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Temperature dependency of the electrical parameters of CIGS solar cells
4.1 Introduction
When solar modules, including CIGS, are exposed to elevated temperatures, their
conversion efficiency is influenced negatively. The efficiency of CIGS modules
with respect to temperature is of great relevance, for example for promising space
applications where panels are subjected to temperatures varying from -160 to 100 ⁰C
within a few minutes after eclipse [1], but also in terrestrial applications where they
could be subjected to environmental temperatures as high as 70⁰C [2]. Additionally,
modules heat up faster than their surroundings, so the temperatures at the back of
o
modules as high as 71C have been measured, even at moderate climate [3]. There
have been extensive studies in literature [4-9] for the temperature dependency of
crystalline silicon PV as well as for other types of thin film solar cells like amorphous
silicon or CdTe. However, the temperature dependency of CIGS solar cells and
modules has not been studied extensively. It should be noted that module producers
often only give a single value for the temperature dependency of their module [10-
13]. Within other studies, the values for the temperature dependency of mostly the
current, voltage and efficiency dependency are incidentally shown [1, 7, 14-17], but no
systematic studies are available.
The main goal of this study was to systematically investigate the impact of exposure
to temperatures varying from room temperature (25ºC) to elevated temperatures
(105ºC) on the electrical parameters of CIGS solar cells and modules. For this purpose,
we have produced multiple types of CIGS solar cells, following cell designs that are
applicable in CIGS modules. These samples were placed in a temperature controlled
chamber combined with 1.5 AM illumination. This setup allowed the slow increase of
the temperature of the solar cells (0.1 to 0.2 C/minute) combined with the continuous
o
measurement of the current voltage (IV) curves of the samples. The temperature
coefficients for the main electrical parameters were then calculated from the IV curves.
CIGS photovoltaics is not yet a standardised technology with respect to both
substrates and deposition processes. Additionally, it is well known that all the
different types of CIGS solar cells and modules have different electrical behaviour. In
order to get a good idea of the temperature dependency of different types of CIGS
solar cells and modules, in total 42 samples of two types of clearly different CIGS
solar cells for modules were tested. One type of samples was deposited on soda lime
glass substrates by the relatively standard three stage coevapouration process, while
the second batch has been deposited on flexible polyimide substrate by ion-beam
assisted coevapouration at relatively low temperatures. Apart from these differences,
these two types of CIGS solar cells have different topologies for the collection of the
107
4.1 Introduction
When solar modules, including CIGS, are exposed to elevated temperatures, their
conversion efficiency is influenced negatively. The efficiency of CIGS modules
with respect to temperature is of great relevance, for example for promising space
applications where panels are subjected to temperatures varying from -160 to 100 ⁰C
within a few minutes after eclipse [1], but also in terrestrial applications where they
could be subjected to environmental temperatures as high as 70⁰C [2]. Additionally,
modules heat up faster than their surroundings, so the temperatures at the back of
o
modules as high as 71C have been measured, even at moderate climate [3]. There
have been extensive studies in literature [4-9] for the temperature dependency of
crystalline silicon PV as well as for other types of thin film solar cells like amorphous
silicon or CdTe. However, the temperature dependency of CIGS solar cells and
modules has not been studied extensively. It should be noted that module producers
often only give a single value for the temperature dependency of their module [10-
13]. Within other studies, the values for the temperature dependency of mostly the
current, voltage and efficiency dependency are incidentally shown [1, 7, 14-17], but no
systematic studies are available.
The main goal of this study was to systematically investigate the impact of exposure
to temperatures varying from room temperature (25ºC) to elevated temperatures
(105ºC) on the electrical parameters of CIGS solar cells and modules. For this purpose,
we have produced multiple types of CIGS solar cells, following cell designs that are
applicable in CIGS modules. These samples were placed in a temperature controlled
chamber combined with 1.5 AM illumination. This setup allowed the slow increase of
the temperature of the solar cells (0.1 to 0.2 C/minute) combined with the continuous
o
measurement of the current voltage (IV) curves of the samples. The temperature
coefficients for the main electrical parameters were then calculated from the IV curves.
CIGS photovoltaics is not yet a standardised technology with respect to both
substrates and deposition processes. Additionally, it is well known that all the
different types of CIGS solar cells and modules have different electrical behaviour. In
order to get a good idea of the temperature dependency of different types of CIGS
solar cells and modules, in total 42 samples of two types of clearly different CIGS
solar cells for modules were tested. One type of samples was deposited on soda lime
glass substrates by the relatively standard three stage coevapouration process, while
the second batch has been deposited on flexible polyimide substrate by ion-beam
assisted coevapouration at relatively low temperatures. Apart from these differences,
these two types of CIGS solar cells have different topologies for the collection of the
107
