Plasmonic Light-Trapping Concept for Nanoabsorber Photovoltaics

Subscriber access provided by Macquarie University

Article

A Plasmonic Light-Trapping Concept for Nanoabsorber Photovoltaics Brendan Brady, Volker Steenhoff, Benedikt Nickel, Arthur M. Blackburn, Martin Vehse, and Alexandre G. Brolo ACS Appl. Energy Mater., Just Accepted Manuscript • DOI: 10.1021/acsaem.9b00039 • Publication Date (Web): 11 Feb 2019 Downloaded from http://pubs.acs.org on February 11, 2019

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 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 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.

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 39 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 Applied Energy Materials

A

Plasmonic

Light-Trapping

Concept

for

Nanoabsorber Photovoltaics Brendan Brady1,2, Volker Steenhof3, Benedikt Nickel3, Arthur M. Blackburn1, Martin Vehse3, Alexandre G. Brolo*,1,2

1Centre

for Advanced Materials and Related Technology, University of Victoria,

Canada, V8W 2Y2 2

Department of Chemistry, University of Victoria, Canada, V8N 2Y2

3DLR

Institute of Networked Energy Systems, 26129 Oldenburg, Germany

*[email protected]

KEYWORDS: light-trapping, nano-photonics, localized surface plasmons, photovoltaics, solar cells

ACS Paragon Plus Environment

1

ACS Applied Energy Materials 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 39


2

Page 3 of 39 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


ABSTRACT Plasmonic nanoparticles were once sought to harness enormous potential for light-trapping in inorganic thin-film photovoltaics. However, the incorporation of such metallic nanostructures near solar cell absorbing layers without inducing overall harm to performance has proven to be a major obstacle. Herein, we demonstrate a solar cell design which integrates a periodic array of plasmonic Ag nanoparticles within the p-i-n structure of a-Ge:H ultra-thin optical cavity solar cells. The plasmonic solar cells showed a 33% short-circuit current density increase relative to geometrically identical cells where the Ag nanoparticles were replaced by SiO2.

We

experimentally mapped the localized surface plasmon excitations on the surface of Ag nanoparticles embedded in the optoelectronic device using electron energy loss spectroscopy and correlated the results to the device performance. Using 3-dimensional optical simulations, we further explored the light-trapping mechanisms responsible for the observed performance enhancements. The nanostructured cells produced localized and tunable charge carrier generation enhancements while maintaining the planar geometry of the ultra-thin absorbing layer. Therefore, this design concept provides a direct and useful avenue for initial light-trapping efforts in next-generation photovoltaics based on ultrathin nanoabsorbers, such as few layer transition metal dichalcogenides.

Keywords: Plasmonic solar cell, metallic nanoparticles, photovoltaic devices, surfaceplasmon resonance, TMDC


3


Page 4 of 39


4

Page 5 of 39 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


INTRODUCTION Cost reductions, improved environmental sustainability, and unique opportunities for building integration are the driving factors behind thin-film photovoltaics (PV). However, thin-film solar cells typically suffer from low light absorption predominantly near the bandgap. Wavelength scale nanostructures, such as photonic crystals,1-2 diffraction gratings,3-9 optical resonant cavities,10-13 and plasmonic nanostructures,14-24 have been explored for their abilities to trap light inside absorbing layers and subsequently increase charge carrier generation. Light-trapping by nanoparticle (NP) arrays has received much attention for inorganic thin-film solar cells since recent advances in nanofabrication techniques permit the facile incorporation of such structures on the solar cell front14, 16, 22-24 and back contacts,3, 5-8, 20, 21, 25-30 with control over NP material, size, and periodicity.31-35 Although plasmonic effects in metallic NPs were sought to harness enormous light-trapping potential due to their large scattering and absorption cross sections at the localized surface plasmon resonance (LSPR)

4, 36-39,

the experimental realization of


5


such benefits has proven to be a major challenge

40.

Page 6 of 39

Periodic NP arrays placed on the

back contact have been shown to increase current generation via diffraction modes of the 2-dimensional grating coupling into transverse optical waveguide modes within the solar cell absorbing layers.3,

25

The nature of the NP material, whether metallic or

dielectric, played little role in the coupling efficiency in that case, and plasmonic near and far-field effects did not seem to contribute significantly to performance enhancements.20 Random arrays of plasmonic NPs on the front contact generally yield decreased light in-coupling to the semiconducting absorber due to thermal losses in the NP and Fano resonance effects giving rise to increased reflections at wavelengths below the LSPR.14, 16, 41, 42 Broadband enhanced current generation has been achieved by embedding periodic metallic NP arrays in dielectric anti-reflective coatings (ARCs), but this requires the careful tailoring of both the diffractive and the plasmonic scattering effects.43 In regards to plasmonic NPs embedded within the absorbing layers of inorganic solar cells, we are not aware of any published experimental work that shows overall performance enhancements. This is likely due to NP-induced cell shunting and charge carrier recombination near the NP (metallic) surface in real devices.15 Full-area


6

Page 7 of 39 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


closed buffer layers deposited between the NP and absorbing semiconducting layers have been applied to avoid these electronic losses, but they resulted in significantly reduced plasmonic near-field intensity in the absorber region, and thus nullify any nearfield plasmonic benefit to charge carrier generation.20 Moreover, the relatively fast nonradiative relaxation of surface plasmons leads to ohmic losses and thus parasitic absorption. Due to the discussed disadvantages of metallic NPs in thin-film solar cells, the overall interest in plasmonic light-trapping schemes has declined in the past halfdecade. Currently, transition metal dichalcogenides (TMDC) monolayers have emerged as an exciting class of materials for optoelectronic devices due to their excellent light absorption properties and semiconducting characteristics.44, 45 However, a single pass through a TMDC monolayer still leads to less than 11% light absorption due to the 2dimensional nature of the material and is not sufficient for use in solar cells without additional absorption enhancement.46 As the first working solar cell devices based on TMDC 2-dimensional absorbers emerge in the scientific literature, there will be a renewed interest in light-trapping by plasmonic materials due to their unique ability to


7


Page 8 of 39

concentrate light-energy on the nanometer scale. For such nanostructure design concepts to be applicable in TMDC-based solar cells, the plasmonic nanostructures and their growth process must be compatible with delicate 2-dimensional absorbing layers, and thus must not rely on their conformal growth over structured or rough substrates.

