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Optical Modeling of a-Si:H Thin Film Solar Cells with Rough Interfaces Speaker ： Hsiao-Wei Liu 08/18/2010 Wed

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Outline Introduction Parameters to describe a rough interface Optical modeling and data fitting Conclusion

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Introduction Light trapping has become a standard to increase absorption of the incident light in the active layer. In highly a-Si:H solar cells is mainly on use of texture substrates and highly reflective back contact. The light path in the layer is increased and the light absorption enhanced.

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Introduction For light incident the rough interface

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Introduction For light incident a rough interface ， the relation between the diffuse part and the total light is as follow C: haze parameter F angle dependence The rough interface would be describe by rms roughness and scattering data. scattering data

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Rms roughness The parameter “σ r ” is the root-mean- square value of the thickness variation on the interface. In this paper the rms roughness is the average form 20 measurements carried out on 3*3 um^2 scanned area.

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Asahi U-type TCO Scattering parameter Haze parameter defined as the ratio between the diffuse part of transmitted light to the total transmitted light. Measure total and specular transmittance and calculated the diffuse transmittance to obtain the haze parameter

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Scattering parameter Angular dependence angular distribution function of the transmitted light this article is obtained from the ARS measurements the angular distribution function of the transmitted diffuse part of light could be fitted by a Gaussian distribution function as follow Asahi U-type TCO

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Optical modeling Relation between surface roughness and scattering is important since we usually cannot measure the haze parameter of each layer in the solar cell structure. For σ r comparable or small than λ of the incident medium Rs is related to σ r by Bennett and Porteus’s theory

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Optical modeling The ratio of Rd to R0 as a function of wavelength for several values of the rms roughness of the rough interface: (a)Asahi U-type TCO material and (b) n-type a-Si:H.

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Optical modeling Assumed the diffuse transmittance is similar to the diffuse reflection : For the normal incident and introduce correction factors C1.C2:

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Optical modeling To fit the Asahi a-Si:H TCO, extracted the following formula The ratio of T d to T 0 as function of wavelength for several values of σ r for: (a)the TCO/p interface and (b)the p/i interface.

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Optical modeling The haze parameter H T would be a formula as follow: In this formula C is a factor that depends on the two media.

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Assuming C =1 the simulated H T as a function of wavelength for different σ r and measured H T for Asahi U-type TCO with σr = 40 nm for simulation of HT of Asahi U-type TCO/air interface C= 0.5 is a better match

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Conclusion The angular distribution function for the transmitted light can be fitted by a Gaussian distribution function Using optical modeling we obtain the relationship between surface roughness and haze parameter. But need to modify if not render a good agreement with experimental results The measured haze parameter and angular distribution function will be incorporated in the optical model for a-Si:H solar cells that we are developing, in order to get accurate simulation results for a-Si:H solar cells.

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Thanks for your kind attention!

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