Subscriber access provided by Gothenburg University Library
Letter
Texture of the viola flower for light harvesting in photovoltaics Raphael Schmager, Benjamin Fritz, Ruben Hünig, Kaining Ding, Uli Lemmer, Bryce Sydney Richards, Guillaume Gomard, and Ulrich Wilhelm Paetzold ACS Photonics, Just Accepted Manuscript • DOI: 10.1021/acsphotonics.7b01153 • Publication Date (Web): 13 Oct 2017 Downloaded from http://pubs.acs.org on October 15, 2017
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
ACS Photonics is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 7
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Photonics
Texture of the viola flower for light harvesting in photovoltaics Raphael Schmager*,†, Benjamin Fritz§, Ruben Hünig§, #, Kaining Ding∥, Uli Lemmer†,§, Bryce S. Richards†,§, Guillaume Gomard*,†,§, Ulrich W. Paetzold*,†,§ †
Institute of Microstructure Technology, Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany §
Light Technology Institute, Karlsruhe Institute of Technology (KIT), Engesserstrasse 13, 76131 Karlsruhe, Germany
∥
IEK-5 Photovoltaik, Forschungszentrum Jülich GmbH, 52428 Jülich, Germany
KEYWORDS: photovoltaics, solar cells, light management, biomimetics, retro-reflection ABSTRACT: Nature’s evolution provides a multitude of answers to scientific and key technological challenges such as the light harvesting. In this work, we investigate the optical properties of the unique texture of viola petals for the purpose of improved light harvesting in photovoltaics. We find that crystalline silicon solar cells encapsulated with a transparent coating show a 6% improvement in power conversion efficiency if the viola petal texture is replicated onto the front surface. This gain is based on a broadband enhancement in current generation which originates from the exceptional optical properties of the viola surface texture, combining micro- and nano-texture. The micro-cones of this hierarchical texture demonstrate strong and broadband light incoupling effects as well as retro-reflection capabilities, and the nano-wrinkles further decrease the reflection losses. Using rigorous optical simulation, we analyze and explain the working principle ruling the light harvesting properties of this dual-scale texture.
Over the last decades, photovoltaic (PV) power generation has reached all continents and most markets1. The exponential growth of newly installed capacity significantly contributed to the share of renewable energy electricity generation2. Further increasing the power conversion efficiency (PCE) of all solar cell technologies remains a key objective of research to reduce costs. With regard to light management, the fundamental strategies to achieve this objective are: (i) improving light incoupling at the front surface3,4; (ii) enhancing light absorption in weakly absorbing wavelength regions by light trapping5; and (iii) reducing any optical losses in contact, passivation and transport layers6,7. Enormous research efforts were directed during the last decades towards identifying novel concepts to improve light management by artificial and top-down designed textures, encompassing plasmonic nano-structures8,9, diffraction gratings10–12, photonic crystals13,14, randomly textured scattering surfaces15,16, nanowires17–19, metamaterials20 and surface textures like honeycomb structures21 or inverted pyramids22. In addition, research focused on biomimetic lightharvesting textures stemming from animals or plants23. The former attracted an increasing attention in the context of PV as they often operate over broad spectral and angular ranges. Prominent examples are the sub-wavelength structure of the moth eye24–27, and the butterfly wing28. Conversely, only little research was conducted on plant surfaces for light harvesting in PV29–32, although evolution optimized nature’s vegetation on their survival25,33. Especially leaves’ and petals’ fundamental interaction with sunlight should be of key importance. Hereby, leaves assure the survival by providing energy, while petals secure the reproduction of the plants by attracting pollinators. In order to maximize the attractiveness for pollinators, many flowers have evolved brightly colored petals34,35. High color saturation is achieved by the combina-
tion of pigments with an optically broadband light incoupling texture at the surface of the petals34,36. In a recent publication of our group, we have investigated the light harvesting of various plant textures30. As a general guideline, we identified that biomimetic textures with increased aspect ratios of their conical surface elements correlate with reduced reflection losses at the front side of solar cells and solar modules. At the time, the champion texture was a replicate of Rosa ‘El Toro’, which exhibits an aspect ratio of 0.6. For prototype organic photovoltaic devices, this texture demonstrated already an efficiency increase of 13%. Following the guideline discussed above and seeking for even better biomimetic textures, we investigate in this work the viola flower (species: Viola×wittrockiana37) (see Figure 1). The aspect ratio of the viola texture is around 1.2, highly exceeding the aspect ratio and demonstrating significantly lower reflection losses at arbitrary angle compared to any petal investigated previously (see also Figure S2 and S3). Based on these promises, we study in this work the complex and optically ingenious texture of the viola petal for light harvesting in PV. We demonstrate improved performance for a crystalline silicon (c-Si) solar cell encapsulated with a viola textured transparent resist. As can be seen in Figure 1, the texture of the viola petal combines both micro- and nano-scale textures. The micro-cones of this hierarchical structure are in the order of tens of micrometers, whereas the dimensions of the nano-wrinkles coincide with the visible wavelength regime. Thus, identifying the working principle of the dualscale surface texture based on rigorous optical simulations is a further emphasis of our study. Finally, we discuss the relevance of viola petal texture for light harvesting for a broad range of solar cell technologies.