In this work, we employed a resonant-cavity-enhanced a-Ge:H nanoabsorber solar cell as a model system for 2-dimensional absorber devices. This model system allowed us to develop and test new light-trapping concepts before working large-scale TMDC solar cells are available. We placed plasmonic NPs above and adjacent to the aGe:H layer to effectively couple in plasmonic light-scattering contributions while maintaining the horizontal planar geometry of the ultra-thin absorber. By locally encapsulating the plasmonic NPs in SiO2, we minimized the previously discussed detrimental effects of direct contact between the metallic NPs and the n-i-p solar cell structure. We then used the working solar cells to demonstrate, for the first time, the use of electron energy loss spectroscopy (EELS) within a scanning transmission electron microscope (STEM) to map the surface plasmon resonances of a metallic NP


8

Page 9 of 39 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


embedded in an optoelectronic device. By correlating these maps to the performance of our devices, we confirmed enhanced current generation from LSPR effects. We additionally used full 3-dimensional finite-difference time-domain (FDTD) optical simulations to support and further explore our experimental results. This work illustrates a plasmonic-based light-trapping design that can be directly transferred to other ultrathin solar cell technologies, such as emerging TMDC PV.

RESULTS AND DISCUSSION

Solar Cell Structure. Figure 1 (a) shows a schematic of the solar cell layer stack used in this work. The design is centered around a 25 nm intrinsic (i) a-Ge:H absorber layer. Beneath the absorber is 50 nm of intrinsic a-Si:H that acts as a spacer layer followed by 50 nm of n-doped a-Si:H that serves as the electron transport layer. The a-Ge:H absorber is covered above by a 10 nm intrinsic μc-Si:H buffer layer followed by 80 nm of p-doped μc-Si:H as the hole transport layer. The thicknesses of the Si layers were tuned


9


Page 10 of 39

such that the optical cavity resonance positioning overlaps effectively with the a-Ge:H absorber.

10-12

These semiconductor layers form the p-i-n solar cell diode framework

which is sandwiched by 80 nm transparent conducting oxide (TCO) electrode layers on the top and bottom. The solar cell is fabricated on top of a Ag coated glass substrate. The plasmonic version of the cell incorporates an array of SiO2 encapsulated Ag NPs embedded within the intrinsic μc-Si:H buffer layer (see Fig. 1(b)). The bottom edges of the Ag NPs are approximately 10 nm from the a-Ge:H absorber, which is within the plasmonic evanescent near-field decay length.20 A reference cell where Ag is replaced by SiO2 in the NP array was also fabricated. This reference cell preserves the geometry of the plasmonic solar cell, while avoiding the light-trapping effects related to localized surface plasmons. The pyramidal shape of the individual NPs allows for the investigation of various distinct surface plasmon modes and thus these NPs serve as an interesting platform for EELS surface plasmon mapping.47, 48

The Ag/TCO/p-i-n diode/TCO base structure of the solar cells forms a planar optical cavity that can support Fabry-Pérot resonant modes. Coupling of incident light to


10

Page 11 of 39 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


these optical cavity modes is indicated as “light-trapping mechanism 1” in Figure 1 (a). The contribution from these resonant modes to increase current generation in a-Ge:H nanoabsorber solar cells has been thoroughly investigated by Steenhoff et al.10-12 “Light-trapping mechanisms 2 and 3” in Figure 1 (a) arise from the periodic NP array that is embedded within the optical cavity. In particular, “light-trapping mechanism 2” represents the excitation of transverse waveguide modes within the solar cell coupled in by diffraction from the periodic NP array, as discussed by Ferry et al.3, 25 “Light-trapping mechanism 3” represents near and far-field scattering effects from LSPR modes of the individual metallic NPs.


11


Page 12 of 39

Figure 1. (a) Schematic representation of solar cell layer stack showing the three light-trapping mechanisms in our devices, namely (1) optical cavity standing waves, (2) transverse waveguide excitation, and (3) plasmonic scattering effects. (b) NP array configuration within solar cell layer stack and general structure of the encapsulated plasmonic NPs. Top view SEM images of the NP array before (c) and after (d) deposition of the p-doped μc-Si:H and top TCO contact, respectively. (e) Cross-sectional STEM image showing the solar cell layer stack and one Ag NP with an elemental map inset.

Figure 1 (c) and (d) show top view scanning electron microscope (SEM) images of the NP array before and after growth of the p-doped μc-Si:H and TCO layers, respectively. Both images indicate that the p-doped μc-Si:H and TCO conform around the NP pyramidal geometry to form protruding dome-shaped structures on the top surface of the cell. Figure 1 (e) is a cross sectional bright-field (BF) STEM image centered on a single plasmonic NP inside the cell. The inset shows an element map


12

Page 13 of 39 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


around the NP obtained via energy dispersive x-ray spectroscopy (EDX). The a-Ge:H absorber can be clearly identified as a full closed layer despite having a thickness of only 25 nm.

