Plasmonics for improved photovoltaic devices

Interaction between plasmonic nanoparticles revisited with transformation optics

The interaction between plasmonic nanoparticles is investigated by means of transformation optics. The optical response of a dimer can be decomposed as a sum of modes whose resonances redshift when the nanoparticles approach each other. The extinction and scattering cross sections as well as the field enhancement induced by the dimer are derived analytically taking into account radiation damping. Interestingly, some invisibility dips occur in the scattering spectrum and originate from a destructive interference between each surface plasmon mode.

Plasmon-modulated light scattering from gold nanocrystal-decorated hollow mesoporous silica microspheres

Localized surface plasmon resonances of noble metal nanocrystals are powerful in enhancing a variety of linear and nonlinear optical signals and photorelated processes. Here we demonstrate the plasmonic enhancement of the light scattering from hollow mesoporous silica microspheres by attaching a dense layer of gold nanocrystals onto the outer surface of the microspheres. The attachment of gold nanocrystals induces both the shift and intensity increase in the resonant scattering peaks of the microspheres. The spectral region of the resonant scattering enhancement can be controlled by using gold nanocrystals with different plasmon resonance wavelengths. The spectral region of the enhancement is independent of the microsphere diameter. The scattering enhancement factor ranges from 20 to 130, depending on the plasmonic properties and surface coverage of the attached gold nanocrystals. The systematic evolution of the scattering spectra of the individual microspheres is also revealed by chemically etching away the attached gold nanocrystals gradually.

Transfer-matrix formalism for the calculation of optical response in multilayer systems: from coherent to incoherent interference

We present a novel way to account for partially coherent interference in multilayer systems via the transfer-matrix method. The novel feature is that there is no need to use modified Fresnel coefficients or the square of their amplitudes to work in the incoherent limit. The transition from coherent to incoherent interference is achieved by introducing a random phase of increasing intensity in the propagating media. This random phase can simulate the effect of defects or impurities. This method provides a general way of dealing with optical multilayer systems, in which coherent and incoherent interference are treated on equal footing.

Surface plasmon field enhancements in deterministic aperiodic structures

In this paper we analyze optical properties and plasmonic field enhancements in large aperiodic nanostructures. We introduce extension of Generalized Ohm's Law approach to estimate electromagnetic properties of Fibonacci, Rudin-Shapiro, cluster-cluster aggregate and random deterministic clusters. Our results suggest that deterministic aperiodic structures produce field enhancements comparable to random morphologies while offering better understanding of field localizations and improved substrate design controllability. Generalized Ohm's law results for deterministic aperiodic structures are in good agreement with simulations obtained using discrete dipole method.

Design considerations for plasmonic photovoltaics

This paper reviews the recent research progress in the incorporation of plasmonic nanostructures with photovoltaic devices and the potential for surface plasmon enhanced absorption. We first outline a variety of cell architectures incorporating metal nanostructures. We then review the experimental fabrication methods and measurements to date, as well as systematic theoretical studies of the optimal nanostructure shapes. Finally we discuss photovoltaic absorber materials that could benefit from surface plasmon enhanced absorption.

Broadband short-range surface plasmon structures for absorption enhancement in organic photovoltaics

We theoretically demonstrate a polarization-independent nanopatterned ultra-thin metallic structure supporting short-range surface plasmon polariton (SRSPP) modes to improve the performance of organic solar cells. The physical mechanism and the mode distribution of the SRSPP excited in the cell device were analyzed, and reveal that the SRSPP-assisted broadband absorption enhancement peak could be tuned by tailoring the parameters of the nanopatterned metallic structure. Three-dimensional finite-difference time domain calculations show that this plasmonic structure can enhance the optical absorption of polymer-based photovoltaics by 39% to 112%, depending on the nature of the active layer (corresponding to an enhancement in short-circuit current density by 47% to 130%). These results are promising for the design of organic photovoltaics with enhanced performance.

Effect of gold nanopillar arrays on the absorption spectrum of a bulk heterojunction organic solar cell

We report on the effect of arrays of Au nanopillars of controlled size and spacing on the spectral response of a P3HT: PCBM bulk heterojunction solar cell. Prototype nanopillar-patterned devices have nearly the same overall power conversion efficiency as those without nanopillars. The patterned devices do show higher external quantum efficiency and calculated absorption in the wavelength range from approximately 640 nm to 720 nm, where the active layer is not very absorbing. The peak enhancement was approximately 60% at 675 nm. We find evidence that the corresponding resonance involves both localized particle plasmon excitation and multiple reflections/diffraction within the cavity formed by the electrodes. We explore the role of the attenuation coefficient of the active layer on the optical absorption of such an organic photovoltaic device.

Recent advancements in optical DNA biosensors: exploiting the plasmonic effects of metal nanoparticles

The emerging field of plasmonics, the study of electromagnetic responses of metal nanostructures, has revealed many novel signal enhancing phenomena. As applied to the development of label-free optical DNA biosensors, it is now well established that plasmon-based surface enhanced spectroscopies on nanostructured metal surfaces or metal nanoparticles can markedly improve the sensitivity of optical biosensors, with some showing great promise for single molecule detection. In this review, we first summarize the basic concepts of plasmonics in metal nanostructures, as well as the characteristic optical phenomena to which plasmons give rise. We will then describe recent advances in optical DNA biosensing systems enabled by metal nanoparticle-derived plasmonic effects, including the use of surface enhanced Raman scattering (SERS), colorimetric methods, "scanometric" processes, and metal-enhanced fluorescence (MEF).

