Introduction An electrical device which converts the sunlight directly into electricity by the photovoltaic effect is called the solar cell

Introduction
An electrical device which converts the sunlight directly into electricity by the photovoltaic effect is called the solar cell. A solar cell is also called as Photovoltaic cell because solar cell works on the principle of the photovoltaic effect. Today it is an important and fast-growing renewable source. The main goal to produce solar energy is to reduce fossil fuels which change the climatic conditions. It’s an alternative to fossil fuels. It is a new technology compared to other technologies which produce electricity. Latest advances in science and technology have added us with many alternatives to produce energy on a sensible level, such as wind, geothermal, biomass, and solar. Solar is a carbon-free technology, safer and one-time investment for our family and business so that one can immediately reduce their electricity bill. Free from energy costs and increasing carbon dioxide (CO2) emissions. The first photovoltaic effect was discovered by Becquerel in 1839. The light vitality consumed by Earth for an hour from the sun is all that anyone could need to fulfill worldwide vitality requirements for a whole year. For this cause, many scientists started to work on solar cells to find cost-effective and more efficient solar cells, so that the world does not depend on the fossil fuels. This technology provides a number of important benefits. Solar power is a sustainable resource that is available anywhere in the world. Unlike other electricity generated technologies, it is used anywhere. This technology doesn’t need any fuel. Maintenance and operation are low. As long as the sun shines the solar cells produce energy. PV cells are the sustainable and eco-friendly technology of generating energy. CITATION Tae16 l 4105 (Leea, 2016), CITATION Lui18 l 4105 (Ono, 2018)
The proposed project mainly concentrates on the study of solar cells in depth and analysis of this technology. The topics like what are solar cells? How they work to generate energy? What is its energy efficiency? How many different types of solar cells? What are its advantages and limitations? What is the impact on environment? Besides this, the paper also concentrates on analysis of the performance of this technology, economic feasibility of this technology and any recommendations required to improve the effectiveness of this technology.
Types of solar cells
Silicon Solar Cells:
The name silicon solar cells itself defining the type of a solar cell and how it is made. Most of the solar cells on the today’s market are made with silicon. But, silicon can take many forms. Solar cell efficiency depends on the purity of the silicon; purity means the way in which the silicon modules are arranged. The greater the way in which the arrangement of the silicon molecules, the efficient of the solar cell will be high to convert sunlight into electricity. The lesser the way in which solar molecules are arranged, the efficient of the solar cell will be low. Most of the silicon-based solar cells on the market are consists of crystalline silicon. There are two types of crystalline – monocrystalline and polycrystalline.

Monocrystalline Silicon Solar Cells:
Monocrystalline solar cells also called “single crystalline”. Identification of these cells is easy due to their colour. These cells are unusual because the arrangement of silicon is greater. As we know that the purity of the silicon is high then the efficiency to convert sunlight into electricity will be high. So the most efficient solar cells are monocrystalline solar cells. These solar cells are made with the material called “silicon ingots,” This material has the cylindrical shape design which helps to perform better. The edges of these cells are round shape because of the cylindrical design ingots. Other cells have the square shape. Monocrystalline cells are not only most efficient in the conversion of sunlight but also the most space-efficient. Logically it requires less number of solar cells to get unit of electrical output. One more advantage of these cells is that they last longer than any other type of cells. These have the warranty up to 25 years.

Monocrystalline silicon cell
http://sinovoltaics.com/wp-content/uploads/2011/10/Mono-crystalline-solar-cell.jpgPolycrystalline Solar Cells:

Polycrystalline cell
https://c1.staticflickr.com/8/7331/9068489963_0f29070e5f_b.jpgOther names for polycrystalline solar cells are polysilicon and multisilicon cells. These were introduced to the industry in 1981 and were the first solar cells. Polycrystalline cells do not experience the cutting process like monocrystalline cells. Rather, the silicon is dissolved and filled into square boxes; hence these cells are square shaped. There will not be any wastage during the manufacturing process and these are less costly compared to monocrystalline solar cells. Commonly, polycrystalline cells are less productive than the monocrystalline. Typically, polycrystalline solar PV system has the efficiency of 13-16%. Low efficiency is due to lower purity. One more disadvantage of this cell is that it doesn’t bare much heat, so it doesn’t function effectively at high temperatures.
Thin Film Solar Cell:

Thin film solar cell
http://topdiysolarpanels.com/images/thin-film-solar-panel.jpgThin film solar cells are 2nd generation solar cells. It is made up of storing at least one thin layer or thin film of PV material on a substrate like glass, plastic or metal. These solar cells are widely used in many technologies like cadmium telluride (CdTe), copper indium gallium diselenide (CIGS), and amorphous thin-film silicon (a-Si, TF-Si). The thickness of the film is between few nanometres to tens of micrometres. The efficiency of this cell is very less and it is about 7-13%. The cost of these solar cells is high and is the main disadvantage. We can get the bulk amount of energy easily when compared to crystalline-based modules; hence the bulk production cost is comparatively cheap. One of the major disadvantages is that these cells need more space which is not suitable for the residential purpose. The lifespan of these cells is less compared to crystalline cells.

Efficiencies of different types of solar cells:

http://css.umich.edu/factsheets/photovoltaic-energy-factsheet
PV Technology Cell conversion efficiency Module conversion efficiency
Crystalline Monocrystalline silicon 25% 14% – 16%
Multi crystalline Si 21.3% 14% – 16%
Gallium Arsenide (GaAs) 27.5% – 29.1% N/A
Thin film Amorphous Si (a-si) 13.6% 6% – 9%
Cadmium Telluride (CdTe) 21.1% 9% – 12%
CIS/CIGS 22.3% 8% – 14%
http://css.umich.edu/factsheets/photovoltaic-energy-factsheetAdvances in Solar Cell Technology:
Analysts have searched for approaches to enhance the efficiency and cost-viability. A solar PV panel consists of hundreds to thousands of solar cells, which exclusively convert brilliant daylight into electrical streams. The normal solar cell is around 15% efficient, which implies almost 85% of the daylight that hits them doesn’t get changed over into power. In that capacity, researchers have always been exploring different paths regarding new advancements to help this light catch and transformation.

Fig.1. Advances in Solar Technology
https://news.energysage.com/solar-panel-technology-advances-solar-energy/Solar skin design:
Most of the house owners consider that the solar panels as an unattractive home expansion. Fortunately, one new venture has come up with a solution to this problem. Sistine solar, a Boston-based plan firm, is making real walks with the idea of stylish improvement that enables solar panels to have a good look. The MIT start-up has made a “solar skin” item that makes it workable for solar panels to coordinate the presence of a rooftop without interfere with cell productivity or generation. This design is for buildings which do not change the appearance of the roof and its productivity.
Wearable solar:
Wearable solar devices are not new to the market. There so many wearable gadgets have been in the market from many years. The solar gadgets like watches, which made with the hard plastic. Solar cells are now stitched into the material of cloth. This new material idea makes it workable for solar to venture into house items as window shades.

Solar tracking mounts:
A solar tracking system adjusts the panels to the direction of the sun and continues the solar photovoltaic panels at an angle to get the better output. Many solar tracking standards and methods have been introduced to follow the sun efficiently. The thought behind this tracking system is to arrange these modules in a position that can follow the direction of the sun to catch the highest amount of light from the sun. Tracker system has to be set at an angle that can get the better angle of incidence to get the more electrical energy output. The output energy of this system is nearly 50% higher than the fixed-type of the solar cell.