Device Performance. Figure 2 shows J-V curves of the plasmonic (Ag NP) solar cell, the nanostructured reference cell (where the Ag is substituted by SiO2 NPs), and a flat reference cell without NPs. The table inset shows the corresponding values of the shortcircuit current density (JSC), open-circuit voltage (VOC), fill-factor (FF), and power conversion efficiency (PCE). The Ag NP cell shows a 33% JSC increase relative to the SiO2 NP cell. This is among the largest relative JSC enhancement obtained from a direct comparison between plasmonic and non-plasmonic nanostructures of the same shape. Although Figure 2 shows that the Ag NP cell gives a slight drop in FF relative to both the SiO2 NP cell and the flat reference, the Ag NPs do not appear to reduce shunt resistance but instead lead to a rise in VOC. This increase is at least in part due to an improved splitting of the quasi-Fermi levels resulting from the higher electron-hole pair generation rate. Additionally, due to the high charge carrier density in the Ag, it can


13


Page 14 of 39

be assumed that the particles have a large impact on the local Fermi level which may lead to a preferential Fermi level alignment at the ITO/µc-Si:H interface, thus avoiding barrier-related losses. A more detailed investigation would be required to further understand this effect, but that is beyond the scope of this work,

Figure 2. J-V curves and device characteristics of optical cavity solar cells with an encapsulated Ag NP array, an SiO2 NP array, and a flat reference without NPs.

Figure 3 shows the measured (a) and simulated (b) quantum efficiency (QE) spectra of the three cells shown in Figure 2. All three simulated spectra have higher absolute QE values compared to the measured spectra because the simulations assume complete extraction of all optically generated electron-hole pairs. The simulations reproduce all QE peaks present in each measured spectrum suggesting that the


14

Page 15 of 39 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


simulations successfully model all relevant light-trapping mechanisms. All spectra in Figure 3 (a) and (b) show main peaks at approximately 600 and 950 nm. The 600 nm peak corresponds to single-pass absorption within the a-Ge:H absorber while the 950 nm peak corresponds to the 2nd order Fabry-Pérot resonant mode of the optical cavity (see supporting information). The presence of either Ag or SiO2 NPs reduce both the 600 nm and 950 nm peak intensities by oblique angle scattering of the normally incident light and/or parasitic absorption.

Figure 3. Measured (a) and simulated (b) quantum efficiency (QE) spectra of optical cavity solar cells with an encapsulated Ag NP array, a SiO2 NP array, and a flat reference without NPs.

Figure 3 (a) reveals that the JSC enhancement seen in Figure 2 for the Ag NP cell originates from the 650 to 900 nm wavelength range, where there is an approximate


15


Page 16 of 39

absolute 20% QE increase over the SiO2 NP QE. This enhancement region is decorated by distinct peaks at 700 nm and just below 800 nm which are accurately reproduced in the simulated QE spectrum in Figure 3 (b). Both NP cells (Ag and SiO2) additionally show a peak at 700 nm in both the measured and simulated QE spectra. Thus, the light-trapping mechanism at 700 nm is induced by the NP array geometry, and is more efficiently coupled by the Ag NPs, whereas the light-trapping mechanism around 800 nm solely depends on the NP material. The peak around 1000 nm in the simulated spectra for both NP cells is present only as a small shoulder in the measured spectra.

Light-Trapping Mechanisms. To help identify the light-trapping mechanism at 700 nm with more confidence, Figure 4 (a) shows the measured normalized QE near the 700 nm peak of three Ag NP cells with different NP array periods (P). Clearly, an increase in NP array period produces a red-shift in the QE peak. The peak widths and shapes vary between cells from the presence of defects in the NP lattice due to both the variations during the device fabrication and changing overlap with other resonant


16

Page 17 of 39 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


modes. Figure 4 (b) shows the simulated electric fields intensity (|E|2) profiles within the SiO2 NP cell (left) and the Ag NP cell (right), each with P = 607 nm, at 700 nm illumination wavelength. Both the cross-sectional view (top) and view within the horizontal plane of the a-Ge:H absorber (bottom) are shown. The scaling of the electric field intensity is the same in all four profiles and the dashed circles in the horizontal plane profiles represent the projected NP locations within the a-Ge:H layer. The profiles within the plane of the a-Ge:H absorber reveal distinct electric field patterns which are similar for the Ag and SiO2 NP cells, apart from shadowing below the Ag NPs and slight localized field enhancements along the sides of the Ag NPs.

Such localized field

enhancements are characteristic of the plasmonic near-field distribution of pyramidal NPs; however, they likely contribute insignificantly to the current generation of the solar cell due to their overlap with the μc-Si:H layer.47 The results presented in Figure 4 (a) and (b) support that the light-trapping mechanism at 700 nm is likely the coupling of non-zero order grating modes of the 2-dimensional nanostructure array to transverse waveguide modes within the solar cell optical cavity, as discussed previously and labelled as “light trapping mechanism 2” in Figure 1 (a). This agrees well with previous


17


Page 18 of 39

comparisons of Ag and SiO2 NPs in a-Si:H solar cells that show the two nanoparticle materials give similar QE enhancements compared to flat references at 700 nm.20 Interestingly, the 2-dimesional grating of TCO domes on the top surface of the nanostructured cells act as the primary diffractive in-coupling structure as opposed to the NP array itself (see supporting information). In conclusion, the light-trapping mechanism at 700 nm is non-plasmonic in nature, although both the measured and simulated QE spectra suggest that it is additionally enhanced by plasmonic effects.

Figure 4.Waveguide modes at 700 nm. (a) Measured quantum efficiency (QE) spectra normalized to peak value near 700 nm of three optical cavity cells with encapsulated Ag NP arrays of different periods (P). (b) Simulated electric field intensity profiles at 700 nm inside the optical cavity cell with an SiO2 NP array (left) and an encapsulated Ag NP array (right).


