Double plasmonic structure design for broadband absorption enhancement in molecular organic solar cells

Double plasmonic structuredesign for broadbandabsorption enhancement inmolecular organic solar cells

Wenli BaiQiaoqiang GanGuofeng SongLianghui ChenZakya KafafiFilbert Bartoli

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Double plasmonic structure design for broadbandabsorption enhancement in molecular organic solar

cells

Wenli Bai,a,b,c Qiaoqiang Gan,a,d Guofeng Song,b Lianghui Chen,b

Zakya Kafafi,a,e and Filbert Bartolia

a Lehigh University, Electrical and Computer Engineering Department,Bethlehem, Pennsylvania 18015

b Chinese Academy of Sciences, Institute of Semiconductors, Beijing, 100083 Chinac Tsinghua University, Department of Electronic Engineering, Beijing, 100084 China

d State University of New York at Buffalo, Department of Electrical Engineering,Room 215D,Bonner Hall, Buffalo, New York 14260

[email protected] National Science Foundation, Division of Chemistry, Arlington, Virginia 22230

Abstract. Absorption enhancement by a double plasmonic nanostructure in molecular organicphotovoltaics (OPVs) is theoretically investigated. The structure consists of a periodic array ofmetal nanodiscs on one side of the OPV active layers and a thin metal nanohole array on theother side. Excitation of coupled modes of localized surface plasmon polaritons at the nanodiscsand short-range surface plasmon polaritons at the nanohole array causes the electromagneticfield to be highly concentrated within the organic active layers, leading to a polarization-independent, broadband absorption enhancement in the visible and near-infrared portion of thesolar spectrum. Calculations show that an optimized double plasmonic structure can enhance thetotal photon absorption by >125% for molecular OPVs based on a double heterojunction of anelectron donor/hole transporter and an electron acceptor/transporter. C© 2011 Society of Photo-Optical

Instrumentation Engineers (SPIE). [DOI: 10.1117/1.3585876]

Keywords: organic photovoltaics; surface plasmon polaritons; broadband light trapping.

Paper 11179SSR received Feb. 1, 2011; revised manuscript received Apr. 12, 2011; acceptedfor publication Apr. 13, 2011; published online May 4, 2011.

1 Introduction

Photovoltaic (PV) technology has the potential to provide a virtually unlimited source of cleanenergy by efficiently converting incident sunlight into electrical energy. To be successful,however, significant advances are required to reduce cost and increase solar cell efficiency. Atpresent, the photovoltaic market relies heavily on wafer-based polycrystalline silicon devices,which entail relatively high fabrication costs. Thin-film solar cells, on the other hand, can havesignificantly lower cost and improved charge-carrier extraction, but normally at the expense ofsolar light absorption. Hence, effective light-trapping schemes for thin-film PVs are needed toensure effective absorption of the incident sunlight, which is essential for high energy conversionefficiency.

Thin-film solar cells have been fabricated using a variety of inorganic materials, includingamorphous silicon,1 GaAs,2 CuInxGa1−xSe2, and CdTe.3,4 There has also been considerableprogress recently in thin-film organic PVs based on polymers5,6 and small molecules.7–9 Com-pared to their inorganic counterparts, organic photovoltaics (OPVs) offer many advantages,including low cost, large-area fabrication, and flexibility. However, most molecular and

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Bai et al.: Double plasmonic structure design for broadband absorption enhancement...

polymeric materials possess a low charge-carrier mobility and small exciton diffusion length,10,11

which limit the thickness of the active layers in OPVs,12–16 resulting in poor solar light absorptionand insufficient carrier generation. This results in a low power conversion efficiency (∼5.7%for small molecule solar cells17 and ∼7.7% for polymer devices18). Hence, new strategies toenhance solar absorption in OPV active layers are particularly important. In the current work,we address the need for nanophotonic light trapping in OPVs to overcome thickness limitationsand surpass previously achieved OPV power conversion efficiencies.

