Environmental Engineering Reference
In-Depth Information
envisagedatthetime.Buttherelevantscientificresearchcontinued,
and the main breakthroughs made are shown in Table 2.1 [1]. The
first PV solar cell, with an e
ciency of 4.5%, was produced in
1954 at Bell laboratories in the United States [2]. By 1960, 14%
e
cientSisolarcellswerecommerciallyproducedandusedinspace
applications. The first oil crisis, in 1970, kick-started the search for
low-cost alternative methods for terrestrial energy conversion, and
PV research was accelerated throughout the world.
2.2 Si Solar Cell Technology
The fabrication of the interfaces required for PV devices, as
described in chapter 1, needs a light-absorbing electronic material
with the desired semiconducting properties. The most widely used
material is Si, and it has undergone over 60 years of research and
development. The main steps of growth of Si and device fabrication
are given in Fig. 2.2. Si is produced starting with natural sand
(SiO
2
), followed by four processing steps: (a) purification process,
(b) crystallisation and wafer production, (c) processing of Si solar
cells, and (d) assembly of the solar panels. This needs four different
productionlines,andthesearesummarisedinFig.2.3andTable2.2.
Each of these average-sized (
∼
25 MW) production lines could
cost millions of dollars for the initial establishment. In addition,
the whole process of converting sand into solar panels requires
the heating of Si above its melting point (1,414
◦
C), and repeated
heating to high temperatures above 1,000
◦
C, during solar cell
fabrication. These steps demand a high energy input, burning fossil
fuel, and therefore cost reduction is a challenging task for the Si PV
industry.
Figure2.4showsthemainstagesofthemanufacturingprocessof
solarpanelsbasedoncrystallineSi:thegrowthofamonocrystalline
cylindrical crystal boule using Czochralski method, grinding of the
crystal boule in order to produce single-diameter Si wafers, and a
fully assembled solar panel with crystalline Si wafers.
Figure 2.5 shows the main stages of the production process of
multicrystallineSisolarpanelsandtheappearanceofthin-filmsolar
panels manufactured with amorphous Si. By the appearance of the