ACS Paragon Plus Environment
ACS Photonics
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 2 of 7
Figure 1. (a) Photograph of the original viola petal (species: Viola × wittrockiana37). A scanning electron microscopy (SEM) image of the replicated viola surface texture from the top (b) and side (c) illustrates the micro-cone arrangement as well as the nano-wrinkles (shown with green lines) decorating the micro-cones (bounded by orange lines). A schematic illustration (d) displays the planar heterojunction silicon solar cell with applied viola surface texture. The p-type absorber has a thickness of 250 µm (see Figure S1 for more details on the different layers).
RESULTS AND DISCUSSION In order to evaluate the performance of the viola surface texture for light management in PV, the original viola petal surface was replicated on top of a planar heterojunction c-Si solar cell that is encapsulated with a transparent resist. The transparent replica of the viola texture homogeneously covered the complete c-Si solar cell with an active area of 1x1 cm2 (see inset in Figure 2). The solar cell equipped with the viola front texture demonstrates a significant enhancement in PCE of 6% relative to the planar reference (see Figure 2a). The planar reference cell is referred to as the pristine c-Si cell encapsulated with a flat transparent resist layer of same material and thickness as used for the viola texture. It shall be noted, that this configuration mimics the relevant architecture in a solar module. The resist layer is optically thick and has a refractive index similar to glass and the encapsulant of a solar module. The pristine cell on which the planar and viola texture were applied, possessed an indium tin oxide layer of thickness optimized for reduced reflection losses at the air/cell front interface. Moreover, even compared to this pristine c-Si solar cell the solar cell with the viola textured coating still demonstrates a PCE increase of 3% relative. Compared to the planar reference, the short circuit current density Jsc of the viola-textured solar cell is increased from 31.6 mAcm-2 to 33.8 mAcm-2. This enhancement results in a maximum PCE of 15.5%. The fill factor (FF) and open circuit voltage (Voc) of the solar cell are hardly affected (Table 1). As shown in Figure 2b, the improved efficiency of the solar cell with viola texture is based on a broadband enhancement in the spectral response. Correspondingly a broadband reduction of reflection is visible, indicating the origin of the improvement to be an optical effect with almost no spectral dependency. As shown in Figure 3a, the viola surface texture exhibits an extremely low reflectance. The latter is measured for varying
angles of incidence and averaged over the relevant wavelength range of 300-1100 nm. The glass substrate is covered with an almost perfectly absorbing foil, in order to measure exclusively the front side reflection. Compared to the planar reference device, the reflectance at the resist/air interface is reduced from 4.5% to 1% for close to normal incidence. For oblique angles of incidence, this difference further increases. Thus, at an incidence angle of 80°, the viola texture reflects 30% less light than the planar reference. The broadband and angle tolerant light collection property of the viola surface texture is an exceptional example of nature’s evolution process, by which the plant efficiently attracts pollinators and secures the reproduction of their species34,35. Considering the large amount of diffuse irradiation as well as the varying solar altitude, the omnidirectional light incoupling properties of the replicated viola surface texture is of outstanding significance for real world solar cell applications. By almost eliminating the reflection losses for normal incidence, 4% more photons are gained at the front side interface. However, even if one assumes perfect lightincoupling properties, this can only accommodate for a maximum relative enhancement of 4%, which is less than the 6% of relative enhancement. Consequently, the viola texture must exhibit a second key optical effect which results in an enhanced light harvesting. Table 1. Solar cell performance parameters Jsc [mA cm-2]
Voc [mV]
FF [%]
PCE [%]
Pristine
32.8
600
76
15.0
Planar
31.6
610
76
14.6
Viola texture
33.8
605
76
15.5
ACS Paragon Plus Environment
Page 3 of 7
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Photonics
Figure 2. (a) Current density - voltage (J-V) characteristic of the c-Si solar cells. Compared to the planar reference layer, the viola surface texture applied on top of the c-Si solar cell shows an enhanced current density. (b) Corresponding external quantum efficiency (solid lines) and reflectance (dashed lines) of the solar cells. The inset illustrates the replicated viola surface texture on top of the device. The solar cell equipped with the viola surface texture globally shows an improved absorption, which leads to an increased current generation.
