Photovoltaic Devices

Photovoltaic Devices

Ashraf Uddin (University of New South Wales, Australia)
Copyright: © 2013 |Pages: 37
DOI: 10.4018/978-1-4666-1996-8.ch005
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Abstract

Photovoltaics (PV) have been the world’s most rapidly growing energy source, with markets increasing at a compounded rate over the years. The electricity generating capacity of new photovoltaic product manufactured in 2006 exceeded new nuclear power capacity for the first time, with the gap widening in each year. The present continues to be a most exciting and challenging time for photovoltaics. More are recognising the possibility of a future where solar cells provide a significant part of the world’s energy needs, without the environmental problems and escalating costs associated with the present mainstream approaches. Silicon is a semiconductor material which is mostly used for PV devices. Silicon is available in different forms like single crystal, poly crystalline, and amorphous. Most photovoltaic sales are of “first-generation” solar cells made from silicon wafers. First-generation PV research challenges are the cost reduction and further improving efficiency. The rapid growth of the photovoltaic industry is generating widespread interest in past and ongoing innovations of the PV technology. Silicon is quite brittle, so silicon wafers have to be reasonably thick, at least a fraction of a millimetre, to be sufficiently rugged for processing into solar cells with reasonable yields. Without this mechanical constraint, silicon would perform well even if very thin, over 100 times thinner than present wafers.
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Introduction

Thin film or “second-generation” approach gives enormous potential cost savings. Not only are the costly processes involved in making wafers no longer required, but also there is an enormous saving in silicon material and cells can be made more quickly over the entire area of large glass sheets. Thin films of some other poly-crystalline materials like Copper Indium Disengage, Cadmium Telluride, organic polymer materials, etc, are also used in the construction of photovoltaic cells. In large enough production volumes, even these reduced material costs will dominate thin-film costs. This has led to the interest in advanced “third-generation” thin-film solar cells such as all-silicon tandem solar cells, multi-junction solar cells, etc. targeting significant increases in energy-conversion efficiency. Higher conversion efficiency means more power from a given investment in materials, reducing overall power costs. The semiconductor bandgap can be controlled by quantum-confinement of carriers in small quantum-dots dispersed in an amorphous matrix of silicon oxide, nitride, and polymer materials. Cells based on “hot” carriers are also of great interest since they offer the potential for very high efficiency from simple device structures.

The development of a sustainable future energy option is one of the most important challenges facing the human race. The solar energy components of the energy needs will continue to grow in significance as pressures mount rapidly to generate power in a clean and renewable way. Photovoltaics (PV) clearly would be preferable to other options such as nuclear fission or fusion, or biomass – all with fundamental difficulties. The more widespread uptake of the technology would reduce greenhouse gas emissions from the burning of fossil fuels and, if sufficiently inexpensive, reduce the need for on-going investment coal-fired baseload electricity plant. For decades, PV devices have seems the most promising technology to harvest the energy; however, despite gradual growth in use worldwide, PV devices still have not yet lived up to their potential for very high materials and processing cost. Globally research effort has driven towards the low-cost and high efficiency PV devices, resulting second and third generation PV devices. The main challenge with photovoltaics is to greatly reduce costs while improving device performance.

Photovoltaic is the process of converting sunlight directly into electricity using solar cells. Research and development of photovoltaics received its first major boost from the space industry in the 1960s which required a power supply separate from “grid” power for satellite applications. Their application and advantage to the “remote” power supply area was quickly recognized and prompted the development of terrestrial photovoltaics industry. In the 1980s research into silicon solar cells paid off and solar cells began to increase their efficiency. In 1985 silicon solar cells achieved the milestone of 20% efficiency. The year 1997 saw a growth rate of 38% and today solar cells are recognized not only as a means for providing power and increased quality of life to those who do not have grid access, but they are also a means of significantly diminishing the impact of environmental damage caused by conventional electricity generation in advanced industrial countries.

The increasing market for, and profile of photovoltaics means that more applications than ever before are “photovoltaically powered”. These applications range from power stations of several megawatts to solar calculators. Specific materials generally semiconductors are commonly used in fabrication of photovoltaic cells. Silicon is a semiconductor material which is mostly used for this purpose. Silicon is available in different forms like single crystal, poly crystalline and amorphous. Thin films of some poly crystalline materials like Copper Indium Disengage, Cadmium Telluride etc are also used in the construction of photovoltaic cells.

Key Terms in this Chapter

3rd-Generation Solar Cells: Novel solar cell concepts capable of 1-sun efficiencies beyond the Shockley Queisser limit of 31%.

2nd-Generation Solar Cells: Thin film materials types photovoltaic devices.

Tandem Solar Cells: Multi-junction solar cells to use whole sun light spectrum for the super-high efficiency photovoltaic devices.

Glass Texturing: Create rough surfaces of glass substrates for thin film solar cells to increase the light trapping to increase devices conversion efficiency.

First-Generation Solar Cells: Crystalline silicon p-n junction type photovoltaic devices.

Conversion Efficiency: The percentage of sun light energy converts into electrical energy.

Organic Photovoltaic: Polymer materials based photovoltaic devices.

Photovoltaic Device: A device that can convert sun-light energy into electrical power energy.

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