18

Page 19 of 39 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


On the contrary, the light-trapping mechanism just below 800 nm in Figure 3 (a) and (b) is plasmonic in nature. This can be seen in Figure 5 (a) which shows the measured QE spectra from 750 nm to 875 nm of three cells with arrays of NPs with varying Ag core to SiO2 encapsulate thickness volume ratios. The overall NP size (100 nm) is kept approximately constant to probe material effects rather than cell geometry effects. The QE benefits significantly from a higher Ag volume fraction. In addition, the QE peak in Figure 5 (a) shows a slight blue-shift with increasing Ag fraction. A wavelength shift in the LSPR of plasmonic NPs is expected with a change in NP size, shape, and surrounding material, all of which are varied by changing the Ag volume fraction. Figure 5 (b) shows the simulated electric field intensity profiles within the cell with the SiO2 NP array (left) and the cell with the encapsulated Ag NP array (right) at 800 nm. Both the cross-sectional view (top) and horizontal view within the a-Ge:H absorber (bottom) are shown. Figure 5 (b) shows that the Ag NP array provides a substantial overall field enhancement within the entire optical cavity and specifically within the a-Ge:H absorber compared to the cell with the SiO2 NP array, suggesting the light-trapping mechanism at


19


Page 20 of 39

800 nm originates purely from the LSPR near- and far-field scattering effects of the Ag NPs. This result may help explain why previous work concerning a-Si:H cells with similarly shaped and sized Ag NPs did not show any significant plasmonic enhancements, since 800 nm is beyond the absorption range of a-Si:H.20 These field profiles demonstrate the ability for plasmonic NPs to localize charge carrier generation, which has benefits particularly for nanoabsorber materials such as TMDC monolayer and few layer absorber devices.

Figure 5.Plasmonic modes at 800 nm. (a) Measured quantum efficiency (QE) spectra of three optical cavity cells with encapsulated Ag NP arrays of different Ag to SiO2 volume ratios. (b) Simulated electric field intensity profiles at 800 nm inside the optical cavity cell with an SiO2 NP array (left) and an encapsulated Ag NP array (right).


20

Page 21 of 39 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


To further investigate the role of LSPRs in our solar cells, STEM-EELS was used to directly visualize the plasmon modes of a single Ag NP embedded in the solar cell layer stack. The same characterization was done for a SiO2 NP to serve as a nonplasmonic reference. Figure 6 (a) shows a cross-sectional dark-field STEM image centered around a Ag NP. Figure 6 (b) shows electron energy loss maps in the region imaged in (a) taken at four different electron energy loss values with the outline of the Ag NP shown in black. Figure 6 (c) shows a cross-sectional dark-field STEM image centered around a SiO2 NP embedded in the solar cell stack (grey channel) overlaid with an electron energy loss map at 22 eV (green channel) to enhance the contrast of the SiO2 NP within the μc-Si:H layer. Figure 6 (d) shows the corresponding electron energy loss maps to Figure 6 (b) for the SiO2 NP cell. The contrast of each energy loss map was chosen to best highlight the different effects of the Ag and SiO2 NPs.

At 315 nm in Figure 6 (b), the dominant electron energy loss mechanism can be attributed to interband transitions within the Ag NP. The corresponding map in Figure 6 (d) shows the SiO2 NP does not induce the same energy loss intensity and instead


21


Page 22 of 39

results in less intense energy loss than the surrounding semiconducting layers. As 315 nm is outside the operational range of the solar cell, these observed interband transitions in the Ag NP do not hinder solar cell performance. At 620 nm, the dominant electron energy loss for both the Ag and SiO2 NP cells occurs in the a-Ge:H layer. This may be attributed to electron-hole pairs excited by the incident electron beam, which has been studied by STEM-EELS in other semiconducting materials in the past.

49, 50

In

fact, this explanation agrees well with Figure 3 (a) where the measured QE for both the Ag and SiO2 NP cells peak around 600 nm, which we have shown to arise from single pass absorption within the a-Ge:H absorber.

At 750 nm and 825 nm in Figure 6 (b), there is high intensity electron energy loss around the surface of the Ag NP whereas no such losses exist for the SiO2 NP in Figure 6 (d). These energy loss characteristics suggest they originate from LSPR modes of the Ag NP and it appears that 750 nm and 825 nm may each correspond to a distinct resonant mode. The mode at 750 nm is distributed around the top surface of the NP while the mode at 825 nm is focused at the bottom corners of the NP. This result further


22

Page 23 of 39 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


supports that the QE enhancement of the Ag NP cell over the SiO2 NP cell between 650 and 900 nm in Figure 3 (a) arises from near- and far-field scattering contributions of the LSPRs of the Ag NPs. To our best knowledge, this is the first-time direct experimental evidence has been used to verify plasmonic enhancements in thin-film solar cells.

The LSPR resonant modes mapped in Figure 6 (b) do not show a clear and distinct field distribution, like those seen in previous STEM-EELS work focused on LSPR mapping of well-defined and isolated metallic nanostructures.

47, 48

This is

expected as our metallic nanostructures are embedded in semiconductor devices that not only result in a low surface plasmon loss signal, but additionally give rise to other loss mechanisms at similar energies such as electron-hole pair generation. The brightness in the bottom left of the 750 and 825 nm maps in Figure 6 (b) can be attributed to plasmonic resonances in an Ag flake that has broken off from the NP during device fabrication, which can be distinctly seen in Figure 6 (a). In addition, the specimens shown in Figure 6 are thin (< 100 nm thick) cross-sections that contain only slices of the NPs as opposed to the full NPs and thus the imaged LSPR modes likely


23


Page 24 of 39

only resemble the true modes of the Ag NPs. Nonetheless, the direct comparison between plasmonic and non-plasmonic NPs shown in Figure 6 provides sufficient evidence to suggest that the Ag NPs in our solar cells support LSPRs around 750 and 825 nm, which matches well with both the simulated and measured QE spectra.

