1. Using the ZnO nanostructured materials in order to improve the efficiency of polycrystalline solar cells operation under low solar radiation conditions

down into ZnO. During the process of obtaining a ZnO by this method a series of gaseous products are released: water (H2O), carbon dioxide (CO2), acetone ((CH3)2CO) and acetic acid (CH3COOH). These products are eliminated around the temperature of 270�C ((1)–(4)). As the

Thus, thermal dehydration of zinc acetate can be considered a process of dehydration, vaporization/decomposition and ZnO formation [22]. Synthesis of ZnO nanowires by the hydrothermal method on the deposited substrate by the dehydratated zinc acetate process, involves the

NH3 þ H2O \$ NH4

Zn<sup>2</sup><sup>þ</sup> <sup>þ</sup> 4NH3 \$ Zn HN ð Þ<sup>3</sup> <sup>4</sup>

HMTA hydrolyzes readily in water to form formic aldehyde (HCHO) and ammonia (NH3), releasing energy, which is associated with its molecular structure, as can be seen in reactions (5) and (7). This stage is critical in the process of increasing ZnO nanowires. If HMTA hydrolyses very quickly, it produces a very large amount of OH� ions—in a very short time, Zn2+ ions from the solution would precipitate quickly due to the basic pH, and this would lead to rapid consumption of precursors and to an inhibition of the growth of ZnO nanoparticles [23]. From reactions (8) and (9), NH3 which originates from hydrolysis HMTA has two essential roles. Firstly it produces the basic medium required for the formation of Zn(OH)2. Secondly, it coordinates the Zn2+ ions and thus stabilizes the aqueous solution. Zn(OH)2 is dehydrated when heated by ultrasonication or even under the sunlight. All five reactions (5), (6), (7), (8) and (9) are in equilibrium and can be controlled by adjusting the reaction parameters: precursor concentration, temperature and growth time, which may have a positive or negative influence on the balance of reactions. Thus, precursor concentration determines the nanoparticle density, temperature and growth time controls. It also controls the morphology and nanoparticle size ratio. In reaction (5) it can be seen that seven moles of reactants produce ten moles of reaction products, which means an increase in entropy during the reaction, resulting an increase of the temperature, and finally the result is the shift of equilibrium to the reaction products. The rate of hydrolysis of HMTA increases with the increase of the basicity of the environment and vice versa. Also, the five reactions continue at room temperature but at a very low speed. For example, the solution with a precursor concentration of less than 10 mmol/L remains transparent and clear at room temperature for several months. If microwaves are used

Zn CH ð Þ 3COO <sup>2</sup>:2H2O ! Zn CH ð Þ 3COO <sup>2</sup> þ 2H2O (1)

Zn4O CH ð Þ 3COO <sup>6</sup> þ 3H2O ! 4ZnO þ 6CH3COOH (3)

Zn4O CH ð Þ 3COO <sup>6</sup> ! 4ZnO þ 3CH3COCH3 þ 3CO2 (4)

HMTA þ 6H2O \$ 4NH3 þ 6HCHO (5)

Zn<sup>2</sup><sup>þ</sup> <sup>þ</sup> OH� \$ Zn OH ð Þ<sup>2</sup> (8)

Zn OH ð Þ<sup>2</sup> \$ ZnO þ H2O (9)

<sup>þ</sup> þ OH� (6)

<sup>2</sup><sup>þ</sup> (7)

New Energy Harvesting Systems Based on New Materials

http://dx.doi.org/10.5772/intechopen.72613

23

4Zn CH ð Þ 3COO <sup>2</sup> þ 2H2O ! Zn4O CH ð Þ 3COO <sup>6</sup> þ 2CH3COOH (2)

temperature increases, ZnO nanoparticles are formed following chemical reactions:

reactions:

