*1.3.2 Open-circuit voltage*

The open-circuit voltage is usually presented as *V*oc, which is the maximum voltage generated from a solar cell when there is no current. The *V*oc corresponds to the amount of forward bias on solar cell due to bias of solar cell junction with light-generated current. The power (*P*) produced by solar cell in Watt can be easily calculated alone by *I-V* curve using the equation, *P* = *IV*. The voltage and current at maximum power from point are denoted as *Vmp* and *Imp*, respectively.

### *1.3.3 Maximum power output*

For a given bias voltage, the power output of solar cell is the product of measured cell current and voltage. The *J*sc and *V*oc are the maximum current and voltage, respectively, from a solar cell. However, at both of these operating points, the power from solar cell is zero.

**65**

*Nanostructures in Dye-Sensitized and Perovskite Solar Cells*

) is defined as the ratio of the maximum power from the solar

× 100 (1)

× 100 (2)

× 100 (3)

<sup>=</sup> *ImpVmp* \_\_\_\_\_\_ *JscVoc*

cell to the product of Voc and *Jsc*. Graphically, *ff* is a measure of "squareness" of solar cell and also an area of the largest rectangle which will fit in the *I-V* curve. Typically, the range of *ff* is from 0.50 to 0.82 or 50 to 82% as the *ff* is also represented in

*JscVoc*

sometimes referred to also as the "external quantum efficiency" (EQE), is an important parameter of solar cell device. The IPCE can be under light intensity of

(AM1.5), which is estimated in the following equation:

where photocurrent density (*J*) is generated by monochromatic light with

The solar-to-electrical power conversion efficiency (*η*%) is an essential parameter to confirm the performance of one solar cell under testing. The *η* is defined as the ratio of energy output from the solar cell to an energy input from the Sun. In addition to reflecting performance of the solar cell itself, *η* depends on the spectrum and intensity of the incident sunlight and temperature of the solar cell. Therefore, terrestrial solar cells are measured under air mass 1.5 conditions in addition to a temperature of 25°C. The solar cells intended for space use are measured under air mass "0" conditions. It is well known that an overall η (%) of the solar cells can be determined by *Jsc, Voc, ff*, and the intensity of the incident

> *Pout Pin*

<sup>=</sup> *Jsc Voc ff* \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ *Pin*

In 1873, Vogel and Berlin invented dye sensitization technique, but until the 1970s DSSCs' mechanism was unclear. Therefore, compared with silicon-based photovoltaic devices, the performance of these early DSSCs was poor (*η* = <1%). The major obstacle in poor performance was relatively low adsorption of dye molecules into the metal oxide photoanode surface. Few improvements in efficiency were achieved by coating a thick layer of dye molecules onto the metal oxide photoanode surface [5]. Nevertheless, the power conversion efficiency was limited to ≤2% due to the low-light harvesting and charge collection from the adsorbed dye molecules. In the 1990s, Prof. Michel Gratzel and his team creatively demonstrated a practical photoelectrochemical cell device with a certified power conversion efficiency of 11.9%,

The incident monochromatic photon-to-current conversion efficiency (IPCE),

*<sup>P</sup>*(*W*) <sup>×</sup> \_\_\_\_\_\_ <sup>1240</sup> λ(*nm*)

*DOI: http://dx.doi.org/10.5772/intechopen.83803*

*ff*

percentage using the following relation:

*ff(%)* <sup>=</sup> *Pmp* \_\_\_\_\_

*1.3.5 Incident photon-to-current conversion efficiency*

*IPCE*(%)= *Jsc*(*A*) \_\_\_\_\_

*1.3.6 Solar-to-electrical power conversion efficiency*

η(%) = \_\_\_

**1.4 History of dye-sensitized and perovskite solar cells**

wavelength (*λ*) and intensity (*P*)*.*

light (*Pin*) as follows:

*1.3.4 Fill factor*

100 mW cm2

The fill factor (

*Nanostructures in Dye-Sensitized and Perovskite Solar Cells DOI: http://dx.doi.org/10.5772/intechopen.83803*

### *1.3.4 Fill factor*

*Nanostructures*

**1.2 Photovoltaic cell**

communications, and signaling applications.