Figure 3. Optical characterization of viola texture: (a) Reflectance of the viola surface texture applied on glass. Compared to a planar resist layer, the viola surface texture reduces front side reflection for all angles of incidence. The front side reflection is obtained by placing an absorber at the back of the glass substrate. (b) Transmittance of the viola surface texture for normal incidence for front and back side illumination. By changing the illumination direction, the viola surface texture shows a significant difference in transmittance.
This second optical effect is observed experimentally in transmission measurements, as shown in Figure 3b. By illuminating the replicated viola surface texture on top of a glass substrate from both sides, a strong difference in transmitted light is observed. It can be seen, that the transmittance for front side lighting is more than 30% higher than for the illumination of the back side. The structure, thus, has retro-reflection properties38,39. With regard to our silicon solar cell, this implies, that light, which is reflected at the resist/solar cell interface will be retro-reflected towards the solar cell again. To further analyze the optical working principle of the viola texture, we simulated the micro- and nano-texture separately and investigated their respective contribution to the improved light-harvesting. The micro-structure (Figure 1b-c) was modelled by cones with a mean width and height of 50 µm and 60 µm, respectively, and simulated by ray tracing. In addition, we conducted the analysis of the nano-wrinkles (average width of 500 nm and height of 300 nm) using the finite-difference time-domain (FDTD) method, accounting for the wave-optical effects involved.
The working principle of the micro-cones covering the viola surface texture can be demonstrated in three steps (Figure 4). Firstly, the incident light is scattered to higher propagation angles inside the resist layer (see also Figure S4 for varying aspect ratio of the micro-cones). Secondly, in case of a not perfectly absorbing solar cell, a portion of the transmitted light will be reflected at the resist/solar cell interface. Thirdly, light reaching the micro-cones from below, will be efficiently retroreflected towards the solar cell, giving a second chance for the photons to be absorbed. Since the angular distribution of the transmitted light Tf for front side illumination concentrates its intensity around θt = 30°, a planar reflection of light at the solar cell will impinge the cones under the same angle from below. However, as shown in Figure 4f for this angular range (indicated by the greyed area), the reflectance back on the solar cell is nearly 60%. This implies that the probability of light escaping the solar cell with viola surface texture is highly reduced. Thus, the micro-cones provide an efficient light harvesting scheme, since they reduce the front side reflection and simultaneously limit light out-coupling due to the retro-reflection properties.
ACS Paragon Plus Environment
ACS Photonics
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 4 of 7
Figure 4. Ray tracing simulation on micro-cones as found on the viola petal surface. (a) Light incident on the micro-cones is transmitted (b) and will be angularly broadened (e) by the cone surface. For light being planar reflected at the solar cell interface (c) the reflectance after the second interaction for various scatter angles (d) is simulated (f).
of incidence. While θin = 0° corresponds to the dashed line in the inset of Figure 5, normal incidence on the viola texture is visualized by the greyed area. Therefore, the omnidirectional decrease of reflection by the nano-wrinkles, adorned on the micro-cone texture, act as an additional anti-reflection coating. Altogether, both, the anti-reflection effect of the nanowrinkles and the enhanced light incoupling as well as retroreflection effect of the micro cones can well describe the measured improvement in PCE of the silicon solar cell.
CONCLUSION AND OUTLOOK
Figure 5. FDTD simulation of the integrated reflectance for the nano-wrinkles compared to a planar reference layer. The SEM image of the viola surface texture illustrates the angle of incidence θw, which is defined to the surface normal of the wrinkles lying on the cones.