#### 1.1. Current state regarding obtaining of the ZnO nanoparticles

ZnO is a II–VI semiconductor with direct banned band of 3.37 eV. Nanostructured ZnO is used to obtain LED's (light-emitting diode – electroluminescent diode), in the manufacture of gas sensors and photovoltaic cells, both because of its electron transport properties and antireflective coatings. In recent years, a number of articles have been reported to present the results obtained from studies to obtain ZnO nanoparticles. The use of the hydrothermal method for obtaining these nanostructures using water as solvent and the Zn(NO3)2 – HMTA system, at low temperatures (below 100C), is among the processes that have begun to be used in recent years. ZnO nanoparticles are relatively easy to synthesize due to the hexagonal columnar structure of the unit cell. Once with getting the nanobelts of ZnO in 2001 [1], the research of ZnO nanostructures with different morphologies has seen rapid growth. The different methods of synthesizing these nanoparticles have been developed in recent years; they include vapor–liquid–solid techniques [2, 3], chemical vapor deposition [4], thermal evaporation [5] and hydrothermal method [6, 7]. The hydrothermal method does not involve the use of catalysts and facilitates the growth of nanoparticles on large surfaces. The increase in the gaseous phase can be achieved using one of the following methods: chemical deposition of metal–organic vapors (MOCVD) [8, 9], chemical transport from vapor [10, 11] and deposition by laser ablation [12]. With these methods, high-quality nanoparticles of micron size [13, 14] can be obtained. The process presents a number of disadvantages: it requires a temperature of 450–900C, a series of limitations related to the substrate are imposed like morphology and its area [15]. In contrast, growth from the solution is a process that takes place at temperatures below 100C, [16, 17], and the advantage of this process is to obtain nanoparticles with optical and electrical properties necessary for their use in the field of photovoltaic cells (antireflection coatings, electrode transparent, etc.).

#### 1.2. Preparation of antireflective coating based on ZnO nanoparticles for application on the substrate

Anti-reflection technology plays an important role in the fabrication of high-efficiency solar cells by increasing light coupling into the active region of devices. A complex process is used for obtaining ZnO nanostructures for antireflective coatings. The process is suitable to silicone solar cells and can be used in order to increase their efficiency under low solar radiation, allowing the control of the morphological and optical properties of ZnO nanostructures deposited on glass through ZnO seed layer deposition process. The ZnO nanowires were prepared using the hydrothermal method of deposition on the seed layer by a new and complex process, [18]. To obtain the ZnO nanoparticles, two steps are required: obtaining the ZnO seed layer (on which ZnO nanoparticles are formed) and a second stage consisting of the actual growth of ZnO nanoparticles. ZnO seeded layers were prepared using a solution of zinc acetate dissolved in 1-propanol. Zinc decomposition or hydrolysis to obtain ZnO nanocrystals are a method often used [19–21]. Subsequent decomposition of zinc acetate at temperatures between 100C 280C leads to the formation of Zn4O(CH3CO2)6, which eventually breaks down into ZnO. During the process of obtaining a ZnO by this method a series of gaseous products are released: water (H2O), carbon dioxide (CO2), acetone ((CH3)2CO) and acetic acid (CH3COOH). These products are eliminated around the temperature of 270�C ((1)–(4)). As the temperature increases, ZnO nanoparticles are formed following chemical reactions:

1. Using the ZnO nanostructured materials in order to improve the efficiency of polycrystalline solar cells operation under low

