Photonic Crystal Back Reflectors for Enhanced Absorption in Amorphous Silicon Solar Cells

AbstractPhotonic crystal back reflectors offer enhanced optical absorption in thin-film solar cells, without undesirable losses. Rigorous simulations of photonic crystal back reflectors predicted maximized light absorption in amorphous silicon solar cells for a pitch of 700-800 nm. Simulations also predict that for typical 250 nm i-layer cells, the periodic photonic crystal back reflector can improve absorption over the ideal randomly roughened back reflector (or the ‘4n2classical limit') at wavelengths near the band edge. The PC back reflector provides even higher enhancement than roughened back reflectors for cells with even thinner i-layers. Using these simulated designs, we fabricated metallic photonic crystal back reflectors with different etch depths and i-layer thicknesses. The photonic crystals had a pitch of 760 nm and triangular lattice symmetry. The average light absorption increased with the PC back reflectors, but the greatest improvement (7-8%) in short circuit current was found for thinner i-layers. We have studied the dependence of cell performance on the etch depth of the photonic crystal. The photonic crystal back reflector strongly diffracts light and increases optical path lengths of solar photons.

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Enhanced Absorption in Amorphous Silicon Solar Cells Using Plasmonic and Photonic Crystals – Measurement and Simulation

MRS Proceedings ◽

10.1557/proc-1248-d05-03 ◽

2010 ◽

Vol 1248 ◽

Author(s):

Benjamin Curtin ◽

Rana Biswas ◽

Vikram Dalal

Keyword(s):

Thin Film ◽

Solar Cells ◽

Photonic Crystal ◽

Photonic Crystals ◽

Amorphous Silicon ◽

Near Infrared ◽

Silicon Solar Cells ◽

Back Reflectors ◽

Back Reflector ◽

Hole Arrays

AbstractWe develop experimentally and theoretically plasmonic and photonic crystals for enhancing thin film silicon solar cells. Thin film amorphous silicon (a-Si:H) solar cells suffer from decreased absorption of red and near-infrared photons, where the photon absorption length is large. Simulations predict maximal light absorption for a pitch of 700-800 nm for photonic crystal hole arrays in silver or ZnO/Ag back reflectors, with absorption increases of ~12%. The photonic crystal improves over the ideal randomly roughened back reflector (or the ‘4n2limit’) at wavelengths near the band edge. We fabricated metallic photonic crystal back-reflectors using photolithography and reactive-ion etching. We conformally deposited a-Si:H solar cells on triangular lattice hole arrays of pitch 760 nm on silver back-reflectors. Electron microscopy demonstrates excellent long range periodicity and conformal a-Si:H growth. The measured quantum efficiency increases by 7-8 %, relative to a flat reflector reference device, with enhancement factors exceeding 6 at near-infrared wavelengths. The photonic crystal back reflector strongly diffracts light and increases optical path lengths of solar photons.

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Photonic crystal based back reflectors for light management and enhanced absorption in amorphous silicon solar cells

Applied Physics Letters ◽

10.1063/1.3269593 ◽

2009 ◽

Vol 95 (23) ◽

pp. 231102 ◽

Cited By ~ 63

Author(s):

Benjamin Curtin ◽

Rana Biswas ◽

Vikram Dalal

Keyword(s):

Solar Cells ◽

Photonic Crystal ◽

Amorphous Silicon ◽

Silicon Solar Cells ◽

Enhanced Absorption ◽

Back Reflectors ◽

Light Management

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Fabrication of Photonic Crystal based Back Reflectors for Light Management and Enhanced Absorption in Amorphous Silicon Solar Cells

MRS Proceedings ◽

10.1557/proc-1153-a07-15 ◽

2009 ◽

Vol 1153 ◽

Cited By ~ 2

Author(s):

Benjamin Curtin ◽

Rana Biswas ◽

Vikram Dalal

Keyword(s):

Solar Cells ◽

Photonic Crystal ◽

Steel Substrate ◽

Back Surface ◽

Enhanced Absorption ◽

Reference Device ◽

Back Reflectors ◽

Light Management ◽

Back Reflector ◽

Microscopy Images

AbstractPhotonic crystal based back-reflectors are an attractive solution for light management and enhancing optical absorption in thin film solar cells, without undesirable losses. We have fabricated prototype photonic crystal back-reflectors using photolithographic methods and reactive-ion etching. The photonic crystal back-reflector has a triangular lattice symmetry, a thickness of 250 nm, and a pitch of 765 nm. Scanning electron microscopy images demonstrate high quality long range periodicity. An a-Si:H solar cell device was grown on this back-reflector using standard PECVD techniques. Measurements demonstrate strong diffraction of light and high diffuse reflectance by the photonic crystal back-reflector. The photonic crystal back-reflector increases the average photon collection by ˜9% in terms of normalized external quantum efficiency, relative to a reference device on a stainless steel substrate with an Ag coated back surface.