Fig.2. Solar Tracking System
http://www.solarlinepower.com/products/solar-trackerAdvances in Solar Cell Manufacturing:
Another zone that has made sun based PV innovations cost restrictive contrasted with conventional fuel sources is the assembling procedure. Researchers are additionally centered on approaches to enhance the productivity of how solar cells are fabricated. While more than 90% of photovoltaic cells available today are contained silicon semiconductors, the main element to changing over daylight into power, numerous trust the up and coming age of sun panels will be made of a thin film innovation that utilizations limit coatings of cadmium telluride in solar cells -this innovation guarantees to be a significantly less expensive and more effective approach to connect with the photovoltaic procedure. One main obstruction for cadmium telluride thin-film cells is that they turn out to be very shaky while assembling procedure, which right now utilizes cadmium chloride. Analysts have contrived another, safe and apparently ease approach to conquer this obstacle by utilizing a material called magnesium chloride in supplanting of cadmium chloride. Magnesium chloride is recuperated from seawater, a bottomless asset, which makes the asset minimal effort, and also non-poisonous. Supplanting the assembling procedure with this material guarantees to expand the effectiveness of these cells from 2% to 15%.

http://www.altenergy.org/renewables/solar/latest-solar-technology.htmlFloating Solar Cells:
Floating solar cells are more efficient because they float on the water. They are built on the water bodies. Floating solar cells are more efficient than the ground mount solar systems because water cools the panels which help to boost their productivity. These floating solar cells are built by Kyocera and Century Tokyo Leasing and these plants are anticipated to generate 3300MWH per year. These platforms are 100% recyclable and are design to endure extreme weather such as storms and typhoons. This technology is about to overcome the usage of vast land areas to build solar panels and the cost of installation and maintenance.

Fig.3. Floating Solar Cells
http://www.seaflex.net/applications/floating-solar-panels/ Working of solar cell:

Cross section of the solar cell
https://www.valuewalk.com/2017/02/solar-panels-expPV cell is made with a wafer of pure silicon. The upper part of the wafer is slightly spread with an “n” dopant like phosphorous and the bottom of the wafer is lightly spread with a “p” dopant, such as boron. The bottom side of the slab where boron is diffused is thousand times broader than the upper side where the phosphorous is diffused. These dopants are alike in atomic form to the primary material. The silicon has lesser electrons in its inner shell than phosphorous, and the boron also has one less electron. When light hits the PV cell, the dopants in the cell help to create the electric field that initiates the electrons to form outside of the cell. Surplus amount of free electrons are given to the slab of silicon by the phosphorous. It has a negative character because of excess electrons. This is called the n-type silicon. Due to an equal number of protons and electrons, the n-type silicon does not charge. Some electrons in the layer are free to go to various locations within the layer. Due to boron nature of attracting electrons, it gives the positive charge to the base of the silicon, so the base of the silicon called as p-type silicon. P-type silicon has positive character but not positive charge due to an equal number of protons and electrons.

p-n junction
http://www.physics-and-radio-electronics.com/electronic-devices-and-circuits/semiconductor-diodes/images/barrier-voltage.png
As we know that the opposite charges like each other, so electrons move from n-type to p-type in a fraction of seconds. To prevent the moving of electrons between the two types forms a barrier at where the two types of silicon meet. The barrier between the two types of silicon is called the p-n junction. Due to movement of electrons to the p-type, it has a negative charge and due to movement of holes to the n-type, it has a positive charge. This phenomenon occurred at the junction of the two types. The p-n junction generates an electric field due to electrical charge imbalance between the two types of silicon. The p-n junction barrier shows in the diagram above.

When the PV cell is placed to the direction of the sun, photons of sunlight hit the electrons in the p-n junction to remove the outermost electron of an atom. These electrons which are moved out of the atom are attracted to the positive charge in the n-type silicon and opposed by the negative charge in the p-type silicon. A wire which conducts connects the p-type silicon to an electrical load, like light or battery, and then the wire connects to the n-type silicon to form a complete circuit. The electrons which are free are forced into the n-type silicon, where they repel each other because like charges repel each other. The wire which is connected creates a way for the electrons to go away from each other. This flow of electrons in an electric circuit that travels from the n-type to the p-type silicon is called the electric current. In addition to these, solar cells contain a metallic grid to collect the electrons which come from the semiconductor and pass them to the external load.
http://solardat.uoregon.edu/download/Lessons/Appendix_E_HowSolarCellsWork.pdfCapital cost of solar system over the years:

Capital cost of PV system over the years
Source: CITATION Amo14 l 4105 (Han, 2014)

Advantages and drawbacks of solar cells:
Advantages:
Renewable and sustainable energy – The energy from comes from the solar cells can be used for both to produce electricity and warm in the house. The source for this energy is the sun; the sun is a renewable source. Solar cells capture the energy from the sunlight and convert that energy into usable electricity.