22 Advanced Electronic Circuits - Principles, Architectures and Applications on Emerging Technologies

ZnO is a II–VI semiconductor with direct banned band of 3.37 eV. Nanostructured ZnO is used to obtain LED's (light-emitting diode – electroluminescent diode), in the manufacture of gas sensors and photovoltaic cells, both because of its electron transport properties and antireflective coatings. In recent years, a number of articles have been reported to present the results obtained from studies to obtain ZnO nanoparticles. The use of the hydrothermal method for obtaining these nanostructures using water as solvent and the Zn(NO3)2 – HMTA system, at low temperatures (below 100C), is among the processes that have begun to be used in recent years. ZnO nanoparticles are relatively easy to synthesize due to the hexagonal columnar structure of the unit cell. Once with getting the nanobelts of ZnO in 2001 [1], the research of ZnO nanostructures with different morphologies has seen rapid growth. The different methods of synthesizing these nanoparticles have been developed in recent years; they include vapor–liquid–solid techniques [2, 3], chemical vapor deposition [4], thermal evaporation [5] and hydrothermal method [6, 7]. The hydrothermal method does not involve the use of catalysts and facilitates the growth of nanoparticles on large surfaces. The increase in the gaseous phase can be achieved using one of the following methods: chemical deposition of metal–organic vapors (MOCVD) [8, 9], chemical transport from vapor [10, 11] and deposition by laser ablation [12]. With these methods, high-quality nanoparticles of micron size [13, 14] can be obtained. The process presents a number of disadvantages: it requires a temperature of 450–900C, a series of limitations related to the substrate are imposed like morphology and its area [15]. In contrast, growth from the solution is a process that takes place at temperatures below 100C, [16, 17], and the advantage of this process is to obtain nanoparticles with optical and electrical properties necessary for their use in the field of photovoltaic cells (antireflection

1.2. Preparation of antireflective coating based on ZnO nanoparticles for application on

Anti-reflection technology plays an important role in the fabrication of high-efficiency solar cells by increasing light coupling into the active region of devices. A complex process is used for obtaining ZnO nanostructures for antireflective coatings. The process is suitable to silicone solar cells and can be used in order to increase their efficiency under low solar radiation, allowing the control of the morphological and optical properties of ZnO nanostructures deposited on glass through ZnO seed layer deposition process. The ZnO nanowires were prepared using the hydrothermal method of deposition on the seed layer by a new and complex process, [18]. To obtain the ZnO nanoparticles, two steps are required: obtaining the ZnO seed layer (on which ZnO nanoparticles are formed) and a second stage consisting of the actual growth of ZnO nanoparticles. ZnO seeded layers were prepared using a solution of zinc acetate dissolved in 1-propanol. Zinc decomposition or hydrolysis to obtain ZnO nanocrystals are a method often used [19–21]. Subsequent decomposition of zinc acetate at temperatures between 100C 280C leads to the formation of Zn4O(CH3CO2)6, which eventually breaks

1.1. Current state regarding obtaining of the ZnO nanoparticles

solar radiation conditions

coatings, electrode transparent, etc.).

the substrate

$$\text{Zn}(\text{CH}\_3\text{COO})\_2\text{2H}\_2\text{O} \to \text{Zn}(\text{CH}\_3\text{COO})\_2 + 2\text{H}\_2\text{O} \tag{1}$$

$$4\text{Zn}(\text{CH}\_3\text{COO})\_2 + 2\text{H}\_2\text{O} \rightarrow \text{Zn}\_4\text{O}(\text{CH}\_3\text{COO})\_6 + 2\text{CH}\_3\text{COOH} \tag{2}$$

$$\text{Zn}\_4\text{O}(\text{CH}\_3\text{COO})\_6 + 3\text{H}\_2\text{O} \rightarrow 4\text{ZnO} + 6\text{CH}\_3\text{COOH} \tag{3}$$

$$\text{Zn}\_4\text{O}(\text{CH}\_3\text{COO})\_6 \to 4\text{ZnO} + \text{3CH}\_3\text{COCH}\_3 + \text{3CO}\_2\tag{4}$$

