**4. Photovoltaic effect in inorganic–organic perovskite solar cells**

Solar power is the one of the world's most abundant energy resource and daily input of this energy to the earth's surface is enough to cover our energy needs, but efficient and costeffective ways of converting it to electricity, have remained as one of the scientist's challenges. Photovoltaic cells are the most promising device for directly converting the photons to electricity and it has been extensively studied in the past 50 years using various combinations of inorganic semiconductors or organic sensitizers. For photovoltaic energy to become competitive with fossil fuels and to capture a worthy place at energy markets, it is necessary to reduce the total cost of solar energy conversion by increasing their power conversion efficiencies or by reducing the cost of photovoltaic cells.

Today there is a lot of material used in photovoltaic structure and installed around the world. The photovoltaic market is currently dominated by crystalline Si solar cells with efficiencies close to 20% that known as First Generation of Solar Cells. This generation that have more than 150 micrometer thick, have the highest efficiency in all type of Solar cells that manufactured, but take a lot of energy to produce and therefore the cost of manufacturing is too high.

As cost-effective devices, thin film solar cell those containing a few micrometers of inorganic materials that known as second generation can be introduced. With a thin photovoltaic film, optical management is an important key for harvesting light while ensuring high efficiency. Thin film solar cell often limit light-harvesting ability because of their materials low absorption coefficients and narrow absorption bands. At least, these flexible cells have lower material costs, but they are also less efficient.

Alternative "third generation" technologies such as dye sensitized solar cells, organic photo‐ voltaics and quantum dot solar cells in both electrochemical and solid-state structures, assure low cost solar power because of low cost fabrication methods based on solution-processing techniques such as blade coating, screen printing and spraying, but high bandgap light absorption by these types has not allowed high performance in quantum conversion and photovoltaic generation.

The first observation of photocurrents in oxide perovskite material can date back to 1956 [1] that have been widely studied. David B. Mitzi in 1990 used organometal halide perovskites in LED [2] and thin-film field-effect transistors [3] and demonstrated its high efficiency as light emitters. Given that we know the good light emitter is a good light absorber, perovskites materials because of their light absorption efficiently over a broad spectrum is convenient option as photovoltaic materials.

Also, because perovskite can directly deposited from solution, manufacturing costs is lower than another type of solar cells. But it should be noted that manufacturing cost could rise due to encapsulation process. Therefore, perovskites could resolve the solar cell industry by matching the output of silicon cells at a lower price than that of thin film, because of their lowcost materials and manufacturing process.

For first time in 2009, perovskites were used as solar cell [4]. As show in Figure 15 this device are built upon the architectural basis for DSSCs and achieved 3.8% efficiencies in a liquid electrolyte configuration where the absorber was regarded as a QDs deposited on tio2. The efficiency was further improved to 6.5% but the enormous drawback to this types, regardless of their low efficiency, were had dissolution of liquid electrolyte away the perovskite that cause short stability for device.

Liquid electrolyte

Electron Selective

Electron Selective

Contact

Perovskite

Glass

*Figure 15. Schematic of first perovskites solar cell* **Figure 15.** Schematic of first perovskites solar cell Introducing of Solid Hole Transporting Layer (HTL) by Nam-Gyu Park and Gratzel [49], and

Hybrid Perovskite

Hybrid

TiO2

Photovoltaic cells are the most promising device for directly converting the photons to electricity and it has been extensively studied in the past 50 years using various combinations of inorganic semiconductors or organic sensitizers. For photovoltaic energy to become competitive with fossil fuels and to capture a worthy place at energy markets, it is necessary to reduce the total cost of solar energy conversion by increasing their power conversion

Today there is a lot of material used in photovoltaic structure and installed around the world. The photovoltaic market is currently dominated by crystalline Si solar cells with efficiencies close to 20% that known as First Generation of Solar Cells. This generation that have more than 150 micrometer thick, have the highest efficiency in all type of Solar cells that manufactured, but take a lot of energy to produce and therefore the cost of manufacturing is too high.

