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Broadband wide-angle antireflection enhancement in AZO/Si shell/core subwavelength grating structures with hydrophobic surface for Si-based solar cells

Jung Woo Leem, Young Min Song, and Jae Su Yu

Open Access Open Access

Abstract

Broadband wide-angle antireflection characteristics of aluminum-doped zinc oxide (AZO)/silicon (Si) shell/core subwavelength grating (SWG) structures with a hydrophobic surface, together with theoretical prediction using a rigorous coupled-wave analysis simulation, were investigated for Si-based solar cells. The AZO films with different thicknesses were deposited on Si SWGs by rf magnetron sputtering method, which forms a shell/core structure. The AZO/Si shell/core SWGs reduced significantly the surface reflection compared to the AZO films/Si substrate. The coverage of AZO films on Si SWGs improved the antireflective property over a wider incident angle. The AZO/Si shell/core SWG structure with a 200 nm-thick AZO layer deposited at an rf power of 200 W exhibited a water contact angle of 123°. This structure also exhibited a low average reflectance of ~2% over a wide wavelength range of 300-2100 nm with a solar weighted reflectance of 2.8%, maintaining a reflectance of < 9.2% at wavelengths of 300-2100 nm up to the incident angle of θi = 70°. The effective electrical properties of AZO films in AZO/Si shell/core SWGs were also analyzed.

©2011 Optical Society of America

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Figures (6)
Fig. 1
Fig. 1 Schematic illustrations and SEM images corresponding to process steps for the fabrication of AZO/Si shell/core SWG structures. The oblique-view SEM images are taken at a 30° tilt angle.

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Fig. 2
Fig. 2 (a) Schematic illustrations and calculated effective refractive index profiles, (b) calculated reflectance spectra, and (c) contour plots of the calculated incident angle dependent for (i) AZO films/Si substrate and (ii) AZO/Si shell/core SWGs with a 100 nm-thick AZO, respectively. The insets of (b) show a three-dimensional model of the AZO/Si shell/core SWGs with a 6-fold hexagonal symmetry structure and the effective refractive index distribution of the AZO/Si shell/core SWG structure used in this simulation.

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Fig. 3
Fig. 3 (a) SEM images and (b) measured reflectance spectra of the AZO/Si shell/core SWG structures with AZO thicknesses of (i) 100 nm, (ii) 200 nm, (iii) 300 nm, and (iv) 500 nm. The insets of (a) and (b) show the cross-sectional SEM images of the corresponding structures and measured reflectance spectra of the AZO films/Si substrate with AZO thicknesses of 100, 200, 300, and 500 nm, respectively. The period of SWGs is 300 nm.

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Fig. 4
Fig. 4 (a) Measured reflectance spectra of AZO (200 nm)/Si shell/core SWGs for different periods and (b) influence of the period of AZO (200 nm)/Si shell/core SWGs with a 6-fold hexagonal array on the calculated reflectance as a function of the wavelength. The insets of (a) show the SEM images of the corresponding structures.

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Fig. 5
Fig. 5 (a) SEM images of the AZO (200 nm)/Si shell/core SWGs deposited at rf powers of (i) 100 W, (ii) 150 W, and (iii) 200 W. The (iv) of (a) shows the 2θ scan XRD patterns of corresponding structures for different rf powers. (b) Effective resistivity, carrier concentration, and Hall mobility of the AZO film with a 200 nm-thick in AZO/Si shell/core SWGs as a function of rf power.

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Fig. 6
Fig. 6 (a) Measured reflectance spectra of the AZO films/Si substrate and AZO/Si shell/core SWG structures with a 200 nm AZO, respectively, deposited at rf powers of 100 W and 200 W and (b) measured angle-dependent reflection spectra of the AZO (200 nm)/Si shell/core SWGs deposited at an rf power of 200 W for the period of 300 nm. The insets of (a) show the photographs of water droplet shapes with contact angles on AZO film/Si substrate and AZO/Si shell/core SWGs with a 200 nm AZO, respectively, deposited at an rf power of 200 W. The insets of (b) show the photographs (left) of AZO film/Si substrate and AZO/Si shell/core SWGs, and the zoom-out SEM image (right) of AZO/Si shell/core SWGs.

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