Investigation into the Production of Organic Photovoltaic Cells from Local Materials

1.0 INTRODUCTION

There has been uproar in global search for alternative sources of energy owing to the fact that conventional fossil fuels are continually posing threat and causing havoc to the environment. It is presently a global concern on the reduction of GreenHouse Gas (GHG) emissions which are largely from the burning of fossil fuels and of course callings for less environmentally brutal energy. Besides that, the alarm of a depleting oil and Natural Gas deposit which is a major energy supply of the world has declared many nations whose energy and economics rest upon fossil fuel restless. Overall, the world energy demand has grown beyond fossil fuels. The yearn for cleaner, cheaper and safer sources of energy has put many hands on deck. Billions of dollars are spent every year on research for a sustainable, renewable and environmentally friendly energy. But unknowingly for many centuries, the energy we seek sits right above us. That is the sun. The sun generates 20TW of energy per hour and the world energy demand is 16TW per year (US Department of Energy, 2010). This implies that the sun supplies in one hour, the total energy needed by the world in a year. And that was the beginning of the world energy revolution. And this revolution gave birth to the world of photovoltaics that are greener and cleaner.

Photovoltaic cells (PVC) are cells that convert sunlight into electricity by employing the principle of photovoltaic effect. (When sunlight strikes the surface of a PVC, The cells absorb photons from the sun. These photons excite electrons in the cell from the valence band to the conduction band creating an electron hole pair which are the drivers of current in a semiconductor material. When a load is connected to the terminals of the cell, there is generation of electricity. The amount of light generated by a PVC depends on several parameters such as intensity and wavelength of light striking the cell, the band gap of the semiconductor materials used,) the power conversion efficiency (P C E) of the cell and so on (Olivia, 1998). These factors coupled with cost of production led to the growth of PVC from semiconductor materials simply converting sunlight to electricity to a more complex matter trying to balance efficiency and cost. And that is the facet of solar energy today.

Furthermore, with current statistics, an average solar cell costs more than fossil fuel but its greenish nature and prospect has kept research ongoing. This is because solar cells are yet to be fully explored, their efficiencies range from less than 1% to 40% (Halls and Friend, 2011). Inorganic photovoltaic cells are recording tremendous improvement in terms of efficiency but with high cost. And that is why greater emphasis is currently on building organic photovoltaic cells with improved efficiency and less cost. Organic photovoltaic cells are gaining wide acceptance even though tremendous achievements have not been recorded (Sethi, 2011). Their ease of construction and diversity is promising and encouraging. However, organic photovoltaics are far less efficient than solid state photovoltaics, but they are less expensive. Research is ongoing in building superefficient organic PVCs that will be of higher efficiency and stability which are the two major challenges of present day organic photovoltaic cells.

In general, Photovoltaic systems remain the most cost effective source of power. Several characteristics make them desirable. Amongst which include: renewability, reliability, environmental friendliness, cost effectiveness, no moving parts which eliminate cases of wear and tears, can be used as independent power to fit different scales. 

P V systems are diversified and can fit into any system based on construction and design

Currently, renewable energy is still under harness compared to other sources of Energy. Renewable energy takes only 2.5% of world’s energy consumption.  Of the 2.5% renewables, Hydro power constitutes 2.2%, wind constitutes 0.2% and solar constitutes 0.1% (Gregg, 2005).

However, globally, solar photovoltaic energy is the fastest growing energy resource. Solar photovoltaics will someday become the dominant source of energy (Chen, 2011). This project seeks to explore the world of photovoltaics from birth to the current day PVCs. Adequate research was made to explore the possibilities, merit and demerit of PVCs and in essence discuss the future of the cells as they are still at their infancy. Obviously, there are a lot of limitations in PVCs and that is why they have not substantially substituted fossil fuels. However, in the near future, solar power will control the world.

1.1 Problem Statement

The world has already started suffering from the environmental hazards from fossil fuels ranging from oil spills, cost, fast depletion, Carbon (IV) emission to GreenHouse effects. These hazards have put the world into a search for a more environmentally friendly, renewable and cost effective source of energy. Solar power gave a sharp response to this call as a green and

clean substitute. But there are rising challenges as to the use of solar power; conventional silicon solar cells are very expensive and are finding it difficult to compete with other sources of Energy. However, a divergence to organic solar cells which are the new phase of world’s energy is gradually setting ablaze the quagmire of silicon high cost. This work seeks to explore into organic solar cell and how they could compete with other forms of energy supplies

1.2 Justification

Organic solar cells have proven to be a classic source of energy supply. It is clean and environmentally friendly and also cheaper to construct than the conventional solid state based solar cells. Organic photovoltaics are easier and cheaper to construct, having high absorptivity, giving it an edge over other photovoltaics. This will increase world energy supply and remove unnecessary costs once a higher efficient organic photovoltaics is achieved.

1.3 Aim and Objectives

The aim of this work is to investigate into the production of Dye Sensitized Solar cells and shall be achieved through:

1. Investigating into the working principles of organic and inorganic PVCs
2. Construction of a Dye Sensitized Solar cell
3. Investigate into the effect of some selected dye materials on the output of the cell
4. Study the output of the cells with respect to time and temperature
5. Compute the Efficiency of the cell

1.4 Scope of Study

The scope of this work is to investigate into the production of Dye sensitized Solar Cells with adequate literature review on Solar cells in general, construct a simple dye sensitized Solar cell, and study the output voltage with respect to time and Temperature

2.0 LITERATURE REVIEW

2.1 History of Photovoltaic Cells 

In 1839, French physicist Edmond Becquerel discovered photosensitivity in certain materials, observing that they could generate small amounts of electricity when exposed to sunlight. This phenomenon, however, remained largely unexplained until Heinrich Hertz’s work in the 1870s, where he demonstrated the effect using silicon and selenium (Gary et al., 1998). Hertz’s success in explaining this effect led to silicon being recognized for its ability to convert sunlight into electricity, with selenium quickly following, especially in the photography industry.