The nano-wrinkles located on top of the micro-cones, reside on the lower edge of the visible wavelength regime. Therefore, they are effectively acting as an anti-reflection coating, by creating an effective medium transition between the ambient air and the resist (see Figure S5). In order to quantify this effect, we performed FDTD simulations on wrinkles of same size as the ones that can be found on the micro-cones (see inset of Figure 5). The wrinkles were simulated in three dimensions, hence different polarizations, angles and planes of incidence were considered. Compared to a planar reference layer, the averaged reflectance for effectively unpolarized light between 300 nm and 1100 nm is clearly reduced for all angles
In this work, we demonstrated a silicon solar cell with the viola surface texture on top, where the textured device outperforms both the optimized pristine cell as well as the planar reference. We show that the enhanced PCE of 6% relative is based on the very particular optical properties of the viola petal surface texture. The texture consists of microcones, with optical properties governed by ray optics, and nano-wrinkles with a periodicity comparable to the wavelength of solar radiation. The former reduces the front side reflection and promotes retro-reflection, and the latter further reduces the reflection losses by increased light incoupling. The excellent light harvesting properties of the viola petal texture can potentially improve any kind of light harvesting device suffering from reflection losses at the front interfaces. We exemplary selected a planar heterojunction silicon solar cell to demonstrate the light harvesting effect of the viola petal texture. It is shown that the possible gain by retro-reflection, relates to the amount of light reflected back from the device. For this reason, state-of-the-art c-Si solar cells with random textures and very low reflection will benefit less from the viola texture compared to planar solar cells. Nevertheless, many thin film technologies such as CIGS, CdTe or perovskite photovoltaics where reflection losses are present are expected to be significantly improved by the viola texture.
ACS Paragon Plus Environment
Page 5 of 7
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Photonics
EXPERIMENTAL SECTION
ASSOCIATED CONTENT
Replication. First, the original viola petal was cast into a polydimethylsiloxane (PDMS) mold. The PDMS was hardened at 60 °C on a hot plate for 4 h and then separated from the viola petal, which left a flexible viola PDMS stamp. In a second step the stamp was used to imprint the texture into a transparent ultraviolet-curable photoresist (NOA88). More details can be found in Ref. [30]. Devices. The planar silicon heterojunction solar cell with a full silicon oxide based buffer (a-SiOx:H) and contact layers (µcSiOx:H) are produced on a flat p-type absorber. Further details on the fabrication and structure of the device can be found in Ref. [40]. The layers and corresponding thicknesses are specified in Figure S1. Characterization. Reflectance and transmittance measurements were performed with a Perkin Elmer Lambda 1050 spectrophotometer equipped with a depolarizer. The term reflectance accounts for both the specular and diffuse components. For strongly specular reflecting samples (planar reference), the minimum incident angle was limited to 8°. The viola texture was applied on 2.5×2.5 cm2 soda lime glass microscope slides (Carl-Roth). To account front side reflection only, the backside of the structured glass was covered with black foil (d-c-fix©, Konrad Hornschuch AG D-74679, Weissbach) with high broadband absorption. The angular resolved reflectance was obtained by the integrating sphere attachment for the spectrophotometer with rotational sample holder. The reflectance of the silicon solar cell shown in Figure 2b was measured at the rear port of the integrating sphere. The external quantum efficiency shown in the same figure is measured with a modulated monochromatic light from 300-1100 nm. The in-house setup has a slit aperture inside the beam path, which restricted the spot size to cover exactly 5 grid lines in each measurement performed. The J–V characteristic was measured on a class AAA (WACOM WXS90S-L2, Japan) solar simulator. The silicon solar cell was covered with a shadow mask with an area of 32 mm2. The obtained short circuit current density was linear offset and thus scaled to the EQE measurement. Simulation Details. Raytracing simulations were carried out with the commercial software LightTools by Synopsys. The overlapping cones were arranged in a hexagonal unit cell with reflecting sidewalls. The obtained reflectance and transmittance were angular resolved. The backside of the model was set to absorb all the rays. Illumination was performed from above and inside the model with 108 parallel rays, which were sufficient for convergence of the model. For the retroreflection curve in Figure 4f, different azimuth angles were averaged. The FDTD simulation was performed with Lumerical Solutions in 3D. One wrinkle with half-cylindrical geometry was embedded in periodic Bloch boundaries. The length is kept at 200 nm, where the width and height are 500 nm and 300 nm, respectively. The refractive index was set to 1.56. To account for effectively unpolarized illumination, different planes of incidence and polarizations were simulated and averaged.