Thus, thermal dehydration of zinc acetate can be considered a process of dehydration, vaporization/decomposition and ZnO formation [22]. Synthesis of ZnO nanowires by the hydrothermal method on the deposited substrate by the dehydratated zinc acetate process, involves the reactions:

$$\text{HMTA} + \text{6H}\_2\text{O} \leftrightarrow \text{4NH}\_3 + \text{6HCHO} \tag{5}$$

$$\text{NH}\_3 + \text{H}\_2\text{O} \leftrightarrow \text{NH}\_4^+ + \text{OH}^- \tag{6}$$

$$\text{Zn}^{2+} + 4\text{NH}\_3 \quad \leftrightarrow \left[\text{Zn}(\text{HN}\_3)\_4\right]^{2+} \tag{7}$$

$$\text{Zn}^{2+} + \text{OH}^- \leftrightarrow \text{Zn}(\text{OH})\_2 \tag{8}$$

$$\text{Zn}(\text{OH})\_2 \leftrightarrow \text{ZnO} + \text{H}\_2\text{O} \tag{9}$$

HMTA hydrolyzes readily in water to form formic aldehyde (HCHO) and ammonia (NH3), releasing energy, which is associated with its molecular structure, as can be seen in reactions (5) and (7). This stage is critical in the process of increasing ZnO nanowires. If HMTA hydrolyses very quickly, it produces a very large amount of OH� ions—in a very short time, Zn2+ ions from the solution would precipitate quickly due to the basic pH, and this would lead to rapid consumption of precursors and to an inhibition of the growth of ZnO nanoparticles [23]. From reactions (8) and (9), NH3 which originates from hydrolysis HMTA has two essential roles. Firstly it produces the basic medium required for the formation of Zn(OH)2. Secondly, it coordinates the Zn2+ ions and thus stabilizes the aqueous solution. Zn(OH)2 is dehydrated when heated by ultrasonication or even under the sunlight. All five reactions (5), (6), (7), (8) and (9) are in equilibrium and can be controlled by adjusting the reaction parameters: precursor concentration, temperature and growth time, which may have a positive or negative influence on the balance of reactions. Thus, precursor concentration determines the nanoparticle density, temperature and growth time controls. It also controls the morphology and nanoparticle size ratio. In reaction (5) it can be seen that seven moles of reactants produce ten moles of reaction products, which means an increase in entropy during the reaction, resulting an increase of the temperature, and finally the result is the shift of equilibrium to the reaction products. The rate of hydrolysis of HMTA increases with the increase of the basicity of the environment and vice versa. Also, the five reactions continue at room temperature but at a very low speed. For example, the solution with a precursor concentration of less than 10 mmol/L remains transparent and clear at room temperature for several months. If microwaves are used as a source of heating, the reactions take place at a very high speed, with a nanofire growth rate of up to 100 nm/min [24].

#### 1.3. The analysis of ZnO seed layer and ZnO nanowires growth by the hydrothermal method

The X-ray diffraction analysis was performed for the ZnO seed layer as well as for the ZnO nanowires growth by the hydrothermal method as shown within Figures 1 and 2 respectively. The structural analysis of the ZnO nanoparticles was performed, by grazing incident X-ray diffraction using an X-ray diffractometer (Bruker AXS D8 Discover) with Cu and Kα irradiation, 40 kV/40 mA, 20–60, 2 Theta domain, 2 seconds/step scan speed and 0.04 step. In the case of the ZnO seed layer, there were identified only the specific peaks of ZnO, confirming the higher purity of the film. ZnO from seed layer presented wurtzite hexagonal structure P63mc as well as structure parameters a = b = 3.242 nm and c = 5.176 nm. The intensity of the diffraction peaks corresponding to (002) and (110) plans displayed low broad peaks in the case of all the analyzed seed layer samples. The XRD analysis showed wurtzite hexagonal structure P63mc and structure parameters a = b = 3.242 nm and c = 5.176 nm when also considering the nanowires. The diffraction pattern highlighted peaks associated to (100), (002), (101) and (102) plans and the correspondence of ZnO. The (002) plan displayed a higher intensity peak in comparison to the corresponding plans (100), (101) and (102), indicating that the ZnO nanowires are predominantly c-axis orientated. Other peaks were not observed, leading to the fact that no other structures besides ZnO were formed. It was confirmed that high purity ZnO is obtained.

