2. Practical and experimental techniques

## 2.1 Synthesis of ZnO nanoparticles

Doped and undoped (i.e., pristine sample which was used as a control specimen) ZnO (DZ and UZ) NPs were prepared by the urea-assisted combustion route. The detailed synthetization of DZ and UZ NPs has been reported elsewhere [16]. Zinc acetate (ZA) dihydrate, (Zn(CH3COO)2. 2(H2O) assay ≥98.9%, Merck Co.), urea (U), (CO(NH2)2, assay ≥99.9%, Merck Co.), and silver nitrate AgNO3 (SN) were used as starting materials (precursors). They were utilized as purchased without further purification. The distilled water (DW) was employed to dissolve

Figure 1. A schematic illustration of the synthesis procedure of UZ and DZ NPs.

stoichiometric amounts of ZA (solutions A) and U (solutions B). Solutions A and B were stirred vigorously for 15 min at room temperature. After that, the two solutions A and B were mixed to produce solution C. A transparent homogeneous solution C was stirred vigorously for 15 min at 60°C in a beaker and was sonicated for 30 min. Solution C was transferred to a muffle furnace maintained at a temperature of 500 � 10°C. Solution C started to boil and undergo dehydration. Due to the exothermic nature of this process, a large amount of heat escaped with a huge flame. In meantime, further decomposition of the reagents and liberating more gases during the evaporation of liquid were happened. After 1 min, the flame damped, and the combustion reaction was accomplished within 5 min. White foamy and voluminous ash was achieved after spontaneous ignition occurred and underwent smoldering combustion with enormous swelling. The product ash was left to cool down to room temperature. Then, white ash was grounded gently into fine powders using a pestle and mortar:

$$\text{Zn}(\text{CH}\_3\text{COO})\_2\cdot 2\text{H}\_2\text{O} + \text{CO}(\text{NH}\_2)\_2 \rightarrow \text{ZnO} + \text{CO}\_2 + 2\text{CH}\_3\text{COOH} + 2\text{NH}\_3 \quad \text{(1)}$$

The same producers were repeated to prepare the UZ and DZ NPs with different molar concertation of Ag (0.5, 1.0, 1.5, and 5.0%). The obtained powders were characterized without any further post-preparation treatment. The scheme for the synthesis techniques of the DZ and UZ NPs is illustrated schematically in Figure 1. The chemical reaction to derive ZnO NPs from solution combustion-assisted urea is written in Eq. (1).

## 2.2 Fabrication and assembly of the DSSCs devices

The as-synthesized DZ and UZ NPs (which was designed as a reference photoanode) were consumed to fabricate the working electrode (WE) for DSSCs. Two slurry pastes were prepared by mixing a small quantity of the as-synthesized DZ and UZ NPs with polyethylene glycol 400 (PEG 400) and absolute ethanol using a mortar and pestle for 12 min. The obtained homogenous pastes were layered on fluorine-doped tin oxide (FTO) substrates (Sigma-Aldrich, sheet resistance

Nanoplasmonic for Solar Energy Conversion Devices DOI: http://dx.doi.org/10.5772/intechopen.84953

7 Ώ/cm2 ) by doctor blade technique. FTO substrates were washed using ethanol and DW several times followed by ultra-sonication using acetone for 15 min. The coated FTO substrates were heated at 450°C for 45 min. The estimation thickness of the heated layers was 1215 μm with an active covered area 0.25 cm<sup>2</sup> . In this stage, the derived photoanodes from DZ and UZ NPs were fabricated. The fabricated photoanodes were, separately, immersed in eosin Y (EY) dyes. After 24 h, the dyed photoanodes were rinsed in absolute ethanol and were dried in air at room temperature. Finally, the different DSSC devices were assembled by fixing the WE (A Ptcoated FTO substrate) and the counter electrode by paper clips with a spacer between the two electrodes. After that, the redox electrolyte solution was injected between the two electrodes to filling the space. The filling redox electrolyte solution (I-/I-3) was composed of 32 mL p-carbonate, 8 mL acetonitrile, 0.253 g iodine (I2), and 2.672 g lithium iodide. At last, the fabricated DSSC devices were used to measurements.

## 2.3 Characterization technique

Different techniques were conducted to characterize the as-synthesized DZ and DZ NPs. Crystal identification and crystal size analysis were tested by X-ray diffractometer (XRD), Philips Expert, where Cu-Kα radiation (λ = 1.5418 Å) monochromatic by a nickel filter. The values of diffraction angle (2θ) range from 15° to 80° and scan rate about 0.02 s-1. The nanostructures and their lattice images were possessed with a 200 kV high-resolution transmission electron microscopy (HR-TEM) (JEM-2100), 200 kV. Samples for HR-TEM studies were prepared by placing a drop of nanosuspension on a carbon-coated Cu grid, and the solvent was evaporated at room temperature. Double-beam UV–Vis spectrophotometer (Shimadzu UV-1601 PC) was used to carry out the absorption spectra of synthesized UZ and DZ NPs and the absorption of sensitizing dye in the range from 300 to 800 nm in ethanolic solution. Photoluminescence (PL) emission measurements were performed at room temperature in absolute ethanol over the range from 300 to 800 nm with excitation wavelength 320 nm using (SPF-200, Biotech Engineering Management Co., UK) spectrofluorometer with 150 W xenon lamp with a high-sensitivity photomultiplier tube.

#### 2.4 Measurement techniques

The photovoltaic characteristics of the fabricated DSSCs were executed under focusing irradiation using white light (40 W Xenon arc lamp) in ambient atmosphere. In addition, they were simulated with AM 1.5 sunlight illumination with an output power of 100 mWcm<sup>2</sup> . The characteristic curves of the current and the voltage (I-V) of the fabricated cells were carried out by applying an external reverse bias voltage in the range of 1 to 1 V of the solar cell. A personal computer (PC) was connected to Elvis National Instruments (ENI) in combination with a LabVIEW program to collect the data of I-V characteristic curves. The transient open-circuit photovoltage (TOCPV) decay experiment was conducted by monitoring the subsequent decay. This was due to the light source being turned off after illuminating the DSSC devices based on the of 0.32 mM EY dye for 5 min. UV–Vis spectrophotometer double-beam Shimadzu UV-1601 PC with a diffraction grating with a self-aligning was equipped to measure the dye concentration of the desorbed-dye solution as described in the previous work [2]. A deuterium lamp covered the UV where a halogen lamp was the source of the visible region. The colored photoanode was immersed in a 0.1 M NaOH solution of water and ethanol (1:1, v/v).
