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Energy Express

  • Editor: Christian Seassal
  • Vol. 21, Iss. S4 — Jul. 1, 2013
  • pp: A631–A641
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Fabrication of resonant patterns using thermal nano-imprint lithography for thin-film photovoltaic applications

Tanzina Khaleque, Halldor Gudfinnur Svavarsson, and Robert Magnusson  »View Author Affiliations


Optics Express, Vol. 21, Issue S4, pp. A631-A641 (2013)
http://dx.doi.org/10.1364/OE.21.00A631


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Abstract

A single-step, low-cost fabrication method to generate resonant nano-grating patterns on poly-methyl-methacrylate (PMMA; plexiglas) substrates using thermal nano-imprint lithography is reported. A guided-mode resonant structure is obtained by subsequent deposition of thin films of transparent conductive oxide and amorphous silicon on the imprinted area. Referenced to equivalent planar structures, around 25% and 45% integrated optical absorbance enhancement is observed over the 450-nm to 900-nm wavelength range in one- and two-dimensional patterned samples, respectively. The fabricated elements provided have 300-nm periods. Thermally imprinted thermoplastic substrates hold potential for low-cost fabrication of nano-patterned thin-film solar cells for efficient light management.

© 2013 OSA

1. Introduction

In order to achieve efficient light absorption in thin-film solar cells, photonic nano-patterns are of great interest. Two basic approaches are considered to increase light interaction in solar media through nano- and micro-structures. One approach is to use an antireflective layer with a gradually changing refractive index profile to enhance optical transmission [1

1. Y. M. Song, J. S. Yu, and Y. T. Lee, “Antireflective submicrometer gratings on thin-film silicon solar cells for light-absorption enhancement,” Opt. Lett. 35(3), 276–278 (2010). [CrossRef] [PubMed]

]. The other approach is to trap light inside the cell. Common light trapping schemes include use of front and/or back random texturing to scatter light as well as deployment of metallic or dielectric gratings to induce plasmon or quasi-guided modes, respectively, to confine light in the waveguide region [2

2. H. A. Atwater and A. Polman, “Plasmonics for improved photovoltaic devices,” Nat. Mater. 9(3), 205–213 (2010). [CrossRef] [PubMed]

, 3

3. Y.-C. Lee, C.-F. Huang, J.-Y. Chang, and M.-L. Wu, “Enhanced light trapping based on guided mode resonance effect for thin-film silicon solar cells with two filling-factor gratings,” Opt. Express 16(11), 7969–7975 (2008). [CrossRef] [PubMed]

]. Along with one-dimensional (1D) and two-dimensional (2D) patterns, three-dimensional (3D) dome-, cone-, or rod-shaped structures are reported with enhanced conversion efficiencies [4

4. J. Zhu, C. M. Hsu, Z. Yu, S. Fan, and Y. Cui, “Nanodome solar cells with efficient light management and self-cleaning,” Nano Lett. 10(6), 1979–1984 (2010). [CrossRef] [PubMed]

6

6. J. Kim, A. J. Hong, J.-W. Nah, B. Shin, F. M. Ross, and D. K. Sadana, “Three-dimensional a-Si:H solar cells on glass nanocone arrays patterned by self-assembled Sn nanospheres,” ACS Nano 6(1), 265–271 (2012). [CrossRef] [PubMed]

]. The resonant photonic patterns are applicable to silicon solar cells and are promising for third-generation organic photovoltaics. However, additional fabrication steps of nano- or micro-domain features using conventional photolithography and subsequent etching of respective materials adds to production cost. Thus, the main challenge remains to improve low-cost and large-area fabrication techniques of such patterns. To overcome this issue, nano-imprint lithography (NIL) is a promising alternative.

The basic concept of NIL is to transfer a pattern from a master (or a mold) to various substrates under pressure [7

7. K.-J. Byeon and H. Lee, “Recent progress in direct patterning technologies based on nano-imprint lithography,” Eur. Phys. J. Appl. Phys. 59(1), 10001 (2012). [CrossRef]

9

9. K.-S. Han, S.-H. Hong, and H. Lee, “Fabrication of complex nanoscale structures on various substrates,” Appl. Phys. Lett. 91(12), 123118 (2007). [CrossRef]

]. The desired nano-patterns are normally fabricated first as master templates using photolithography or e-beam lithography and wet or dry etching. Various materials such as silicon, quartz, or metals can be used as masters. The substrate may have a spin-coated polymer resist layer that is subsequently cured by ultra-violet (UV) or infrared (IR) light, or it can be a thermoplastic substrate softened by a thermal source. Thermally activated NIL process is also known as hot embossing lithography. The master may or may not need a release agent depending on the type of substrate material used. Laser-assisted direct imprinting on inorganic films using excimer lasers has also been reported [10

10. S. Y. Chou, C. Keimel, and J. Gu, “Ultrafast and direct imprint of nanostructures in silicon,” Nature 417(6891), 835–837 (2002). [CrossRef] [PubMed]

].