A different number of depositions (spray pyrolysis and spin coating) were achieved in order to determine the optimal thickness and morphology of the ZnO seed layer. The optimal seed

Figure 3. Scanning electron microscopy (SEM) images of the ZnO seed layer (a) and (c) as well as SEM images of ZnO

nanowires (b) and (d) respectively [18] (100 kx magnification).

Figure 2. XRD analysis of ZnO nanowires growth by the hydrothermal method [18].

New Energy Harvesting Systems Based on New Materials

http://dx.doi.org/10.5772/intechopen.72613

25

Figure 1. XRD analysis of ZnO seed layer.

Figure 2. XRD analysis of ZnO nanowires growth by the hydrothermal method [18].

as a source of heating, the reactions take place at a very high speed, with a nanofire growth

The X-ray diffraction analysis was performed for the ZnO seed layer as well as for the ZnO nanowires growth by the hydrothermal method as shown within Figures 1 and 2 respectively. The structural analysis of the ZnO nanoparticles was performed, by grazing incident X-ray diffraction using an X-ray diffractometer (Bruker AXS D8 Discover) with Cu and Kα irradiation, 40 kV/40 mA, 20–60, 2 Theta domain, 2 seconds/step scan speed and 0.04 step. In the case of the ZnO seed layer, there were identified only the specific peaks of ZnO, confirming the higher purity of the film. ZnO from seed layer presented wurtzite hexagonal structure P63mc as well as structure parameters a = b = 3.242 nm and c = 5.176 nm. The intensity of the diffraction peaks corresponding to (002) and (110) plans displayed low broad peaks in the case of all the analyzed seed layer samples. The XRD analysis showed wurtzite hexagonal structure P63mc and structure parameters a = b = 3.242 nm and c = 5.176 nm when also considering the nanowires. The diffraction pattern highlighted peaks associated to (100), (002), (101) and (102) plans and the correspondence of ZnO. The (002) plan displayed a higher intensity peak in comparison to the corresponding plans (100), (101) and (102), indicating that the ZnO nanowires are predominantly c-axis orientated. Other peaks were not observed, leading to the fact that no other structures besides ZnO were formed. It was confirmed that high purity

A different number of depositions (spray pyrolysis and spin coating) were achieved in order to determine the optimal thickness and morphology of the ZnO seed layer. The optimal seed

1.3. The analysis of ZnO seed layer and ZnO nanowires growth by the hydrothermal

24 Advanced Electronic Circuits - Principles, Architectures and Applications on Emerging Technologies

rate of up to 100 nm/min [24].

method

ZnO is obtained.

Figure 1. XRD analysis of ZnO seed layer.

Figure 3. Scanning electron microscopy (SEM) images of the ZnO seed layer (a) and (c) as well as SEM images of ZnO nanowires (b) and (d) respectively [18] (100 kx magnification).

layer was obtained by three application stages of spray pyrolysis at a temperature of 100C, three stages of spin coating followed by treatment at 300C for a period of 30 minutes.

samples of ZnO nanowires present a good transparency in the visible range (400–800 nm), with a lower average value of 76% (approximately 5% lower than in the case of glass). This decrease is due to the fact that the transmitted radiation by light diffusion increases the

New Energy Harvesting Systems Based on New Materials

http://dx.doi.org/10.5772/intechopen.72613

27

Following the spectrophotometric analysis, the variation of the optical reflection with wavelength in the range of 400–800 nm is presented in Figure 5. The graph confirms that the reflection is reduced in comparison to the values obtained for simple glass. The ZnO seed layer presents an intermediate value between glass and ZnO nanowires, with an average of 11%. The average value of ZnO nanowires sample for the visible optical reflection is equal to 9%, with 5% lower than the simple glass. By summarizing these optical characteristics, it is concluded that the ZnO nanowire films can be considered as a solution to the antireflective coatings in the solar cells field due to the optical proprieties and low-price manufacturing.

occurrence of the light scattering phenomenon of the ZnO nanowires.

