**1.1. Sources of energy**

Energy makes change; it does things for us. The cars along the road as well as the boats over the water can be moved by energy. A cake in the oven and the ice frozen in the freezer also are been done using energy. It plays our favorite songs on the radio and lights our homes. Energy enables our bodies grow and make our minds to think. Scientists define energy as the ability to do work. Energy sources are classified into renewable and nonrenewable sources as shown in **Figure 1**.

**1.2. Solar energy**

Solar energy develops a large variety of techniques, including photovoltaic systems, concen-

Controlling the Microstructure and Properties of Titanium Dioxide for Efficient Solar Cells

http://dx.doi.org/ 10.5772/intechopen.72494

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Conversion of the light energy into electricity is the main use of photovoltaic solar cells and has been existing for a long time; many applications like solar panels on satellites and smaller uses as calculator or watch energy supply, which is familiar for everyone, enable them to be famous. The solar energy is instituted on the solar cell (photovoltaic) effect, which allows the

Electricity is a necessity in everyday life. The cheapest and available power plays a very crucial role in the economic development of the industrialized nations. At the beginning of the twenty-first century, more than 80% of electricity is generated by burning fossil fuels (coal, gas, and oil) [6]. Because of the limited supply of fossil fuels and the growing concerns about global warming, the use of more and more renewable energy sources in energy production is being encouraged in different parts of the world [7]. Among the various sources of renewable energy, solar energy has been considered to have great potential because of the virtually unlimited (100 KTW) supply of sunlight on the Earth [8]. The technology which harnesses the solar energy and converts it into electrical energy is called photovoltaic (PV) technology.

The semiconductor of choice for making dye-sensitized solar cells (DSSCs) due to its good

less water-insoluble inorganic material that is related to the family of transition metal oxide

in the absence of light, particular safety measures are needed when handling nanosized tita-

of TiIV+ and O2– ions. The conduction band is formed by the 3d orbital of titanium, and the

The most common form of this oxide in nature is rutile. Another form is brookite. A third form of this oxide is anatase, which is the thermodynamically stable crystalline form at high pressure. In all of them, each titanium is surrounded by six oxygen atoms, leading to more or less

dron is connected with 10 neighbors (two sharing edge oxygen pairs and eight sharing corner oxygen atoms), while for the anatase and brookite structures, every moiety is in contact with eight neighbors (four sharing an edge and four sharing a corner) as shown in **Figure 2**. Three-

, also known as titania. This material is a cheap and harm-

2− units [12]. For the rutile structure, each octahe-

is commercially available and

is a chemically inert substance and it does not promote chemical reactions

2− octahedrons. Crystal structures differ by the distortion of each octahedron

network is obtained from a mixture of corner-sharing and edge-sharing

has a strong ionic character and can be noticed as being constituted

trating solar power, passive solar systems, solar hot water, and solar process heat [5].

conversion of light (photons) to electricity (electrons).

**1.3. Photovoltaic (PV) technology**

**1.4. Titanium dioxide**

[9]. Although TiO<sup>2</sup>

distorted TiO<sup>6</sup>

dimensional TiO2

octahedral units [13].

nia [10]. Moreover, TiO2

properties is titanium dioxide, TiO<sup>2</sup>

widely used in industrial applications [11].

and by the assembly patterns of the TiO6

valence band is obtained by the 2p orbital of oxygen. TiO<sup>2</sup>

Most of our energy is extracted from nonrenewable energy sources. Coal, petroleum, natural gas, propane, and uranium are nonrenewable energy sources. The name of nonrenewable energy sources has appeared because their supplies are limited. Petroleum, for example, was formed millions of years ago from the remains of ancient sea plants and animals. A long period of time is needed to deposit more crude oil.

Renewable energy sources include biomass, geothermal energy, hydropower, solar energy, and wind energy. They are replenished in a short time, so they are called renewable. Electricity is mainly produced from renewable energy sources. Sunlight, or solar energy, can be used directly for heating, lighting, generating electricity, and many other applications [1, 2]. Indirectly, sun's heat also creates winds, whose energy is used to generate electricity by wind turbines, which is called wind energy. Plants are grown by sunlight. Biomass is the organic matter which is composed of plants. It can be used, for example, to produce electricity and transport fuels. Furthermore, geothermal energy absorbs the Earth's internal heat and can be used for a large variety of applications such as building heating and electricity production. Ocean energy draws on energy of the ocean waves, currents, and tides which can under favorable conditions be used for the production of electricity. Global energy consumption consists of six primary sources: 44% petroleum, 26% natural gas, 25% coal, 2.5% hydroelectric power, 2.4% nuclear power, and 0.2% non-hydro renewable energy [3]. Between 1990 and 2010, worldwide consumption of petroleum, coal, and natural gas is enhanced by 22, 27, and 71%, respectively.

**Figure 1.** Renewable and nonrenewable energy sources. From Ref. [4]. Reprinted with permission from WordPress.
