Page 66 - Mirjam-Theelen-Degradation-of-CIGS-solar-cells
P. 66
Chapter 2
lying absorber and buffer layers in the CIGS cell can also negatively impact the damp
heat stability of the ZnO:Al film.
The more expensive ITO is generally more stable than ZnO:Al in the presence of hu-
midity and elevated temperatures. Conditions that favour the deposition of damp heat
resistant films are higher substrate temperatures and lower partial pressures of oxy-
gen. Degradation of ITO can be caused by the migration of water and alkaline species
into the layer. It was also observed that decomposition of the layer into tin and indium
containing materials occurred due to the heterogeneous division of these elements.
Furthermore, the degradation of both ZnO:Al and ITO was often accompanied by the
formation of spots.
Interaction between the TCO and barrier material also plays a large role for CIGS module
stability: a barrier with a high WVTR can prevent the ingression of water into the TCO.
It was reported that alongside to the materials specifically designed to function as wa -
ter barrier, i-ZnO, ITO and SnO also showed barrier properties. Alternatively, the barrier
2
properties of various materials for CO could be considered.
2
2.4 Degradation of the device
While chapter 2.3 was focused on the degradation of the individual layers in a CIGS solar
cell, this chapter describes the degradation of the complete solar cell stacks. The focus
will lay on the changes actually occurring in the CIGS solar cell itself, but since many arti -
cles include information on complete modules as well as encapsulated cells and (mini-)
modules, these devices can also be described in this chapter. In this chapter, the litera -
ture about the degradation of complete devices is reviewed. First, an overview of the
changes in electrical properties of the considered solar cells and modules is depicted in
graphs. Chapter 2.4.2 gives information on the degradation of CIGS cells and mini-mod -
ules without encapsulation under damp heat testing, while chapter 2.4.3 describes the
impact of exposure to damp heat combined with illumination or a bias. Chapter 2.4.4
gives an example that multiple degradation reactions can occur within one degradation
process. Finally chapter 2.4.5 focuses on articles in which the influence of barrier and en -
capsulant materials on the stability of CIGS solar cells and modules is taken into account.
2.4.1 Overview of device degradation data
The change in electrical parameters of both encapsulated and non-encapsulated CIGS
solar cells and minimodules in depicted in the additional information in the electronic
version. In this chapter, various graphs are shown, depicting aspects of the degradation
of the samples.
First of all, Figure 2.10 shows the degradation rate of the efficiency in relative percent
64
lying absorber and buffer layers in the CIGS cell can also negatively impact the damp
heat stability of the ZnO:Al film.
The more expensive ITO is generally more stable than ZnO:Al in the presence of hu-
midity and elevated temperatures. Conditions that favour the deposition of damp heat
resistant films are higher substrate temperatures and lower partial pressures of oxy-
gen. Degradation of ITO can be caused by the migration of water and alkaline species
into the layer. It was also observed that decomposition of the layer into tin and indium
containing materials occurred due to the heterogeneous division of these elements.
Furthermore, the degradation of both ZnO:Al and ITO was often accompanied by the
formation of spots.
Interaction between the TCO and barrier material also plays a large role for CIGS module
stability: a barrier with a high WVTR can prevent the ingression of water into the TCO.
It was reported that alongside to the materials specifically designed to function as wa -
ter barrier, i-ZnO, ITO and SnO also showed barrier properties. Alternatively, the barrier
2
properties of various materials for CO could be considered.
2
2.4 Degradation of the device
While chapter 2.3 was focused on the degradation of the individual layers in a CIGS solar
cell, this chapter describes the degradation of the complete solar cell stacks. The focus
will lay on the changes actually occurring in the CIGS solar cell itself, but since many arti -
cles include information on complete modules as well as encapsulated cells and (mini-)
modules, these devices can also be described in this chapter. In this chapter, the litera -
ture about the degradation of complete devices is reviewed. First, an overview of the
changes in electrical properties of the considered solar cells and modules is depicted in
graphs. Chapter 2.4.2 gives information on the degradation of CIGS cells and mini-mod -
ules without encapsulation under damp heat testing, while chapter 2.4.3 describes the
impact of exposure to damp heat combined with illumination or a bias. Chapter 2.4.4
gives an example that multiple degradation reactions can occur within one degradation
process. Finally chapter 2.4.5 focuses on articles in which the influence of barrier and en -
capsulant materials on the stability of CIGS solar cells and modules is taken into account.
2.4.1 Overview of device degradation data
The change in electrical parameters of both encapsulated and non-encapsulated CIGS
solar cells and minimodules in depicted in the additional information in the electronic
version. In this chapter, various graphs are shown, depicting aspects of the degradation
of the samples.
First of all, Figure 2.10 shows the degradation rate of the efficiency in relative percent
64
