A Simple Optical Model Well Explains Plasmonic-Nanoparticle-Enhanced Spectral Photocurrent in Optically Thin Solar Cells
- 1.1k Downloads
A simple optical model for photocurrent enhancement by plasmonic metal nanoparticles atop solar cells has been developed. Our model deals with the absorption, reflection, and scattering of incident sunlight as well as radiation efficiencies on metallic nanoparticles. Our calculation results satisfactorily reproduce a series of experimental spectral data for optically thin GaAs solar cells with Ag and Al nanoparticles of various dimensions, demonstrating the validity of our modeling approach. Our model is likely to be a powerful tool for investigations of surface plasmon-enhanced thin-film solar cells.
KeywordsGaAs Solar Cell Metal Nanoparticles Radiation Efficiency Complex Dielectric Function
Solar cell structures have been suffering from the following trade-off related to the thickness of their active photovoltaic layers: thinner photovoltaic layers exhibit weaker light absorption while thicker layers exhibit stronger bulk carrier recombination. Both of these factors yield conversion loss of the incident sunlight energy to the solar cell electrical output. Therefore, the thickness of the active photovoltaic layer is usually optimized for maximizing the energy conversion efficiency by considering the above trade-off. Metal nanoparticles placed on the solar cell surface can enhance sunlight collection, owing to their large extinction cross-section near the surface plasmon resonance, which is dominated by scattering rather than by absorption for appropriately chosen particle sizes [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]. Thus, metal nanoparticles scatter the incident light into a wide range of angles and increase the optical path length in the absorber layer for enhancing overall photoabsorption. This effect can potentially allow to reduce the cell cost and weight by utilization of thinner absorber layers and can also yield efficiency enhancement associated with an increased carrier excitation level. We previously experimentally investigated the effect of arrays of subwavelength-sized metal particles on GaAs solar cell absorption and photocurrent . Spectral response measurements for optically thin GaAs solar cells, in which the photovoltaic active layer is much thinner than the optical absorptive decay length, were performed with and without Ag and Al metal nanoparticles; short circuit current and efficiency enhancement were observed under the air mass 1.5 global solar spectrum for GaAs cells with metal nanoparticle arrays, relative to reference GaAs cells with no metal nanoparticles.
Research groups have been primarily using the laborious finite-difference time-domain calculations to analyze or design surface plasmon-enhanced solar cells. However, such monochromatic, three-dimensional time-domain calculations are time-consuming, typically requiring more than several tens of hours of calculation by relatively powerful computers, even for a single wavelength of incident sunlight. In the present work, we propose and demonstrate a simple numerical simulation scheme for obtaining photocurrent enhancement spectra of plasmonic solar cells, which enables obtaining instant results for the entire sunlight spectrum, for providing future directions for device improvement. We demonstrate that our computational scheme is quite simple yet satisfactorily reproduces the experimental results for the photocurrent enhancement in solar cells with metal nanoparticle surface decorations.
Note that a, b, and c are the outer radii of the spheroid or the core radii. To compare with the experimental photocurrent enhancement data, we considered the ratio of the absorbance from Eq. 4 to the absorbance without nanoparticles. In this study, we assumed that the absorption enhancement in the photovoltaic active layer of a cell with metal nanoparticles relative to a reference cell without metal nanoparticles represents the photocurrent enhancement.
Results and Discussion
out of the angular distribution of the light intensity scattered by subwavelength-sized particles in the quasistatic limit shown in Eq. 2, accounting for the waveguide-mode coupling from the total internal reflection. Such a simple modification of the formalism in our calculation enables to test a completely novel device structure, which demonstrates another capability of our model, namely its flexibility and extensibility. Thus, in Fig. 16, we show a significantly higher photocurrent enhancement by adopting such a waveguide-like photovoltaic layer structure and converting the incident sunlight into waveguide optical modes owing to the scattering induced by the metal nanoparticles, which indicates a great potential for the future development of plasmon-enhanced solar cells. Note also that the presently investigated scheme for utilization of optical waveguide modes differs from another enhancement scheme for utilization of surface plasmon modes  by coupling the incident light into surface plasmon polaritons propagating at semiconductor/metal interfaces via some subwavelength-sized features such as nanoscale grooves [30, 31, 32, 33].