Surface plasmon polaritons (SPPs) are collective oscillations of electromagnetic waves andfree electrons at the interface of a metal and a dielectric or semiconductor material.19,20 By prop-erly designing plasmonic nanostructures, light can be strongly confined to the thin active layerof the solar cell, thereby increasing its absorption. Various plasmonic nanostructures, includingnanoparticles21–23 and nanogratings,24,25 have been investigated for light trapping26 in thin-filmphotovoltaics, exploiting near-field optical enhancement or scattering processes to increase theabsorption of thin active layers. Recent theoretical investigations of plasmonic nanostructuresin thin-film solar cells27–29 have demonstrated effective absorption enhancement, and studies ofthe fundamental limits of light trapping in solar cells indicate that further enhancement in thin-film PVs is achievable.30,31 For effective light trapping in thin-film organic solar cells, a broadabsorption enhancement is desired. Short-range SPP (SRSPP) modes on thin metallic filmssurrounded by strongly asymmetric dielectric materials have a very broad resonance bandwidthand the potential to provide the broadband absorption enhancement needed for OPVs.

In a recent study, we employed an ultrathin nanopatterned metal cathode to enhance theoptical absorption in polymeric OPVs.32 Through the excitation of SRSPP modes within the30-nm-thick active polymer layer, a broad absorption enhancement was achieved. In this paper,we extend this design concept to molecular OPVs and introduce a novel double plasmonic nanos-tructure that consists of an array of metallic nanodisks at the front interface and a nanopatternedthin metal film at the rear interface with the active layers. In this study, we first calculate thebroadband spectral absorptivity of the active layers introduced by the plasmonic nanostructures,explore the tunability of the absorption enhancement, and investigate its effect on the deviceperformance.

2 Broadband Absorption Enhancement Introduced by Double PlasmonicNanostructures

In this section, we employ three-dimensional (3-D) finite-difference time-domain (FDTD) mod-eling to design a novel double plasmonic nanostructure for broadband absorption enhance-ment of molecular OPVs. Unlike previous two-dimensional studies on polarization-dependentgratinglike nanostructures,24,25,27–29 we demonstrate that 3-D full-field electromagnetic sim-ulations lead to a polarization-independent, solar light absorption enhancement. Figure 1 il-lustrates the proposed double plasmonic nanostructure incorporated in a molecular OPV,which consists of a glass substrate covered with a 50-nm-thick indium tin oxide layer thatserves as the transparent anode. Next, a two-dimensional periodic array of metal nanodisksis imbedded in a spin-coated 20-nm-thick highly conductive hole transport layer, poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate), followed by a vapor-deposited 10-nm-thickelectron donor layer, copper phthalocyanine (CuPc), and a 10-nm-thick electron acceptor layer,3,4,9,10-perylenetetracarboxylic bis-benzimidazole (PTCBI). The metal back reflector com-monly used in thin-film PV cells is replaced by a 20-nm-thick nanopatterned silver film witha periodic nanohole array capable of supporting SRSPPs, which are known to strongly confineoptical fields over a broad spectral range. Although the two metal layers can function individ-ually to enhance the absorption in the two active layers, the localized surface plasmon of thenanodisks and SRSPP of the nanohole array overlap and form coupled plasmonic modes with acomplex field distribution that is sensitive to the geometry of the nanostructure. The nanodiskdiameter (D1), the nanohole diameter (D2), and the nanohole array period (P) can be tuned to




Fig. 1 Schematic of the proposed thin-film double plasmonic nanostructure molecular OPV withnanodisks and nanoholes placed next to the hole- (CuPc) and electron-transporting (PTCBI)layers, respectively.

optimize the absorption enhancement in the two active layers and, consequently, the currentdensity in the OPV device.

In our simulations, the experimental data for the spectrally dispersive dielectric propertiesof CuPc and PTCBI molecular films in solar region21,33,34 are used. To test the reliability ofour calculations, we first model the optical absorptivities of active layers employed in thisOPV structure. As shown in Fig. 2, the optical absorptivity spectra of a 100-nm CuPc filmand a 100-nm PTCBI film are individually calculated and compared to the experimentallymeasured spectra. The simulated absorptivity spectra of the two active layers were found toagree reasonably well with those experimentally measured. Now we employ the modeling toinvestigate optical absorption enhancement in the proposed nanostructured OPV. By employingthe periodic boundary condition in the numerical simulations, the periods of the nanodisks and

Fig. 2 Comparison between the simulated (dashed line) and measured absorptivity spectra (solidline) of a 100-nm-thick CuPc film and a 100-nm-thick PTCBI film.




nanohole array are assumed to be identical. Nonuniform mesh sizes are employed in 3-D FDTDmodeling; the edge grid size in all three directions is 1 nm, and the body grid size is 2 nm. Allthe simulations discussed in this paper are modeled in a 16-core high-performance computer.

