13.4
13.4.1
process can be categorized between solid-phase (SPC) and liquid-phase crystallization
(LPC). SPC can be done for example in a thermal annealing step. Because of the low
electrical quality of the defect-rich SPC silicon films, the maximally achieved efficiency is
10.5% which was achieved by the company CSG Solar [74]. In LPC, the amorphous Si
film is molten using, for example, an electron beam or a laser. Then, the molten silicon
recrystallizes with grain sizes up to several centimetres in the growth direction and up to
several millimetres orthogonal to the growth direction. These large grains lead to opencircuit voltages comparable to the wafer-based Si solar cells with reported maximum
values of 656 mV [75] and efficiencies of 11.8% have been demonstrated [76].
The highest efficiencies are reached with silicon layers grown in an epitaxy process,
just as for the high performance III-V solar cells. The epitaxy films then are transferred
onto glass. The current record cell made with this method has an efficiency of 20.1% on a
43 μm thick substrate and was fabricated by the American company SOLEXEL [77].
Chalcogenide solar cells
The third class of thin-film solar cells that we discuss are the large class of chalcogenide
solar cells, where our focus will mainly be on copper indium gallium selenide (CIGS) and
cadmium telluride (CdTe) solar cells. The term chalcogenides refers to all chemical
compounds consisting of at least one chalcogen anion from the group 16 (also known as
group VI) with at least one or more electropositive elements. Five elements belong to
group 16: oxygen (O), sulphur (S), selenium (Se), tellurium (Te), and the radioactive
polonium (Po). Typically, oxides are not included in discussions of chalcogenides.
Because of its radioactivity, compounds with Po are of very limited relevance for
semiconductor physics.
Chalcopyrite solar cells
The first group of chalcogenide solar cells that we discuss are chalcopyrite solar cells. The
name of this class of materials is based on chalcopyrite (copper iron disulphide, CuFeS 2 ).
Like all the chalcopyrites, it forms tetragonal crystals, as illustrated in Figure 13.19.
13.4.1
process can be categorized between solid-phase (SPC) and liquid-phase crystallization
(LPC). SPC can be done for example in a thermal annealing step. Because of the low
electrical quality of the defect-rich SPC silicon films, the maximally achieved efficiency is
10.5% which was achieved by the company CSG Solar [74]. In LPC, the amorphous Si
film is molten using, for example, an electron beam or a laser. Then, the molten silicon
recrystallizes with grain sizes up to several centimetres in the growth direction and up to
several millimetres orthogonal to the growth direction. These large grains lead to opencircuit voltages comparable to the wafer-based Si solar cells with reported maximum
values of 656 mV [75] and efficiencies of 11.8% have been demonstrated [76].
The highest efficiencies are reached with silicon layers grown in an epitaxy process,
just as for the high performance III-V solar cells. The epitaxy films then are transferred
onto glass. The current record cell made with this method has an efficiency of 20.1% on a
43 μm thick substrate and was fabricated by the American company SOLEXEL [77].
Chalcogenide solar cells
The third class of thin-film solar cells that we discuss are the large class of chalcogenide
solar cells, where our focus will mainly be on copper indium gallium selenide (CIGS) and
cadmium telluride (CdTe) solar cells. The term chalcogenides refers to all chemical
compounds consisting of at least one chalcogen anion from the group 16 (also known as
group VI) with at least one or more electropositive elements. Five elements belong to
group 16: oxygen (O), sulphur (S), selenium (Se), tellurium (Te), and the radioactive
polonium (Po). Typically, oxides are not included in discussions of chalcogenides.
Because of its radioactivity, compounds with Po are of very limited relevance for
semiconductor physics.
Chalcopyrite solar cells
The first group of chalcogenide solar cells that we discuss are chalcopyrite solar cells. The
name of this class of materials is based on chalcopyrite (copper iron disulphide, CuFeS 2 ).
Like all the chalcopyrites, it forms tetragonal crystals, as illustrated in Figure 13.19.