducting oxide can be optimized for
increased transmittance and conductance.
We eventually hope to replace this with a
cheaper, more abundant TCO such as TiO2
or ZnO.
References
Results
Although the nanowire geometry will suffer from a decreased quantum efficiency due
to the spacing between the individual wires, it will be able to convert more energy
from each incident photon that strikes the active area. This is called harvesting hot
carriers. A hot carrier is a photon with an energy above the band gap of the material.
Normally these will be absorbed and the excess energy above the band gap will be
lost thermally, but with the decreased distance to the contacts in the nanowire
geometry more of this excess energy will be converted into electricity.
The actual material is a mix of CuO and Cu2O
Conclusion
Motivation and Significance
Comparison to traditional Si solar cell
Band diagram of the
pn junction between
ZnO and Cu2O
Rakhshani, A.E., Preparation, characteristics and photovoltaic
properties of cuprous oxide--a review. Solid-State Electronics,
1986. 29(1): p. 7-17.
An early sample of the nanowire cell.
McKubre, M.C.H. and D.D. Macdonald, The Dissolution and
Passivation of Zinc in Concentrated Aqueous Hydroxide.
Journal of the Electrochemical Society, 1981. 128(3): p. 524530.
C. Wadia, A. P. Alivisatos, and D. M. Kammen, "Materials
Availability Expands the Opportunity for Large-Scale
Photovoltaics Deployment," Environmental Science &
Technology, vol. 43, pp. 2072-2077, Mar 15 2009.
• Entire cell is less than 15μm thick.
• Cell weighs ≈15mg/cm2
• Material costs are <$1USD per m2
http://nanolab.ece.tufts.edu/
S. Ishizuka, K. Suzuki, Y. Okamoto, M. Yanagita, T. Sakurai, K.
Akimoto, N. Fujiwara, H. Kobayashi, K. Matsubara, and S. Niki,
"Polycrystalline n-ZnO/p-Cu2O heterojunctions grown by RFmagnetron sputtering," physica status solidi (c), vol. 1, pp.
1067-1070, 2004.
IV curve of Flat cell on glass
Contact: [email protected]
http://reap.ece.tufts.edu