Figure 6. (a) Cross-sectional dark-field STEM image centered around a Ag NP embedded in the solar cell layer stack, (b) electron energy loss intensity maps within the region depicted in (a) with outline of the Ag NP, (c) cross-sectional dark-field STEM image centered around a SiO2 NP superimposed with an electron energy loss spectrum image at 22 eV(green channel), and (d) electron energy loss intensity maps within the region depicted in (c) with outline of the SiO2 NP. Scalebars in (a) and (c) are 50 nm.

CONCLUSION The incorporation of plasmonic NPs within inorganic thin-film solar cells has been widely investigated in the scientific literature for their promising light-trapping properties but the


24

Page 25 of 39 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


experimental realizations have not met expectations. In this work, we incorporate periodic arrays of plasmonic Ag NPs adjacent to the absorber in ultra-thin a-Ge:H optical cavity solar cells. The Ag NPs were buffered with thin SiO2 layers to minimize the detrimental effects of metallic NPs within the p-i-n solar cell layer stack. We observed a striking 33% JSC enhancement for cells with Ag NP arrays compared to cells with geometrically identical SiO2 NP arrays. Experimentally measured QE spectra were reproduced accurately using full 3-dimensional FDTD electromagnetic simulations. Furthermore, we applied STEM-EELS to map the LSPR modes of a plasmonic NP embedded in a working device for the first time and found results correspond well with the solar cell performance. The localization and tunability of charge carrier generation enhancements by plasmonic NPs without disrupting the planar geometry of the ultra-thin absorbing layer demonstrated in this work provides a direct and useful avenue for initial lighttrapping efforts in next-generation 2-dimensional monolayer absorber PV.

EXPERIMENTAL METHODS Solar Cell Fabrication: Silicon and germanium layers were grown by plasma-enhanced chemical vapor deposition (PECVD), TCOs were grown by dc magnetron sputtering, and Ag and SiO2 layers were deposited by e-beam evaporation. Indium tin oxide (ITO) was used as the top TCO while aluminum doped zinc oxide (AZO) was used as the bottom TCO. Further deposition details along with a more detailed description of the


25


Page 26 of 39

base structure of the optical cavity solar cell can be found in works by Steenhoff et al..10, 11

Solar cells were grown on 5 x 5 cm² glass substrates and cell areas of 0.2 cm2 were

defined by structuring the front TCO using a marker lift-off process.

NP Synthesis: NP arrays were fabricated using nanosphere lithography as described in detail in previous work by our group.20 In short, a self-assembled hexagonally packed monolayer of polystyrene beads, purchased from microParticles GmbH Berlin with 607 nm diameter (unless otherwise indicated) was used as an evaporation mask covering the entire 5 x 5 cm² solar cell substrate. Nanosphere lithography has been demonstrated to effectively nanostructure module-sized areas

31.

Ag was chosen as the

plasmonic NP material because 100 nm Ag NPs have a surface plasmon resonance wavelength within the conversion range of our solar cells.20 The encapsulated Ag NPs were fabricated by electron-beam evaporating in a SiO2 (5nm)/Ag (90nm)/ SiO2 (5nm) sequence through the nanosphere mask while SiO2 NPs were fabricated by only evaporating 100 nm of SiO2. This NP encapsulation eliminates the need for a full area closed diffusion buffer layer between the metallic NP array and the semiconducting


26

Page 27 of 39 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


layers, which is typically required to prevent Ag contamination of the PECVD chambers during solar cell fabrication. Thus, this NP encapsulation technique permits the NP array to be placed within the p-i-n diode structure without destroying the electrical integrity of the solar cell.

Solar Cell Characterization: SEM images were taken with a Hitachi S-4800 FESEM (Field Emission SEM) and STEM images were taken with Hitachi HF-3300V S/TEM (Scanning Transmission Electron Microscope) equipped with a Bruker XFlash Detector 5030 EDX system. Cross-sectional specimens for imaging STEM-EELS were prepared via a standard lift-out technique using a Hitachi FB-2100 FIB (Focused Ion Beam). STEM-EELS measurements were performed at 200 kV and energy filtering to 0.05 eV resolution was accomplished using a Gatan Quantum SE spectrometer. The electron beam probe was rastered over the cross-sectional specimen to obtain spectrum images of 28 (width) x 24 (height), 7.1 nm square pixels with 5 spectra per pixel at a dwell time of 0.5 sec per spectrum. The beam convergence half angle was 8 mrad and the collection half angle was 10 mrad. Spectrum image analysis was accomplished using


27


Page 28 of 39

MATLAB based software produced by Krenn et al..51 Useful data was separated from the zero-loss peak via Richardson-Lucy deconvolution using the zero-loss peak spectrum measured in vacuum as the point spread function. J-V curves were measured under AM1.5g illumination at standard test conditions using a WACOM dual lamp solar simulator. QE spectra were determined by differential spectral response measurements at 0V bias and were scaled according to the measured JSC as a means of negating any additional contact resistance arising from the conformally nanostructured top contact.

Simulation: 3-dimensional optical simulations of the solar cells were done using the commercially available Lumerical FDTD Solutions software. The simulated QE was calculated as the sum of the electromagnetic energy absorbed in all the intrinsic semiconductor layers of the solar cell as a fraction of the total incident electromagnetic energy from the plane wave source and thus assumes full charge carrier extraction. Further simulation details can be found in the supporting information.


