Enhancement of light trapping for thin film solar cells
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MRS Advances © 2018 Materials Research Society DOI: 10.1557/adv.2018.637
Enhancement of light trapping for thin film solar cells Yasha Yi1,2*, Wei Guo1 and Yueheng Peng1 1
Integrated Nano Optoelectronics Laboratory, University of Michigan, 4901 Evergreen Rd., Dearborn, MI 48128, USA
2
Energy Institute, University of Michigan, 2301 Bonisteel Blvd., Ann Arbor, MI 48109, USA
*[email protected]
ABSTRACT
Light trapping is one of the key challenges for next generation thin film solar cells. In this work, we have identified the distinct light trapping effects for short and long wavelength solar spectrum range, by investigating lighting trapping structures on both sides of Si thin film solar cells. The sub-wavelength photonic front surface by wet etching and multi-layer photonic crystal reflector on the bottom surface are studied in detail for its solar energy absorption characteristics. Our study reveals the drastic difference of the light trapping effects within the solar spectrum wavelength. This work may provide guidance for the efficiency enhancement for next generation thin film photovoltaic cells.
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INTRODUCTION Next generation thin film solar cells (inorganic or organic) are generating wide interests recently as it promises to reduce the materials usage and significantly lower the cost of electricity generated by solar cells [1-3]. One of the main types of thin film solar cells, with Si as the absorbing layer, presents two main challenges for further development; (1) how to achieve broadband antireflection at the front surface; (2) how to achieve broadband light trapping at the bottom surface (especially at longer wavelength) within the AM1.5 solar spectrum. With the rapid progress of nanotechnology, many nano scale photonic devices as small as 30nm have been realized, which is very promising for achieving manipulation of photons at chip scale and having broad applications in renewable energy (photovoltaic cells, solid state lighting), telecommunications and the bio medical field [4]. Accordingly, there are many routes to enhance the light absorption for thin film. Various methods of enhancing optical absorption have been proposed, including the use of dielectric photonic structures [5-12] or plasmonic metallic nanoparticles [1315]; most of which are mainly focused on either front side antireflection film, or light trapping structures on the back side. Few works have been proposed that take into account the two challenges stated above; broadband antireflection photonic structures on the front side and light trapping photonic structures at the bottom side, as well as their correlation for enhancing the light absorption for thin film solar cells. In this work, we have studied light trapping effects utilizing both top and bottom nanophotonic structures. We propose broadband nano scal
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