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Coatings 2017, 7(12), 236; https://doi.org/10.3390/coatings7120236

Photonic Structures for Light Trapping in Thin Film Silicon Solar Cells: Design and Experiment

1,2,3
,
3,4
,
5
and
1,2,3,*
1
Institute of Photoelectronic Thin Film Devices & Technology, Nankai University, Tianjin 300071, China
2
Key Laboratory of Photoelectronic Thin Film Devices & Technology of Tianjin, Nankai University, Tianjin 300071, China
3
Key Laboratory of Optical Information Science & Technology, Ministry of Education, Nankai University, Tianjin 300350, China
4
School of Electrical Engineering and Automation, Tianjin Polytechnic University, Tianjin 300387, China
5
Department of Electrical and Computer Engineering, Michigan State University, East Lansing, MI 48824, USA
*
Author to whom correspondence should be addressed.
Academic Editor: Mario Pagliaro
Received: 27 October 2017 / Revised: 12 December 2017 / Accepted: 12 December 2017 / Published: 21 December 2017
(This article belongs to the Special Issue Plasma Etching and Deposition)

Abstract

One of the foremost challenges in designing thin-film silicon solar cells (TFSC) is devising efficient light-trapping schemes due to the short optical path length imposed by the thin absorber thickness. The strategy relies on a combination of a high-performance back reflector and an optimized texture surface, which are commonly used to reflect and scatter light effectively within the absorption layer, respectively. In this paper, highly promising light-trapping structures based on a photonic crystal (PC) for TFSCs were investigated via simulation and experiment. Firstly, a highly-reflective one-dimensional photonic crystal (1D-PC) was designed and fabricated. Then, two types of 1D-PC-based back reflectors (BRs) were proposed: Flat 1D-PC with random-textured aluminum-doped zinc oxide (AZO) or random-textured 1D-PC with AZO. These two newly-designed BRs demonstrated not only high reflectivity and sufficient conductivity, but also a strong light scattering property, which made them efficient candidates as the electrical contact and back reflector since the intrinsic losses due to the surface plasmon modes of the rough metal BRs can be avoided. Secondly, conical two-dimensional photonic crystal (2D-PC)-based BRs were investigated and optimized for amorphous a-SiGe:H solar cells. The maximal absorption value can be obtained with an aspect ratio of 1/2 and a period of 0.75 µm. To improve the full-spectral optical properties of solar cells, a periodically-modulated PC back reflector was proposed and experimentally demonstrated in the a-SiGe:H solar cell. This periodically-modulated PC back reflector, also called the quasi-crystal structure (QCS), consists of a large periodic conical PC and a randomly-textured Ag layer with a feature size of 500–1000 nm. The large periodic conical PC enables conformal growth of the layer, while the small feature size of Ag can further enhance the light scattering. In summary, a comprehensive study of the design, simulation and fabrication of 1D-PC- and 2D-PC-based back reflectors for TFSCs was carried out. Total absorption and device performance enhancement were achieved with the novel PC light-trapping systems because of their high reflectivity or high scattering property. Further research is necessary to illuminate the optimal structure design of PC-based back reflectors and high solar cell efficiency. View Full-Text
Keywords: photonic crystal; light-trapping; thin-film silicon solar cell; back reflector photonic crystal; light-trapping; thin-film silicon solar cell; back reflector
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Ding, Y.; Chen, P.; Fan, Q.H.; Hou, G. Photonic Structures for Light Trapping in Thin Film Silicon Solar Cells: Design and Experiment. Coatings 2017, 7, 236.

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