Abstract
The present paper reports on a simulation study carried out to determine and optimize the effect of porous silicon (PS) layer at the rear side on the performance of thin polysilicon solar cells. It analytically solved the complete set of equations necessary to determine the contribution that this material has with regard to the internal quantum efficiency (IQE) of the cell when acting as a backside reflector. The contribution of the different regions of the cell, the increase in IQE, and the effects of high porosity and number of PS layers were derived and compared to conventional BSF solar cells. The findings revealed that the IQE of the solar cell with a PS layer at the backside was higher than that of conventional BSF, particularly in terms of medium and long wavelength range λ > 0.5 μm. This improvement was more significant with thin cells, large grain widths, and well-passivated grain boundaries. Furthermore, while the use of the PS layer had a significant effect on the contribution of the base, it exerted no effect on the contribution of the emitter and depletion regions. Overall, the maximum level of IQE improvement was recorded with three double-porosity structures in the PS layer, reaching a high porosity value of about 80 %.
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Abbreviations
- q :
-
Electron charge
- \(L_{n} \left( {L_{n}^{*} } \right)\) :
-
Diffusion length of minority carriers in the base (PS) region
- \(D_{n} \left( {D_{n}^{*} } \right)\) :
-
Diffusion constant of minority carriers in the base (PS) region
- N a (N + a ):
-
Doping level in the base (back) region
- N d :
-
Doping level in the emitter region
- \(\alpha (\lambda ) (\alpha^{*} (\lambda ))\) :
-
Absorption coefficient in the polysilicon (PS) at a wavelength λ
- ϕ(λ):
-
Incident photon flux
- \(R(\lambda ) (R_{d} (\lambda ))\) :
-
Reflection coefficient at the front surface (back region)
- W b(W e):
-
Base (emitter) thickness
- \(W_{{P^{ + } }}\) :
-
PS layer thickness
- W 1 :
-
Emitter and space charge thickness
- W 2 :
-
Total cell thickness without PS layer
- H :
-
Total cell thickness with PS layer
- d :
-
Grain width
- \(S_{n}^{ + } (S_{p} )\) :
-
Recombination velocity at the back (front) contact
- \(\Delta n\) :
-
Excess electron density in the base region
- J refph :
-
Reflected photocurrent density by the back contact
- J PSph :
-
Photocurrent density contributed by the PS layer
- \({\text{IQE}}^{\text{E}} ({\text{IQE}}^{\text{D}} )\) :
-
Contribution of the emitter (depletion region) to the IQE
- IQEB :
-
Contribution of the base to the IQE
- \({\text{IQE}}^{\text{ref}} ({\text{IQE}}^{\text{PS}} )\) :
-
Contribution of the reflected light by the high porous layer (absorbed light in the low porous layer) to the IQE
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The authors wish to express their gratitude to Mr. Anouar Smaoui from the English Section at the Sfax Faculty of Science for carefully proofreading the manuscript of the current paper.
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Trabelsi, A., Zouari, A. Internal quantum efficiency improvement in polysilicon solar cells with porous silicon layer on the rear side. Appl. Phys. A 122, 36 (2016). https://doi.org/10.1007/s00339-015-9567-4
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DOI: https://doi.org/10.1007/s00339-015-9567-4