Supporting Information Figure S1 – details on the planar heterojunction silicon solar cell Figure S2 – reflectance of different plant textures compared to the viola surface texture Figure S3 – reflectance of various plant textures for different angles of incidence and wavelengths Figure S4 – further details on ray tracing simulation of cones of different aspect ratios Figure S5 – additional details on FDTD simulations This material is available free of charge via the Internet at http://pubs.acs.org
AUTHOR INFORMATION Corresponding Author: *E-mail (R. Schmager):
[email protected] *E-mail (G. Gomard):
[email protected] *E-mail (U.W. Paetzold):
[email protected] Current address of R. Hünig: # Zentrum für Sonnenenergie- und Wasserstoff-Forschung BadenWürttemberg (ZSW), Meitnerstraße 1, 70563 Stuttgart, Germany
ACKNOWLEDGEMENTS The authors would like to thank M. Langenhorst, I. M. Hossain, and Dr. E. Klampaftis for their fruitful discussion and assistance in the lab. The authors are grateful to the IEK-5 and especially to M. Smeets for providing the silicon solar cells. The authors would also like to gratefully acknowledge financial support of the Initiating and Networking funding of the Helmholtz Association (HYIG of Dr. U.W. Paetzold; Recruitment Initiative of Prof. B.S. Richards; the Helmholtz Energy Materials Foundry (HEMF); and the Science and Technology of Nanostructures research programme), the Helmholtz Postdoc programme of Dr. G. Gomard, as well as the Karlsruhe School of Optics and Photonics.
REFERENCES (1) (2) (3)
(4) (5)
(6)
(7)
(8)
(9)
U.S. Energy Information Administration (EIA). Annual Energy Outlook 2017 with Projections to 2050; 2017. Philipps, S.; Warmuth, W. Photovoltaics Report; 2017. Minot, M. J. Single-Layer, Gradient Refractive Index Antireflection Films Effective from 035 to 25 Μ. J. Opt. Soc. Am. 1976, 66, 515. Southwell, W. H. Gradient-Index Antireflection Coatings. Opt. Lett. 1983, 8, 584. Campbell, P.; Green, M. A. Light Trapping Properties of Pyramidally Textured Surfaces. J. Appl. Phys. 1987, 62, 243– 249. Boriskina, S. V; Green, M. A.; Catchpole, K.; Yablonovitch, E.; Beard, M. C.; Okada, Y.; Lany, S.; Gershon, T.; Zakutayev, A.; Tahersima, M. H.; Sorger, V. J.; Naughton, M. J.; Kempa, K.; Dagenais, M.; Yao, Y.; Xu, L.; Sheng, X.; Bronstein, N. D.; Rogers, J. A.; Alivisatos, A. P.; Nuzzo, R. G.; Gordon, J. M.; Wu, D. M.; Wisser, M. D.; Salleo, A.; Dionne, J.; Bermel, P.; Greffet, J.-J.; Celanovic, I.; Soljacic, M.; Manor, A.; Rotschild, C.; Raman, A.; Zhu, L.; Fan, S.; Chen, G. Roadmap on Optical Energy Conversion. J. Opt. 2016, 18, 73004. Rau, U.; Paetzold, U. W.; Kirchartz, T. Thermodynamics of Light Management in Photovoltaic Devices. Phys. Rev. B Condens. Matter Mater. Phys. 2014, 90, 35211. Stuart, H. R.; Hall, D. G. Absorption Enhancement in Siliconon-Insulator Waveguides Using Metal Island Films. Appl. Phys. Lett. 1996, 69, 2327. Pillai, S.; Catchpole, K. R.; Trupke, T.; Green, M. A. Surface
5
ACS Paragon Plus Environment
ACS Photonics
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
(10)
(11)
(12)
(13) (14)
(15)
(16)
(17)
(18)
(19) (20)
(21)
(22)
(23)
(24)
(25)
(26)
(27)
(28)
(29)