NIL is applied in vast topical areas including organic and inorganic thin-film transistors, light emitting diodes (LEDs) and organic LEDs, and organic and thin-film solar cells [7

7. K.-J. Byeon and H. Lee, “Recent progress in direct patterning technologies based on nano-imprint lithography,” Eur. Phys. J. Appl. Phys. 59(1), 10001 (2012). [CrossRef]

]. For thin-film solar cell applications in particular, NIL technique is mostly applied to fabricate antireflection layers. One- or double-sided imprinted films are fabricated separately and later attached on top of the solar cells [11

11. C.-J. Ting, M.-C. Huang, H.-Y. Tsai, C.-P. Chou, and C.-C. Fu, “Low cost fabrication of the large-area anti-reflection films from polymer by nanoimprint/hot-embossing technology,” Nanotechnology 19(20), 205301 (2008). [CrossRef] [PubMed]

14

14. S.-J. Liu and C.-T. Liao, “Fast fabrication of nano-structured anti-reflection layers for enhancement of solar cells performance using plasma sputtering and infrared assisted roller embossing techniques,” Opt. Express 20(5), 5143–5150 (2012). [CrossRef] [PubMed]

]. For light trapping, imprinted randomly textured substrates are fabricated to scatter light in thin films of solar cells [15

15. M. Fonrodona, J. Escarré, F. Villar, D. Soler, J. M. Asensi, J. Bertomeu, and J. Andreu, “PEN as substrate for new solar cell technology,” Sol. Energy Mater. Sol. Cells 89, 37–47 (2005).

17

17. K. Söderström, J. Escarré, O. Cubero, F.-J. Haug, S. Perregaux, and C. Ballif, “UV-nano-imprint lithography technique for the replication of back reflectors for n-i-p thin film silicon solar cells,” Prog. Photovolt. Res. Appl. 19(2), 202–210 (2011). [CrossRef]

]. In contrast to scattering, light trapping through coupling quasi-guided or leaky modes into the waveguide region of solar cells requires resonant structures with precise shape and periodicity on the order of the operating wavelength. Few studies have been done on periodic nano-pattern fabrication using soft-NIL and nanomoulding [18

18. V. E. Ferry, M. A. Verschuuren, M. C. Lare, R. E. I. Schropp, H. A. Atwater, and A. Polman, “Optimized spatial correlations for broadband light trapping nanopatterns in high efficiency ultrathin film a-Si:H solar cells,” Nano Lett. 11(10), 4239–4245 (2011). [CrossRef] [PubMed]

, 19

19. C. Battaglia, J. Escarré, K. Söderström, M. Charrière, M. Despeisse, F.-J. Haug, and C. Ballif, “Nanomoulding of transparent zinc oxide electrodes for efficient light trapping in solar cells,” Nat. Photonics 5(9), 535–538 (2011). [CrossRef]

], and simple and easy fabrication techniques based on these concepts still needs to be conquered.

We have reported on enhanced solar uptake in thin-film hydrogenated amorphous silicon solar cells through guided-mode resonance (GMR) effects [20

20. T. Khaleque and R. Magnusson, “Experiments with resonant thin-film hydrogenated amorphous silicon solar cells,” Proc. SPIE 8470, 847008, 847008-8 (2012). [CrossRef]

]. Here we complement our research by presenting a simple, easy, and faster fabrication approach of the nano-patterns with periods smaller than the operating wavelength using thermal nano-imprinting lithography. The technique involves fewer processing steps than soft-NIL and nanomoulding, circumvents solution process spin coating or UV-source curing, ensures high repeatability and a large printing area, and uses low-cost materials. These characteristics make the method suitable as an integrated step in production of thin-film photovoltaic devices.

