Page 17 - Mirjam-Theelen-Degradation-of-CIGS-solar-cells
P. 17
Introduction
(CBD). Some CIGS solar cell designs avoid this material due to environmental con -
cerns regarding the use of cadmium, or its wetchemical deposition method
using substances such as Zn(O,OH,S) or InS instead. Within this thesis, only
2 3
CBD CdS has been used.
Front contact: Intrinsic ZnO (i-ZnO): This highly resistive material is used to prevent
the formation of shunt paths within CIGS solar cells. This layer is normally ap-
plied by RF sputtering.
Front contact: Aluminium-doped ZnO (ZnO:Al): This n-type semiconductor is both
transparent and conductive. These characteristics are critical, since this layer
should be transparent to enable light to penetrate through to the CIGS ab-
sorber layer and conductive to transport the electrons. Other conductive and
transparent oxides, such as the more expensive indium tin oxide (ITO) can also
be used. In this work, RF sputtered ZnO:Al has been used as front contact.
1.4 Reliability of the CIGS PV technology
For large scale market introduction of CIGS modules, reliability of product perfor-
mance is, alongside with initial costs and efficiency, an important prerequisite. Reli-
ability is defined as the probability of failure-free performance over a given lifetime,
under specified operating conditions. In order to optimise this reliability of solar mod -
ules, two factors of the product performance should be assessed:
* Performance stability ‘How long does the module generate electricity in an
economically attractive way?’ This time is called the economic ‘lifetime’ and
is often defined as the period that the module produces 80% or more of the
original power.
*Predictability ‘How well can we predict their lifetime?’ and ‘How reproducible
is the lifetime of modules?’
These factors greatly impact the cost of electricity obtained with solar modules (Fig-
ure 1.8 ). First of all, lower electricity costs can be obtained for stable long lifetime solar
modules. Additionally the predictability of the performance is also important: finan-
ciers, home-owners, utilities, planners and especially module producers need to be
able to predict when a module will no longer function in order to evaluate their finan -
cial risks. Therefore, reliability aspects are very important in order to obtain the lowest
and best predictable electricity costs. In order to comply with market demands, most
suppliers provide a guarantee that the modules will still provide at least 90% of their
initial efficiency after 10 years or 80% after 25 years [12].
15
(CBD). Some CIGS solar cell designs avoid this material due to environmental con -
cerns regarding the use of cadmium, or its wetchemical deposition method
using substances such as Zn(O,OH,S) or InS instead. Within this thesis, only
2 3
CBD CdS has been used.
Front contact: Intrinsic ZnO (i-ZnO): This highly resistive material is used to prevent
the formation of shunt paths within CIGS solar cells. This layer is normally ap-
plied by RF sputtering.
Front contact: Aluminium-doped ZnO (ZnO:Al): This n-type semiconductor is both
transparent and conductive. These characteristics are critical, since this layer
should be transparent to enable light to penetrate through to the CIGS ab-
sorber layer and conductive to transport the electrons. Other conductive and
transparent oxides, such as the more expensive indium tin oxide (ITO) can also
be used. In this work, RF sputtered ZnO:Al has been used as front contact.
1.4 Reliability of the CIGS PV technology
For large scale market introduction of CIGS modules, reliability of product perfor-
mance is, alongside with initial costs and efficiency, an important prerequisite. Reli-
ability is defined as the probability of failure-free performance over a given lifetime,
under specified operating conditions. In order to optimise this reliability of solar mod -
ules, two factors of the product performance should be assessed:
* Performance stability ‘How long does the module generate electricity in an
economically attractive way?’ This time is called the economic ‘lifetime’ and
is often defined as the period that the module produces 80% or more of the
original power.
*Predictability ‘How well can we predict their lifetime?’ and ‘How reproducible
is the lifetime of modules?’
These factors greatly impact the cost of electricity obtained with solar modules (Fig-
ure 1.8 ). First of all, lower electricity costs can be obtained for stable long lifetime solar
modules. Additionally the predictability of the performance is also important: finan-
ciers, home-owners, utilities, planners and especially module producers need to be
able to predict when a module will no longer function in order to evaluate their finan -
cial risks. Therefore, reliability aspects are very important in order to obtain the lowest
and best predictable electricity costs. In order to comply with market demands, most
suppliers provide a guarantee that the modules will still provide at least 90% of their
initial efficiency after 10 years or 80% after 25 years [12].
15