As cost-effective devices, thin film solar cell those containing a few micrometers of inorganic materials that known as second generation can be introduced. With a thin photovoltaic film, optical management is an important key for harvesting light while ensuring high efficiency. Thin film solar cell often limit light-harvesting ability because of their materials low absorption coefficients and narrow absorption bands. At least, these flexible cells have lower material

Alternative "third generation" technologies such as dye sensitized solar cells, organic photo‐ voltaics and quantum dot solar cells in both electrochemical and solid-state structures, assure low cost solar power because of low cost fabrication methods based on solution-processing techniques such as blade coating, screen printing and spraying, but high bandgap light absorption by these types has not allowed high performance in quantum conversion and

The first observation of photocurrents in oxide perovskite material can date back to 1956 [1] that have been widely studied. David B. Mitzi in 1990 used organometal halide perovskites in LED [2] and thin-film field-effect transistors [3] and demonstrated its high efficiency as light emitters. Given that we know the good light emitter is a good light absorber, perovskites materials because of their light absorption efficiently over a broad spectrum is convenient

Also, because perovskite can directly deposited from solution, manufacturing costs is lower than another type of solar cells. But it should be noted that manufacturing cost could rise due to encapsulation process. Therefore, perovskites could resolve the solar cell industry by matching the output of silicon cells at a lower price than that of thin film, because of their low-

For first time in 2009, perovskites were used as solar cell [4]. As show in Figure 15 this device are built upon the architectural basis for DSSCs and achieved 3.8% efficiencies in a liquid electrolyte configuration where the absorber was regarded as a QDs deposited on tio2. The efficiency was further improved to 6.5% but the enormous drawback to this types, regardless of their low efficiency, were had dissolution of liquid electrolyte away the perovskite that cause

efficiencies or by reducing the cost of photovoltaic cells.

costs, but they are also less efficient.

238 Solar Cells - New Approaches and Reviews

photovoltaic generation.

option as photovoltaic materials.

short stability for device.

cost materials and manufacturing process.

Introducing of Solid Hole Transporting Layer (HTL) by Nam-Gyu Park and Gratzel [49], and replace liquid electrolyte by it, solve this problem in 2012 and rose the efficiency to 9%. (Figure 16) Introducing of Solid Hole Transporting Layer (HTL) by Nam-Gyu Park and Gratzel [5], and replace liquid electrolyte by it, solve this problem in 2012 and rose the efficiency to 9%. (Figure 16) *Figure 15. Schematic of first perovskites solar cell* Introducing of Solid Hole Transporting Layer (HTL) by Nam-Gyu Park and Gratzel [49], and replace liquid electrolyte by it, solve this problem in 2012 and rose the efficiency to 9%. (Figure 16) replace liquid electrolyte by it, solve this problem in 2012 and rose the efficiency to 9%. (Figure 16) Electron Selective

Metal Contact

Glass

Glass

 In the late 2012s, research topics towards to materials engineering and switch structure by *Figure 16. Nam-Gyu Park and Gratzel perovskites solar cell* **Figure 16.** Nam-Gyu Park and Gratzel perovskites solar cell

manufacturing methods to increase the Efficiency of these type of solar cells. Henry Snaith [50] in Oxford University Switched TiO2 to an insulating Aluminum oxide scaffold in Gratzel perovskites solar cell that show in Figure 17. This switch, surprisingly increase efficiency to 10.9%. Hybrid TiO2 Hybrid Al2O3 In the late 2012s, research topics towards to materials engineering and switch structure by manufacturing methods to increase the Efficiency of these type of solar cells. Henry Snaith [50] in Oxford University Switched TiO2 to an insulating Aluminum oxide scaffold in Gratzel perovskites solar cell that show in Figure 17. This switch, surprisingly increase efficiency to 10.9%. In the late 2012s, research topics towards to materials engineering and switch structure by manufacturing methods to increase the Efficiency of these type of solar cells. Henry Snaith [6] in Oxford University Switched TiO2 to an insulating Aluminum oxide scaffold in Gratzel perovskites solar cell that show in Figure 17. This switch, surprisingly increase efficiency to 10.9%. *Figure 16. Nam-Gyu Park and Gratzel perovskites solar cell* In the late 2012s, research topics towards to materials engineering and switch structure by manufacturing methods to increase the Efficiency of these type of solar cells. Henry Snaith [50] in Oxford University Switched TiO2 to an insulating Aluminum oxide scaffold in Gratzel perovskites solar cell that show in Figure 17. This switch, surprisingly increase efficiency to 10.9%.