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Light-trapping in Thin Film Silicon Solar Cells with a Combination of Periodic and Randomly Textured Back-reflectors

MRS Proceedings ◽

10.1557/opl.2012.888 ◽

2012 ◽

Vol 1426 ◽

pp. 117-123 ◽

Cited By ~ 1

Author(s):

Sambit Pattnaik ◽

Nayan Chakravarty ◽

Rana Biswas ◽

D. Slafer ◽

Vikram Dalal

Keyword(s):

Thin Film ◽

Solar Cells ◽

Light Absorption ◽

Nanoimprint Lithography ◽

Light Trapping ◽

Silicon Solar Cells ◽

Long Wavelength ◽

Thin Film Silicon ◽

Back Reflectors ◽

Back Reflector

ABSTRACTLight trapping is essential to harvest long wavelength red and near-infrared photons in thin film silicon solar cells. Traditionally light trapping has been achieved with a randomly roughened Ag/ZnO back reflector, which scatters incoming light uniformly through all angles, and enhances currents and cell efficiencies over a flat back reflector. A new approach using periodically textured photonic-plasmonic arrays has been recently shown to be very promising for harvesting long wavelength photons, through diffraction of light and plasmonic light concentration. Here we investigate the combination of these two approaches of random scattering and plasmonic effects to increase cell performance even further. An array of periodic conical back reflectors was fabricated by nanoimprint lithography and coated with Ag. These back reflectors were systematically annealed to generate different amounts of random texture, at smaller spatial scales, superimposed on a larger scale periodic texture. nc-Si solar cells were grown on flat, periodic photonic-plasmonic substrates, and randomly roughened photonic-plasmonic substrates. There were large improvements (>20%) in the current and light absorption of the photonic-plasmonic substrates relative to flat. The additional random features introduced on the photonic-plasmonic substrates did not improve the current and light absorption further, over a large range of randomization features.

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See-through amorphous silicon solar cells with selectively transparent and conducting photonic crystal back reflectors for building integrated photovoltaics

Applied Physics Letters ◽

10.1063/1.4833542 ◽

2013 ◽

Vol 103 (22) ◽

pp. 221109 ◽

Cited By ~ 17

Author(s):

Yang Yang ◽

Paul G. O’Brien ◽

Geoffrey A. Ozin ◽

Nazir P. Kherani

Keyword(s):

Solar Cells ◽

Photonic Crystal ◽

Amorphous Silicon ◽

Silicon Solar Cells ◽

Building Integrated Photovoltaics ◽

Back Reflectors

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Novel approaches of light management in thin-film silicon solar cells

MRS Proceedings ◽

10.1557/proc-0910-a25-01 ◽

2006 ◽

Vol 910 ◽

Cited By ~ 12

Author(s):

Janez Krc ◽

M. Zeman ◽

A. Campa ◽

F. Smole ◽

M. Topic

Keyword(s):

Thin Film ◽

Solar Cells ◽

Solar Cell ◽

Photonic Crystal ◽

Amorphous Silicon ◽

Wavelength Region ◽

Silicon Solar Cells ◽

Novel Approaches ◽

Back Reflector ◽

High Reflectance

AbstractIn order to improve light trapping in thin-film silicon solar cells two novel approaches are investigated in this article: angle-selective management of light scattering inside the solar cell and wavelength-selective manipulation of high reflectance or transmittance of light. Diffraction gratings are analyzed as a representative of the first approach. Haze and angular distribution function of scattered (diffracted) light in reflection are measured for aluminum-based rectangular periodic gratings with different period and height of the rectangles. High haze values in specific wavelength region and scattering angles of the investigated gratings measured in air and water agree very well with the theoretical predictions. Considering the actual optical situation in microcrystalline silicon solar cells, optimal period and height of the rectangular gratings applied as a back reflector are calculated for obtaining the total reflection at the front interfaces. In the frame of the second approach, photonic-crystal-like structures are introduced. By means of optical simulations photonic-crystal-like structures are investigated for two possible applications: an intermediate reflector in a micromorph silicon solar cell with wavelength-selective reflectivity and a dielectric back reflector with a high reflectance in the long-wavelength region. The photonic crystal structure consisting of sequences of n-doped amorphous silicon and ZnO layers is designed for the efficient intermediate reflector. For the back reflector with a high reflectance the structures with intrinsic amorphous silicon, SiO2, MgF2 and TiO2 are proposed.

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Optical Losses in Amorphous Silicon Solar Cells due to Back Reflectors

MRS Proceedings ◽

10.1557/proc-467-777 ◽

1997 ◽

Vol 467 ◽

Cited By ~ 3

Author(s):

B. L. Sopori ◽

J. Madjdpour ◽

B. Von Roedern ◽

W. Chen ◽

S. S. Hegedus

Keyword(s):

Solar Cells ◽

Numerical Model ◽

Amorphous Silicon ◽

Short Circuit ◽

Short Circuit Current ◽

Silicon Solar Cells ◽

Optical Losses ◽

Back Reflectors ◽

Current Densities ◽

Initial Results

ABSTRACTWe have used a new numerical model and here present initial results on how texturing and backreflectors affect the maximum achievable short-circuit current densities in amorphous silicon solar cells.

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