Figure 5. Optical reflection of glass, ZnO seed layer and ZnO nanowires film.

Figure 6. The modular photovoltaic conversion system, connected to the DC/DC converter with isolation.

The microscopy micrographs shown within Figure 3 were recorded by using a field scanning electron microscope or by employing the annular in-lens detector for a second set of electron images with magnification of 100.000 X and an accelerating voltage of 2000 V. The surface morphology and structure of the nanoparticles were examined by employing a scanning electron microscope (FESEM, Carl Zeiss Auriga) at an accelerating voltage of 2.00 kV. The imaging was performed at a high magnification of 100 kx while the optical transmission and reflection spectra was recorded in the wavelength range of 400–800 nm by using a double beam UV–Vis–NIR spectrophotometer (UV–VIS Spectrophotometer 570 Jasco). The morphology of the ZnO seed layer surface influences the morphology of the ZnO nanowire. These layers operate as seed crystals in order to ensure the epitaxial growth of ZnO nanowires. In the case of thicker films, ZnO clusters are observed (grains with dimensions larger than 100 nm) consisting of agglomerations that influence the nanowires growth by a reduced order, scattered across the surface and random orientated (Figure 3a and b). The morphology and growth of the zinc oxide nanowires are influenced by the thickness and geometry of the seed layer (uniform grain, 30–55 nm) (as seen from Figure 3c and d). In this case, due to the seed layer uniformity and lack of agglomerations, the nanowires growth was orientated, with homogenous dimensions as well as displayed on the entire substrate surface. In this case, there was obtained a perfectly balanced seed layer and also a homogenous nanowire growth with lengths of ~200 nm and 50 nm diameter. Besides the high density of the ZnO nanowire arrays, other nanostructures are not observed.

The resulting seed layer presented suitable growth proprieties by the hydrothermal method of uniform and vertical ZnO nanowires. The variation of the optical transmission is shown within Figure 4, with wavelength found in the range of λ = 400–800 nm for glass, ZnO seed layer and ZnO nanowires. The ZnO seed layer has presented a good transparency of approximately 80%, similar to the glass value due to the reduced thickness (50 nm) and surface uniformity. The

Figure 4. Optical transmission of glass, ZnO seed layer and ZnO nanowires film.

samples of ZnO nanowires present a good transparency in the visible range (400–800 nm), with a lower average value of 76% (approximately 5% lower than in the case of glass). This decrease is due to the fact that the transmitted radiation by light diffusion increases the occurrence of the light scattering phenomenon of the ZnO nanowires.

layer was obtained by three application stages of spray pyrolysis at a temperature of 100C,

The microscopy micrographs shown within Figure 3 were recorded by using a field scanning electron microscope or by employing the annular in-lens detector for a second set of electron images with magnification of 100.000 X and an accelerating voltage of 2000 V. The surface morphology and structure of the nanoparticles were examined by employing a scanning electron microscope (FESEM, Carl Zeiss Auriga) at an accelerating voltage of 2.00 kV. The imaging was performed at a high magnification of 100 kx while the optical transmission and reflection spectra was recorded in the wavelength range of 400–800 nm by using a double beam UV–Vis–NIR spectrophotometer (UV–VIS Spectrophotometer 570 Jasco). The morphology of the ZnO seed layer surface influences the morphology of the ZnO nanowire. These layers operate as seed crystals in order to ensure the epitaxial growth of ZnO nanowires. In the case of thicker films, ZnO clusters are observed (grains with dimensions larger than 100 nm) consisting of agglomerations that influence the nanowires growth by a reduced order, scattered across the surface and random orientated (Figure 3a and b). The morphology and growth of the zinc oxide nanowires are influenced by the thickness and geometry of the seed layer (uniform grain, 30–55 nm) (as seen from Figure 3c and d). In this case, due to the seed layer uniformity and lack of agglomerations, the nanowires growth was orientated, with homogenous dimensions as well as displayed on the entire substrate surface. In this case, there was obtained a perfectly balanced seed layer and also a homogenous nanowire growth with lengths of ~200 nm and 50 nm diameter. Besides

three stages of spin coating followed by treatment at 300C for a period of 30 minutes.