2. Experiments

2.1 Master fabrication

The master grating is made of quartz, and Fig. 1
Fig. 1 Schematic view of nano-patterned master fabrication steps on quartz substrate.
schematically shows the fabrication steps. A 1x1-inch2 quartz substrate is cleaned with acetone, isopropanol, and deionized water; the substrate is then dried with blown nitrogen. An 80-nm-thick bottom antireflection coating (BARC) is spin-coated at 1200 rpm and baked for 60 seconds on a heating plate adjusted to 205°C. A 300-nm-thick photoresist (PR) layer is subsequently spin-coated at 1100 rpm and baked for 90 seconds on a heating plate at 110°C. Both 1D and 2D grating patterns with a period of 300 nm are transferred to the PR using UV laser interferometric lithography. 2D grating patterns require double exposure with 90° sample rotation between exposures. After developing, the BARC layer in the PR windows is removed by oxygen plasma. Quartz is etched down to 66 nm for the 1D and 75 nm for the 2D grating using argon (Ar) and trifluromethane (CHF3) gas mixture in a reactive-ion etch (RIE) chamber. The remaining PR and BARC are removed using oxygen plasma.

2.2 Imprinted plexiglas fabrication

Plexiglas (polymethyl methacrylate, PMMA) is a thermoplastic material transparent to visible light. It has a luminous transmittance of 92%. Figure 2
Fig. 2 Measured transmittance of plexiglas.
shows the measured transmittance over the 400-nm to 700-nm wavelength range. The refractive index is 1.49 at the 589.3-nm wavelength [21

21. R. M. Waxler, D. Horowitz, and A. Feldman, “Optical and physical parameters of plexiglas 55 and lexan,” Appl. Opt. 18(1), 101–104 (1979). [CrossRef] [PubMed]

], and the glass transition temperature (Tg) is 105°C. Plexiglas with higher Tg, up to 165°C, is also available. A ~1.5-mm thick plexiglas sheet is used for the experiments.

A schematic view of the pattern transfer setup is shown in Fig. 3
Fig. 3 Schematic summarizing thermal nano-imprinting.
. A quartz master is placed on a heating plate, and the plexiglas substrate sits on top of it. A load in the form of a metal chunk is applied from the top side to create a pressure of 1.57 bar (22.8 psi). The pressure is applied before the heating plate is turned on. When the temperature rises above Tg, the plexiglas behaves as a viscous liquid and under pressure allows the quartz grating to penetrate the substrate. The temperature of the heating is adjusted so that the temperature of the master, as measured by a thermocouple, is maintained at 160°C. After 60 minutes at 160°C, the heating plate is turned off and cooled down to 60°C after which the pressure is released. The imprinted plexiglas is ejected without any adhesion or damage to the master. We notice that the fabricated grating area on the master and the imprinted area on plexiglas is the same, 5x5mm2. With a larger fabricated master grating area and uniform application of pressure over plexiglas, larger imprinted grating areas can be obtained.

The grating geometry of a GMR element is defined by the period (Λ), fill factor (F), and grating depth (dg); Fig. 4
Fig. 4 Schematic view of grating geometry showing period (Λ), fill factor (F), and grating depth (dg).
shows a schematic picture. Atomic force microscope (AFM) images and scanning electron microscope (SEM) images are taken to characterize the profile dimensions of the fabricated nano-patterns. The AFM images of 1D and 2D master grating profiles are shown in Figs. 5
Fig. 5 AFM images of the quartz master 1D grating.
and 6
Fig. 6 AFM images of the quartz master 2D grating.
, respectively. Figures 7
Fig. 7 AFM images of the imprinted plexiglas 1D grating.
and 8
Fig. 8 AFM images of the imprinted plexiglas 2D grating.
present the AFM images of respective imprinted plexiglas. Table 1