To investigate the absorption enhancement in the active layers, we first calculate the spectralabsorptivity [A(λ)] of the organic active layers (CuPc and PTCBI), which is defined as the ratioof absorbed and incident optical intensities at each wavelength. Absorption by the metal layersdoes not contribute to the formation of excitons in the active layers and is not considered inthe calculation of A(λ). Figure 3(a) shows the calculated spectral absorptivity for the CuPc andPTCBI active layers without the plasmonic nanostructures (black dashed line), with only a frontnanodisk array (curve 1), with only a rear nanohole array (curve 2), and with both front nanodiskand rear nanohole arrays (curve 3). One can see that the front (curve 1) and rear plasmonicnanostructures (curve 2) independently contribute to significant absorption enhancement. Forwavelengths in the vicinity of the 525-nm absorptivity band, the nanohole array (curve 2)is found to enhance absorption more strongly than the nanodisk array. Conversely, the frontnanodisk array (curve 1) has a greater impact on absorption at wavelengths between 550 and800 nm. As has been reported previously, the magnitude, bandwidth, and resonant wavelengthof the localized SPP and SRSPP resonances can be tuned by changing the shape, size, anddistribution of the nanoparticles and nanohole arrays.23,32,35 Combining these two metallic

Fig. 3 Absorptivity spectra of different active layers with a flat silver substrate having no plasmonicnanostructures (black dashed line), with a flat silver substrate and a front nanodisk array (curve1), with a rear nanohole array (curve 2), and with both front nanodisk and rear nanohole arrays(curve 3). Results are shown for D1 = 100 nm, D2 = 100 nm, and P = 200 nm. (a) Absorptivityspectra of the organic active layers (CuPc and PTCBI), (b) absorptivity spectra of the CuPc activelayer, and (c) absorptivity spectra of the PTCBI active layer.




nanostructure arrays into a single OPV device structure gives rise to coupled modes and resultsin a stronger and broader absorption enhancement throughout the solar spectrum (see curve 3a).

To delineate the physical nature and origin of the strong broadband absorption enhancementintroduced by the double nanostructure, we calculate the separate absorptivity spectra of eachactive layer (CuPc or PTCBI) and determine the enhancement due to the nanohole or nanodiskarray only or the combined double nanostructure (nanohole and nanodisk arrays). We thenanalyze the 3-D mode distribution in the OPV device structure.

2.1 Absorptivity Spectra of the Two Active Layers

Figure 3(b) shows the calculated spectral absorptivity for the CuPc active layer without theplasmonic nanostructures (black dashed line), with only a front nanodisk array (curve 1), withonly a rear nanohole array (curve 2), and with both front nanodisk and rear nanohole arrays(curve 3). By integrating over the entire spectral range, the total absorption enhancement factorof the CuPc layer (primarily between 550 and 800 nm) is calculated to be 55, 22, and 62.7%for the nanodisk array, nanohole array, and double-layered nanostructure, respectively. In thiscase, the nanodisk array adjacent to the CuPc layer leads to much more significant enhancementthan the nanohole array. No significant enhancement in the absorptivity of the CuPc layer wascalculated in the shorter wavelength blue-green region (400–550 nm), where CuPc is known tobe weakly absorbing. Figure 3(c) shows the calculated spectral absorptivity for the PTCBI activelayer without the plasmonic nanostructures (black dashed line), with only a front nanodisk array(curve 1), with only a rear nanohole array (curve 2), and with both nanodisk and nanohole arrays(curve 3). The total absorption enhancement factor of the PTCBI layer is calculated to be 106,110.5, and 177.5% for the nanodisk array, nanohole array, and double-layered nanostructure,respectively. This enhancement for PTCBI is considerably larger than that calculated for theCuPc layer and occurs over a broad spectral range, covering the entire visible solar spectrum.The broad enhancement is consistent with that seen in our previous simulations of a single-layered SRSPP nanostructure for polymer-based OPV devices.32 The absorptivity enhancementintroduced in the two active organic layers by the nanodisk and nanohole arrays in the double-layered nanostructure demonstrates the field enhancement of the hybrid mode, especially in thevicinity of the PTCBI layer. This should be taken into consideration in the design of plasmonicnanostuctures for OPV devices with enhanced performance.

