Page 179 - A Comprehensive Guide to Solar Energy Systems

9

Crystalline Silicon Solar Cell

and Module Technology

Vítezslav Benda
ˇ
CZECH TECHNICAL UNIVERSITY, PRAGUE, CZECH REPUBLIC
benda@fel.cvut.cz

9.1 Introduction

Over the last 40 years, photovoltaic (PV) cells have shown an impressive reduction in price,
decreasing by more than 20% every time the cumulative sold volume of PV modules has
doubled. This has resulted in a considerable decrease in the overall cost of PV power sys-
tems and, consequently, in a decrease of the cost of electrical energy produced by PVs. This
cost is now close to the long-term cost of traditionally produced and supplied grid power.
Since 1970, crystalline silicon (c-Si) has been the most important material for PV cell and
module fabrication and today more than 90% of all PV modules are made from c-Si. De-
spite 4 decades of research and manufacturing, scientists and engineers are still finding
new ways to improve the performance of Si wafer-based PVs and at the same time new
ways of reducing the cost. The present state of art and future trends in silicon wafer-based
technology will be discussed in this chapter.

9.2 Semiconductor Silicon

Silicon is the most commonly occurring element on the earth. In nature, it never occurs
free but in the form of oxides and silicates. In its elementary form, silicon crystallizes in a
diamond cubic structure. Some material properties are given in Table 9.1.
c-Si can be prepared in the form of single crystals (monocrystalline silicon, mono
c-Si). In this form the lattice parameters and orientation are constant throughout the
material. Usually the c-Si is in the form of polycrystalline silicon (poly c-Si) consist-
ing of silicon single-crystal grains separated by grain boundaries. The crystalline grains
in poly c-Si can have different sizes and crystalline orientation. The grain size can be
sorted into
• multicrystalline silicon (multi c-Si, mc-Si) is composed of many smaller silicon grains
of varied crystallographic orientation, typically >1 mm in size (1 mm–10 cm);
• poly c-Si is composed of many silicon grains of varied crystallographic orientation of
grain size between 1 µm and 1 mm;
A Comprehensive Guide to Solar Energy Systems. http://dx.doi.org/10.1016/B978-0-12-811479-7.00009-9 181
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