Table 1. Characteristic numbers of grating profiles obtained from AFM and SEM images

table-icon
View This Table
gives the profile dimensions obtained from the AFM/SEM images. The period of both master and imprinted gratings is 300 nm as measured with AFM. The 1D master grating depth is 66 nm whereas the imprinted grating depth is 65 nm as measured with AFM. The 2D master grating and the imprinted grating depths are 75 nm as measured with AFM; the fill factors are 0.45 and 0.55, respectively. The dimensions obtained from the AFM images closely match the SEM images shown in Fig. 9
Fig. 9 SEM images of the (a) 1D quartz master grating, (b) 1D imprinted plexiglas grating, (c) ITO-coated 1D imprinted plexiglas grating, (d) 2D quartz master grating, (e) 2D imprinted plexiglas grating, and the (f) ITO-coated 2D imprinted plexiglas grating.
. Figure 9(a) and 9(d) show the SEM images of quartz masters with a 1D and 2D grating, respectively, and Figs. 9(b) and 9(e) show the corresponding imprinted plexiglas. These topological SEM images show that the fill factor is approximately the same in the copy as in the master. Small cracks are observed on the imprinted plexiglas, which are due to the gold films deposited for improved visibility of the SEM images.

2.3 ITO and a-Si film deposition on plexiglas grating

To observe the optical absorbance enhancements enabled via the imprinted grating structures, 80-nm-thick indium-tin-oxide (ITO) layers and 200-nm-thick amorphous silicon (a-Si) layers are deposited via sputtering over the imprinted plexiglas. As a reference sample, identical films are deposited on top of a planar plexiglas substrate. In principle, the presence of the ITO film has little effect on the optical enhancement but is applied to mimic a thin-film solar cell in order to demonstrate the potential of the imprint method for solar cell fabrication. Light is shone from the plexiglas side to realize a superstrate configuration of a solar cell with ITO serving as the front transparent conducting oxide. Figure 10
Fig. 10 Schematic view of fabricated nano-patterned a-Si film; arrows indicate the directions of the incident, reflected, and transmitted beams.
gives a schematic view of the structure with incident (I), reflected (R), and transmitted (T) beams. Figures 11
Fig. 11 AFM surface images of the ITO-coated patterned plexiglas substrate 1D grating.
and 12
Fig. 12 AFM surface images of the ITO-coated patterned plexiglas substrate 2D grating.
visualize the AFM surface image of ITO-coated patterned plexiglas. The grating depths after ITO coating remain similar, 67 nm for the 1D grating and 76 nm for the 2D grating. The SEM images of the ITO-coated nano-patterns are included in Fig. 9. Shallow grating patterns with grating depths of approximately 22 nm for the 1D grating and 35 nm for the 2D grating are transferred to the top surface of the a-Si layer after a 200-nm-thick a-Si deposition over the ITO pattern as shown in Fig. 13
Fig. 13 AFM surface images of a-Si over an ITO layer. (a) 1D and (b) 2D grating.
.

3. Results and discussion

A fiber optic spectrometer is used to measure the transmitted and reflected light from the fabricated devices shown in Fig. 13. Light is shone normally from the plexiglas side as Fig. 10 depicts. Taking the refractive index of plexiglas as 1.49 and the period of the grating as 300 nm, the Rayleigh wavelength of the patterned structure is λR = nΛ ≈450nm. Hence, only zero-order diffraction prevails beyond 450 nm. Reflectance (R0) and transmittance (T0) spectra normalized to the source spectrum are measured, and the absorbance is obtained as A = 1-R0-T0. Figure 14
Fig. 14 Unpolarized absorbance spectra of planar reference and imprinted patterned samples at normal incidence of light.
shows the comparison of unpolarized absorbance between patterned and unpatterned reference samples at normal incidence. Integrated optical absorbance enhancement of about 25% for 1D and 45% for 2D nano-patterns is observed over the 450-nm to 900-nm wavelength range. Figure 15
Fig. 15 TE (electric field vector normal to the plane of incidence) and TM (electric field vector parallel to the plane of incidence) polarized components of absorbance of the 1D grating patterned sample at normal incidence of light.
gives the polarization dependent absorbance for a 1D grating pattern.

Conversely, the 2D grating pattern exhibits a polarization-independent response as shown in Fig. 17
Fig. 17 TE and TM polarized components of absorbance of the 2D grating patterned sample at normal incidence of light.
. In general, for both 1D and 2D patterned devices, the absorbance response and enhancement will vary widely for different photovoltaic absorbing materials and embodiments. Indeed, the occurrence and density of GMRs depends on the complex dielectric constant and its dispersion properties as well as on the thickness, fill factor, and grating modulation strength of the absorbing waveguide-grating layer system.

As visualized by the surface images in Fig. 13, the sharpness of the 1D and 2D patterns decreases on account of the ITO deposition and still further upon a-Si film deposition. This does not substantially affect the optical enhancement obtained since the pattern period and dimensional regularity persist.

