Green Synthesis, Characterization of Zinc Oxide Nanoparticles, and Examination of Properties for Dye-Sensitive Solar Cells Using Various Vegetable Extracts

The production of zinc oxide nanoparticles (ZnO NPs) utilizing di ﬀ erent vegetable extracts (onion, cabbage, carrot, and tomato) was performed in this research owing to its excellency over other methods of synthesis, namely, simplicity, environmental friendliness, and the elimination of harmful compounds. Fresh extracted onion, cabbage, carrot, and tomato of ZnO NPs are characterized by Fourier transform infrared (FTIR), X-ray di ﬀ raction (XRD), scanning electron microscopy (SEM), and UV-visible spectroscopy. FTIR ﬁ ndings demonstrate that the prepared nanoparticles were observed in the spectrum of 626cm -1 – 1219 cm -1 with some other functional groups. Wurtzite hexagonal structure of the prepared ZnO NPs was observed from XRD results. In addition, the prepared nanoparticles were failed into nanoscales (17 nm, 18 nm, 24nm, and 15nm) calculated from Scherrer ’ s equation. Nearly spherical shapes were seen from SEM image for onion and tomato extraction while rod and tube for carrot and cabbage, respectively. Two broad peaks were observed from UV-vis spectroscopy results for each extract. The presence of a wide range of energy bandgaps in the region of 3-4eV was detected, indicating that ZnO NP material can be employed in metal oxide semiconductor-based systems. The dye-sensitive solar cell based on ZnO NPs has been successfully synthesized, and the e ﬃ ciency of the device has been evaluated by measuring the current density-voltage behaviour under the presence of arti ﬁ cial sunshine. The increased e ﬀ ectiveness of the manufactured dye-sensitive solar cell is attributable to a large improvement in dye molecular adsorption onto the surface of ZnO NPs. Thus, the usage of the green produced ZnO NPs with creating dye sensitivity solar cell is a simple and viable way for the well-being of our future.


Introduction
Power originates in numerous forms as a result of burning forests to produce fire in ancient times to electrical produc-tions in the contemporary era. Its usage is among the most significant aspects in everyday living interaction of human beings. Nevertheless, the primary resources of energy that human beings utilized in the reaping have exhibited signs of insufficiency due to the rise in industrial development in a large number of countries. As an outcome, growing concerns about energy crisis, global warming, lack in fossil fuels, and environmental problems are encouraging the research work to produce clean, affordable, and sustainable sources of the energy that will propel the world into the future [1]. Latest advancement in solar energy transformation innovations that use biosemiconductors as the light harvesting layer makes use of metallic oxide semiconductor (MOS) nanostructures for reliability. Both electrode and the biomolecules are involved in charge extraction and transportation, according to the National Renewable Energy Laboratory [2]. Nanoscience is a broad topic that concerns of the research and implementation of materials on a nanoscale. It is becoming increasingly popular. When compared to their bulk counterparts, nanoparticles (NPs) demonstrate new and enhanced qualities as a result of changes in their characteristics such as form size, size distribution, and a greater measure of the relationship between surface area and volume [3]. Metal nanoparticles (metal NPs) have found a wide range of applications in the fields of science and innovation in recent years, owing to their distinctive electrical, mechanical, optical, and magnetic characteristics [1][2][3]. Because of its vital applications as antibacterial agents, photovoltaic cells, textile fabrics, and polymers to eradicate microorganisms, zinc oxide nanoparticles (ZnO NPs) have garnered a considerable deal of interest from researchers in recent years [3].
The need for environmentally friendly energy sources has prompted extensive study into nanomaterials to meet these needs. When it comes to technology, nanotechnology is a branch that analyzes diverse materials on a nanometric scale. Its applications can be discovered in materials science, engineering, and electronic engineering. Nanoparticles exhibit a wide range of magnetic and optoelectronic properties that are influenced by their size and form distribution, as well as their composition. Due to the fact that this technique of synthesis eliminates the need for harmful chemicals, as well as its ease and environmental friendliness, the synthesis of nanoparticles employing vegetable extract is becoming increasingly popular [3][4][5]. In addition to its unique characteristics and high excitonic binding energy, zinc oxide (ZnO) is used in this application [1][2][3][4][5].
It is routinely possible to synthesize ZnO NPs using various methods, including but not limited to hydrothermal, solvothermal, sol-gel, direct oxidation, chemical vapour deposition (CVD), electrodeposition (ED), sonochemical, chemical bath deposition (CBD), microwave, and other approaches [5]. These approaches, on the other hand, are expensive, hazardous, and unfriendly to the natural environment. Nowadays, there is a growing demand for developing ZnO that has excellent yielding, has moderate cost, and is nontoxic by utilizing biological sources and environmentally acceptable techniques of exploration and production. To synthesize zinc oxide nanoparticles using a green synthesis approach, environmentally friendly resources including such plant extracts (leaf/flower/bark/root/seed/peel) and also the bacteria/fungi/enzymes are used for the manufacture of zinc oxide nanoparticles [6]. Vegetable removal was employed in this investigation due to its plentiful affordability. It has been observed that diverse vegetable extracts can be used to pro-duce zinc oxide nanoparticles [6][7][8]. Different scholars have documented the usage of ZnO NPs in the production of dyesensitive solar cells in their research. The green synthesis of zinc oxide nanoparticles employing onion, cabbage, carrot, and tomatoes as a resource for dye-sensitive solar cell implementation has not been documented, and no comparisons have been done between them. In the present research, ZnO nanoparticles are synthesized using the green synthesis technique, with preparations of tomato, onion, cabbage, and carrot serving as reducing and stabilising agents in addition to the ZnO. The nanoparticles that were synthesized were analyzed using a variety of techniques, including Fourier transform infrared, X-ray diffraction, scanning electron microscopy, and an ultraviolet/visible spectroscope. One of the objectives of this research is to synthesize and analyze zinc oxide nanoparticles based on extracts of onion and cabbage. Another is in order to look into the use of zinc oxide nanoparticles in the manufacture of dye-sensitive solar cells utilizing extracts of carrot and tomato.

