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Performance evaluation of thin film silicon solar cell based on dual diffraction grating.

Dubey RS, Saravanan S, Kalainathan S - Nanoscale Res Lett (2014)

Bottom Line: Accordingly, new design engineering of solar cells has been emphasized and found to be effective to achieve improved performance.Use of metal layer as a part of back reflector has found to be promising for minimum requirement of DBR pairs.The effect of grating and anti-reflection coating thicknesses are also investigated for absorption enhancement.

View Article: PubMed Central - PubMed

Affiliation: Advanced Research Laboratory for Nanomaterials and Devices, Department of Nanotechnology, Swarnandhra College of Engineering and Technology, Seetharampuram, Narsapur, Andhra Pradesh, India, rag_pcw@yahoo.co.in.

ABSTRACT
Light-trapping structures are more demanding for optimal light absorption in thin film silicon solar cells. Accordingly, new design engineering of solar cells has been emphasized and found to be effective to achieve improved performance. This paper deals with a design of thin film silicon solar cells and explores the influence of bottom grating and combination of top and bottom (dual) grating as a part of back reflector with a distributed Bragg reflector (DBR). Use of metal layer as a part of back reflector has found to be promising for minimum requirement of DBR pairs. The effect of grating and anti-reflection coating thicknesses are also investigated for absorption enhancement. With optimization, high performance has been achieved from dual grating-based solar cell with a relative enhancement in short-circuit current approximately 68% while it was approximately 55% in case of bottom grating-based solar cell. Our designing efforts show enhanced absorption of light in UV and infrared part of solar spectrum.

No MeSH data available.


Photonic band structure (a) and schematic diagram of designed solar cell structure (b) and electric field distribution profile (c).
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Fig1: Photonic band structure (a) and schematic diagram of designed solar cell structure (b) and electric field distribution profile (c).

Mentions: Distributed Bragg reflector is composed of low and high refractive index layers arranged periodically in one direction. Plane wave method is one of the well-known techniques used to calculate band structure of photonic crystals. Here, we have designed a DBR which is composed of alternate layers of indium tin oxide and amorphous silicon (ITO/a-Si) respectively with their periodicity in x direction. For simulation, we have used plane wave method by applying perfectly matched layer boundary condition to y and z directions. Figure 1a shows band diagram of a DBR for both TE and TM polarizations. The considered values of refractive index are na-Si = 3.6 and nITO = 1.85, thickness ta-Si = 56 nm and tIT0 = 108 nm, and lattice constant Ʌ = ta-Si + tITO = 164 nm with center wavelength approximately 800 nm. At normal incidence, a complete photonic band gap is obtained at frequency 0.162 to 0.242 (in the units of ωa/2πc) and so longer wavelength light can be trapped and enforced towards active silicon region after total internal/Bragg reflection. This designed DBR is further incorporated into a design of 5 μm thickness solar cell in between grating and metal layer as shown in Figure 1b. This solar cell consists of indium tin oxide-antireflection coating layer (ITO), crystalline silicon (C-si)-active region, and a back reflector composed of diffraction grating, DBR, and metal layer.Use of DBR as a part back reflector doubles path length of longer wavelength photons due to evanescent decay in DBR and enforcing them into active region after total internal or Bragg reflections. Figure 1c shows electric field profile in designed solar cell. Grating diffracts longer wavelength light of single passed from active silicon region as short wavelength light is already being absorbed before it crosses active region. In simple words, once the light made incident onto the solar cell, the shorter wavelength light is being absorbed; however, longer wavelength light is passed through active silicon region and reaches to DBR where it decays evanescently and coming back after reflections. The occurrence of diffraction and scattering prolongs the optical path length in the absorbing layer which supports coupling of light and hence enhancement of solar cell performance can be expected.Figure 1


Performance evaluation of thin film silicon solar cell based on dual diffraction grating.

Dubey RS, Saravanan S, Kalainathan S - Nanoscale Res Lett (2014)

Photonic band structure (a) and schematic diagram of designed solar cell structure (b) and electric field distribution profile (c).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4494017&req=5

Fig1: Photonic band structure (a) and schematic diagram of designed solar cell structure (b) and electric field distribution profile (c).
Mentions: Distributed Bragg reflector is composed of low and high refractive index layers arranged periodically in one direction. Plane wave method is one of the well-known techniques used to calculate band structure of photonic crystals. Here, we have designed a DBR which is composed of alternate layers of indium tin oxide and amorphous silicon (ITO/a-Si) respectively with their periodicity in x direction. For simulation, we have used plane wave method by applying perfectly matched layer boundary condition to y and z directions. Figure 1a shows band diagram of a DBR for both TE and TM polarizations. The considered values of refractive index are na-Si = 3.6 and nITO = 1.85, thickness ta-Si = 56 nm and tIT0 = 108 nm, and lattice constant Ʌ = ta-Si + tITO = 164 nm with center wavelength approximately 800 nm. At normal incidence, a complete photonic band gap is obtained at frequency 0.162 to 0.242 (in the units of ωa/2πc) and so longer wavelength light can be trapped and enforced towards active silicon region after total internal/Bragg reflection. This designed DBR is further incorporated into a design of 5 μm thickness solar cell in between grating and metal layer as shown in Figure 1b. This solar cell consists of indium tin oxide-antireflection coating layer (ITO), crystalline silicon (C-si)-active region, and a back reflector composed of diffraction grating, DBR, and metal layer.Use of DBR as a part back reflector doubles path length of longer wavelength photons due to evanescent decay in DBR and enforcing them into active region after total internal or Bragg reflections. Figure 1c shows electric field profile in designed solar cell. Grating diffracts longer wavelength light of single passed from active silicon region as short wavelength light is already being absorbed before it crosses active region. In simple words, once the light made incident onto the solar cell, the shorter wavelength light is being absorbed; however, longer wavelength light is passed through active silicon region and reaches to DBR where it decays evanescently and coming back after reflections. The occurrence of diffraction and scattering prolongs the optical path length in the absorbing layer which supports coupling of light and hence enhancement of solar cell performance can be expected.Figure 1

Bottom Line: Accordingly, new design engineering of solar cells has been emphasized and found to be effective to achieve improved performance.Use of metal layer as a part of back reflector has found to be promising for minimum requirement of DBR pairs.The effect of grating and anti-reflection coating thicknesses are also investigated for absorption enhancement.

View Article: PubMed Central - PubMed

Affiliation: Advanced Research Laboratory for Nanomaterials and Devices, Department of Nanotechnology, Swarnandhra College of Engineering and Technology, Seetharampuram, Narsapur, Andhra Pradesh, India, rag_pcw@yahoo.co.in.

ABSTRACT
Light-trapping structures are more demanding for optimal light absorption in thin film silicon solar cells. Accordingly, new design engineering of solar cells has been emphasized and found to be effective to achieve improved performance. This paper deals with a design of thin film silicon solar cells and explores the influence of bottom grating and combination of top and bottom (dual) grating as a part of back reflector with a distributed Bragg reflector (DBR). Use of metal layer as a part of back reflector has found to be promising for minimum requirement of DBR pairs. The effect of grating and anti-reflection coating thicknesses are also investigated for absorption enhancement. With optimization, high performance has been achieved from dual grating-based solar cell with a relative enhancement in short-circuit current approximately 68% while it was approximately 55% in case of bottom grating-based solar cell. Our designing efforts show enhanced absorption of light in UV and infrared part of solar spectrum.

No MeSH data available.