In this work, we developed a relatively simple optical model for photocurrent enhancement by plasmonic metal nanoparticles atop solar cells. Our model considers the absorption, reflection, and scattering of the incident sunlight as well as the radiation efficiencies on metallic nanoparticles. Our calculation results satisfactorily reproduce a series of experimental spectral data in  for optically thin GaAs solar cells with Ag and Al nanoparticles of various dimensions, demonstrating the validity of our modeling scheme. We fitted our model calculations for the experimental results of GaAs solar cells in this study, but needless to say, our highly generalized model presented in this study is applicable for any kind of photovoltaic material. Our model can be used as a powerful tool for investigations of surface plasmon-enhanced thin-film solar cells to provide design principles for the improvement of device performance.
We thank Harry A. Atwater of the California Institute of Technology and Keisuke Nakayama of the JX Nippon Oil and Energy Corporation for discussions. This work was partially supported by JSPS, MEXT, and NEDO.
- 1.Ihara M, Tanaka K, Sakaki K, Honma I, Yamada K (1997) Enhancement of the absorption coefficient of cis-(NCS) bis(2,2'-bipyridyl-4,4'-dicarboxylate)ruthenium(II) dye in dye-sensitized solar cells by a silver island film. J Phys Chem B 101:5153Google Scholar
- 2.Stuart HR, Hall DG (1998) Island size effects in nanoparticle-enhanced photodetectors. Appl Phys Lett 73:3815Google Scholar
- 3.Wen C, Ishikawa K, Kishima M, Yamada K (2000) Effects of silver particles on the photovoltaic properties of dye-sensitized TiO2 thin films. Sol Ener Mater Sol Cells 61:339Google Scholar
- 4.Barnes WL, Dereux A, Ebbesen TW (2003) Surface plasmon subwavelength optics. Nature 424:824Google Scholar
- 5.Okamoto K, Niki I, Shvartser A, Narukawa Y, Mukai T, Scherer A (2004) Surface-plasmon-enhanced light emitters based on InGaN quantum wells. Nature Mater 3:601Google Scholar
- 6.Rand BP, Peumans P, Forrest SR (2004) Long-range absorption enhancement in organic tandem thin-film solar cells containing silver nanoclusters. J Appl Phys 96:7519Google Scholar
- 7.Schaadt DM, Feng B, Yu ET (2005) Enhanced semiconductor optical absorption via surface plasmon excitation in metal nanoparticles. Appl Phys Lett 86:063106Google Scholar
- 8.Pillai S, Catchpole KR, Trupke T, Zhang G, Zhao J, Green MA (2006) Enhanced emission from Si-based light-emitting diodes using surface plasmons. Appl Phys Lett 88:161102Google Scholar
- 9.Nakayama K, Tanabe K, Atwater HA (2008) Plasmonic nanoparticle enhanced light absorption in GaAs solar cells. Appl Phys Lett 93:121904Google Scholar
- 10.Atwater HA, Polman A (2010) Plasmonics for improved photovoltaic devices. Nature Mater 9:205Google Scholar
- 11.Hylton NP, Li XF, Giannini V, Lee K-H, Ekins-Daukes NJ, Loo J, Vercruysse D, Van Dorpe P, Sodabanlu H, Sugiyama M, Maier SA (2013) Loss mitigation in plasmonic solar cells: Aluminium nanoparticles for broadband photocurrent enhancements in GaAs photodiodes. Sci Rep 3:2874Google Scholar
- 12.Li XH, Li PC, Hu DZ, Schaadt DM, Yu ET (2013) Light trapping in thin-film solar cells via scattering by nanostructured antireflection coatings. J Appl Phys 114:044310Google Scholar