Economy-friendly energy – One who use solar cells to generate electricity do not pay the electric bill. Solar cells facilitate a good chance to save your electricity bill. You have a chance to make money with your solar system by selling the excess electricity to the electricity network but need to install grid to the solar system.
Eco-friendly energy – We all know the fact that solar cells do not produce greenhouse gases which are responsible for changes in climatic conditions. The solar system does not make the sound while producing electricity. A Solar system is a carbon free system. No discharge of waste and pollution.
Innovative energy – Hot topic in green energy is photovoltaic. To prevent climatic changes, this technology is accepted to be a good solution. In this way, this is an inventive market under consistent innovative work.

Endless Energy – When you have the chance to capture energy from the sunlight, this is a source of energy that will never be depleted. In this manner, there will be a source to produce electricity.

Long-term energy – PV frameworks normally have a more life-span and ability to withstand any situations. These panels have a minimum of 25 years guarantee.

Solar cells stored the energy which is produced during the daytime, utilise at night time.

Regional and national governments are encouraging this technology by giving financial incentives because they recognise the importance of solar energy. The government continued to support this technology by giving incentives and subsidy to business and house owners. CITATION Gre15 l 4105 (Match, 2015)Drawbacks:
One of the major disadvantages of the solar cell is that cannot produce electricity at night. The effectiveness in the production of electricity will be decreased if there is any obstruction on the surface of the solar cell, like dirt, snow or a shadow of an object which blocks the sunlight. To overcome this, install storage batteries to the solar panels, so that the energy produced by the solar system stored in the battery for later use.

Seasonal energy – Some parts of the world have limited sun. To overcome this, the grid has to connect to the solar installations so that energy can be purchased from the public electricity whenever required. Comparing with other types of renewable energy, the solar energy is a seasonal energy.

Accommodation of solar cells – Accommodation of solar cells depends on the construction of the house. Installing solar panels to an older house might be harder because of their different design.
To get the best results the solar system has to be fixed at certain angel, so that we require proper place to install the solar panels to maximize the production CITATION Gre15 l 4105 (Match, 2015)
Environmental impacts of solar cells:
Even though solar cells do not produce greenhouse gases, there are some positive and negative impacts on environment.

Positive Impacts on the Environment:
Solar cell technology produces carbon and pollution free electrical energy using the renewable source of energy (solar energy).

The solar cell technology produces clean and sustainable energy. We can limit dependence on fossil fuels by using the solar cell technology to produce electricity. The limitation to the use of fossil fuels, coal and nuclear reactors will have a very positive impact on our environment. CITATION pos18 l 4105 (positive and negative environmental impacts of solar cell technology, 2018)Use of solar cell technology will reduce the emissions of the greenhouse gases like CO2 and NO2 and prevention of toxic gas emissions like SO2 particulates. CITATION Tso05 l 4105 (Tsoutsos, 2005)Negative Impacts on the Environment:
Require huge amount of energy while manufacturing the elements used in the solar cell technology.

Use of toxic chemical while extracting the minerals, which are used for manufacturing components used in the solar cell technology CITATION pos18 l 4105 (positive and negative environmental impacts of solar cell technology, 2018)There will be an excessive use of land and habitat loss if the system is planned to establish on large scale.
There are some global warming emissions while manufacturing, transportation, installation and maintenance of the elements used in the solar cell technology. CITATION Uni13 l 4105 (Scientists, 2013)The main complication is the reuse of the solar panels used in this system. High utilization of metals in the assembling of solar panels without recycling may result in lack of metals. CITATION Gre15 l 4105 (Match, 2015) Though the solar cell system has limited negative environmental impacts it produces highly clean, and sustainable electrical energy with less damage compared to fossil fuels.