The definition of sustainable energy development is the growth of the energy sector in terms of producing, distributing and utilizing energy according to sustainability principles [1]. Energy systems in both industrialized and emerging nations will have a substantial impact on the environment. As a result, the world's sustainable energy system needs to minimize emissions and optimize efficiency [2]. Recent decades have seen a notable increase in the use of solar energy as a clean, sustainable power source. This is mostly because solar energy offers the ability to reduce environmental effects while meeting the world's expanding energy needs [3].

The optical losses in solar cells are a major concern in current photovoltaic science. In crystalline silicon solar cells, optical losses typically result in an efficiency loss of 7% [4]. As a result, the conversion efficiency of silicon solar cells may greatly benefit from a decrease in optical loss [5]. Anti-Reflection Coating (ARC) is essential for lowering reflection and minimizing optical loss, which raises the solar cells' conversion efficiency [6]. ARC uses the idea of phase variations in light and the relationship between reflectivity and refractive index to reduce reflection. Since the fabrication of the solar cell, numerous researchers have employed various ARCs and they are currently looking for a suitable ARC that can be utilized to increase the solar cell's efficiency [7,8].

Porous Silicon-(PS) is a-silicon crystal with a network of spaces within it. A sponge-like structure of pores and channels encircled by a skeleton of crystalline silicon nanowires is produced by the nanosized gaps in the bulk siliconm [7,9]. PS solar cells have become a viable option for effective photovoltaic energy generation in the field of solar energy conversion technologies [10]. Cost-effectiveness, simplicity of manufacture and compatibility with large-scale production techniques are only a few benefits of porous silicon [11,12]. Scientific communities have been very interested in the coupling system made up of semiconductor Nanocrystals (NCs) and metal nanoparticle NPs [7].

Transitional metal oxides, including ZnO, CuO, TiO2, Fe3O4 and NiO nanoparticles, have demonstrated effective applications as advanced nano-substances in the fields of energy, biology and the environment [13]. Because of their electrical, magnetic, optical and physical properties, copper oxide nanoparticles (CuO NPs) are particularly interesting among the oxides of transition metals [14] and they will used as ARC in this work. 

The power produced by the solar cell can be calculated along with the I-V diagram by using the equation (P=IV), at the short circuit current (I_sc) and open circuit voltage (V_oc) points. Figure 1 shows the voltage and the current at this maximum power point are denoted as Vm and Im respectively [15].

The Fill Factor (F.F.) is an imported measure of the quality of the solar cell. It is calculated by comparing the maximum power (P_max) to the theoretical power (P_Th= V_oc´I_sc, as given in the following equation [17]:

                                                                  (1)

Efficiency (η)is the ratio of the output electrical power (P_out) to the solar input power (P_in) in the PV cell. P_out can be taken to be

since the solar cell can be operated up to its maximum power output to get the maximum efficiency [18]:

                                                                  (2)

Efficiency is related to current density J_sc and V_oc using F.F as the following equation:

                                                              (3)

Figure 1: Maximum Power on I-V diagram of Si solar cell [16] 

Figure 2: (a) the setup of the ECE process (b)PS image

These four quantities

are the key performance characteristicsof a solar cell. 

Experimental Work

CuO NPs are produced by the simple chemical process known as electrolysis, which has been used in earlier research [9]. For this, the electrolysis cell is employed, a gold plate serving as the positive electrode and a copper plate serving as the negative electrode of the electrolysis’ cell, with dimensions (3, 2 and 0.2) cm in length, width and thickness, respectively for each electrode. DC voltage of 5 volts is connected in series with the cell's anode. The electrolyte liquid used was water mixed with Hydrochloric Acid (HCl) at a ratio of roughly 8:1 and the procedure took about 25 minutes [8].

Spin coating was used to create CuO NSs thin films, the centripetal force produced by spinning movement helps to form a homogenous layer. Thin coatings can be deposited on flat substrates (2 cm * 2.5 cm) made of glass and PS at the end of this group production procedure. By depositing and spinning a viscous film at a high speed (about 3000 rpm), the film is forced to spread across the substrate. To remove residue and impurities, glass substrates were cleaned with alcohol in an ultrasonic bath at the beginning.

ECE process was performed to produce PS. Wafers of p-type silicon with an orientation (100), a thickness of 508 μm and a resistivity of 4 to 20 (ohm. cm) are used. The etching solution, contained in a Teflon cell, is a mixture of HF (48%) and ethanol (99.99) in equal proportions, with a current density of 10 mA/cm² applied for ten minutes at room temperature. Utilizing a gold ring as a cathode, the current traversed the electrolyte from the rear surface to the upper surface, resulting in the formation of an etched region on the silicon sample of 0.785 cm², as illustrated in Figure 2. The samples were stored in a plastic container containing methanol to prevent oxidation of the PS surface.

X-ray diffractometer supplied by SHIMADZU, XRD-6000 was used to get X-ray diffraction pattern of PS and CuO NSs. It uses Cu Kα radiation line of wavelength of 1.54 Å in 2Theta ranging from 20° to 80°. The morphology of the CuO NSs examined by atomic force microscopy (AA 3000 Scanning Probe Microscope. FESEM studies have been done on TESCAN, Czech Republic, JSM-6335F. The OPTIMA, SP 3000 UV-VIS spectrophotometer was used to record the absorption spectrum of the CuO NPs, which covered a wavelength range (200-1100) nm.