Plasmon Enhanced Silicon Solar Cells. J. Appl. Phys. 2007, 101, 93105. Sheng, P.; Bloch, A. N.; Stepleman, R. S. Wavelength-Selective Absorption Enhancement in Thin-Film Solar Cells. Appl. Phys. Lett. 1983, 43, 579–581. Dewan, R.; Knipp, D. Light Trapping in Thin-Film Silicon Solar Cells with Integrated Diffraction Grating. J. Appl. Phys. 2009, 106, 74901. Ram, S. K.; Desta, D.; Rizzoli, R.; Falcão, B. P.; Eriksen, E. H.; Bellettato, M.; Jeppesen, B. R.; Jensen, P. B.; Summonte, C.; Pereira, R. N.; Larsen, A. N.; Balling, P. Efficient LightTrapping with Quasi-Periodic Uniaxial Nanowrinkles for ThinFilm Silicon Solar Cells. Nano Energy 2017, 35, 341–349. Zhou, D.; Biswas, R. Photonic Crystal Enhanced Light-Trapping in Thin Film Solar Cells. J. Appl. Phys. 2008, 103, 93102. Bermel, P.; Luo, C.; Zeng, L.; Kimerling, L. C.; Joannopoulos, J. D. Improving Thin-Film Crystalline Silicon Solar Cell Efficiencies with Photonic Crystals. Opt. Express 2007, 15, 16986. Rockstuhl, C.; Fahr, S.; Bittkau, K.; Beckers, T.; Carius, R.; Haug, F.-J.; Söderström, T.; Ballif, C.; Lederer, F. Comparison and Optimization of Randomly Textured Surfaces in Thin-Film Solar Cells. Opt. Express 2010, 18 Suppl 3, A335–A341. Battaglia, C.; Söderström, K.; Escarré, J.; Haug, F. J.; Dominé, D.; Cuony, P.; Boccard, M.; Bugnon, G.; Denizot, C.; Despeisse, M.; Feltrin, A.; Ballif, C. Efficient Light Management Scheme for Thin Film Silicon Solar Cells via Transparent Random Nanostructures Fabricated by Nanoimprinting. Appl. Phys. Lett. 2010, 96, 213504. Lu, H.; Gang, C. Analysis of Optical Absorption in Silicon Nanowire Arrays for Photovoltaic Applications. Nano Lett. 2007, 7, 3249–3252. Han, S. E.; Chen, G. Optical Absorption Enhancement in Silicon Nanohole Arrays for Solar Photovoltaics. Nano Lett. 2010, 10, 1012–1015. Garnett, E.; Yang, P. Light Trapping in Silicon Nanowire Solar Cells. Nano Lett. 2010, 10, 1082–1087. Khan, M. R.; Wang, X.; Bermel, P.; Alam, M. A. Enhanced Light Trapping in Solar Cells with a Meta-Mirror Following Generalized Snell’s Law. Opt. Express 2014, 22, A973. Zhao, J.; Wang, A.; Green, M. A.; Ferrazza, F. 19.8% Efficient “Honeycomb” Textured Multicrystalline and 24.4% Monocrystalline Silicon Solar Cells. Appl. Phys. Lett. 1998, 73, 1991–1993. Campbell, P.; Green, M. A. High Performance Light Trapping Textures for Monocrystalline Silicon Solar Cells. Sol. Energy Mater. Sol. Cells 2001, 65, 369–375. Martín-Palma, R. J.; Lakhtakia, A. Progress on Bioinspired, Biomimetic, and Bioreplication Routes to Harvest Solar Energy. Appl. Phys. Rev. 2017, 4, 21103. Wilson, S. J.; Hutley, M. C. The Optical Properties of “Moth Eye” Antireflection Surfaces. Opt. Acta Int. J. Opt. 1982, 29, 993–1009. Parker, A. R.; Hegedus, Z.; Watts, R. A. Solar-Absorber Antireflector on the Eye of an Eocene Fly (45 Ma). Proc. R. Soc. London B Biol. Sci. 1998, 265, 811–815. Huang, Y.-F.; Chattopadhyay, S.; Jen, Y.-J.; Peng, C.-Y.; Liu, T.-A.; Hsu, Y.-K.; Pan, C.-L.; Lo, H.-C.; Hsu, C.-H.; Chang, Y.H.; Lee, C.-S.; Chen, K.-H.; Chen, L.-C. Improved Broadband and Quasi-Omnidirectional Anti-Reflection Properties with Biomimetic Silicon Nanostructures. Nat. Nanotechnol. 2007, 2, 770–774. Chen, J. Y.; Chang, W.-L.; Huang, C. K.; Sun, K. W. Biomimetic Nanostructured Antireflection Coating and Its Application on Crystalline Silicon Solar Cells. Opt. Express 2011, 19, 14411. Siddique, R. H.; Gomard, G.; Hölscher, H. The Role of Random Nanostructures for the Omnidirectional Anti-Reflection Properties of the Glasswing Butterfly. Nat. Commun. 2015, 6, 6909. Bone, R. a; Lee, D. W.; Norman, J. M. Epidermal Cells Functioning as Lenses in Leaves of Tropical Rain-Forest Shade Plants. Appl. Opt. 1985, 24, 1408.