2.2 3-D Mode Distribution in the Device

Here we provide the mode distribution at the wavelength of 525 nm as an example to furtherdemonstrate the physics of the absorption enhancement. For time-harmonic electromagneticfields, the average power absorbed by the active material is determined from the divergence ofthe Poynting vector36 and given by

ua = 1

2

∫ωε′′|E|2dxdydz, (1)

where |E|2 is the square of the magnitude of the electric field, ω is the frequency of the incidentlight, ε′′ is the imaginary part of the permittivity for the absorbing materials, and the imaginarypart of the permeability μ′′ is assumed to be zero. The spatial distribution of the enhancedabsorption in the active layer can be inferred from the |E|2 distribution obtained by 3-D FDTDsimulations, which is shown in Fig. 4 for a wavelength of 525 nm. A series of X-Y sliced planesat different Z positions illustrate the 3-D |E|2 patterns in the active layers for an OPV devicewith the double plasmonic nanostructures. Figure 4 illustrates that at 525 nm, the electric fieldis strongly enhanced in the organic active layers, particularly in the vicinity of the rear interface.




Fig. 4 X-Y sliced planes of |E|2 distribution at different Z positions inside the active layers at thewavelengths of 525 nm. The electric component of the incident light is parallel to the X-axis.

The electric field is mainly concentrated around nanoholes at the four corners of the simulationunit due to the excitation of the coupled localized SPP and SRSPP modes.

It should be noted that the distance between these two nanostructures on the front and rearinterfaces of the organic active layers is only 20 nm. Consequently, the SPP modes supported bythese interfaces are coupled with each other and more complex than those supported by single-layered nanostructures. The parameters of these two nanostructures can be independently tunedto maximize the spectral band of the enhanced absorption. In this design, the circular nanodiskarray above the active layer and the array of square symmetrically distributed nanoholes37 at therear are insensitive to polarization.

3 Tunability of the Double Plasmonic Nanostructure

As discussed in Sec. 2, the double plasmonic nanostructure enables the incident light to coupleto complex hybrid modes in the active layers. These modes retain characteristics of localizedSPPs and SRSPPs, and their optical properties can be tuned by varying the structural parametersof the front or rear nanostructures. In this section, FDTD numerical modeling is performed toinvestigate the tunability of the absorption enhancement. We first consider tuning the geometryof nanohole arrays in an ultrathin metal film at the rear interface. As previously reported,32

the optical properties of SRSPPs supported by ultrathin nanostructured metal films have afunctional dependence on the period of the nanopatterned array. Figure 5(a) shows the mapof the absorptivity as a function of wavelength and nanohole array period (P). For simplicity,the diameters of the nanodisks and nanoholes were kept constant in the modeling (D1 = D2

= 100 nm). Although the spectral absorptivity varies with the nanohole period, a very highabsorptivity is observed (e.g., > 0.6, with a peak value of ∼0.7) over a broad spectral rangefrom 500 to 800 nm for periods in the range of 140–300 nm. This broadband absorption tunabilityis characteristic of SRSPPs in nanopatterned ultrathin metal films32 and can be realized over awide range of periods, providing excellent fabrication tolerance for practical devices.

