204
A. Romeo
8.2.3 Performance and Degradation
Nowadays, CIGS modules are commercially produced by different companies, such
as Solar Frontier (Japan), Avancis (Germany-China), Solopower (USA), SolibroHanergy (Sweden-China), Global Solar (USA-China), MiaSolé (USA-China),
Flisom (CH).
Efficiencies of completed modules can exceed 19% as produced by Solar Frontier,
with an area of 841 cm
2 and 15% for larger modules as produced by MiaSolé, with
an area of 9703 cm
2 [1], moreover it has been demonstrated that the stability of the
modules is comparable, if not higher than the stability of c-Si modules.
Main remaining issues can come from shading-induced hot spots, metastabilities
(induced by light soaking after dark storage) and potential induced degradation that
can be enhanced by Na migration from glass and impurity diffusion through grain
boundaries and for this reason strongly depends on the quality of the module.
8.3 CdTe/CdS Solar Cells
8.3.1 Introduction
CdTe, is a semiconductor with a high absorption coefficient and a direct bandgap
of 1.45 eV this value is very near to the optimum bandgap value. It is a robust and
reliable material that can be deposited at low or high temperatures; it evaporates
congruently (Cd and Te evaporate with the same rate) and it is basically very easy to
keep a 1:1 Cd-Te composition with most of the deposition techniques.
When deposited at high temperatures on a transparent buffer layer, CdTe cells
have reached efficiencies up to 22.1% [1].
8.3.2 Structure of CdTe Based Solar Cells
From the early eighties until 2015, the typical CdTe solar cells in superstrate configuration
6 were composed of (see Fig. 8.4): a transparent conductive oxide (TCO),
CdS as n-part of the junction and window layer, CdTe as p-part of the junction and
absorber layer and back contact. The front and the back contacts can be composed
of different layers; this will be described later.
In this configuration, the supporting substrate obviously needs to be transparent.
Considering that in a thin-film device more than 98% of the material is glass, the
choice of soda lime glass as substrate allows keeping the final price low. However,
soda lime glass has two disadvantages: (1) the presence of sodium and potassium that
6 Superstrate configuration: when light shines through the glass to reach the underlying solar cell.
A. Romeo
8.2.3 Performance and Degradation
Nowadays, CIGS modules are commercially produced by different companies, such
as Solar Frontier (Japan), Avancis (Germany-China), Solopower (USA), SolibroHanergy (Sweden-China), Global Solar (USA-China), MiaSolé (USA-China),
Flisom (CH).
Efficiencies of completed modules can exceed 19% as produced by Solar Frontier,
with an area of 841 cm
2 and 15% for larger modules as produced by MiaSolé, with
an area of 9703 cm
2 [1], moreover it has been demonstrated that the stability of the
modules is comparable, if not higher than the stability of c-Si modules.
Main remaining issues can come from shading-induced hot spots, metastabilities
(induced by light soaking after dark storage) and potential induced degradation that
can be enhanced by Na migration from glass and impurity diffusion through grain
boundaries and for this reason strongly depends on the quality of the module.
8.3 CdTe/CdS Solar Cells
8.3.1 Introduction
CdTe, is a semiconductor with a high absorption coefficient and a direct bandgap
of 1.45 eV this value is very near to the optimum bandgap value. It is a robust and
reliable material that can be deposited at low or high temperatures; it evaporates
congruently (Cd and Te evaporate with the same rate) and it is basically very easy to
keep a 1:1 Cd-Te composition with most of the deposition techniques.
When deposited at high temperatures on a transparent buffer layer, CdTe cells
have reached efficiencies up to 22.1% [1].
8.3.2 Structure of CdTe Based Solar Cells
From the early eighties until 2015, the typical CdTe solar cells in superstrate configuration
6 were composed of (see Fig. 8.4): a transparent conductive oxide (TCO),
CdS as n-part of the junction and window layer, CdTe as p-part of the junction and
absorber layer and back contact. The front and the back contacts can be composed
of different layers; this will be described later.
In this configuration, the supporting substrate obviously needs to be transparent.
Considering that in a thin-film device more than 98% of the material is glass, the
choice of soda lime glass as substrate allows keeping the final price low. However,
soda lime glass has two disadvantages: (1) the presence of sodium and potassium that
6 Superstrate configuration: when light shines through the glass to reach the underlying solar cell.