Experimental Details
2.1. Synthesis Methods. Fresh onion, carrot, cabbage, and tomato were acquired in a market of Dambi Dollo Town. Zinc acetate dihydrates (99.7%) and ethanol (99.5%) as a solvent were also purchased from the market. First, the onion, cabbage, carrot, and tomato were chopped into tiny slices and rinsed three times with distilled water. Next, the onion, cabbage, carrot, and tomato were weighed and blended into the distilled water, and the process was repeated three more times. Aqueous extracts were obtained after mixing 22 grams of onion powder, 30 grams of cabbage powder, 20 grams of carrot powder, and 22 grams of tomato powder in 200 millilitres of distilled water in various beakers for 20 minutes at a time until the mixtures came to a boil. Following freezing, the combinations were filtered through what man paper and kept at 40°C until they were needed for another application. The green syntheses of ZnO NPs were performed out in accordance with published procedures [9]. 2 M concentration of zinc acetate dihydrate Zn(CH 3 COO) 2 ·2H 2 O was made in a beaker using sonication to dissolve 15 g of Zn(CH 3 COO) 2 ·2H 2 O in 1 litre of distilled water. The mixture was stored in the refrigerator until it was needed. The preparations of onion (10 mL), tomato (10 mL), cabbage (10 mL), and carrot (10 mL) were combined with a 10 mL solution of Zn(CH 3 COO) 2 ·2H 2 O in a beaker using a stirrer for 10 minutes and then allowed to stand at room temperature for 24 h before testing. The decrease of Zn-ion was seen as a change in colour from white to pale brown and then to a deep brown over time, as shown by the shifting of colour to white to light brown and then to dark brown. Because of the manufacture of ZnO NPs, the texture of the mixture had been changing. In the following 24 hours, the produced nanoparticles were whirled at 12000 rpm for 15 minutes and rinsed six times using ethanol and distilled water before being used. Following collection of the samples, they were moved to a Petri dish and dried for 12 hours at 70°C in a vacuum oven. In order to study and characterize the connected functional groups to a surface of the synthesized ZnO nanoparticles, the PerkinElmer FTIR Spectrum One was used with a scanning spectrum of 4000-400 cm -1 and a resolution of 4 cm -1 for the analysis of the connected functional groups to the exterior of the synthesized ZnO nanoparticles. For both the FTIR evaluations, the specimen was consistently and appropriately mixed with solid KBr, which was squeezed to settle down on an extremely thin film, and this relatively thin film was used for the FTIR analysis, which was stored in the scanning chamber of the instrument.

