Synthesis and Characterization of )CeO(x-) CuO(1-x Nanocomposite by Simple Aqueous Route for Solar Cell Application

This work concludes the synthesis of CeO-CuO nanocomposite by one-pot preparation method using three different molar ratios. The resulted nanocomposite was characterized using UV-Vis, XRD, SEM, EDX and TEM and the results show that this nanocomposite was found as spherical-like nanoparticles with high purity and the average particle size is in the range of 10-20 nm.. Furthermore, this nanocomposite was used in the solar cell application as photo anode and the results showed that the eciency increase with increase of (x) content in the (CuO)x–(CeO 2 )1-x.


Introduction
In addition to specifying the comprehensive applications of binary metallic oxide powders or lms like ZnO-CeO 2 , CeO 2 -TiO 2 and NiCuO2, the design and synthesis have recently continued to attract interest from both academia and industry [1][2][3][4][5][6][7][8]. A mixture comprising two stages with a different chemical composition is part of the binary material analysis. From both realistic and fundamental viewpoints, this has received a lot of attention. The combination of the physical properties of such materials will lead to the creation of the desired response material. The magnetic or optical features can be different if the particle size is reduced to very small dimensions. The interest in the binary oxide region has grown considerably. Binary materials are of outstanding quality including high melting points, high hardness, low temperature coe cients, low density, high stability of chemicals, high thermal conductivity, high expansion, as well as better mechanical qualities such as increasing resistance to wear, high speci c resistance and special modulus. [9][10][11][12][13][14][15]. The intense interactions between the binary oxide systems and intimately packaged nanoparticles on the surface are widely recognized as not just an easy overlap of the properties of the individual components with the characteristics of the binary materials obtained. The goal of the synthesis of multi-component materials was therefore to combine the developments of different stages so that their applications could be improved and further extended. A type of metal oxide semiconductor is copper oxide (CuO), that is narrow energy gap (1.2 eV) [16]. Due to its broad use in gas sensors and as a catalyst and optoelectronic components [17,18], A lot of attention has been drawn.
Cerium oxide of rare earth (CeO2) is an n-type metal semiconductor with a wide band gap (3.0-3.2 eV) [19] and a wide band gap. In other areas, as catalysts, ultraviolet lters and mechanical and chemical polishing there are also various applications [20,21]. In different new applications of the material sciences, a mixture of p-type and n-type metal oxide semiconductors may be used. CuO-TiO 2 , SnO 2 -NiO and CuO-SnO 2 can be prepared in different presses for the various forms of composite semiconductor oxides. As CuO-CeO2 is more commonly used in catalysis, water gas shifts and solid oxide-powered cell (SOFC) [22], the semiconductor binary oxide nanomaterials have become very interested. Binary metal oxide nanomaterials will typically boost these functions in comparison with their elements. In order to create a compound which has the ideal properties, the researchers have de ned and developed CuO-CeO2 with various structural features, in order to make the combined bene ts of two compounds. To synthesize CuO-CeO 2 nanomaterial, various techniques such as sono-chemical, hydrothermal, mechano-chemical and solvo-thermal methods have been used [23][24][25]. However, due to the related complex procedures, most of these approaches present di culties with their use in industrial development, leading to many reaction conditions like severe reaction conditions. Another downside to the technologies is the toxic by-product/toxic reagent that release during the synthesis process. New aspect of the current research is that the approach can have many bene ts over the above approaches, some of which are brie y summarized: the production can be achieved without any harmful pollutants, highly adaptable and easy to use in many high-purity applications.

Materials
Cerium nitrate Ce(NO 3 ) 2 .6H 2 O (99%) and Copper nitrate Cu(NO 3 ) 2 .3H 2 O (99%) were used as a precursors materials without any puri cation steps, purchased from Sigma-Aldrich. The following materials were purchase from Fluka; sodium hydroxide and ammonia to complete the reaction in addition to the stabilizer, urea was used to simplify the dispersal of nanoparticles.

Preparation of binary metal oxides
Different molar ratios from cerium nitrate and copper nitrate (0.25, 0.5, 0.75) were dissolved in 40 ml of deionized water separately then sodium hydroxide was added drop by drop to copper nitrate under stirring at 50C o with 1:2 ratio and ammonia was dropped to cerium nitrate under 1200 rpm stirrer speed.
After that 5 g from urea was dissolved in 50 ml of de-ionized water and added to the mixture solutions under stirring at 60C o until blush brown suspension was formed. The mixture of metals oxide washed two times for distilled water and ethanol then the powder was separated by centrifuge, then dried in the oven at 90 C o for 5h. The mixture was calcinated at 400C o for half an hour to get dark brown color product.