TiO2

15

On the other hand, Snaith and coworkers [17] demonstrated efficient planar solar cells of CH3NH3PbI3-xClx formed by dual source evaporation of PbCl2 and CH3NH3I. The film was evaporated on a compact TiO2 layer (as an electron transport layer) and then a Spiro-OMeTAD layer (as a hole transport layer) was spin coated over it (Figure 18). The evaporated films containing crystalline structures on the length scale of hundreds of nanometers are enormously uniform [32].

15

15

(as a hole transport layer) was spin coated over it (Figure 18). The evaporated films containing crystalline structures on the length scale of hundreds of nanometers are enormously uniform [32].

(as a hole transport layer) was spin coated over it (Figure 18). The evaporated films containing crystalline structures on the length scale of hundreds of nanometers are enormously uniform [32]. CH3NH3PbI3-xClx formed by dual source evaporation of PbCl2 and CH3NH3I. The film was evaporated on a compact TiO2 layer (as an electron transport layer) and then a Spiro-OMeTAD layer *Figure 17. Switching TiO2 to an Al2O3 in Gratzel perovskites solar cell* **Figure 17.** Switching TiO2 to an Al2O3 in Gratzel perovskites solar cell

Perovskite

Al2O3

On the other hand, Snaith and coworkers [17] demonstrated efficient planar solar cells of CH3NH3PbI3-xClx formed by dual source evaporation of PbCl2 and CH3NH3I. The film was evaporated on a compact TiO2 layer (as an electron transport layer) and then a Spiro-OMeTAD layer (as a hole transport layer) was spin coated over it (Figure 18). The evaporated films containing crystalline structures on the length scale of hundreds of nanometers are enormously uniform [32].

*Figure 18. Schematic of Snaith hybrid perovskite solar cell* **Figure 18.** Schematic of Snaith hybrid perovskite solar cell

and coworkers, that report 12.1 % efficiency for their device.

TiO2

Finally they reported 15.4% efficiency for their device and another research in this area, reported the difference efficiency by using different material for example Pbl2 that Graetzel and Bolink [51] used (device efficiency was 12.04 %) or difference evaporation method for example as show in Figure 19 employs both solution based deposition and vapor phase transformation by Graetzel [21] and coworkers, that report 12.1 % efficiency for their device. Finally they reported 15.4% efficiency for their device and another research in this area, reported the difference efficiency by using different material for example Pbl2 that Graetzel and Bolink [7] used (device efficiency was 12.04 %) or difference evaporation method for example as show in Figure 19 employs both solution based deposition and vapor phase transformation by Graetzel [21] and coworkers, that report 12.1 % efficiency for their device. *Figure 18. Schematic of Snaith hybrid perovskite solar cell* Finally they reported 15.4% efficiency for their device and another research in this area, reported the difference efficiency by using different material for example Pbl2 that Graetzel and Bolink [51] used (device efficiency was 12.04 %) or difference evaporation method for example as show in Figure 19 employs both solution based deposition and vapor phase transformation by Graetzel [21]

*Figure 19. Gratzel sticks with the TiO2 structure and tinkered with the deposition step.* **Figure 19.** Gratzel sticks with the TiO2 structure and tinkered with the deposition step.

Inorganic

Inorganic

Substrate film

Substrate film

These deposition techniques had two important drawbacks: first challenging for large-scale industrial production and second is that the all-solution process results in decreased film quality, and the vacuum process requires expensive equipment and uses a great deal of energy. Yang Yang [16] from UCLA university present new method named "Vapor-assisted solution process" that organic material infiltrates the inorganic matter and forms a compact perovskite film. These films is significantly more uniform than the films produced by the wet technique (Figure 20). Organic vapor *Figure 19. Gratzel sticks with the TiO2 structure and tinkered with the deposition step.* These deposition techniques had two important drawbacks: first challenging for large-scale industrial production and second is that the all-solution process results in decreased film quality, and the vacuum process requires expensive equipment and uses a great deal of energy. Yang Yang [16] from UCLA university present new method named "Vapor-assisted solution process" that organic material infiltrates the inorganic matter and forms a compact perovskite film. These films is significantly more uniform than the films produced by the wet technique (Figure 20). These deposition techniques had two important drawbacks: first challenging for large-scale industrial production and second is that the all-solution process results in decreased film quality, and the vacuum process requires expensive equipment and uses a great deal of energy. Yang Yang [16] from UCLA university present new method named "Vapor-assisted solution process" that organic material infiltrates the inorganic matter and forms a compact perovskite film. These films is significantly more uniform than the films produced by the wet technique (Figure 20).

