Lakhasly

CHAPTER 1
INTRODUCTION AND THEORETICALL
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1-1 Introduction
"Due to the importance of thin film compounds in many practical applications, we study materials like thin film
Cadmium sulphide (CdS). This compound holds significance in various technological advancements, particularly in
the realm of renewable energy."
1-2 The History and Culture of Energy
The history and culture of energy are deeply intertwined with the development and progression of human civilization.
From ancient times to the modern era, energy has played a pivotal role in shaping societies, economies, and cultures
around the world.
1-2-1 Ancient Civilizations: Early human societies relied on renewable energy sources such as biomass (wood,
animal dung) and muscle power (human labor, animal labor) for their survival. These civilizations developed
agricultural practices, built structures, and engaged in trade and commerce driven by the energy available to them.
Ancient cultures often revered natural elements such as the sun, wind, and water, recognizing their importance as
sources of energy [1].
1-2-2 Medieval and Renaissance Periods: During the medieval and Renaissance periods, advancements in
technology led to the utilization of water wheels and windmills for grinding grain, pumping water, and other
mechanical tasks. The harnessing of water and wind energy marked significant milestones in the history of energy
usage, enabling communities to expand agricultural production and industrial activities [2].
1-2-3 Industrial Revolution: The Industrial Revolution, beginning in the late 18th century, marked a profound shift
in energy usage. The invention of the steam engine fueled by coal ushered in an era of unprecedented industrial growth
and urbanization. Coal became the dominant energy source, powering factories, transportation, and urban
infrastructure. The rise of coal mining and industrialization profoundly transformed societies, leading to the
emergence of new social classes and labor movements [3].
1-2-4 The Age of Electricity: The late 19th and early 20th centuries saw the advent of electricity as a transformative
energy source. The development of electric generators, transmission systems, and electrical appliances
revolutionized industries, communication, and domestic life. Electricity enabled the widespread adoption of electric
lighting, electric motors, and eventually, electrified transportation [4].
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1-2-5 Modern Energy Landscape: In the 20th and 21st centuries, the energy landscape has become increasingly
diverse, with the emergence of oil, naturalgas, nuclear power, and renewable energy sources such as solar, wind, and
hydropower. Technological advancements have expanded the possibilities forenergy production, distribution, and
consumption, leading to debates about sustainability, environmental impacts, and energy security [5].
1-2-6 Cultural Perspectives: Energy has also influenced cultural expressions, artistic movements, and societal
values. Literature, art, and cinema often reflect themes related to energy, technology, and the human relationship with
nature. Energy-rich societies have seen the emergence of consumer culture, leisure activities, and lifestyles dependent
on energy-intensive technologies [6].
1-2-7 Challenges and Opportunities: Today, the world faces complex challengesrelated to energy sustainability,
climate change, and access to energy resources. There is growing recognition of the need to transition towards cleaner,
renewable energy sources and promote energy efficiency and conservation measures. Cultural shifts towards
sustainability, environmentalstewardship, and renewable energy adoption are becoming increasingly prevalent[7].In
conclusion, the history and culture of energy illuminate the intricate connections between human societies,
technological advancements, and the natural environment. Understanding the past and present dynamics of energy
usage is crucial for addressingthe challenges and opportunities that lie ahead in building a sustainable energy future.
1-3 What is energy?
Regarding energy, a frequently found definition in common literature as well as in textbooks is “energy is the ability
to do work” or slightly more detailed “energy is thecapacity of a system to do work. Energy can be converted
between the different energy forms, shown in Figure1.1 .
Figure 1-1 Energy forms
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1-4 Sources of Energy:
There are two types of sources of energy in the world:
1-4-1 Renewable Sources
Renewable resources are unlimited natural resources that can be replenished in a short period of time[8] , like Solar
and others you can see it in Figure 1.2 .
1-4-2 Non-renewable Sources
A non-renewable resource is a limited natural resource that cannot be re-made or re-grown in a short amount of time
at a scale comparable to its consumption [8], like fuel and others you can see it in Figure 1.2 .Table 1-1
Figure1-2 Examples of renewable and non-renewable.
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RENEWABLE ENERGY NON-RENEWABLE ENERGY
Advantages Disadvantage Advantages Disadvantage
Consistent and reliable energy Acid Rain
supply
Intermittent energy
production
Low carbon emissions
Much easier to produce and Effect on Human Health
use
High initial infrastructure
costs
Sustainable and abundant
Non-renewable energies seem Rising Prices
abundant
Land use and ecosystem
impact
Reduced dependence on
fossil fuels
Finite Resources Depleting
reserves over time
Well-established infrastructure
for extraction
Reliance on weather
conditions
Job creation and economic
growth
Table 1-1 advantages and disadvantages of energy sources [9].
1-5 Solar energy
Every day, the sun emits an enormous amount of energy in the form of heat and radiation, known as solar energy
[10]. The sun serves as a vast source of solar energy, providing energy to all living creatures on Earth. Solar energy
is renewable and clean, producing approximately 10,000 times more energy than the Earth can produce in the 21st
century alone.
Solar energy is considered a green energy source because it is renewable and sustainable. Unlike fossil fuels, which
are finite and contribute to pollution and climate change, solar energy is abundant and has minimal environmental
impact. It does not produce greenhouse gas emissions or contribute to global warming.
One of the significant advantages of solar energy is its versatility. Solar energy can be harnessed through various
technologies, including photovoltaic cells and solar thermal systems. Photovoltaic cells convert sunlight directly into
electricity, while solar thermal systems use sunlight to heat water or air for use in homes, businesses, and industries.