X-Ray
Diffraction and SEM Analysis. The X-ray diffraction (XRD) distribution of ZnO nanoparticles was acquired using an X'Pert Pro X-ray diffractometer that generated Cu Kα radiation (with an angular resolution of 1.5418 angstrom). It is being employed to evaluate the crystalline particle sizes that have been manufactured. For the purposes of characterization, a tiny quantity of powder sample was used. At room temperature, X-ray generators were running at a voltage of 40 kV and applying a current of 30 mA to the target. Temperature-dependent strengths were recorded at ambient temperature in steps of 0.02, throughout a range of 100 to 800°C, with the diffractometer attached to a computer for data collection and characterization displays. It was necessary to authenticate the structure of the crystal by comparing its peak positions with those of the existing standard data. For each sample, about 0.6 g of the produced ZnO NPs was ground to tiny powders and quantified using a beam balance before being transferred to a metal plate. Once the nanoparticles had been formed, the particle morphology was examined by utilizing a scanning electron microscope (Hitachi, H-7600) that operates under high vacuum and has magnifications ranging from 20x to about 30,000x, as well as spatial resolutions of 50 to 100 nm. Greater magnification of ZnO NPs was attained by decreasing the raster width of the sample, and vice versa, for the fixed sizes of the ZnO NPs. A quartz cuvette with a diameter of 1 cm was used to measure the absorbance spectra of obtained ZnO NPs employing UV-vis spectroscopy (PerkinElmer LAMBDA 950), which was operated throughout a wavelength range of 200-500 nm. Approximately 0.3 g of ZnO NPs was mixed with double distilled water before being placed into a quartz cuvette to form their solutions. After that, the cuvette was placed in an ultraviolet visible spectrophotometer, where the absorption spectra of ZnO NPs were determined.

Results and Discussion
3.1. FTIR Analysis. In order to identify the probable functional groups in biomolecules contained with the presence of a natural extract that are due to the reduction of the zinc ion into ZnO NPs, a Fourier transform infrared spectral analysis (FTIR) was performed. FTIR spectra of the prepared ZnO NPs with vegetable extracts are observed in Figure 1. 3.2. X-Ray Diffraction Analysis. The XRD pattern of ZnO NPs that were generated utilizing samples of onion, cabbage, carrot, and tomato is presented in Figure 2, and it can be seen in Figure 3.  [14] is incongruous in accordance with the trend illustrated in Figure 2. Thus, utilizing XRD, the formation of ZnO NPs was established. The dimensions of the nanoparticles were determined using the assistance of the following Scherrer's equation.
where t is the mean dimension of nanoparticles, k is the frequency of radiation, β is the whole width half peak in radians, and θ is the degree diffraction [12][13][14]. Onion, cabbage, carrot, and tomato preparations have been used to synthesize nanoparticles with mean sizes of 17 nm, 18 nm, 24 nm, and 15 nm, respectively. The average sizes of the nanoparticles produced with onion, cabbage, carrot, and tomato extracts are seen in Table 1. Based on the foregoing findings, it can be inferred that throughout the instance of tomato extracts, smaller nanoparticles are generated. Figure 3 demonstrates the SEM morphology of the extracted ZnO nanoparticles synthesized by onion, cabbage, carrot, and tomato, respectively. SEM images depict the spherical surface morphology in the case of onion and tomato extractions, while nearly nanorod and nanotube are synthesized using carrot and cabbage, 3 Journal of Nanomaterials respectively. Because of their small size, the green synthesized structures are uniform in nature, with little aggregation. Instead of using costly and harmful capping agents to minimize agglomeration, plant extract works as a reducing agent as well as a capping agent. As a result, this process is more cost-effective and environmentally benign than the other certain technique of producing ZnO NPs. The narrow assimilation SEM image in onion and tomato extracts of the prepared ZnO NPs depicts detail wurtzite hexagonal structure where their adjacent contacting surface is smooth and has well-defined shapes [15][16][17][18].