**1.3 Photovoltaic parameters**

*1.3.1 Short-circuit current density*

*1.3.2 Open-circuit voltage*

*1.3.3 Maximum power output*

from solar cell is zero.

the junction, exposure of incident light, etc.

energy. As the Sun provides a considerable amount of energy for our planet, the energy it provided is approximately 10,000 times more than global demand

(i.e., 31,024 J/year); conversion of its 0.1% that is received by the Earth's surface using solar cells with power conversion efficiency of 10% would fulfill our present needs [1].

Photovoltaic device generates electrical power by converting sunlight into electricity in the presence of semiconducting materials using the phenomenon, the so-called photovoltaic effect. At first, French scientist Alexandre Becquerel in 1839 discovered photovoltaic effect [2]. After that more than 100 years later, Reynolds et al. in 1954 developed silicon solar cell that was primarily used in space applications until about the mid-1970s [3]. Recently, various kinds of photovoltaic devices are being developed, including silicon solar cells (Si-SCs), dye-sensitized solar cells (DSSCs), quantum dot-sensitized solar cells (QD-DSSCs), organic photovoltaic cells (OPVs), perovskite solar cells (PSCs), etc. Presently, solar cell devices are being used in customer electronics, small-scale remote residential power systems,

In addition to series and shunt resistance, the photovoltaic solar cells' performance is mainly characterized by six important parameters, (1) short-circuit current density, (2) open-circuit voltage, (3) maximum power output, (4) fill factor, (5) incident photon-to-current conversion efficiency, and (6) solar energy to power

The short-circuit current density is usually written as *Jsc*, which corresponds to the current that passes through the solar cell of one square centimeter area when the impedance is low and voltage across solar cell is zero. The *J*sc arises due to generation and collection of light-generated charge carriers. For ideal solar cell, at most moderate resistive loss mechanisms, the *J*sc and light-generated current are identical. Basically, *J*sc depends upon the area of the solar cell, number of photons reaching at

The open-circuit voltage is usually presented as *V*oc, which is the maximum voltage generated from a solar cell when there is no current. The *V*oc corresponds to the amount of forward bias on solar cell due to bias of solar cell junction with light-generated current. The power (*P*) produced by solar cell in Watt can be easily calculated alone by *I-V* curve using the equation, *P* = *IV*. The voltage and current at

For a given bias voltage, the power output of solar cell is the product of measured cell current and voltage. The *J*sc and *V*oc are the maximum current and voltage, respectively, from a solar cell. However, at both of these operating points, the power

maximum power from point are denoted as *Vmp* and *Imp*, respectively.

conversion efficiency, which are thoroughly discussed as follows [4].

**64**

The fill factor (*ff*) is defined as the ratio of the maximum power from the solar cell to the product of Voc and *Jsc*. Graphically, *ff* is a measure of "squareness" of solar cell and also an area of the largest rectangle which will fit in the *I-V* curve. Typically, the range of *ff* is from 0.50 to 0.82 or 50 to 82% as the *ff* is also represented in percentage using the following relation:

 *ff(%)* <sup>=</sup> *Pmp* \_\_\_\_\_ *JscVoc* <sup>=</sup> *ImpVmp* \_\_\_\_\_\_ *JscVoc* × 100 (1)

### *1.3.5 Incident photon-to-current conversion efficiency*

The incident monochromatic photon-to-current conversion efficiency (IPCE), sometimes referred to also as the "external quantum efficiency" (EQE), is an important parameter of solar cell device. The IPCE can be under light intensity of 100 mW cm2 (AM1.5), which is estimated in the following equation:

$$IPCE \text{ (\%)} = \frac{I\_{\kappa}(A)}{P(\mathcal{W})} \times \frac{1240}{\lambda \text{(mm)}} \times 100 \tag{2}$$

where photocurrent density (*J*) is generated by monochromatic light with wavelength (*λ*) and intensity (*P*)*.*

