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2021B1761

BL19B2In-situ X-ray Powder Diffraction of Electrodeposited n- type Cu2O and p-typeCu2O to Identify Phase Transformations and Thermal Expansion
K. M. D. C. Jayathilaka a, L. S. R. Kumara b, C. Dewasiri c, O. Seo b, R. Wijesundera a and S. Jayanetti daUniversity of Kelaniya, b JASRI, c Infinics Pvt. Ltd., d University of Colombon-type and p-type Cu2O films were electrochemically deposited on a Ti substrate in an acetate bath andlactate bath respectively. In-situ x-ray powder diffraction of electrodeposited n- type Cu2O and p-type Cu2O
clearly shows same crystal orientation at room temperature and similar behaviour up to 400 ℃. At 450 ℃
n-Cu2O completely converted to the CuO and p-Cu2O partially converted to the CuO.

Keywords: Cuprous Oxide, Electrodeposition, In-situ x-ray powder diffraction
Introduction
The increasing global demand for energy, limited fossil fuel supplies on the planet and global climate changes
due to greenhouse gas emissions from fossil fuel burning have made it necessary to use renewable, clean energy
sources as energy alternatives. Among the various technologies available, photovoltaics is considered one of thecleanest ways to achieve this objective. However, the difficult task of solar cell manufacturers is to reduce
production costs in relation to the resulting output power of the solar modules with a view to enhance theirmarketability and use. In order to solve this problem, a number of materials are being studied for their use inapplications based on solar energy. Among them, recent studies show that cuprous oxide (Cu2O) has become akey candidate as it has the potential to meet global demand for electricity and reduce photovoltaic costs comparedto other materials [1].
One of the main challenges for the production of Cu2O-based solar cell devices is to fabricate Cu2O p-nhomojunctions. Since the homojunction should not present any interfacial deformation resulting from the latticemismatch between p-type and n-type materials, the separation of photoinduced charges in the Cu2O
homojunction can be considerably improved, hence improving the photoelectric conversion performance [2].
However, research on the fabrication of Cu2O homojunctions is insufficient to date due to the lack of studies onthe production of n-type Cu2O films. Since the demonstration of the growth of n-type Cu2O films using theelectrodeposition method by our laboratory [3] several other methods have been reported on preparation of ntype Cu2O films on various substrates. One way to enhance the efficiency is to improve the quality of the n-type
and p-type surface and interface of the p-n junction. In this experiment thermal behavior of structural propertiesof individual films were examined.
Experimentn-type Cu2O films were electrochemically deposited on a Ti substrate in an aqueous solution containing 0.01 M
copper acetate and 0.1 M sodium acetate at solution pH of 6.2, a deposition potential of -200 mV vs. Saturated
Calomel Electrode (SCE) and at a temperature of 60 ℃. p-Cu2O films were deposited on Ti substrates in an
aqueous solution containing 0.4 M copper sulfate and 3 M sodium lactate at a solution pH of 11, the deposition
potential of -450 mV vs. SCE and at a temperature of 60 ℃. In order to perform powder XRD, electrodeposited
sulfur treated Cu2O thin films were pealed off from Ti substrates and filled in to Lindemann glass capillary tubesof 0.3 mm internal diameter. Diffraction data of powdered samples were obtained using 25 keV photon energyX rays of wavelength around 0.49592 Å. An XRD peak that was absent in previously reported laboratory XRD
patterns could be observed using the powder XRD experiments. Thermal stablility of Cu2O samples wereinvestigated using in-situ X-ray powder diffraction with low signal to noise ratio and low background in thescattering angle range from 2 to 85 degree using MYTHEN detectors installed in the two-axis diffractometer atBL19B2.
Results
Figure 1 shows the in-situ powder XRD patterns of electrodeposited (a) n-Cu2O thin films prepared at pH 6.2
in the acetate bath (b) electrodeposited p-Cu2O thin films prepared at pH 11 in the lactate bath.

(a)

(b)

Figure 1 In-situ powder XRD patterns of electrodeposited (a) n-Cu2O thin films prepared at pH 6.2 in theacetate bath (b) electrodeposited p-Cu2O thin films prepared at pH 11 in the lactate bath.
Laboratory XRD was not sensitive enough to detect possible formation of phases such as CuxO and small
variation of crystallinity due to annealing. On the other hand, as shown in figure 1 the use of synchrotron powder
XRD can divulge more accurate structural information due to high-energy beam with high flux as well as highcounting statistics from little amount of powder sample.
In figure 1, in-situ powder XRD of electrodeposited n- type Cu2O and p-type Cu2O clearly shows same crystal
orientation at room temperature and show that several CuO peaks have evolved after annealing at 300 ℃ due tothe oxidation of Cu2O into CuO phase with similar behavior up to 400 ℃. At 450 ℃ n-Cu2O completely
converted to the CuO and p-Cu2O partially converted to the CuO.
Next Step
We will obtain crystal structure information such lattice parameters and unit cell volume of n-Cu2O and p-Cu2O
using FullProf suit under the Rietveld refinement method for a Pseudo-Voigt function.
References[1] C. Wadiya, A. P. Alivisatos, D. M. Kammen, Environ. Sci. Technol. 43, 2072-2077 (2009).
[2] A. Baltakesmez, S. Tekmen, S. Tüzemen, J. Appl. Phys. 110, 054502 (2011).
[3] W. Siripala, J. R. P. Jayakody, Sol. Energy Mater. 14, 23-27 (1986).