SEM Analysis.
The optical bandwidth of the produced ZnO NPs was studied using UV-vis spectroscopy [16,18]. To obtain a homogeneous solution, the produced ZnO NPs were scattered evenly in the triple filtered water employing an ultrasonicator for 5 minutes. The UV-visible spectrum of the green produced ZnO NPs retrieved from onion, cabbage, carrot, and tomato is shown in Figure 4. The spectrum reveals a wide absorption peak at 276 nm and 375 nm for onionextracted nanoparticles. In addition, 217 nm and 310 nm, 214 nm and 338 nm, and 215 nm and 343 nm are for cabbage-, carrot-, and tomato-extracted zinc oxide nanoparticles, respectively. These peaks are caused by ZnO NPs' surface plasmon absorption characteristics. When electromagnetic waves impact the surface plasmon absorption, a phenomenon happens owing to the cumulative oscillation of the open conduction band electrons [17,18].
This current study of UV-visible absorption peak for ZnO NPs is similar to prior results [19]. Planck's equation was used to compute the bandgap energy (E) of the produced ZnO nanoparticles. 1219 c 9 9 9 9 9 9 9 m -1 626 cm -1 Figure 1: FTIR spectra of onion-, cabbage-, carrot-, and tomato-extracted ZnO NPs by green synthesizing methods. 20 Table 2 shows the computed bandgap energy value for greatest wavelengths. ZnO's inherent bandgap absorption is caused by electron transitions between the valences to the conduction bands. Because ZnO nanoparticles absorb UV light, they can be employed in medicinal purposes such as sunscreen protection or antibacterial ointments [16]. A wide range of energy bandgaps was discovered in the 3-4 eV range, indicating that ZnO NP powder can be employed in metal oxide semiconductor-based systems [19].
The characterization of the extracted zinc oxide nanoparticles was calculated using fill factor for dye-sensitive solar cell by using the following equation: where J max , V max , J sc , and V oc represent the peak power point current density and voltage, small current density (J sc ) of an observed current at 0 V, and open-circuit voltage (V oc ), respectively [21].
When compared to research having comparable ZnO nanoparticle architectures in the literature, it was discovered that the ZnO-based DSSC made n percent quite good [22]. The immersion duration of ZnO NPs together into sensitizing dye had been demonstrated to be an important factor in the solar cell properties of the ZnO-based DSSC [34]. When compared to similar research [12][13][14][15], the manufactured ZnO-based DSSC showed better performance in a lesser   Journal of Nanomaterials period of sinking time [35][36][37][38][39][40][41][42][43][44]. The enhanced absorption due to the larger amount and the better performance can also be expressed by the dye molecules that have been adsorbed onto the ZnO surface which can also expressed the better performance. As a result of the simplicity of the approach and the ease with which the specimens can be generated, through utilization of ZnO nanoparticles in photovoltaics seems to hold long-term prospects. The current density was discovered to be considerably lower. The photocurrent is the greatest significant parameter that defines the system's total performance limit. Then, because of their high surface area, parental substances act differently, and surface energy increases when the particle dimension is going towards that of a nanoscale [23,24,34]. The average crystallite dimensions of the ZnO nanoparticles were generated to be within 15 nm and 20 nm. As a result, we can anticipate considerable photochemical characteristics. A low hardness factor, reflection or dispersion, minimal injection performance, and charge collecting efficiency can all contribute to a low [16][17][18]. As the light intensity rose, the shortcircuit voltage output grew progressive to near-saturation levels. Increased photogenerated excitons were linked to the linear increase in J sc [20-22, 34, 45]. As a result, at greater light intensities, larger electron densities were transmitted to ZnO. Table 3 shows that "n" and "J sc " readings improved even as applied light density has improved. The improvement in charge generation is a result of an elevation in light intensity. Comparable outcomes had previously been reported for ZnO-based DSSC materials [19,20,45]. These findings reveal that increasing the intensity of illumination to 100 mW cm -2 has no effect on transport, injection, or recombination mechanisms as shown in Figure 5.

Conclusion
ZnO NPs were completely synthesized through simple and eco-friendly vegetable-mediated green synthesizing technique from onion, cabbage, carrot, and tomato fruit extraction. FTIR, XRD, SEM, and UV-visible spectroscopy were accustomed to characterize the produced nanopowders. The crystal structures of synthesized ZnO NPs were with particle sizes where observed from XDR results. According to Scherrer's equation, the produced ZnO NPs have a single-phase hexagonal geometry having mean particle sizes of 17 nm, 18 nm, 24 nm, and 15 nm. Small agglomeration of the extracted nanoparticles was observed from SEM results. Because extract capping agents are poisonous, they were not employed to minimize the clustering; nonetheless, the vegetable retrieving itself would work as a diminishing agent or a capping agent depending on the situation. As a result, the green synthesizing process is more cost-effective and environmentally friendly than conventional ways for   Journal of Nanomaterials producing ZnO NPs. The ZnO NP UV-visible spectroscopy revealed a large surface plasmon resonance absorption spike of the dye-sensitive solar cell based on ZnO NPs was effectively manufactured, and its performance was studied using current density-voltage behaviour below the influence of artificial sunlight. Due to a significant enhancement in dye molecule absorption upon this surface of ZnO NPs, a significant rise in the performance of the produced DSSC can be attributed to this. As a result, the employment of the green produced ZnO nanoparticles in the construction of dyesensitive solar cells is a simple and promising strategy for the future's well-being. ZnO nanoparticles can be used as intelligent weapons toward a wide range of drug-resistant microbes, as well as a capable antibiotic replacement.

Data Availability
The data used to support the findings of this study are included within the article.

Conflicts of Interest
The authors declare that there are no conflicts of interest