The X-ray diffraction pattern of CuO NSs is shown in Figure 3, it illustrates the crystalline particles by the peak corresponding to standard Brag reflections (111) at an angle equal to 38.1554°. The CuO NSs had a monoclinic crystal structure. The broadening of the peak at this angle is proof that monocrystalline copper oxide was formed. The inset chart illustrates the XRD pattern of the p-type PS layer. It showed a monocrystalline structure, with strong peak broadening corresponding to the diffraction angle (69.28°), which is interpreted as a nanocrystalline size effect.

By using the width of a peakwhich appears at the angle on the 2θ scale inScherer law [8]: 

                                                                              (4)

Table 1: The values of the grain size, FWHM, strain (d), and the dislocating density η of CuO NSs and p-type PS

Table 2: The values of the CuONSs' average diameter, roughens average and root mean square

Figure 3: The XRD pattern of CuO NSs and the inset chart XRD of p-type PS

Figure 4: AFM image of CuO NSs and distribution chart

where, D is the grain size, β represents the Full Width At Half Maximum (FWHM) in degrees and θ is the diffraction angle, the size of the generated CuO NSs was 40.33 nm and 87.75 for PS. Microstrainvalue (d) and the dislocating density(η) values are measured by using the following equations [8] (Table 1):

                                                                                (5)

                                                                                 (6)

Figure 4 illustrates the surface morphology of CuO NSs, which was investigated using AFM and possesses exceptionally smooth and homogeneous structures. The average grain size is approximately 78 nm using software and AFM analysis (Table 2).

The FTIR spectrum of CuO NPs formed by electrolysis is shown in Figure 5. The important bands of absorbance at peaks (3430.32,1630.42 and 558.00) cm^-1 are displayed in this figure. The O-H expansion pattern of the hydroxyl group is related to the broad absorption peak at around 3430.32 cm^-1 because a high surface-to-volume ratio in CuO NPs therefore it absorbs moisture. It is brought on by the adsorbed water molecules and this is agreed with other researchers [19]. While the C=O band is associated with the band in the range 1630.42cm^-1. The stretching vibration of the Cu-O bond is responsible for the high absorption band at 558 cm^-1.

Figure 6 shows the FESEM image of CuO NSs deposited on a glass substrate. It is observed that the morphology of the CuO NSs was mostly spherical i with a tiny size range from (20.47 to 33.50) nm.

The optical range gap of a material can be better understood in terms of its electrical nature by studying UV-VIS absorption spectroscopy. Figure 7 shows the absorption spectra of CuO NPs, with the absorption edge around 315 nm suggesting that associated electron processes within the sample are responsible for near-ultraviolet absorption. It was concluded that the material is effective because it has strong absorption in a UV range of 316 nm.

Figure 5: FTIR spectrum of CuO NPs

Figure 6: FESEM image of CuO NSs

Figure 7: UV-VIS absorption spectrum of CuO NPs

The energy band gaps of CuO NPs, according to a mathematical model, the square of (α hυ) is plotted against (hυ). The straight line is extrapolated to (αhυ)² =0 and it results in the value of the energy gap as shown in Figure 8. The value of the optical band gap of CuO NPs is about 3.3eV due to the direct band-to-band transition. The increase in the energy gap is due to nano-sized particles being formed and this is backed by AFM and FESEM.

Figures (9a and b) show the open-circuit voltage when the load resistanceis greater than the device resistanceand the current value is zero ofthe solar cells (PS/p-Si/Al and CuO NSs /PS/p-Si/Al) respectively. From these figures, it can be calculated the values of V_oc, I_sc, V_{m and} I_m. By using equations1 and 2, it can be calculated the values of fill factors and the efficiencies of these solar cells respectively. All samples were tested under the illumination of a light source with a light intensity of (33mW/cm²).

Figure 8: (αhν)² versus hv of CuO NPs

Figure 9: The efficiency0of (a) 0PS/p-Si/Al solar cell and (b) 0CuONSs/PS/p-Si/Al solar cell

Table 3:  The values of the photovoltaic characteristics of PS/p-Si/Al solar cells with and without adding the CuO NPs

The enhancement in efficiency can be interpreted as that the CuO NSs, act as an anti-reflected layer covering the porous silicon solar cells, increasing the absorption ratio of the light, thus reducing the reflection losses in PS/Si/Al solar cells.

It is clear from the results illustrated in Table 3 that the solar cells of PS/p-Si/Al prepared at etching time (10 min) have low efficiency equal to 0.268%, but this value is enhanced after depositing CuO NPs. It increased to 2.97%. The enhancement in efficiency can be interpreted as the CuO NSs acting as an anti-reflected layer covering the porous silicon solar cells led to an increase in the absorption ratio of the light, thus reducing the reflection losses in PS/Si/Al solar cells.

CuO NPs were successfully synthesized using the electrolysis method. The CuO NPs were deposited onto the glass substrates and porous silicon substrates using the spin coating technique. This method allowed for the formation of a uniform and controlled thin film, essential for optimizing the anti-reflective properties of the coating. The nanoparticles demonstrated remarkable optical characteristics due to their homogeneous dispersion and tiny size. CuO NPs greatly decreased the surface reflectance of Porous Silicon (PS) solar cells when used as an anti-reflective coating, enabling higher light absorption. This resulted in a measurable improvement in the efficiency of the CuO NSs/PS/Si/Al solar cells. CuO NPs' simplified synthesis and low cost, combined with their ability to improve light capture, show that they have potential as a material for photovoltaic applications.

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