4. Conclusion

A low-cost approach to nano-pattern fabrication of resonant thin-film solar cells for efficient light trapping is proposed and experimentally demonstrated. The process includes a single step to fabricate the pattern on a substrate, which eliminates the need for photolithography and RIE steps. Imprinted 1D and 2D elements containing nano-patterns with a 300-nm period on thermoplastic substrates are designed and fabricated. The spectral variation of optical absorbance in thin a-Si films is measured, and it shows integrated absorption enhancement of ~25% for 1D and ~45% for 2D grating patterns across the 450-nm to 900-nm wavelength range, referenced to planar samples, for the particular device embodiments studied. Future research work may extend this methodology to real thin-film p-i-n solar cell fabrication over patterned imprinted substrates. Single-step fabrication methods facilitate production by enabling roll-to-roll printing of substrates for thin-film solar cells including organic photovoltaics. The thermal nano-imprint fabrication technique described in this study is not limited in shape or dimension of the pattern profile. Once a master grating is fabricated with a desired photonic structure and reasonable aspect ratios, concomitant patterns can be replicated with high repeatability and a long master lifetime.

Acknowledgments

This research was supported in part by the Energy Research Fund of the National Power Company of Iceland and by the UT System Texas Nanoelectronics Research Superiority Award funded by the State of Texas Emerging Technology Fund. Additional support was provided by the Texas Instruments Distinguished University Chair in Nanoelectronics endowment.

References and links

1.

Y. M. Song, J. S. Yu, and Y. T. Lee, “Antireflective submicrometer gratings on thin-film silicon solar cells for light-absorption enhancement,” Opt. Lett. 35(3), 276–278 (2010). [CrossRef] [PubMed]

2.

H. A. Atwater and A. Polman, “Plasmonics for improved photovoltaic devices,” Nat. Mater. 9(3), 205–213 (2010). [CrossRef] [PubMed]

3.

Y.-C. Lee, C.-F. Huang, J.-Y. Chang, and M.-L. Wu, “Enhanced light trapping based on guided mode resonance effect for thin-film silicon solar cells with two filling-factor gratings,” Opt. Express 16(11), 7969–7975 (2008). [CrossRef] [PubMed]

4.

J. Zhu, C. M. Hsu, Z. Yu, S. Fan, and Y. Cui, “Nanodome solar cells with efficient light management and self-cleaning,” Nano Lett. 10(6), 1979–1984 (2010). [CrossRef] [PubMed]

5.

E. Garnett and P. Yang, “Light trapping in silicon nanowire solar cells,” Nano Lett. 10(3), 1082–1087 (2010). [CrossRef] [PubMed]

6.

J. Kim, A. J. Hong, J.-W. Nah, B. Shin, F. M. Ross, and D. K. Sadana, “Three-dimensional a-Si:H solar cells on glass nanocone arrays patterned by self-assembled Sn nanospheres,” ACS Nano 6(1), 265–271 (2012). [CrossRef] [PubMed]

7.

K.-J. Byeon and H. Lee, “Recent progress in direct patterning technologies based on nano-imprint lithography,” Eur. Phys. J. Appl. Phys. 59(1), 10001 (2012). [CrossRef]

8.

S. Y. Chou, P. R. Krauss, and P. J. Renstrom, “Imprint of sub-25nm vias and trenches in polymers,” Appl. Phys. Lett. 67(21), 3114–3116 (1995). [CrossRef]

9.

K.-S. Han, S.-H. Hong, and H. Lee, “Fabrication of complex nanoscale structures on various substrates,” Appl. Phys. Lett. 91(12), 123118 (2007). [CrossRef]

10.

S. Y. Chou, C. Keimel, and J. Gu, “Ultrafast and direct imprint of nanostructures in silicon,” Nature 417(6891), 835–837 (2002). [CrossRef] [PubMed]

11.

C.-J. Ting, M.-C. Huang, H.-Y. Tsai, C.-P. Chou, and C.-C. Fu, “Low cost fabrication of the large-area anti-reflection films from polymer by nanoimprint/hot-embossing technology,” Nanotechnology 19(20), 205301 (2008). [CrossRef] [PubMed]

12.

J. Y. Chen and K. W. Sun, “Enhancement of the light conversion efficiency of silicon solar cells by using nanoimprint anti-reflection layer,” Sol. Energy Mater. Sol. Cells 94(3), 629–633 (2010). [CrossRef]

13.