28

Page 29 of 39 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



29


Page 30 of 39

Associated Content Supporting Information Available: Additional simulation details and additional results including more measured and simulated quantum efficiency spectra of flat optical cavity solar cells and simulated animations of electric field profiles showing transverse waveguide

mode

excitation.

This

material

is

available

free

of

charge

at

http://pubs.acs.org.

Author Information Corresponding Author *Tel: +1 (250) 721-7167. Fax: +1 (250) 721-7147. E-mail: [email protected] Notes The authors declare no competing financial interest.

Acknowledgments The authors would like to thank M. Kellermann and M. Barg for plasma-enhanced chemical vapor depositions, and C. Lattyak, R. Ravekes, and P. H. Wang for fruitful discussions.


30

Page 31 of 39 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


Funding Sources This work was partially funded by the Natural Sciences and Engineering Research Council of Canada (NSERC) – Collaborative Research and Training Experience Program (CREATE). B. Brady acknowledges funding from the exchange program IPID4all - Mobile Doctorates in System Integration of Renewable Energy, which is funded by the DAAD (German Academic Exchange Service).

Abbreviations PV, photovoltaic; NP, nanoparticle; LSPR, localized surface plasmon resonance; ARC, anti-reflective coating; TMDC, transition metal dichalcogenides; STEM, scanning transmission electron microscope; EELS, electron energy loss spectroscopy; FDTD, finite-difference time-domain; TCO, transparent conducting oxide; SEM, scanning electron microscope; BF, bright field; EDX, energy dispersive x-ray spectroscopy; JSC short-circuit current density; VOC, open-circuit voltage; FF, fill factor; PCE, power conversion efficiency; QE, quantum efficiency; P, period; PECVD, plasma-enhanced chemical vapor deposition; ITO, indium tin oxide; AZO, aluminum zinc oxide; FESEM, field emission scanning electron microscope; STEHM, scanning transmission electron holography microscope; FIB, focused ion beam.


31


Page 32 of 39

References 1. 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, 16986-17000. 2. De Zoysa, M.; Ishikazi, K.; Tanaka, Y.; Sai, H.; Matsubara, K.; Noda, S. Enhanced Efficiency of Ultrathin (~500 nm)-Film Microcrystalline Silicon Photonic Crystal Solar Cells. Appl. Phys. Express 2017, 10, 0123021-0123024. 3. Ferry, V. E.; Verschuuren, M. A.; Li, H. B. T.; Verhagen, E.; Walters, R. J.; Schropp, R. E. I.; Atwater, H. A.; Polman, A. Light Trapping in Ultrathin Plasmonic Solar Cells. Opt. Express 2010, 18, A237-A245. 4. Pala, R. A.; White, J.; Barnard, E.; Liu, J.; Brongersma, M. L. Design of Plasmonic Thin-Film Solar Cells with Broadband Absorption Enhancements. Adv.

Mater. 2009, 21, 3504-3509. 5. Pahud, C.; Savu, V.; Klein, M.; Vazquez-Mena, O.; Haug, F.-J.; Brugger, J.; Ballif, C. Stencil-Nanopatterned Back Reflectors for Thin-Film Amorphous Silicon n-i-p Solar Cells. IEEE J. Photovolt. 2013, 3, 22-26. 6. Smeets, M.; Smirnov, V.; Meier, M.; Bittkau, K.; Carius, R.; Rau, U.; Paetzold, U. W. On the Geometry of Plasmonic Reflection Grating Back Contacts for Light Trapping in Prototype Amorphous Silicon Thin-Film Solar Cells. J. Photonics

Energy 2014, 5, 0570041-05700411. 7. Bhattacharya, J.; Chakravarty, N.; Pattnaik, S.; Slafer, W. D.; Biswas, R.; Dalal, V. L. A Photonic-Plasmonic Structure for Enhancing Light Absorption in Thin Film Solar Cells. Appl. Phys. Lett. 2011, 99, 1311141-1311143.


32

Page 33 of 39 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


8. Sai, H.; Kondo, M. Effect of Self-Orderly Textured Back Reflectors on Light Trapping in Thin-Film Microcrystalline Silicon Solar Cells. J. Appl. Phys. 2009,

105, 0945111-0945118. 9. Lattyak, C.; Ravekes, R.-E.; Steenhoff, V.; Vehse, M.; Agert, C. Ultrathin Resonant-Cavity-Enhanced Amorphous Germanium Solar Cells on ZnO Honeycomb Electrodes. IEEE J. Photovolt. 2018, 8, 3-7. 10. Steenhoff, V.; Theuring, M.; Vehse, M.; von Maydell, K.; Agert, C. Ultrathin Resonant-Cavity-Enhanced Solar Cells with Amorphous Germanium Absorbers.

Adv. Opt. Mater. 2015, 3, 182-186. 11. Steenhoff, V.; Neumüller, A.; Sergeev, O.; Vehse, M.; Agert, C. Integration of a-Ge:H Nanocavity Solar Cells in Tandem Devices. Sol. Energy Mater. Sol. Cells 2016, 145, 148-153. 12. Steenhoff, V.; Juilfs, M.; Ravekes, R.-E.; Vehse, M.; Agert, C. Resonant-CavityEnhanced a-Ge:H Nanoabsorber Solar Cells for Application in Multijunction Devices. Nano Energy 2016, 27, 658-663. 13. Kats, M. A.; Blanchard, R.; Genevet, P.; Capasso, F. Nanometre Optical Coatings Based on Strong Interference Effects in Highly Absorbing Media. Nat.