16

16

*Figure 20. Vapor-assisted solution process*

Organic vapor

*Figure 20. Vapor-assisted solution process*

Perovskite

Perovskite

significantly more uniform than the films produced by the wet technique (Figure 20).

*Figure 19. Gratzel sticks with the TiO2 structure and tinkered with the deposition step.*

These deposition techniques had two important drawbacks: first challenging for large-scale industrial production and second is that the all-solution process results in decreased film quality, and the vacuum process requires expensive equipment and uses a great deal of energy. Yang Yang [16]

*Figure 18. Schematic of Snaith hybrid perovskite solar cell*

Glass

and coworkers, that report 12.1 % efficiency for their device.

Metal Contact

HTL

TiO2 mesoporous Hole transporting layer

Finally they reported 15.4% efficiency for their device and another research in this area, reported the difference efficiency by using different material for example Pbl2 that Graetzel and Bolink [51] used (device efficiency was 12.04 %) or difference evaporation method for example as show in Figure 19 employs both solution based deposition and vapor phase transformation by Graetzel [21]

Hybrid perovskite

Metal Contact

Electron Selective Contact

PbI2 CH3NH3I

*Figure 20. Vapor-assisted solution process* **Figure 20.** Vapor-assisted solution process

On the other hand, Snaith and coworkers [17] demonstrated efficient planar solar cells of CH3NH3PbI3-xClx formed by dual source evaporation of PbCl2 and CH3NH3I. The film was evaporated on a compact TiO2 layer (as an electron transport layer) and then a Spiro-OMeTAD layer (as a hole transport layer) was spin coated over it (Figure 18). The evaporated films containing crystalline structures on the length scale of hundreds of nanometers are enormously

Glass

Glass

*Figure 18. Schematic of Snaith hybrid perovskite solar cell*

Finally they reported 15.4% efficiency for their device and another research in this area, reported the difference efficiency by using different material for example Pbl2 that Graetzel and Bolink [7] used (device efficiency was 12.04 %) or difference evaporation method for example as show in Figure 19 employs both solution based deposition and vapor phase transformation by Graetzel [21] and coworkers, that report 12.1 % efficiency for their device.

*Figure 18. Schematic of Snaith hybrid perovskite solar cell*

*Figure 19. Gratzel sticks with the TiO2 structure and tinkered with the deposition step.*

*Figure 19. Gratzel sticks with the TiO2 structure and tinkered with the deposition step.*

These deposition techniques had two important drawbacks: first challenging for large-scale industrial production and second is that the all-solution process results in decreased film quality, and the vacuum process requires expensive equipment and uses a great deal of energy. Yang Yang [16] from UCLA university present new method named "Vapor-assisted solution process" that organic material infiltrates the inorganic matter and forms a compact perovskite film. These films is significantly more uniform than the films produced by the wet technique

significantly more uniform than the films produced by the wet technique (Figure 20).

significantly more uniform than the films produced by the wet technique (Figure 20).

Inorganic

**Figure 19.** Gratzel sticks with the TiO2 structure and tinkered with the deposition step.

Inorganic

These deposition techniques had two important drawbacks: first challenging for large-scale industrial production and second is that the all-solution process results in decreased film quality, and the vacuum process requires expensive equipment and uses a great deal of energy. Yang Yang [16] from UCLA university present new method named "Vapor-assisted solution process" that organic material infiltrates the inorganic matter and forms a compact perovskite film. These films is

These deposition techniques had two important drawbacks: first challenging for large-scale industrial production and second is that the all-solution process results in decreased film quality, and the vacuum process requires expensive equipment and uses a great deal of energy. Yang Yang [16] from UCLA university present new method named "Vapor-assisted solution process" that organic material infiltrates the inorganic matter and forms a compact perovskite film. These films is

Organic vapor

Organic vapor

and coworkers, that report 12.1 % efficiency for their device.

and coworkers, that report 12.1 % efficiency for their device.