K.-S. Han, J.-H. Shin, W.-Y. Yoon, and H. Lee, “Enhanced performance of solar cells with anti-reflection layer fabricated by nano-imprint lithography,” Sol. Energy Mater. Sol. Cells 95(1), 288–291 (2011). [CrossRef]

14.

S.-J. Liu and C.-T. Liao, “Fast fabrication of nano-structured anti-reflection layers for enhancement of solar cells performance using plasma sputtering and infrared assisted roller embossing techniques,” Opt. Express 20(5), 5143–5150 (2012). [CrossRef] [PubMed]

15.

M. Fonrodona, J. Escarré, F. Villar, D. Soler, J. M. Asensi, J. Bertomeu, and J. Andreu, “PEN as substrate for new solar cell technology,” Sol. Energy Mater. Sol. Cells 89, 37–47 (2005).

16.

A. Bessonov, Y. Cho, S.-J. Jung, E.-A. Park, E.-S. Hwang, J.-W. Lee, M. Shin, and S. Lee, “Nanoimprint patterning for tunable light trapping in large-area silicon solar cells,” Sol. Energy Mater. Sol. Cells 95(10), 2886–2892 (2011). [CrossRef]

17.

K. Söderström, J. Escarré, O. Cubero, F.-J. Haug, S. Perregaux, and C. Ballif, “UV-nano-imprint lithography technique for the replication of back reflectors for n-i-p thin film silicon solar cells,” Prog. Photovolt. Res. Appl. 19(2), 202–210 (2011). [CrossRef]

18.

V. E. Ferry, M. A. Verschuuren, M. C. Lare, R. E. I. Schropp, H. A. Atwater, and A. Polman, “Optimized spatial correlations for broadband light trapping nanopatterns in high efficiency ultrathin film a-Si:H solar cells,” Nano Lett. 11(10), 4239–4245 (2011). [CrossRef] [PubMed]

19.

C. Battaglia, J. Escarré, K. Söderström, M. Charrière, M. Despeisse, F.-J. Haug, and C. Ballif, “Nanomoulding of transparent zinc oxide electrodes for efficient light trapping in solar cells,” Nat. Photonics 5(9), 535–538 (2011). [CrossRef]

20.

T. Khaleque and R. Magnusson, “Experiments with resonant thin-film hydrogenated amorphous silicon solar cells,” Proc. SPIE 8470, 847008, 847008-8 (2012). [CrossRef]

21.

R. M. Waxler, D. Horowitz, and A. Feldman, “Optical and physical parameters of plexiglas 55 and lexan,” Appl. Opt. 18(1), 101–104 (1979). [CrossRef] [PubMed]

22.

W. Wu and R. Magnusson, “Total absorption of TM polarized light in a 100 nm spectral band in a nanopatterned thin a-Si film,” Opt. Lett. 37(11), 2103–2105 (2012). [CrossRef] [PubMed]

23.

T. K. Gaylord and M. G. Moharam, “Analysis and applications of optical diffraction by gratings,” Proc. IEEE 73(5), 894–937 (1985). [CrossRef]

24.

D. Shin, S. Tibuleac, T. A. Maldonado, and R. Magnusson, “Thin-film optical filters with diffractive elements and waveguides,” Opt. Eng. 37(9), 2634–2646 (1998). [CrossRef]

OCIS Codes
(230.7370) Optical devices : Waveguides
(310.1860) Thin films : Deposition and fabrication
(310.2790) Thin films : Guided waves
(350.6050) Other areas of optics : Solar energy
(110.4235) Imaging systems : Nanolithography
(050.6624) Diffraction and gratings : Subwavelength structures

ToC Category:
Photovoltaics

History
Original Manuscript: April 15, 2013
Revised Manuscript: May 17, 2013
Manuscript Accepted: May 18, 2013
Published: May 23, 2013

Citation
Tanzina Khaleque, Halldor Gudfinnur Svavarsson, and Robert Magnusson, "Fabrication of resonant patterns using thermal nano-imprint lithography for thin-film photovoltaic applications," Opt. Express 21, A631-A641 (2013)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-21-S4-A631