Solar energy offers numerous benefits beyond environmental sustainability. It reduces dependence on fossil fuels,
enhances energy security, and creates job opportunities in the growing solar industry. Additionally, solar energy
systems can be installed on rooftops, in remote areas, and even in space, providing energy access to diverse
communities worldwide.
As technology advances and economies of scale improve, the cost of solar energy continues to decline, making it
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increasingly affordable and accessible to consumers. Government incentives, tax credits, and renewable energy
policies further incentivize the adoption of solar energy, driving its widespread adoption globally [11].
1-6 solar PV Technology:
Solar cell also called photovoltaic (PV) cell is basically a technology that convert sunlight (photons) directly into
electricity (voltage and electric current) at the atomic level you can see it in figure (1-3). They are arranged in such
away so that they can capture as sunlight as possible.
This can be obtained through the photovoltaic effect, process in which two dissimilar materials in close contact
produce an electrical voltage when struck by light or other radiant energy. Essentially, solar cells are composed of
two different types of semiconductors: an n- and a p-type that are joined together to create a p-n junction. By joining
these two types of semiconductors, an electric field is formed in the region of the junction as electrons move to the
positive p-side and holes move to the negative n-side. This field causes negatively charged particles to move in one
direction and positively charged particles in the other direction, thus, producing an electrical voltage. On the other
hand, PV energy is also a renewable, versatile technology that can be used for almost anything that requires electricity,
from small and remote applications to large, central power stations [12].
Figure 1-3 Solar cell
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1-6-1 Photovoltic effect
When a photon of light is absorbed by a valence electron of an atom, the energy of the electron is increased by the
amount of energy of the photon. If the energy of the photon is equal to or more than the band gap of the semiconductor,
the electron with excess energy will jump into the conduction band where it can move freely. If, however, the photon
energy is less than the band gap, the electron will not have sufficient energy to jump into the conduction band. In this
case, the excess energy of the electrons is converted to excess kinetic energy of the electrons, which manifests in
increased temperature. If the absorbed photon had more energy than the band gap, the excess energy over the band gap
simply increases the kinetic energy of the electron. It must be noted that a photon can free up only one electron even
if the photon energy is a lot higher than the band gap. This fact is a big reason for the low conversion efficiency of PV
devices. The key to using the PV effect for generating useful power is to channel the free electrons through an external
resistance before they recombine with the holes. This is achieved with the help of the p–n junction [13].
Figure 1-4 Schematic of a PV device
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1-6-2 Photovoltic effect processes
The PV effect is described by three basic process :
1-6-2-1. Generation of charge carriers due to the absorption of photons in the materials that form a junction.
Absorption of a photon in a material means that its energy is used to excite an electron from an initial energy level Ei
to a higher energy level Ef , as shown in Fig. 1-5 (a). Photons can only be absorbed if electron energy levels Ei and Ef
are present so that their difference equals to the photon energy, hν = Ef − Ei . In an ideal semiconductor electrons can
populate energy levels below the so-called valence band edge, EV, and above the so called conduction band edge, EC.
Between those two bands no allowed energy states exist, which could be populated by electrons. Hence, this energy
Figure 1-5: The absorption of a photon in a semiconductor
difference is called the bandgap, Eg = EC − EV. If a photon with an energy smaller than Eg reaches an ideal
semiconductor, it will not be absorbed but will traverse the material without interaction.
If an electron is excited from Ei to Ef , a void is created at Ei . This void behaves like a particle with a positive
elementary charge and is called a hole. The absorption of a photon therefore leads to the creation of an electron-hole
pair, as illustrated in Fig. 1-6 ❶.
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Figure 1-6: A very simple solar cell model.
1-6-2-2 Subsequent separation of the photo-generated charge carriers in the junction.
Usually, the electron-hole pair will recombine, i.e. the electron will fall back to the initial energy level Ei , as illustrated
in Fig. 1-6 ❷. The energy will then be released either as photon (radiative recombination) or transferred to other
electrons or holes or lattice vibrations (nonradiative recombination). If one wants to use the energy stored in the
electron-hole pair for performing work in an external circuit, semipermeable membranes must be present on both
sides of the absorber, such that electrons only can flow out through one membrane and holes only can flow out through
the other membrane, as illustrated in Fig. 1-6❸. In most solar cells, these membranes are formed by n- and p-type
materials.
1-6-2-3 Collection of the photo-generated charge carriers at the terminals of the junction.
Finally, the charge carriers are extracted from the solar cells with electrical contacts so that they can perform work in
an external circuit (Fig. 1-6❹). The chemical energy of then electron-hole pairs is finally converted to electric energy.
After the electrons passed through the circuit, they will recombine with holes at a metal absorber interface, as
illustrated in Fig. 1-6 ❺ [14].
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1-7 Semiconductor Materials in Periodic Table:
In the periodic table of chemical elements, semiconductor materials are available in different groups. So the properties
of these materials are associated with their atomic characteristics & also vary from one group to another group.
Designers & researchers utilize the benefits of these dissimilarities to enhance the design & select the best material
for a required applicationThe semiconductor materials are atoms within a semiconductor that are available from
different groups in a periodic table as a combination of group III & V or either group IV or combinations of group II
& VI. In the periodic table, different semiconductors are designed with different materials from several groups, but
their properties vary between different semiconductors. In the periodic table, Silicon (Si) material is a group IV
element and it is the most frequently used semiconductor material because it forms the base for ICs or integrated
circuits. So, most of the solar cells are Si (Silicon) based. The diagram of semiconductor materials in the periodic
table is shown below. In a periodic table section, common semiconductor materials are indicated in the above fig (1-
7). Generally, a semiconductor is a single element like silicon, germanium, a compound like GaAs, CdTe/ InP, or an
alloy like AlxGa(1-x)As/ SixGe(1-x), where ‘x in these materials are the part of