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Research Papers

A Study of Back Electrode Stacked With Low Cost Reflective Layers For High-Efficiency Thin-Film Silicon Solar Cell

[+] Author and Article Information
Tsung-Wei Chang, Chao-Te Liu, Wen-Hsi Lee

Department of Electrical Engineering,
National Cheng Kung University,
Tainan 701, Taiwan

Yu-Jen Hsiao

National Nano Device Laboratories,
Tainan 701, Taiwan

Contributed by the Solar Energy Division of ASME for publication in the JOURNAL OF SOLAR ENERGY ENGINEERING. Manuscript received January 4, 2013; final manuscript received September 25, 2013; published online January 10, 2014. Assoc. Editor: Santiago Silvestre.

J. Sol. Energy Eng 136(3), 031002 (Jan 10, 2014) (6 pages) Paper No: SOL-13-1005; doi: 10.1115/1.4025581 History: Received January 04, 2013; Revised September 25, 2013

In this study, commercially available white paint is used as a pigmented dielectric reflector (PDR) in the fabrication of a low-cost back electrode stack with an Al-doped ZnO (AZO) layer for thin-film silicon solar cell applications. An initial AZO film was deposited by the radio-frequency magnetron sputtering method. In order to obtain the highest transmittance and lowest resistivity of AZO film, process parameters such as sputtering power and substrate temperature were investigated. The optimal 100-nm-thick AZO film with low resistivity and high transmittance in the visible region are 6.4 × 10−3 Ω·cm and above 80%, respectively. Using glue-like white paint doped withTiO2 nanoparticles as the PDR enhances the external quantum efficiency (EQE) of a microcrystalline silicon absorptive layer owing to the doped white particles improving Fabry–Pérot interference (FPI), which raises reflectance and scattering ability. To realize the cost down requirement, decreasing the noble metal film thickness such as a 30-nm-thick silver reflector film, and a small doping particle diameter (D50 = 135 nm) and a high solid content (20%) lead to FPI improvement and a great EQE, which is attributed to improved scattering and reflectivity because of optimum diameter (Dopt) and thicker PDR film. The results indicate that white paint can be used as a reflector coating in low-cost back-electrode structures in high-performance electronics.

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Figures

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Fig. 1

(a) Conventional and (b) modified superstrate structures

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Fig. 2

Resistivity results of 100-nm-thick ZnO:Al films deposited at 1 mTorr and various (a) substrate temperatures (RF sputtering power = 90 W) and (b) RF sputtering powers (substrate temperature = 450 °C)

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Fig. 3

Optical transmission spectra of ZnO:Al films sputtered at various (a) substrate temperatures and (b) RF sputtering powers

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Fig. 4

SEM images of 100-nm-thick ZnO:Al thin films sputtered at 1 mTorr, 90 W, and substrate temperatures of (a) 150, (b) 250, (c) 350, and (d) 450 °C

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Fig. 5

Reflectivity as a function of wavelength for samples (a) D135-20, (b) D230-12, (c) D230-15, (d) D230-20, (e) D320-12, and (f) D320-15

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Fig. 6

Haze values for 1200-μm-thick PDR layer with various doping content levels as a function of wavelength

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Fig. 7

EQE spectra of a-Si:H/μc-Si:H thin-film solar cells (a) without PDR layers as standard specimens (Std-A, Std-B, and Std-C). Other specimens with various PDR films coated onto the 30-nm-thick Ag back-contact of (b) Std-A, (c) Std-B, and (d) Std-C.

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Fig. 8

EQE spectra of a-Si:H/μc-Si:H thin-film solar cells (a) without PDR layers as standard specimens (Std-D and Std-E). Other specimens with various PDR films coated onto the 50-nm-thick Ag back-contact of (b) Std-D and (c) Std-E.

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