Next, we discuss the tunability of the nanodisk array at the front interface. For these sim-ulations, the period was kept constant (P = 200 nm) and the nanodisk diameter (D1) varied.The map of the absorptivity as a function of wavelength and D1 is shown in Fig. 5(b). One cansee that the active layer absorptivity is much higher and spectrally broader for larger nanodiscdiameters (D1). This behavior is consistent with the optical properties of metallic nanoparticles




Fig. 5 (a) Map of the absorptivity of the two active layers versus wavelength and period (P) whenD1 = D2 = 100 nm. (b) Map of the absorptivity of the two active layers versus wavelength andfront nanodisk diameter (D1) when P = 200 nm and D2 = 100 nm.

reported previously.23,26 Larger nanoparticles scatter light more strongly than absorb it, and lighttrapping occurs primarily via scattering into the active organic layers. Dynamic depolarizationand radiation damping effects lead to a broadening of the plasmon resonance. Smaller metalnanoparticles, on the other hand, strongly absorb light rather than scatter it into the active layers.The broader absorption enhancement depicted in Fig. 5(b) for the larger nanodisks indicate thatthe hybrid modes supported by the double-layered nanostructure have similarities to scatteredlight from localized SPPs. The two metallic nanostructures discussed earlier contribute cooper-atively in the proposed device to achieve a broader band absorption enhancement, which couldultimately lead to enhanced device performance.

4 Optimization of the Device Performance of Molecular OrganicPhotovoltaics

Optimization of the absorption enhancement in the double plasmonic molecular OPV device isexplored next, employing the standard air mass (AM1.5) solar irradiance [S(λ)] to calculate theabsorbed photon flux density in the active layer. This enhanced absorption of sunlight resultsin increased formation of excitons inside the active layers, a larger short-circuit current density,and consequently, improved device performance. The total photon absorptivity (Aphoton) of theplasmonic solar cell is calculated and compared to the reference cell. The geometric parametersof the plasmonic double nanostructure are then varied to optimize the absorption enhancementfactor.

The solar photon flux density, defined as Fs(λ) = S(λ) · λ/hc, is given by the top curve inFig. 6(a). The absorbed photon flux density, A(λ)Fs(λ), for the double plasmonic OPV devicewas determined by FDTD simulation and plotted as the middle curve in Fig. 6(a). For comparison,the absorbed photon flux density is also shown in the bottom of Fig. 6(a) for the reference OPVdevice with a 20-nm-thick flat metal backreflector. The results show a significant broadbandenhancement. The total photon absorptivity, Aphoton, can be calculated using

Aphoton =∫ λmax

λminA(λ)�s(λ)dλ∫ λmax

λmin�s(λ)dλ

, (2)

where Aphoton represents the fraction of the total solar photon flux density that is absorbed inthe active layers of the OPV. The value of Aphoton-ref calculated for the reference OPV withouta plasmonic nanostructure is ∼0.2, indicating that only 20% of the total solar photon energy isutilized in the reference sample. Figures 6(b) and 6(c) show the calculated Aphoton for the doubleplasmonic OPV devices (circles) as a function of nanoarray period (P) and nanodisc diameter




Fig. 6 (a) Solar (top line) and absorbed photon flux density of the organic solar cells with (centerline) and without (bottom line) the double plasmonic nanostructure (P = 160 nm, D1 = 80 nmand D2 = 100 nm). (b) Total photon absorptivity of the plasmonic OPV as a function of period(P) for D1 = D2 = 100 nm. (c) Total photon absorptivity of the plasmonic OPVs as a functionof the nanodisc diameter (D1) for P = 200 nm and D2 = 100 nm. (d) Total photon absorptivityenhancement factor (Aphoton/Aphoton-ref – 1) of the plasmonic OPVs as a function of period (P) forthe nanodisk diameter (D1) varying from 20 to 100 nm and D2 = 100 nm.

(D1), respectively. The results are appreciably larger than for the reference solar cell and varysignificantly with the geometry of the nanostructure (for the same range of parameters used inFig. 5). Aphoton > 0.33 for all periods and nanodisk diameters considered, with a maximum valueof >0.45. This indicates that for the highest value of Aphoton , the proposed double plasmonicOPV devices can effectively utilize nearly half the total solar photon energy, a significantenhancement in absorption relative to that of the reference OPV [dashed line in Figs. 6(b) and6(c)].

