130
photovoltage (V oc ). Extensive efforts have been exerted to improve the PV parameters using nanotextured substrates for light management purpose. In this regard,
nanostructures can be stacked to the transparent side of the device as an anti-reflection layer or they can be employed as substrates for the device fabrication. In both
cases, optimization of the geometry for these nanostructures such as periodicity,
shape, and aspect ratio is required to efficiently improve the PCE of the devices.
Without this step, the performance of device is compromised by large surface area
inducing defects and additional charge recombination, particularly for device fabricated on nanotextured substrates. Consequently, fabrication of a uniform thin film
on nanotextured structures can address some issues in this field such as the parasitic
absorption and surface recombination. An overall view of nanotextured based solar
cells will help to have a better understanding from the advantages of these architectures on the fabrication of high-performance devices.
This chapter begins with the fabrication of nanostructures with optimum geometries for light management purpose. Then, their applications in the perovskite solar
cells such as anti-reflection layer and device substrates have been explained.
2 Design of Nanostructures
In order to fabricate efficient solar cell devices, the enhancement of light absorption
is an important step, which needs to be taken into the consideration. In the past
years, extensive studies on device architecture innovation have been performed to
boost the device performance. For instance, anti-reflection layers, back-reflector
coatings, and nanotextured substrates were investigated to minimize the reflection
and trap the sun light within the device [1–3]. Among these techniques, utilization
of nanostructures as a substrate or anti-reflection layer is an efficient approach to
enhance the light absorption and device performance. For this purpose, there are
various types of nanostructures such as nanocone (NC), nanopillar (NPL) or nanowire (NW), nanospike (NSP), nanowells, etc. These nanostructures are strong candidates for enhancement of light harvesting efficiency for a solar cell [4–7]. The
material consumption and the thickness of light absorber can be significantly
reduced due to light trapping properties. Because nanostructures can improve the
optical absorption and enhance the charge carrier collection [2]. To further improve
the light harvesting properties of nanostructures, the proper design and optimization
of geometry are key factors. On the other hand, fabrication of the nanotextured
device may increase the complexity of fabrication process and it is a bit challenging
as compared to planar structure. In some cases, the utilization of nanostructures
increases the surface recombination due the increase in surface area, which can
reduce the device performance. In order to design an efficient solar cell device, it is
important to understand how much of the absorbed light comes from nanotextured
active layer as opposed to the passive materials in the device such as electrodes,
since the photo-generated carriers in active materials can only contribute into the
photocurrent [8, 9]. Thus, optical absorption enhancement by nanotextured
M. M. Tavakoli
photovoltage (V oc ). Extensive efforts have been exerted to improve the PV parameters using nanotextured substrates for light management purpose. In this regard,
nanostructures can be stacked to the transparent side of the device as an anti-reflection layer or they can be employed as substrates for the device fabrication. In both
cases, optimization of the geometry for these nanostructures such as periodicity,
shape, and aspect ratio is required to efficiently improve the PCE of the devices.
Without this step, the performance of device is compromised by large surface area
inducing defects and additional charge recombination, particularly for device fabricated on nanotextured substrates. Consequently, fabrication of a uniform thin film
on nanotextured structures can address some issues in this field such as the parasitic
absorption and surface recombination. An overall view of nanotextured based solar
cells will help to have a better understanding from the advantages of these architectures on the fabrication of high-performance devices.
This chapter begins with the fabrication of nanostructures with optimum geometries for light management purpose. Then, their applications in the perovskite solar
cells such as anti-reflection layer and device substrates have been explained.
2 Design of Nanostructures
In order to fabricate efficient solar cell devices, the enhancement of light absorption
is an important step, which needs to be taken into the consideration. In the past
years, extensive studies on device architecture innovation have been performed to
boost the device performance. For instance, anti-reflection layers, back-reflector
coatings, and nanotextured substrates were investigated to minimize the reflection
and trap the sun light within the device [1–3]. Among these techniques, utilization
of nanostructures as a substrate or anti-reflection layer is an efficient approach to
enhance the light absorption and device performance. For this purpose, there are
various types of nanostructures such as nanocone (NC), nanopillar (NPL) or nanowire (NW), nanospike (NSP), nanowells, etc. These nanostructures are strong candidates for enhancement of light harvesting efficiency for a solar cell [4–7]. The
material consumption and the thickness of light absorber can be significantly
reduced due to light trapping properties. Because nanostructures can improve the
optical absorption and enhance the charge carrier collection [2]. To further improve
the light harvesting properties of nanostructures, the proper design and optimization
of geometry are key factors. On the other hand, fabrication of the nanotextured
device may increase the complexity of fabrication process and it is a bit challenging
as compared to planar structure. In some cases, the utilization of nanostructures
increases the surface recombination due the increase in surface area, which can
reduce the device performance. In order to design an efficient solar cell device, it is
important to understand how much of the absorbed light comes from nanotextured
active layer as opposed to the passive materials in the device such as electrodes,
since the photo-generated carriers in active materials can only contribute into the
photocurrent [8, 9]. Thus, optical absorption enhancement by nanotextured
M. M. Tavakoli