### *1.3.6 Solar-to-electrical power conversion efficiency*

The solar-to-electrical power conversion efficiency (*η*%) is an essential parameter to confirm the performance of one solar cell under testing. The *η* is defined as the ratio of energy output from the solar cell to an energy input from the Sun. In addition to reflecting performance of the solar cell itself, *η* depends on the spectrum and intensity of the incident sunlight and temperature of the solar cell. Therefore, terrestrial solar cells are measured under air mass 1.5 conditions in addition to a temperature of 25°C. The solar cells intended for space use are measured under air mass "0" conditions. It is well known that an overall η (%) of the solar cells can be determined by *Jsc, Voc, ff*, and the intensity of the incident light (*Pin*) as follows:

$$\mathbf{\eta(\%)} \quad = \frac{P\_{\text{out}}}{P\_{\text{in}}} \quad = \frac{I\_{\text{sc}} V\_{\text{ac}} f \mathbf{f}}{P\_{\text{in}}} \times \mathbf{100} \tag{3}$$

#### **1.4 History of dye-sensitized and perovskite solar cells**

In 1873, Vogel and Berlin invented dye sensitization technique, but until the 1970s DSSCs' mechanism was unclear. Therefore, compared with silicon-based photovoltaic devices, the performance of these early DSSCs was poor (*η* = <1%). The major obstacle in poor performance was relatively low adsorption of dye molecules into the metal oxide photoanode surface. Few improvements in efficiency were achieved by coating a thick layer of dye molecules onto the metal oxide photoanode surface [5]. Nevertheless, the power conversion efficiency was limited to ≤2% due to the low-light harvesting and charge collection from the adsorbed dye molecules. In the 1990s, Prof. Michel Gratzel and his team creatively demonstrated a practical photoelectrochemical cell device with a certified power conversion efficiency of 11.9%,

presenting excellent market competitiveness and commercial prospect [6]. However, such DSSCs of a liquid-state electrolyte are with highly volatile solvents, which not only affect the long-term stability of the device but also limit its large-scale production. In 1998, Gratzel et al. unveiled a solid-state organic hole-transporting material, i.e., 2,2,7,7-tetrakis (N,N-di-p-methoxy-phenylamine)-9,9-spirobifluorene (spiro-OMeTAD), to replace the conventional liquid-state electrolyte for a solidstate DSSCs [7]. From 1998 to 2011, the power conversion efficiency of solid-state DSSCs increased steadily from 0.74% to 7.2% but still much lower than that obtained by liquid-state electrolyte-based DSSCs [8]. In 2009, Miyasaka and co-workers improved the power conversion efficiency of perovskite solar cell to 3.8% by replacing bromine (MAPbBr3) with iodine (MAPbI3) [9]. In 2011, Park et al. prepared MAPbI3 perovskite as quantum dots with a size of ca. 2–3 nm, resulting in an enhanced power conversion efficiency of 6.5% [10]. In the family of photovoltaic device, PSCs have demonstrated much stronger absorption than the standard N719 dye, but the limitation in perovskite-based solar cells was the rapid degradation of the device performance resulting in the dissolution of perovskites in liquidstate electrolytes. In 2012, Park's group works together with Gratzel's group and introduced perovskite-sensitized solar cell by using solid-state spiro-OMeTAD as a hole-transporting material by replacing liquid-state electrolytes [11], where the solid-state spiro-OMeTAD not only solved the problem of perovskite dissolution but also significantly improved the stability and power conversion efficiency (9.7%). Remarkable progress of perovskite solar cell has been made during 2013–2014 as the power conversion efficiency increased to a certified 16.2% and 20.1% [12, 13]. Sahil et al. prepared fully textured monolithic perovskite/silicon tandem solar cells with 25.2% certified power conversion efficiency. Besides the breakthrough in efficiency, novel designs of device architectures aiming for low-cost and highly stable DSSCs and PSCs have also been developed [14].