Although Figs. 6(b) and 6(c) explore the solar absorption enhancement by tuning the ge-ometric parameters of the two nanostructures independently, performance optimization of theproposed plasmonic solar cell requires that the nanoarray period P and nanodisk diameter D1

be tuned simultaneously. Figure 6(d) shows the enhancement factor (Aphoton/Aphoton-ref − 1) as afunction of the P for a series of nanodisk diameters. Each point on these curves involved cal-culating the spectral absorptivity for all wavelengths within the solar spectrum. The maximumenhancement of ∼128% is obtained for the optimal structural parameters, P = 160 nm and D1

= 80 nm. Note that these are the same parameters used above to calculate the spectrum of theabsorbed photon flux density [center line in Fig. 6(a)]. The results in Fig. 6(d) demonstratesignificantly enhanced total photon absorption for a wide range of geometric parameters. En-hancements of >60% are achieved for D1 > 50 nm and P between 120 and 320 nm, providingconsiderable device fabrication tolerance. The lower enhancement factors observed for smallnanodisk diameters is consistent with the previous reports of reduced coupling into the active




layers by small nanoparticles.23 In an OPV device based on a double heterojunction, the en-hanced photon absorption will increase the generation of excitons and the formation of electronsand holes at the interface of the electron donor (CuPc) and acceptor (PTCBI) organic active lay-ers, resulting in an enhancement in the short-circuit current density Jsc = e ∫λmax

λminA(λ)�s(λ)dλ

and, consequently, OPV device performance. For the ideal case of 100% internal quantum ef-ficiency, the enhancement in short circuit current density of the photovoltaic device would becomparable to the absorption enhancement in the active organic layers.

The maximum photon absorption enhancement of 128% presented in this work for a total of20-nm-thick molecular active layers (CuPc and PTCBI) compares well to and, in some cases,may surpass previously reported results for polymer OPVs based on bulk heterojunctions (47%for P3HT:PC70BM and 130% for PCPDTBT:PCBM),32 and molecular OPVs based on a doubleheterojunction using a one-dimensional metallic grating. Usually, small molecular PV deviceshave a flat silver cathode with a thickness of around 100–150 nm, which has a high reflectance.To compare ro the absorption enhancement introduced by the flat and thick metal cathode,additional calculations were performed on a device with an unpatterened 100-nm-thick Agfilm. Although the thicker Ag film has a higher reflectance, it does not have the light-trappingcapability. Compared to the 100-nm-thick flat Ag film, the proposed nanopatterned structure(with optimal structural parameters, P = 160 nm, D1 = 80 nm, and D2 = 100 nm) exhibits aneven greater absorption enhancement (data not shown here). Because of the excitation of hybridplasmonic modes, the proposed plasmonic nanostructure can concentrate the energy into theactive layer, leading to the enhanced absorption.

5 Conclusion

In conclusion, a novel double plasmonic nanostructure is proposed in which the active or-ganic layers are sandwiched between two nanoplasmonic layers, consisting of a front nanodiskarray and a rear nanohole array. Three-dimensional FDTD modeling was performed to investi-gate thin-film molecular OPV structures with improved performance. Broadband, polarization-independent photon absorption enhancement was achieved due to the excitation of localizedSPP and SRSPP modes in the coupled double plasmonic nanostructure. Calculations show thatthe total photon absorptivity could be enhanced by 128% compared to a reference OPV with noplasmonic nanostructure. The theoretical design concepts outlined in this paper are quite generaland can be employed in a systematic way to optimize the performance of organic and inorganicphotovoltaic devices using novel plasmonic nanostructures. Further calculations on the effect ofvarying the dimensions of the nanoholes in this OPV structure as well as experimental studiesto verify the validity of the theoretical model are underway.

Acknowledgments

The authors thank Dr. Paul Lane (Naval Research Laboratory) for providing the experimen-tally measured absorptivity spectra for CuPc and PTCBI films. Three of the authors (W. Bai,Q. Gan, and F. Bartoli) acknowledge NSF funding of this work (Award No. ECCS-0901324).Two authors (G. Song and L. Chen) thank the Chinese Academy of Sciences (Grant No.GJHZ200804) for support through the External Collaboration Program.

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Wenli Bai is currently a PhD candidate working on nanophotonics in theNano-Optoelectronics Laboratory, Institute of Semiconductors, ChineseAcademy of Sciences. He received his BS from the Department of Electri-cal Science and Technology, Jilin University, Changchun, China, in 2007.From September 2009 to October 2010, he worked as a research associateon plasmonics and nanophotonics in the Electrical & Computer Engineer-ing (ECE) at Lehigh University. His current research interests includenanophotonics, plasmonics, and photovoltaic technologies.

