Chapter 3
Solar Cells: Basics
Arvind Shah
Abstract The present chapter is a central chapter of this book. In this chapter, we
will attempt to explain and illustrate the functioning of a solar cell. It is divided into
six sections:
• Section 3.1 explains the interaction between Light and a Semiconductor, like
silicon—which is the main material used in solar cells. This section involves
physical concepts, which may possibly be new for the Reader, but should not be too
difficult to understand. As a result of light being absorbed in the solar cell, electrons
and “holes” (= “missing” electrons) are generated within the semiconductor.
• Section 3.2 is the “key section” of the present chapter. As most solar cells are
constituted of semiconductor diodes, this section will introduce the mathematical
description of a diode. The characteristics of such a device can, in general, be
described by an exponential function—a fact that is well established, both theoretically and experimentally. The exponential function used to describe diodes
(and solar cells), has two main parameters:
– The diode ideality factor n. Basically, n should be equal to 1, but for practical
reasons n is usually higher than 1. The interpretation of this fact goes beyond
the scope of the present book.
– The diode reverse saturation current density J 0 . This parameter should be as
low as possible, to ensure a high performance of the diode and, thus, of the
entire solar cell.
Afterwards, we will introduce a light source. The diode becomes a photodiode or
a solar cell. This is simply done by adding a photo-generation term to the diode
equation, a procedure that is well established, but not easy to justify theoretically.
• Section 3.3 describes how the internal electric field present in all diodes is instrumental in separating electrons and “holes” and, thus, providing a current to the
contacts of the solar cell.
• Section 3.4 deals with the electrical characteristics of the solar cell: Equivalent
circuits and key parameters.
A. Shah (B)
EPFL (PV-Lab), Neuchâtel, Switzerland
e-mail: arvind.shah@epfl.ch
© Springer Nature Switzerland AG 2020
A. Shah (ed.), Solar Cells and Modules, Springer Series in Materials Science 301,
https://doi.org/10.1007/978-3-030-46487-5_3
33
Solar Cells: Basics
Arvind Shah
Abstract The present chapter is a central chapter of this book. In this chapter, we
will attempt to explain and illustrate the functioning of a solar cell. It is divided into
six sections:
• Section 3.1 explains the interaction between Light and a Semiconductor, like
silicon—which is the main material used in solar cells. This section involves
physical concepts, which may possibly be new for the Reader, but should not be too
difficult to understand. As a result of light being absorbed in the solar cell, electrons
and “holes” (= “missing” electrons) are generated within the semiconductor.
• Section 3.2 is the “key section” of the present chapter. As most solar cells are
constituted of semiconductor diodes, this section will introduce the mathematical
description of a diode. The characteristics of such a device can, in general, be
described by an exponential function—a fact that is well established, both theoretically and experimentally. The exponential function used to describe diodes
(and solar cells), has two main parameters:
– The diode ideality factor n. Basically, n should be equal to 1, but for practical
reasons n is usually higher than 1. The interpretation of this fact goes beyond
the scope of the present book.
– The diode reverse saturation current density J 0 . This parameter should be as
low as possible, to ensure a high performance of the diode and, thus, of the
entire solar cell.
Afterwards, we will introduce a light source. The diode becomes a photodiode or
a solar cell. This is simply done by adding a photo-generation term to the diode
equation, a procedure that is well established, but not easy to justify theoretically.
• Section 3.3 describes how the internal electric field present in all diodes is instrumental in separating electrons and “holes” and, thus, providing a current to the
contacts of the solar cell.
• Section 3.4 deals with the electrical characteristics of the solar cell: Equivalent
circuits and key parameters.
A. Shah (B)
EPFL (PV-Lab), Neuchâtel, Switzerland
e-mail: arvind.shah@epfl.ch
© Springer Nature Switzerland AG 2020
A. Shah (ed.), Solar Cells and Modules, Springer Series in Materials Science 301,
https://doi.org/10.1007/978-3-030-46487-5_3
33