- 13.Bohren CF, Huffman DR (1983) Absorption and scattering of light by small particles, vol chap. 3 and 5. Wiley-VCH, WeinheimGoogle Scholar
- 15.Gregory DA, Peng G (2001) Random facet Fresnel lenses and mirrors. Opt Eng 40:713Google Scholar
- 16.Lim SH, Mar W, Matheu P, Derkacs D, Yu ET (2007) Photocurrent spectroscopy of optical absorption enhancement in silicon photodiodes via scattering from surface plasmon polaritons in gold nanoparticles. J Appl Phys 101:104309Google Scholar
- 18.Donges A (1998) The coherence length of black-body radiation. Eur J Phys 19:245Google Scholar
- 19.Royer P, Goudonnet JP, Warmack RJ, Ferrell TL (1987) Substrate effects on surface-plasmon spectra in metal-island films. Phys Rev B 35:3753Google Scholar
- 20.Madrazo A, Carminati R, Nieto-Vesperinas N, Greffet J-J (1998) Polarization effects in the optical interaction between a nanoparticle and a corrugated surface: Implications for apertureless near-field microscopy. J Opt Soc Am A 15:109Google Scholar
- 21.Knoll B, Keilmann F (2000) Enhanced dielectric contrast in scattering-type scanning near-field optical microscopy. Opt Commun 182:321Google Scholar
- 22.Catchpole KR, Polman A (2008) Plasmonic solar cells. Opt Express 16:21793Google Scholar
- 23.Palik ED (ed) (1985) Handbook of optical constants of solids. Academic Press, OrlandGoogle Scholar
- 24.Jeurgens LPH, Sloof WG, Tichelaar FD, Borsboom CG, Mittemeijer EJ (1999) Determination of thickness and composition of aluminium-oxide overlayers on aluminium substrates. Appl Surf Sci 144–145:11Google Scholar
- 25.Zhu W, Hirschmugl CJ, Laine AD, Sinkovic B, Parkin SSP (2001) Determination of the thickness of Al oxide films used as barriers in magnetic tunneling junctions. Appl Phys Lett 78:3103Google Scholar
- 26.Moskovits M (1985) Surface-enhanced spectroscopy. Rev Mod Phys 57:783Google Scholar
- 27.Zeman EJ, Schatz GC (1987) An accurate electromagnetic theory study of surface enhancement factors for Ag, Au, Cu, Li, Na, AI, Ga, In, Zn, and Cd. J Phys Chem 91:634Google Scholar
- 28.Hao E, Schatz GC (2004) Electromagnetic fields around silver nanoparticles and dimers. J Chem Phys 120:357Google Scholar
- 29.Ferry VE, Sweatlock LA, Pacifici D, Atwater HA (2008) Plasmonic nanostructure design for efficient light coupling into solar cells. Nano Lett 8:4391Google Scholar
- 30.Lezec HJ, Thio T (2004) Diffracted evanescent wave model for enhanced and suppressed optical transmission through subwavelength hole arrays. Opt Express 12:3629Google Scholar
- 31.Gay G, Alloschery O, De Lesegno BV, O'Dwyer C, Weiner J, Lezec HJ (2006) The optical response of nanostructured surfaces and the composite diffracted evanescent wave model. Nature Phys 2:262Google Scholar
- 32.Chen L, Robinson JT, Lipson M (2006) Role of radiation and surface plasmon polaritons in the optical interactions between a nano-slit and a nano-groove on a metal surface. Opt Express 14:12629Google Scholar
- 33.Pacifici D, Lezec HJ, Atwater HA (2007) All-optical modulation by plasmonic excitation of CdSe quantum dots. Nature Photon 1:402Google Scholar
Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.