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References

  1. Y. M. Song, J. S. Yu, and Y. T. Lee, “Antireflective submicrometer gratings on thin-film silicon solar cells for light-absorption enhancement,” Opt. Lett.35(3), 276–278 (2010). [CrossRef] [PubMed]
  2. H. A. Atwater and A. Polman, “Plasmonics for improved photovoltaic devices,” Nat. Mater.9(3), 205–213 (2010). [CrossRef] [PubMed]
  3. Y.-C. Lee, C.-F. Huang, J.-Y. Chang, and M.-L. Wu, “Enhanced light trapping based on guided mode resonance effect for thin-film silicon solar cells with two filling-factor gratings,” Opt. Express16(11), 7969–7975 (2008). [CrossRef] [PubMed]
  4. J. Zhu, C. M. Hsu, Z. Yu, S. Fan, and Y. Cui, “Nanodome solar cells with efficient light management and self-cleaning,” Nano Lett.10(6), 1979–1984 (2010). [CrossRef] [PubMed]
  5. E. Garnett and P. Yang, “Light trapping in silicon nanowire solar cells,” Nano Lett.10(3), 1082–1087 (2010). [CrossRef] [PubMed]
  6. J. Kim, A. J. Hong, J.-W. Nah, B. Shin, F. M. Ross, and D. K. Sadana, “Three-dimensional a-Si:H solar cells on glass nanocone arrays patterned by self-assembled Sn nanospheres,” ACS Nano6(1), 265–271 (2012). [CrossRef] [PubMed]
  7. K.-J. Byeon and H. Lee, “Recent progress in direct patterning technologies based on nano-imprint lithography,” Eur. Phys. J. Appl. Phys.59(1), 10001 (2012). [CrossRef]
  8. S. Y. Chou, P. R. Krauss, and P. J. Renstrom, “Imprint of sub-25nm vias and trenches in polymers,” Appl. Phys. Lett.67(21), 3114–3116 (1995). [CrossRef]
  9. K.-S. Han, S.-H. Hong, and H. Lee, “Fabrication of complex nanoscale structures on various substrates,” Appl. Phys. Lett.91(12), 123118 (2007). [CrossRef]
  10. S. Y. Chou, C. Keimel, and J. Gu, “Ultrafast and direct imprint of nanostructures in silicon,” Nature417(6891), 835–837 (2002). [CrossRef] [PubMed]
  11. C.-J. Ting, M.-C. Huang, H.-Y. Tsai, C.-P. Chou, and C.-C. Fu, “Low cost fabrication of the large-area anti-reflection films from polymer by nanoimprint/hot-embossing technology,” Nanotechnology19(20), 205301 (2008). [CrossRef] [PubMed]
  12. J. Y. Chen and K. W. Sun, “Enhancement of the light conversion efficiency of silicon solar cells by using nanoimprint anti-reflection layer,” Sol. Energy Mater. Sol. Cells94(3), 629–633 (2010). [CrossRef]
  13. K.-S. Han, J.-H. Shin, W.-Y. Yoon, and H. Lee, “Enhanced performance of solar cells with anti-reflection layer fabricated by nano-imprint lithography,” Sol. Energy Mater. Sol. Cells95(1), 288–291 (2011). [CrossRef]
  14. S.-J. Liu and C.-T. Liao, “Fast fabrication of nano-structured anti-reflection layers for enhancement of solar cells performance using plasma sputtering and infrared assisted roller embossing techniques,” Opt. Express20(5), 5143–5150 (2012). [CrossRef] [PubMed]
  15. M. Fonrodona, J. Escarré, F. Villar, D. Soler, J. M. Asensi, J. Bertomeu, and J. Andreu, “PEN as substrate for new solar cell technology,” Sol. Energy Mater. Sol. Cells89, 37–47 (2005).
  16. A. Bessonov, Y. Cho, S.-J. Jung, E.-A. Park, E.-S. Hwang, J.-W. Lee, M. Shin, and S. Lee, “Nanoimprint patterning for tunable light trapping in large-area silicon solar cells,” Sol. Energy Mater. Sol. Cells95(10), 2886–2892 (2011). [CrossRef]
  17. K. Söderström, J. Escarré, O. Cubero, F.-J. Haug, S. Perregaux, and C. Ballif, “UV-nano-imprint lithography technique for the replication of back reflectors for n-i-p thin film silicon solar cells,” Prog. Photovolt. Res. Appl.19(2), 202–210 (2011). [CrossRef]
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