Mater. 2013, 12, 20-24. 14. Beck, F. J.; Polman, A.; Catchpole, K. R. Tunable Light Trapping for Solar Cells Using Localized Surface Plasmons. J. Appl. Phys. 2009, 105, 1143101-1143107. 15. Santbergen, R.; Liang, R.; Zeman, M. a-Si:H Solar Cells with Embedded Silver Nanoparticles. 35th IEEE Photovoltaics Specialists Conference 2010, 748-753. 16. Daif, O. E.; Tong, L.; Figeys, B.; Van Nieuwenhuysen, K.; Dmitriev, A.; Van Dorpe, P.; Gordon, I.; Dross, F. Front Side Plasmonic Effect on Thin Silicon Epitaxial Solar Cells. Sol. Energ. Mat. Sol. Cells 2012, 104, 58-63. 17. Kulkarni, A. P.; Noone, K. M.; Munechika, K.; Guyer, S. R.; Ginger, D. S. PlasmonEnhanced Charge Carrier Generation in Organic Photovoltaic Films Using Silver Nanoprisms. Nano Lett. 2010, 10, 1501-1505.


33


Page 34 of 39

18. Diukman, I.; Tzabari, L.; Berkovitch, N.; Tessler, N.; Orenstein, M. Controlling Absorption Enhancement in Organic Photovoltaic Cells by Patterning Au Nano Disks within the Active Layer. Opt. Express 2010, 19, A64-A71. 19. Choi, H.; Lee, J.-P.; Ko, S.-J.; Jung, J.-W.; Park, H.; Yoo, S; Park, O.; Jeong, J.R.; Park, S.; Kim, J. Y. Multipositional Silica-Coated Silver Nanoparticles for HighPerformance Polymer Solar Cells. Nano Lett. 2013, 13, 2204-2208. 20. Theuring, M.; Wang, P. H.; Vehse, M.; Steenhoff, V.; von Maydell, K.; Agert, C.;

Brolo, A. G. Comparison of Ag and SiO2 Nanoparticles for Light Trapping Applications in Silicon Thin Film Solar Cells. J. Phys. Chem. Lett. 2014, 5, 3302-3306. 21. Paetzold, U. W.; Moulin, E.; Michaelis, D.; Böttler, W.; Wächter, C.; Hagemann, V.; Meier, M.; Carius, R.; Rau, U. Plasmonic Reflection Grating Back Contacts for Microcrystalline Silicon Solar Cells. Appl. Phys. Lett. 2011, 99, 1811061-1811063. 22. Schuster, C. S.; Morawiec, S.; Mendes, M. J.; Patrini, M.; Martins, E. R.; Lewis, L.; Crupi, I.; Krauss, T. F. Plasmonic and Diffractive Nanostructures for Light Trapping – An Experimental Comparison. Optica 2015, 2, 2334-2536. 23. Matheu, P.; Lim, S. H.; Derkacs, D.; McPheeters, C.; Yu, E. T. Metal and Dielectric Nanoparticle Scattering for Improved Optical Absorption in Photovoltaic Devices.

Appl. Phys. Lett. 2008, 93, 1131081-1131083. 24. Uhrenfeldt, C.; Villesen, T. F.; Johansen, B.; Jung, J.; Pedersen, T. G.; Nylandsted Larsen, A. Diffractive Coupling and Plasmon-Enhanced Photocurrent Generation in Silicon.

Opt. Express 2013, 21, A774-A785. 25. Ferry, V. E.; Verschuuren, M. A.; Clair van Lare, M.; Schropp, R. E. I.; Atwater, H. A.; Polman, A. Optimized Spatial Correlations for Broadband Light Trapping Nanopatterns in High Efficiency Ultrathin Film a-Si:H Solar Cells. Nano Lett. 2011,

10, 4239-4245. 26. Hsu, C.-M.; Battaglia C.; Pahud, C.; Ruan, Z.; Haug, F.-J.; Fan, S.; Ballif, C.; Cui, Y. HighEfficiency Amorphous Silicon Solar Cell on a Periodic Nanocone Back Reflector.

Adv. Energ. Mater. 2012, 2, 628-633.


34

Page 35 of 39 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


27. Yan, W.; Tao, Z.; Ong, T. M. B.; Gu, M. Highly Efficient Ultrathin-Film Amorphous Silicon Solar Cells on Top of Imprinted Periodic Nanodot Arrays. Appl. Phys. Lett. 2015, 106, 0939021-0939024.

28. Pattnaik, S.; Chakravarty, N.; Biswas, R.; Dalal, V.; Slafer, D. Nano-Photonic and Nano-Plasmonic Enhancements in Thin Film Silicon Solar Cells. Sol. Energ. Mater.

& Sol. Cells 2014, 129, 115-123. 29. van Dijk, L.; van de Groep, J.; Veldhuizen, L. W.; Vece, M. D.; Polman, A.; Schropp, R. E. I. Plasmonic Scattering Back Reflectors for Light Trapping in Flat NanoCrystalline Silicon Solar Cells. ACS Photonics 2016, 3, 685-691. 30. Wang, P. H.; Nowak, R.-E.; Geißendörfer, S.; Vehse, M.; Reininghaus, N.; Sergeev, O.; von Maydell, K.; Brolo, A. G.; Agert, C. Cost-Effective Nanostructured Thin-Film Solar Cell with Enhanced Absorption. Appl. Phys. Lett. 2014, 106, 18310611831065.