26 Advanced Electronic Circuits - Principles, Architectures and Applications on Emerging Technologies

the high density of the ZnO nanowire arrays, other nanostructures are not observed.

Figure 4. Optical transmission of glass, ZnO seed layer and ZnO nanowires film.

The resulting seed layer presented suitable growth proprieties by the hydrothermal method of uniform and vertical ZnO nanowires. The variation of the optical transmission is shown within Figure 4, with wavelength found in the range of λ = 400–800 nm for glass, ZnO seed layer and ZnO nanowires. The ZnO seed layer has presented a good transparency of approximately 80%, similar to the glass value due to the reduced thickness (50 nm) and surface uniformity. The Following the spectrophotometric analysis, the variation of the optical reflection with wavelength in the range of 400–800 nm is presented in Figure 5. The graph confirms that the reflection is reduced in comparison to the values obtained for simple glass. The ZnO seed layer presents an intermediate value between glass and ZnO nanowires, with an average of 11%. The average value of ZnO nanowires sample for the visible optical reflection is equal to 9%, with 5% lower than the simple glass. By summarizing these optical characteristics, it is concluded that the ZnO nanowire films can be considered as a solution to the antireflective coatings in the solar cells field due to the optical proprieties and low-price manufacturing.

Figure 5. Optical reflection of glass, ZnO seed layer and ZnO nanowires film.

Figure 6. The modular photovoltaic conversion system, connected to the DC/DC converter with isolation.

#### 1.4. Prototyping and testing the modular photovoltaic conversion system

Modular photovoltaic conversion system, designed for energy harvesting applications has been achieved, using four photovoltaic cells, Figure 6. A commercial polycrystalline silicone solar cell manufactured by Conrad Electronic SE was selected and covered by a nanostructured ZnO disposed on glass in order to be tested. The technical data related to the considered polycrystalline solar panel (123 cm2 ) consist of 1.35 W output power, 9 V nominal voltage, 10.5 V open circuit voltage and 150 mA short-circuit current. The determination of the solar cells functional parameters (efficiency, short circuit current, open circuit voltage and output power) has led to the conclusion that all the values are superior in the case of the solar cells with ZnO nanowires on glass showing that the performance of the solar cell depends on the

New Energy Harvesting Systems Based on New Materials

http://dx.doi.org/10.5772/intechopen.72613

29

Figure 9. Tested of the photovoltaic module covered by a nanostructured ZnO disposed on glass, for 200 W/m2 test

Figure 10. Tested of the photovoltaic module covered by a nanostructured ZnO disposed on glass, for 400 W/m2 test

irradiance and antireflective coating.

conditions.

conditions.

Figure 7. Pasan Meyer Burger HighLight 3 solar simulator, used to test of the modular photovoltaic conversion system, view from flash box.

Figure 8. Tested of the photovoltaic module covered by a nanostructured ZnO disposed on glass, for 100 W/m2 test conditions.

cells functional parameters (efficiency, short circuit current, open circuit voltage and output power) has led to the conclusion that all the values are superior in the case of the solar cells with ZnO nanowires on glass showing that the performance of the solar cell depends on the irradiance and antireflective coating.

1.4. Prototyping and testing the modular photovoltaic conversion system

28 Advanced Electronic Circuits - Principles, Architectures and Applications on Emerging Technologies

polycrystalline solar panel (123 cm2

view from flash box.

conditions.