Qiaoqiang Gan is an assistant professor in the Department of ElectricalEngineering at the State University of New York at Buffalo. He receivedhis BS from Fudan University, Shanghai, China in 2003, his MS in 2006in nanophotonics at the Nano Optoelectronics Lab in the Institute of Semi-conductors at the Chinese Academy of Sciences, and his PhD from LehighUniversity in 2010. He received the IEEE Photonic Society Student Fellow-ship Award in 2009. His current research interests include nanophotonics,plasmonics, and biophotonics. His research publications include over 40technical papers and four patents.



http://dx.doi.org/10.1364/OE.16.021793

http://dx.doi.org/10.1063/1.3141402

http://dx.doi.org/10.1364/OL.34.003725



http://dx.doi.org/10.1021/nl8022548


http://dx.doi.org/10.1021/nl904057p

http://dx.doi.org/10.1364/OE.18.00A366

http://dx.doi.org/10.1073/pnas.1008296107

http://dx.doi.org/10.1364/OE.18.00A620

http://dx.doi.org/10.1080/713738799

http://dx.doi.org/10.1103/PhysRevLett.103.203901


Guofeng Song received the first PhD from Beijing Institute of Tech-nology, Beijing, China, in 2000, and the second PhD from the NationalAstronomical Observatories, Beijing, in 2001. He is currently the directorof the Nano-Optoelectronics Laboratory, Institute of Semiconductors, Chi-nese Academy of Sciences, Beijing, China. His current research interestsinclude photoelectronics devices.

Lianghui Chen received his BS from Fudan University, Shanghai, China,in 1963. After graduation, he then worked with the Institute of Semi-conductors, Beijing, China. He is currently a professor and leader of theNano-Optoelectronics Laboratory, Institute of Semiconductors, ChineseAcademy of Sciences, Beijing. He was elected as the member of the Chi-nese Academy of Engineering in 1999. His current research interests in-clude photoelectronics devices, nanophotonics, and biophotonics.

Zakya Kafafi is an adjunct professor in the Department of Electrical andComputer Engineering at Lehigh University. In the past three years sheserved as the director of the Division of Materials Research at the NationalScience Foundation. Previously, she was at the Naval Research Labora-tory, where she served as a group leader and a section head of OrganicOptoelectronics. Her research is motivated by newly emerging technolo-gies based on organic electronics and photonics, such as organic nonlinear,light-emitting, and photovoltaic materials and devices. Her studies spanneda wide spectrum of disciplines in condensed matter physics and solid-state

chemistry following elementary reaction mechanisms and, probing energy and charge transferprocesses using various tools such optical, infrared, matrix isolation, fluorescence, and elec-troluminescence spectroscopies. She published more than 200 manuscripts, and book chapters,in addition to several U.S. Patents. She is the editor of more than 20 books and proceed-ings volumes. Recently, she became the editor-in-chief of the newly launched SPIE electronicJournal of Photonics for Energy. She is a member of the American Chemical Society (ACS), theMaterials Research Society (MRS), and Sigma Xi. She is a fellow of the American Associationfor the Advancement of Science (AAAS), the International Society for Optical Engineering(SPIE), and the Optical Society of America (OSA).

Filbert Bartoli is currently the Chandler Weaver Chair and professor ofElectrical & Computer Engineering (ECE) at Lehigh University, and chairof the Electrical and Computer Engineering Department. From 2000 to2005, he served as a program director in the Division of Electrical andCommunications Systems at the National Science Foundation. Prior tothat he was at the Naval Research Laboratory, where he was the headof the Advanced Materials Section in the Optical Sciences Division. Heis a Fellow of OSA and IEEE, and currently serves as IEEE PhotonicsSociety vice president for finance and administation and editor-in-chief

for the IEEE Journal of Selected Topics in Quantum Electronics. His research activities haveincluded a broad range of topics, such as infrared detection, inorganic and organic optoelec-tronics, semiconductor physics, quantum-well device physics, and nonlinear optics. His currentresearch interests include nanophotonics and plasmonics for biosensors, solar cells, and slowlight applications. His research publications include over 320 technical papers and 18 patents.



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