Metal Contact

Metal Contact

Substrate film

Substrate film

Hole transporting layer

Hole transporting layer

**Figure 18.** Schematic of Snaith hybrid perovskite solar cell

Finally they reported 15.4% efficiency for their device and another research in this area, reported the difference efficiency by using different material for example Pbl2 that Graetzel and Bolink [51] used (device efficiency was 12.04 %) or difference evaporation method for example as show in Figure 19 employs both solution based deposition and vapor phase transformation by Graetzel [21]

Finally they reported 15.4% efficiency for their device and another research in this area, reported the difference efficiency by using different material for example Pbl2 that Graetzel and Bolink [51] used (device efficiency was 12.04 %) or difference evaporation method for example as show in Figure 19 employs both solution based deposition and vapor phase transformation by Graetzel [21]

Hybrid perovskite

Hybrid perovskite

Metal Contact

Metal Contact

Electron Selective Contact

Electron Selective Contact

PbI2 CH3NH3I

PbI2 CH3NH3I

Perovskite

Perovskite

16

16

*Figure 20. Vapor-assisted solution process*

*Figure 20. Vapor-assisted solution process*

uniform [32].

240 Solar Cells - New Approaches and Reviews

HTL

HTL

(Figure 20).

TiO2 mesoporous

TiO2 mesoporous

In conjunction with these exciting device-centric advancements, fundamental studies into the photoexcited species and their photogeneration and recombination dynamics in perovskites also began in earnest. In conjunction with these exciting device-centric advancements, fundamental studies into the photoexcited species and their photogeneration and recombination dynamics in perovskites also

16 At least one of the remaining question is "Is the Solar Cell Excitonic?" Perovskite solar cell had similar diffusion lengths for electron and hole that average is about 100 to 300 nm [8] that put these cells in conventional solar cell class. On other hand either indicate similar mobilities for both holes and electrons [9] and this classify these cells in excitonic solar cell group (Figure 21). began in earnest. At least one of the remaining question is "Is the Solar Cell Excitonic?" Perovskite solar cell had similar diffusion lengths for electron and hole that average is about 100 to 300 nm [52] that put these cells in conventional solar cell class. On other hand either indicate similar mobilities for both holes and electrons [53] and this classify these cells in excitonic solar cell group (Figure 21).

Conventional Solar Cell

Excitonic Solar Cell

*Figure 21. Schematic of conventional and excitonic solar cell* **Figure 21.** Schematic of conventional and excitonic solar cell

Chemical Physics 1963; 38 2042–2043.

wells. Solid State Communications 1994; 92 295–301.

Accordingly, due to the common properties of these types of solar cells, between Conventional and excitonic solar cell, researchers cannot exactly determine whether the photoexcited species are excitons or free charges. Accordingly, due to the common properties of these types of solar cells, between Conventional and excitonic solar cell, researchers cannot exactly determine whether the photoexcited species are excitons or free charges.

#### In this section we have presented the synthesis and characterization of organic-inorganic hybrid **5. Conclusion**

**5) Conclusion** 

guarantee improved optical and electronic properties by combining organic and inorganic components together. The unusual features and versatile characteristics of hybrid organic-inorganic perovskites open up promising applications in many fields such as electronics, optics, optoelectronics, mechanics, environment, medicine and biology. The application of these materials in the solar cells as a novel class of low-cost materials for high efficiency hybrid semiconductor photovoltaic cells has been explained in more detail. **6) References**  [1]. Agranovich V, Gartstein Y N, Litinskaya M. Hybrid Resonant Organic-Inorganic Nanostructures In this section we have presented the synthesis and characterization of organic-inorganic hybrid perovskite. Hybrid organic-inorganic materials represent an alternative to present materials as they guarantee improved optical and electronic properties by combining organic and inorganic components together. The unusual features and versatile characteristics of hybrid organic-inorganic perovskites open up promising applications in many fields such as electronics, optics, optoelectronics, mechanics, environment, medicine and biology. The application of these materials in the solar cells as a novel class of low-cost materials for high efficiency hybrid semiconductor photovoltaic cells has been explained in more detail.

[2]. Pope M, Kalmann H, Magnante P. Electroluminescence in Organic Crystals The Journal of

[3]. Agranovich V, Atanasov R, Bassani F. Hybrid interface excitons in organic-inorganic quantum

[4]. Agranovich V, La Rocca G C, Bassani F. Efficient electronic energy transfer from a

semiconductor quantum well to an organic material. JETP Letters 1997; 66 748–751.

for Optoelectronic Applications. Chemical Reviews 2011; 111 5179–5214.

perovskite. Hybrid organic-inorganic materials represent an alternative to present materials as they