(30)
(31)
(32)
(33) (34)
(35)
(36)
(37)
(38) (39)
(40)
Page 6 of 7 Hünig, R.; Mertens, A.; Stephan, M.; Schulz, A.; Richter, B.; Hetterich, M.; Powalla, M.; Lemmer, U.; Colsmann, A.; Gomard, G. Flower Power: Exploiting Plants’ Epidermal Structures for Enhanced Light Harvesting in Thin-Film Solar Cells. Adv. Opt. Mater. 2016, 4, 1487–1493. Schulte, A. J.; Droste, D. M.; Koch, K.; Barthlott, W. Hierarchically Structured Superhydrophobic Flowers with Low Hysteresis of the Wild Pansy (Viola Tricolor) - New Design Principles for Biomimetic Materials. Beilstein J. Nanotechnol. 2011, 2, 228–236. Fritz, B.; Hünig, R.; Schmager, R.; Hetterich, M.; Lemmer, U.; Gomard, G. Assessing the Influence of Structural Disorder on the Plant Epidermal Cells’ Optical Properties: A Numerical Analysis. Bioinspir. Biomim. 2017, 12, 36011. Vukusic, P.; Sambles, J. R. Photonic Structures in Biology. Nature 2003, 424, 852–855. Whitney, H. M.; Kolle, M.; Andrew, P.; Chittka, L.; Steiner, U.; Glover, B. J. Response to Comment on “Floral Iridescence, Produced by Diffractive Optics, Acts As a Cue for Animal Pollinators.” Science (80-. ). 2009, 325, 1072–1072. Vignolini, S.; Davey, M. P.; Bateman, R. M.; Rudall, P. J.; Moyroud, E.; Tratt, J.; Malmgren, S.; Steiner, U.; Glover, B. J. The Mirror Crack’d: Both Pigment and Structure Contribute to the Glossy Blue Appearance of the Mirror Orchid, Ophrys Speculum. New Phytol. 2012, 196, 1038–1047. Gorton, H. L.; Vogelmann, T. C. Effects of Epidermal Cell Shape and Pigmentation on Optical Properties of Anfirrhinum Petals at Visible and Ultraviolet Wavelengths’. Plant Physiol 11, 879–8238. Yoshioka, Y.; Iwata, H.; Hase, N.; Matsuura, S.; Ohsawa, · R; Ninomiya, · S; Ninomiya, S. Genetic Combining Ability of Petal Shape in Garden Pansy (Viola × Wittrockiana Gams) Based on Image Analysis. Euphytica 2006, 151, 311–319. Trowbridge, T. S. Retroreflection from Rough Surfaces. J. Opt. Soc. Am. A 1978, 68, 1225–1242. Ulbrich, C.; Gerber, A.; Hermans, K.; Lambertz, A.; Rau, U. Analysis of Short Circuit Current Gains by an Anti-Reflective Textured Cover on Silicon Thin Film Solar Cells. Prog. Photovoltaics Res. Appl. 2013, 21, 1672–1681. Ding, K.; Aeberhard, U.; Finger, F.; Rau, U. Silicon Heterojunction Solar Cell with Amorphous Silicon Oxide Buffer and Microcrystalline Silicon Oxide Contact Layers. Phys. status solidi - Rapid Res. Lett. 2012, 6, 193–195.
6
ACS Paragon Plus Environment
Page 7 of 7
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Photonics
Insert Table of Contents artwork here
7
ACS Paragon Plus Environment