A major breakthrough in commercializing photovoltaic cells (PVCs) occurred in the 1940s with the development of the Czochralski process, which enabled the production of highly pure crystalline silicon. By 1954, Bell Laboratories used this process to create the first crystalline silicon PV cell, achieving a 4% efficiency rate (Green et al., 2010). In the late 1950s, PVCs became vital in space exploration. For example, the 1958 U.S. Vanguard satellite used a small PV array to power its radio. At the time, the high cost limited their use to large organizations, but their reliability ensured widespread adoption in space programs, and today, all satellites rely on solar cells (Kenji et al., 1998).

The computer industry also advanced photovoltaics through its work on semiconductors, with transistor research contributing crucial knowledge for PV technology (Chidichimo and Filippelli, 2010). Despite these innovations, photovoltaic systems remained too expensive for widespread terrestrial use until the 1970s. The oil crisis drove renewed interest in making solar power more affordable and efficient, prompting significant investments in research and development (Wang et al., 2000). These efforts focused largely on crystalline silicon, which had proven highly efficient, reliable, and durable. Other materials such as polycrystalline silicon, amorphous silicon, cadmium telluride (CdTe), copper indium diselenide (CIS), and gallium arsenide have also been explored. Today, commercial PV systems achieve efficiency rates between 5% and 15% (Benagli et al., 2009).

The development of photovoltaic cells can be divided into three generations: first-generation crystalline silicon cells, second-generation thin-film cells, and third-generation advanced technologies.

2.1.1 First Generation PVCs

First-generation photovoltaic cells are made of single PN-junction monocrystalline or polycrystalline silicon. They dominate the market, comprising about 90% of photovoltaics due to silicon’s wide use as a semiconductor (Jenna, 2010). The theoretical maximum power conversion efficiency (PCE) for a 90-micrometer thick silicon solar cell is 29% (Kerr et al.). However, much energy is lost as heat because a portion of sunlight isn’t energetic enough to excite electrons past silicon’s band gap. First-generation solar cells offer high efficiency and long lifespans but are expensive to produce, making them less economically competitive. As of August 2010, solar electricity cost about 35 cents per kWh, compared to 2–4 cents for coal (Sever, 2008). Although costs have fallen, the price of silicon remains a limiting factor. In 2008, silicon cost around $165/kg (renewableenergyworld.com, 2008), leading to the development of alternative technologies.

2.1.2 Second Generation PVCs

To reduce costs and silicon usage, second-generation PVCs introduced thin-film solar cells (Shaheen et al., 2006). These cells are made by depositing semiconductor materials like amorphous silicon, copper indium gallium diselenide (CIGS), or cadmium telluride (CdTe) on cheaper substrates like plastic, glass, or paper using physical or chemical vapor deposition (Benagli et al., 2009). CIGS cells achieved an efficiency of 19.6% (Brian and Mark, 2002), close to that of monocrystalline silicon, and they are faster and cheaper to produce.

2.1.3 Third Generation PVCs

Third-generation PVCs introduced new designs like organic photovoltaics (OPVs), dye-sensitized solar cells (DSSCs), and multi-junction cells, making solar technology more cost-effective. OPVs use polymers to absorb light, while DSSCs rely on organic dyes to boost photoexcitation (Benagli et al., 2009). Multi-junction cells stack different semiconductors, each with a unique band gap, to capture more of the solar spectrum. Theoretical efficiency for multi-junction cells can reach 66%, with lab-produced triple-junction cells achieving over 40% (LoCascio, 2002). The National Renewable Energy Laboratory (NREL) set a world record with 41.6% efficiency for a triple-junction cell in 2008 (Green et al., 2010). Although OPVs and DSSCs have lower efficiencies—8.3% and 10.4% respectively (Berkley, 2009)—they offer lower production costs.

Table 2.1 Generations of PVCs

2.2 Energy calculation of the sun

 Power

The sun has a radius R = 6.95 x 108 m and a surface temperature of 5800 K. the total power radiated by the sun’s surface, treating it as a perfect radiator Can be calculated using  Stefan-Boltzmann law with α = 1.

P=σAT4 …………………………………………………………… (2.1)

Where: 

A=4πR2…………………………………………………………….. (2.2)

R = suns radius = 6.95 x 108

P = (6.95 x 108 x 4π x 6.95 x 108 x 58004) = 3.89 x 1026 W

Intensity

I = P/A = σT4…………………………………………………………. (2.3)

2.3 Working Principle of a PV Cell

In order to study the working principle of a PV cell, a typical silicon based cell is studied. The basic building block of PV technology is the photovoltaic cell. Different materials are used to produce PV cells, but silicon is the most common basic material. Silicon, a common semiconductor material, is relatively cheap because it is widely available and used in other things, such as televisions, radios, and computers. But it becomes relatively expensive as highly pure silicon is required for PV technology. Much of its cost goes into the purification (Gary et al., 1995).

When a photon of sufficient energy strikes a valence electron, it may impart enough energy to free it from its connection to the atom. This leaves a space in the crystal structure where an electron once resided (and bonded), called a “hole.” The electron is now free to travel about the crystal lattice. The electron is now a part of the conduction band, so called because these free electrons are the means by which the crystal conducts electricity. Meanwhile, the atom left behind by the freed electron contains a net positive charge in the form of the generated hole. This positive hole can move almost as freely about the crystal lattice as a free electron in the conduction band, as electrons from neighboring atoms switch partners. These light generated charges, both positive and negative, are the constituents of electricity (Krebs, 2006).

3.0 MATERIALS AND METHOD