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Principles of Solar Cells, LEDs and Diodes The role of the PN junction Download PDF

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Principles of Solar Cells, LEDs and Diodes The role of the PN junction
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The "Principles of Solar Cells, LEDs, and Diodes" explains the functioning of these devices by focusing on the role of the p-n junction.
A p-n junction is a region where a p-type semiconductor material and an n-type semiconductor material meet. This creates a depletion region, where there is an absence of mobile charge carriers, that acts as a barrier to the flow of current. When a voltage is applied across the p-n junction, it creates an electric field that modulates the flow of current.
In solar cells, the p-n junction is used to generate a voltage and a current when light is absorbed by the material. In LEDs (Light Emitting Diodes), the p-n junction is used to recombine electrons and holes, producing light. In diodes, the p-n junction is used to control the flow of current, allowing it to flow in only one direction.
In summary, the p-n junction is a key component in solar cells, LEDs, and diodes, and understanding its behavior is crucial to understanding the functioning of these devices.
The book is aimed at senior undergraduate levels (years three and four). An introductory background in quantum mechanics is assumed, together with general knowledge of junior mathematics, physics, and chemistry; however, no background in electronic materials is required. As such this book is designed to be relevant to all engineering students with an interest in semiconductor devices and not specifically to electrical or engineering physics/engineering science students only. This is intentional since solar cells and LEDs involve a wide range of engineering disciplines and should not be regarded as belonging to
only one branch of engineering.
In Chapter 1, the physics of solid state electronic materials is covered in detail starting from the basic behaviour of electrons in crystals. The quantitative treatment of electrons and holes in energy bands is presented along with the important concepts of excess carriers that become significant once semiconductor devices are either connected to sources of power or illuminated by light. A series of semiconductor materials and their important properties is also reviewed. The behaviour of semiconductor surfaces and trapping concepts are also introduced since they play an important role in solar cell and LED device performance.
In Chapter 2, the basic physics and important models of a p-n junction device are presented. 
The approach taken is to present the diode as a semiconductor device that can be
understood from the band theory covered in Chapter 1. Various types of diode behaviour,
including tunnelling, metal-semiconductor contacts and heterojunctions, are presented as
well as reverse breakdown behaviour.
Chapter 3 introduces the theory of photon emission and absorption, a topic that books
on semiconductor devices frequently pay less attention to. The standard description that
a photon is created when an electron and a hole recombine, or a photon is absorbed
when an electron and a hole are generated, is not adequate for a deeper understanding of
photon emission and absorption processes. In this chapter the physics of photon creation
is explained with a minimum of mathematical complexity, and these concepts are much
better understood by following radiation theory and describing the oscillating dipole both
classically and using simple quantum mechanics. A section of Chapter 3 describes the
exciton relevant to inorganic semiconductors as well as the molecular exciton for organic
semiconductors. In addition lineshapes predicted for direct-gap semiconductors are derived.
Finally the subject of photometric units introduces the concepts of luminance and colour
coordinates that are essential to a discussion of organic and inorganic light emitting diodes.
Chapter 4 covers inorganic solar cells. The concepts regarding the p-n junction introduced
in Chapter 2 are further developed to include illumination of the p-n junction and the simplest
possible modelling is used to illustrate the behaviour of a solar cell. Then a more realistic
solar cell structure and model are presented along with the attendant surface recombination
and absorption issues that must be understood in practical solar cells. A series of solar cell
technologies are reviewed starting with bulk single and multicrystalline silicon solar cell
technology. Amorphous silicon materials and device concepts are presented. Solar cells
made using other semiconductors such as CdTe are introduced followed by multijunction
solar cells using layered, lattice-matched III-V semiconductor stacks.
Chapter 5 on inorganic LEDs considers the basic LED structure and its operating principles. The measured lineshape of III-V LEDs is compared with the predictions of Chapter
3. LEDs must be engineered to maximize radiative recombination, and energy loss mechanisms are discussed. The series of developments that marked the evolution of current,
high-efficiency LED devices is presented starting from the semiconductors and growth
techniques of the 1960s, and following trends in succeeding decades that brought better materials and semiconductor growth methods to the LED industry. The double heterojunction
is introduced and the resulting energy well is analysed on the basis of the maximum current
density that can be accommodated before it becomes saturated. LED optical outcoupling,
which must also be maximized to achieve overall efficiency, is modelled and strategies to
optimize outcoupling are discussed. Finally the concept of spectral down-conversion using
phosphor materials and the white LED are introduced.
Chapter 6 introduces new concepts required for an understanding of organic semiconductors in general, in which conjugated molecular bonding gives rise to π bands and
HOMO and LUMO levels in organic semiconductors. The organic LED is introduced by
starting with the simplest single active layer polymer-based LED followed by successively
more complex small-molecule LED structures. The roles of the various layers, including
electrodes and carrier injection and transport layers, are discussed and the relevant candidate molecular materials are described. Concepts from Chapter 3, including the molecular
exciton and singlet and triplet states are used to explain efficiency limitations in the light
generation layer of small-molecule OLEDs. In addition the opportunity to use phosphorescent host-guest light emitting layers to improve device efficiency is explained. The organic
solar cell is introduced and the concepts of exciton generation and exciton dissociation are
described in the context of the heterojunction and the bulk heterojunction. The interest in
the use of fullerenes and other related nanostructured materials is explained for the bulk
All the chapters are followed by problem sets that are designed to facilitate familiarity
with the concepts and a better understanding of the topics introduced in the chapter. In
many cases the problems are quantitative and require calculations; however, a number of
more conceptual problems are presented and are designed to give the reader experience in
using the Internet or library resources to look up further information. These problems are
of particular relevance in Chapters 4, 5 and 6, in which developments in solar cells and
LEDs are best understood by referring to the recent literature once the basic concepts are

Contents Of The Book :

1 Semiconductor Physics
2 The PN Junction Diode
3 Photon Emission and Absorption
4 The Solar Cell
5 Light Emitting Diodes
6 Organic Semiconductors, OLEDs and Solar Cells

Information Of The Book :

Title: Principles of Solar Cells, LEDs and Diodes The role of the PN junction Download PDF
Size: 3 Mb
Pages: 333
Year : 2012
Format: PDF
Language : English
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