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Frontiers in Energy

ISSN 2095-1701

ISSN 2095-1698(Online)

CN 11-6017/TK

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Front. Energy    2017, Vol. 11 Issue (1) : 96-104    https://doi.org/10.1007/s11708-016-0434-6
RESEARCH ARTICLE
Influence of using amorphous silicon stack as front heterojunction structure on performance of interdigitated back contact-heterojunction solar cell (IBC-HJ)
Rui JIA(),Ke TAO,Qiang LI,Xiaowan DAI,Hengchao SUN,Yun SUN,Zhi JIN,Xinyu LIU
Institute of Microelectronics, Chinese Academy of Sciences, Beijing 100029, China
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Abstract

Interdigitated back contact-heterojunction (IBC-HJ) solar cells can have a conversion efficiency of over 25%. However, the front surface passivation and structure have a great influence on the properties of the IBC-HJ solar cell. In this paper, detailed numerical simulations have been performed to investigate the potential of front surface field (FSF) offered by stack of n-type doped and intrinsic amorphous silicon (a-Si) layers on the front surface of IBC-HJ solar cells. Simulations results clearly indicate that the electric field of FSF should be strong enough to repel minority carries and cumulate major carriers near the front surface. However, the over-strong electric field tends to drive electrons into a-Si layer, leading to severe recombination loss. The n-type doped amorphous silicon (n-a-Si) layer has been optimized in terms of doping level and thickness. The optimized intrinsic amorphous silicon (i-a-Si) layer should be as thin as possible with an energy band gap (Eg) larger than 1.4 eV. In addition, the simulations concerning interface defects strongly suggest that FSF is essential when the front surface is not passivated perfectly. Without FSF, the IBC-HJ solar cells may become more sensitive to interface defect density.
Keywords amorphous silicon      front surface field      simulations      interdigitated back contact-heterojunction solar cells     
Corresponding Author(s): Rui JIA   
Just Accepted Date: 12 October 2016   Online First Date: 09 November 2016    Issue Date: 16 November 2016
 Cite this article:   
Rui JIA,Ke TAO,Qiang LI, et al. Influence of using amorphous silicon stack as front heterojunction structure on performance of interdigitated back contact-heterojunction solar cell (IBC-HJ)[J]. Front. Energy, 2017, 11(1): 96-104.
 URL:  
https://academic.hep.com.cn/fie/EN/10.1007/s11708-016-0434-6
https://academic.hep.com.cn/fie/EN/Y2017/V11/I1/96
Fig.1  Cross-section of the simulated IBC-HJ solar cell structure
Parameters n-a-Si i-a-Si n-substrate p-emitter n-BSF
Doping concentration/cm−3 5×1018(varied) None 1015 1×1020 2×1020
Thickness/mm 5×10−3 (varied) 5×10−3 (varied) 300 0.4 0.4
Eg/eV 1.7 1.7 (varied) 1.08 1.08 1.08
Affinity/eV 3.86 3.86 4.17 4.17 4.17
Tab.1  Default structure parameters used in simulations
Parameters n-a-Si i-a-Si
Density of acceptor-like states in the tail distribution/( cm-3·eV-1) 1021 1021
Density of donor-like states in the tail distribution/( cm-3·eV-1) 1021 1021
Characteristic decay energy for the tail distribution of acceptor-like states/eV 0.04 0.019
Characteristic decay energy for the tail distribution of donor-like states/eV 0.06 0.049
Density of acceptor-like states in a Gaussian distribution/( cm-3·eV-1) 4×1018 5×1015
Density of donor-like states in a Gaussian distribution/( cm-3·eV-1) 1016 5×1015
Gaussian distribution peak for acceptor-like states/eV 1.2 1.02
Gaussian distribution peak for donor-like states/eV 0.8 1.12
Characteristic decay energy for the Gaussian distribution of acceptor-like states/eV 0.08 0.08
Characteristic decay energy for the Gaussian distribution of donor-like states/eV 0.15 0.08
Capture cross-section for electrons in a tail distribution of acceptor-like states/cm2 10-17 10-17
Capture cross-section for holes in a tail distribution of acceptor-like states/cm2 10-15 10-15
Capture cross-section for electrons in a tail distribution of donor-like states/cm2 10-15 10-15
Capture cross-section for holes in a tail distribution of donor-like states/cm2 10-17 10-17
Capture cross-section for electrons in a Gaussian distribution of acceptor-like states/cm2 10-15 10-15
Capture cross-section for holes in a Gaussian distribution of acceptor-like states/cm2 10-14 10-14
Capture cross-section for electrons in a Gaussian distribution of Donor-like states/cm2 10-14 10-14
Capture cross-section for holes in a Gaussian distribution of Donor-like states/cm2 10-15 10-15
Tab.2  Default material parameters used in the simulations
Fig.2  Efficiency versus doping level of n-a-Si layers with different thickness
Fig.3  Electric field distribution and current density distribution near front surface with doping level of n-a-Si layers (The position of 0 mm in (b) and (d) corresponds to the front surface of the c-Si substrate. The thicknesses of the n-a-Si and the i-a-Si layer are both 5 nm.)

(a) 5×1018 cm−3; (b) 5×1018 cm−3; (c) 1×1021 cm−3; (d) 1×1021 cm−3

Fig.4  Internal quantum efficiency (IQE) of solar cells with n-a-Si layers having different thicknesses and a constant doping level (1021 cm-3)
Fig.5  Electric field distribution and current density distribution near the front surface with a doping level of 1015 cm−3 and different thicknesses of n-a-Si layers (The position 0 mm in (b) and (d) corresponds to the front surface of n-a-Si layer.)

(a) 5 nm; (b) 5 nm; (c) 20 nm; (d) 20 nm

Fig.6  Influences of thickness of i-a-Si layer on performance of solar cells
Fig.7  IQE data of solar cells with i-a-Si layers of different thicknesses (1 nm, 5 nm, 10 nm, 20 nm)
Fig.8  Influences of Eg of i-a-Si layer on performance of solar cells
Fig.9  Influences of interface state density on performance of IBC-HJ solar cells with FSF
Fig.10  Influences of interface state density on solar cells without FSF
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