Modular photovoltaic conversion system, designed for energy harvesting applications has been achieved, using four photovoltaic cells, Figure 6. A commercial polycrystalline silicone solar cell manufactured by Conrad Electronic SE was selected and covered by a nanostructured ZnO disposed on glass in order to be tested. The technical data related to the considered

10.5 V open circuit voltage and 150 mA short-circuit current. The determination of the solar

Figure 7. Pasan Meyer Burger HighLight 3 solar simulator, used to test of the modular photovoltaic conversion system,

Figure 8. Tested of the photovoltaic module covered by a nanostructured ZnO disposed on glass, for 100 W/m2 test

) consist of 1.35 W output power, 9 V nominal voltage,

Figure 9. Tested of the photovoltaic module covered by a nanostructured ZnO disposed on glass, for 200 W/m2 test conditions.

Figure 10. Tested of the photovoltaic module covered by a nanostructured ZnO disposed on glass, for 400 W/m2 test conditions.

The photovoltaic module was tested for standard test conditions (1000 W/m<sup>2</sup> , 25C, AM 1.5) as well as for reduced solar irradiance by using the Pasan Meyer Burger HighLight 3 solar simulator shown in Figure 7. There were used four masks for the solar irradiance attenuation (100 W/m<sup>2</sup> , 200 W/m<sup>2</sup> , 400 W/m<sup>2</sup> and 700 W/m<sup>2</sup> ) in order to achieve the comparison between the generated powers along with varying the operation conditions. The used simulator is able to adjust the irradiance value between 100 W/m<sup>2</sup> and 1000 W/m<sup>2</sup>

designed for energy harvesting applications

Figure 13. XRD pattern of PZT doped with 1% Nb2O5 sintered at 1120C for 2 hours, [25].

antireflection coatings.

2 hours [25].

mity and light stability below 1%. Accordingly, five characteristics resulted for each of the

The results confirm the advantages of using the ZnO nanowires in solar cells applications for

2. Piezoelectric structures based on new modified PZT zirconate titanate

We propose a piezoelectric ceramic material what can it be integrated into piezoelectric structures for energy harvesting applications. The piezoceramic element has the shape of a disk with diameter of 12 mm while the width is 0.3 mm. On each of the ceramic disk's sides, silver

Figure 14. Scanning electron microscopy images (SEM) image of PZT doped with 1% Nb2O5. Sintered at 1120C for

tested modules for these various operating conditions, Figures 8, 9, 10, 11 and 12.

, with both the light unifor-

31

New Energy Harvesting Systems Based on New Materials

http://dx.doi.org/10.5772/intechopen.72613

Figure 11. Tested of the photovoltaic module covered by a nanostructured ZnO disposed on glass, for 700 W/m2 test conditions.

Figure 12. Tested of the photovoltaic module covered by a nanostructured ZnO disposed on glass, for standard test conditions, 1000 W/m2 .

to adjust the irradiance value between 100 W/m<sup>2</sup> and 1000 W/m<sup>2</sup> , with both the light uniformity and light stability below 1%. Accordingly, five characteristics resulted for each of the tested modules for these various operating conditions, Figures 8, 9, 10, 11 and 12.

The photovoltaic module was tested for standard test conditions (1000 W/m<sup>2</sup>

30 Advanced Electronic Circuits - Principles, Architectures and Applications on Emerging Technologies

, 400 W/m<sup>2</sup> and 700 W/m<sup>2</sup>

(100 W/m<sup>2</sup>

conditions.

conditions, 1000 W/m2

.

, 200 W/m<sup>2</sup>

well as for reduced solar irradiance by using the Pasan Meyer Burger HighLight 3 solar simulator shown in Figure 7. There were used four masks for the solar irradiance attenuation

the generated powers along with varying the operation conditions. The used simulator is able

Figure 11. Tested of the photovoltaic module covered by a nanostructured ZnO disposed on glass, for 700 W/m2 test

Figure 12. Tested of the photovoltaic module covered by a nanostructured ZnO disposed on glass, for standard test

, 25C, AM 1.5) as

) in order to achieve the comparison between

The results confirm the advantages of using the ZnO nanowires in solar cells applications for antireflection coatings.