Fabricated solar cell
Two types of substrate were used in this research to fabricate solar cell: 1. ITO glass (indium tin oxide) cutted into 2*2 cm 2 clean rstly in sonicator for 15 minutes with deionized water, then used ethanol purity 99% in sonicated for 10 minutes 2. Single crystal Si P-type wafer, the thickness 300 µm with an (100) orientation and resistivity ~0.4 (Ω. Cm). The wafer cut into 2*2 cm 2 , chemical etching was done to get rid from impurities, immerse the pieces of silicon wafer in HF acid concentration 10% for 5 minutes, after that clean with distilled water and ethanol then dry with blower.
To produce (CuO)x-(CeO 2 )1-x photo anode, drop cast technique used deposited thin lms of this binary metallic oxide on substrate by used Blade method. 0.1 g (CuO)x-(CeO 2 )1-x powder was mixed with 5 ml of absolute ethanol under ultrasonic for 3 minutes in order to obtain thick solution nanoparticles. The resulted thick solution was applied on a conductive side of ITO glass, then heated the samples at 100 o for an hour to ensure good adhesion the binary metallic oxide nanoparticles with the substrate while heated at 200 o for two hours for samples with silicon wafer substrate. When deposited (CuO)x-(CeO 2 )1-x powder nano particles by spin coating technique [26].
For the purpose of electrical connection with other devices, Al electrode as a back contact curried out using thermal evaporation coating unit Edward (model E306A) evacuated of 6*10 -5 Torr, aluminum foil with purity 99% put in tungsten boat done at room temperature with thickness a round 300 nm.  Optical absorbance and transmittance measurement were conducted for all samples in order to evaluate the optical band gap of the synthesized binary metallic nanoparticles using tauce eqn. The basic composition of the synthesis nanoparticles prepared at various concentrations was analyzed using the EDX technique. The spectrum and atomic composition of the sample of the nanoparticles are showing. Table 3 show the theoretical and practical values of this composition it is clear from the table conformity in theoretical with practical values and no sign of other elements in the spectra were observed. In order to further a rm the homogeneity of the material of the NPs were analyzed by EDAX in mapping mode with synthesized nanoparticles whose information is summarized in Figure 4. This analysis rmly supports the ndings of Figure 3, provides dependent mapping mode ((CuO x )-(CeO 2 ) 1-x ) representations.  Figure 5 clearer the homogeneous morphology of the metallic binary oxides synthesized (CuO) x -(CeO 2 ) 1-x nanoparticles ,for this nanocomposite TEM results clearly show the binary -content nanocomposite (CeO-CuO), i.e clarify the existence of all reaction materials ,the e cient reactions between these two materials and the stable grafting of the prepared nanocomposite material are good evidence of this assignment .The results are clear to be in good agreement with crystal size ranging from (10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) nm at x=(0.25-0.75), respectively.

J-V Characteristic
The J-V properties of (CuO)x-(CeO2)1-x under lighting display a high value at a given voltage which shows that the light absorption by the active binary oxide layer produces photo curricular contributions by a supplementary output at the barrier into free-of-charge transmitters, i.e. the (CuO) x-(CeO2)1-x interface. The free electrons and holes were accelerated towards the electrodes under the in uence of the electric eld at the junction, and crossed the potential barrier at the interface. Fig. ( 8 ) and ( 9 ) show the J-V characteristic for different types of electrode ( ITO, P-Si) and various ratio concentration (x=0.25,0.5,0.75), where current density decreased exponentially with voltage. For all samples, it is obvious that e ciency increase with increase of (x) content for ITO substrate solar cell be (6.48,7.68 and 9.6 %) at (x= 0.25,0.5 and 0.75) respectively ,this indicator that increase of ( x) content lead to increase in surface area to volume because Copper oxide have smallest particle size than Cerium oxide rstly and energy gap at x=0.75 have smallest value Eg=1.9Ev, While e ciency become (14.52%) at (x=0.75 for P-Si substrate as a result for high matching Si substrate with binary metallic oxide .By using (3) and (4) equation, J-V parameters ( Imax, Vmax, Isc, Voc, and F.F) were calculated and list of in table ().It is show from the table that Ics and Voc change in a non-systematic sequence with x content for the two substrate (ITO, P-Si), i.e decrease and increase with the increase of (x) content Pm = maximum power can be generated by the device, Pin = the incident power equal to (100 W / cm 2 ), Im = maximum current (mA), Vm = maximum voltage(V), Voc =Open circuit voltage (V), Isc = Short circuit current (mA) and F.F = ll factor.
The results of solar cell proved that these nano bimetallic composites are able to be used in solar cell applications.