31. Gao, P.; He, J.; Zhou, S.; Yang, X.; Li, S.; Sheng, J.; Wang, D.; Yu, T.; Ye, J.; Cui, Y. Large-Area Nanosphere Self-Assembly by a Micro-Propulsive Injection Method for High Throughput Periodic Surface Nanotexturing. Nano Lett. 2015, 15, 4591-4598. 32. Gao, T.; Wang, B.; Ding, B.; Lee, J.-k.; Leu, P. W. Uniform and Ordered Copper Nanomeshes by Microsphere Lithography for Transparent Electrodes. Nano Lett. 2014, 4, 2106-2110. 33. Ho, W.-J.; Cheng, P.-Y.; Hsiao, K.-Y. Plasmonic Silicon Solar Cell Based on Silver Nanoparticles Using Ultra-Thin Anodic Aluminum Oxide Template. Appl. Surf. Sci. 2015, 354, 25-30. 34. Yesilkoy, F.; Flauraud, V.; Ruegg, M.; Kim, B. J.; Brugger, J. 3D Nanostructures Fabricated by Advanced Stencil Lithography. Nanoscale 2016, 8, 4945-4950. 35. Chanda, D.; Shigeta, K.; Gupta, S.; Cain, T.; Carlson, A.; Mihi, A.; Baca, A. J.; Bogart, G. R.; Braun, P.; Rogers, J. A. Large-Area Flexible 3D Optical Negative Index Metamaterial Formed by Nanotransfer Printing. Nat. Nanotechnol. 2011, 6, 402-407. 36. Hägglund, C.; Apell, S. P. Plasmonic Near-Field Absorbers for Ultrathin Solar Cells.

J. Phys. Chem. Lett. 2012, 3, 1275-1285.


35


Page 36 of 39

37. Lee, J.; Peumans, P. The Origin of Enhanced Optical Absorption in Solar Cells with Metal Nanoparticles Embedded in the Active Layer. Opt. Express 2010, 18, 1007810087. 38. Mendes, M. J.; Luque, A.; Tobías, I.; Martí, A. Plasmonic Light Enhancement in the Near-Field of Metallic Nanospheroids for Application in Intermediate Band Solar Cells. Appl. Phys. Lett. 2009, 95, 0711061-0711063. 39. Rockstuhl, C.; Lederer, F. Photon Management by Metallic Nanodiscs in Thin Film Solar Cells, Appl. Phys. Lett. 2009, 94, 2131021-2131023. 40. Brady, B.; Wang, P. H.; Steenhoff, V.; Brolo, A. G. In Metallic Nanostructures for

Photonics; Kassab, L. R. P., Araujo, C. B. D., Eds.; Elsevier, 2019; Chapter 9, pp 197-221. 41. Lim, S. H.; Mar, W.; Matheu, P.; Derkacs, D.; Yu, E. T. Photocurrent Spectroscopy of Optical Absorption Enhancement via Scattering from Surface Plasmon Polaritons in Gold Nanoparticles. J. Appl. Phys. 2007, 101, 1043091-1043097. 42. Spinelli, P.; Hebbink, M.; de Waele, R.; Black, L.; Lenzmann, F.; Polman, A. Optical Impedance Matching Using Coupled Plasmonic Nanoparticle Arrays. Nano Lett. 2011, 11, 1760-1765. 43. Uhrenfeldt, C.; Villesen, T. F.; Têtu, A.; Johansen, B.; Nylandsted Larsen A. Broadband Photocurrent Enhancement and Light-Trapping in Thin Film Si Solar Cells with Periodic Al Nanoparticle Arrays on the Front. Opt. Express 2015, 23, A525-A538. 44. Wi, S.; Kim, H.; Chen, M.; Nam, H.; Guo, L. J.; Meyhofer, E.; Liang, X. Enhancement of Photovoltaic Response in Multilayer MoS2 Induced by Plasma Doping. ACS Nano 2014, 8, 5270-5281. 45. Zhang, Y.; Liu, W.; Li, Z.; Cheng, H.; Zhang, Y.; Jia, G.; Chen, S.; Tian, J. Ultrathin Polarization-Insensitive Wide-Angle Broadband Near-Perfect Absorber in the Visible Regime Based on Few-Layer MoS2 Films. Appl. Phys. Lett. 2017, 111, 11110911111095.


36

Page 37 of 39 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


46. Liu, J.-T.; Wang, T.-B.; Li, X.-J.; Liu, N.-H. Enhanced Absorption of Monolayer MoS2 with Resonant Back Reflector. J. Appl. Phys. 2014, 115, 193511. 47. Nelayah, J.; Kociak, M.; Stéphan, O.; García De Abajo, J.; Tencé, M.; Henrard, L.; Taverna, D.; Pastoriza-Santos, I.; Liz-Marzán, L. M.; Colliex, C. Mapping surface plasmons on a single metallic nanoparticle. Nat. Phys. 2007, 3, 348-353. 48. Koh, A. L.; Fernández-Domínguez, A. I.; McComb, D. W.; Maier, S. A.; Yang, J. K. W. High-Resolution Mapping of Electron-Beam-Excited Plasmon Modes in Lithographically Defined Gold Nanostructures. Nano Lett. 2011, 11, 1323-1330. 49. Wei, J.; Jiang, N.; Xu, J.; Bai. X.; Liu, J. Strong Coupling between ZnO Excitons and Localized Surface Plasmons of Silver Nanoparticles Studied by STEM-EELS. Nano

Lett. 2015, 15, 5926-5931. 50. Tizei, L. H. G.; Lin, Y.-C.; Mukai, M.; Sawada, H.; Lu, A.-Y.; Li, L.-J.; Kimoto, K.; Suenaga, K. Exciton Mapping at Subwavelength Scales in Two-Dimensional Materials. Phys. Rev. Lett. 2015, 114, 107601. 51. Schmidt, F.-P.; Hofer, F.; Krenn, J. R. Spectrum image analysis tool – A flexible MATLAB solution to analyze EEL and CL spectrum images. Micron 2017, 93, 23-51.


37


Page 38 of 39

TOC graphic


38

Page 39 of 39 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


176x68mm (300 x 300 DPI)


Plasmonic Light-Trapping Concept for Nanoabsorber Photovoltaics

Recommend Documents