Modeling and Analysis of Light Trapping and Internal Quantum Efficiency of Solar Cells
Date Issued
2010
Date
2010
Author(s)
Yang, Kuo-Hui
Abstract
A theoretical analysis of the total internal quantum efficiency (IQE) of flat-band homo-junction silicon solar cell with back reflector using distributed Bragg reflectors and grating structure to improve the light trapping is presented and contributions of different regions of the structure to IQEs are simulated. An optical model for the determination of generation profile of the cell is adopted and multiple light passes are considered and compared to previous single light pass approach. It is found that the spatial widths of the cell, the surface recombination velocities, the front surface transmittance, the diffusion length, transmitted angle and the back reflector have significant impacts on the IQEs. With two light passes and normal incident light, the simulation result shows the IQEs can be increased over the one pass value by 6.34% and with a 60° light reflection angle, the IQEs can be further increased by 9.01% while assuming the reflectance at back structure closed to 100%. The effect on IQEs by back reflectance is more significant than that by front transmittance. Under multiple light passes simulation, up to l=4n^2=51 light trapping passes have been considered at wavelength range 900nm-1000nm, the cell can be enhanced by about 26.98%. With textured cell (facet angle α = 54.75°) and normal incident light, the simulation result shows the total IQE increases as the base thickness increases and is higher than that of the at band cell (α = 0°) by 21.7%. The total IQE becomes higher as the facet angle α varies from 0° to 54.75°. For α < 40°, the IQE of textured cell is similar to that of at band cell and for α > 40° the textured effect (increasing the number of light strikes) becomes more evident. Under fixed facet angle α = 54.75°, when the incident angle β is larger than 70°, the IQEs can be further increased by 8.9% as compared with that of normal incident case. As compared with at band cell with anti-reflection coating (which can reduce the Fresnel reflection loss), the total IQE of the textured cell is slightly lower for wavelength range 450nm-700nm and higher for wavelength range 700nm-1150nm.
With l=4n^2H light trapping paths, the simulation result shows the best IQEs (~IQEb) with transmitted angle can reach to 73% which is 14% more than that with the normal incident. For the case of normal transmitted angle, the IQEb with diffusion length 1000μm is about 81% and is 37% higher than that with diffusion length 25μm. Under l=51 light trapping paths, the best achievable IQEb with grating structure is 49% at cell thickness wb=50μm, and the IQEb with diffraction angle θm=60° is larger than that with transmitted angle θl=0° and without light trapping by 9% and 39%, respectively. For cell thickness (H~wb>150μm), the IQEb with diffraction angle θm=60° is slightly smaller than that with transmitted angle θl=0°. It is observed that in present cell model the IQEs are affected more significantly by cell thickness, diffusion length and diffraction angle. The obtained results can provide essential information for designing a high-efficiency solar cell.
With l=4n^2H light trapping paths, the simulation result shows the best IQEs (~IQEb) with transmitted angle can reach to 73% which is 14% more than that with the normal incident. For the case of normal transmitted angle, the IQEb with diffusion length 1000μm is about 81% and is 37% higher than that with diffusion length 25μm. Under l=51 light trapping paths, the best achievable IQEb with grating structure is 49% at cell thickness wb=50μm, and the IQEb with diffraction angle θm=60° is larger than that with transmitted angle θl=0° and without light trapping by 9% and 39%, respectively. For cell thickness (H~wb>150μm), the IQEb with diffraction angle θm=60° is slightly smaller than that with transmitted angle θl=0°. It is observed that in present cell model the IQEs are affected more significantly by cell thickness, diffusion length and diffraction angle. The obtained results can provide essential information for designing a high-efficiency solar cell.
Subjects
Solar cell
Internal quantum efficiency
Light trapping
Grating
Diffusion length
Pyramid structure
Type
thesis
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