Highly confined hybrid spoof surface plasmons in ultrathin metal-dielectric heterostructures

Highly confined "spoof" surface plasmons (SSPs) are theoretically predicted to exist in a perforated metal film coated with a thin dielectric layer. Strong modes confinement results from the additional waveguiding by the layer. Spectral characteristics, field distribution, and lifetime of these SSPs are tunable by the holes' size and shape. SSPs exist both above and below the light line, offering two classes of applications: "perfect" far-field absorption and efficient emission into guided modes. It is experimentally shown that these plasmonlike modes can turn thin, weakly absorbing semiconductor films into perfect absorbers.

The structure and growth mechanism of Si nanoneedles prepared by plasma-enhanced chemical vapor deposition

Silicon nanowires and nanoneedles show promise for many device applications in nanoelectronics and nanophotonics, but the remaining challenge is to grow them at low temperatures on low-cost materials. Here we present plasma-enhanced chemical vapor deposition of crystalline/amorphous Si nanoneedles on glass at temperatures as low as 250 °C. High resolution electron microscopy and micro-Raman spectroscopy have been used to study the crystal structure and the growth mechanism of individual Si nanoneedles. The H(2) dilution of the SiH(4) plasma working gas has caused the formation of extremely sharp nanoneedle tips that in some cases do not contain a catalytic particle at the end.

Electrospun metal nanofiber webs as high-performance transparent electrode

Transparent electrodes, indespensible in displays and solar cells, are currently dominated by indium tin oxide (ITO) films although the high price of indium, brittleness of films, and high vacuum deposition are limiting their applications. Recently, solution-processed networks of nanostructures such as carbon nanotubes (CNTs), graphene, and silver nanowires have attracted great attention as replacements. A low junction resistance between nanostructures is important for decreasing the sheet resistance. However, the junction resistances between CNTs and boundry resistances between graphene nanostructures are too high. The aspect ratios of silver nanowires are limited to ∼100, and silver is relatively expensive. Here, we show high-performance transparent electrodes with copper nanofiber networks by a low-cost and scalable electrospinning process. Copper nanofibers have ultrahigh aspect ratios of up to 100000 and fused crossing points with ultralow junction resistances, which result in high transmitance at low sheet resistance, e.g., 90% at 50 Ω/sq. The copper nanofiber networks also show great flexibility and stretchabilty. Organic solar cells using copper nanowire networks as transparent electrodes have a power efficiency of 3.0%, comparable to devices made with ITO electrodes.

Charge-selective Raman scattering and fluorescence quenching by "nanometal on semiconductor" substrates

Ag nanoparticles synthesized on n and p-type Si were shown to exhibit charge-selective surface-enhanced Raman scattering and fluorescence quenching. As revealed by electric force microscopy, the polarity and magnitude of the nanoparticle charge is controllable with the metal-semiconductor Fermi level difference and nanoparticle size. It is inferred that the Fermi level alignment is dominantly contributed by the charge-induced nanoparticle voltage. Nanoparticle charging also accounts for self-inhibition of coalescence during chemical reduction, allowing strong plasmon hybridization.

Fundamental limit of nanophotonic light trapping in solar cells

Establishing the fundamental limit of nanophotonic light-trapping schemes is of paramount importance and is becoming increasingly urgent for current solar cell research. The standard theory of light trapping demonstrated that absorption enhancement in a medium cannot exceed a factor of 4n(2)/sin(2)θ, where n is the refractive index of the active layer, and θ is the angle of the emission cone in the medium surrounding the cell. This theory, however, is not applicable in the nanophotonic regime. Here we develop a statistical temporal coupled-mode theory of light trapping based on a rigorous electromagnetic approach. Our theory reveals that the conventional limit can be substantially surpassed when optical modes exhibit deep-subwavelength-scale field confinement, opening new avenues for highly efficient next-generation solar cells.

Resource efficient plasmon-based 2D-photovoltaics with reflective support

For ultrathin (~10 nm) nanocomposite films of plasmonic materials and semiconductors, the absorptance of normal incident light is typically limited to about 50%. However, through addition of a non-absorbing spacer with a highly reflective backside to such films, close to 100% absorptance can be achieved at a targeted wavelength. Here, a simple analytic model useful in the long wavelength limit is presented. It shows that the spectral response can largely be characterized in terms of two wavelengths, associated with the absorber layer itself and the reflective support, respectively. These parameters influence both absorptance peak position and shape. The model is employed to optimize the system towards broadband solar energy conversion, with the spectrally integrated plasmon induced semiconductor absorptance as a figure of merit. Geometries optimized in this regard are then evaluated in full finite element calculations which demonstrate conversion efficiencies of up to 64% of the Shockley-Queisser limit. This is achieved using only the equivalence of about 10 nanometer composite material, comprising Ag and a thin film solar cell layer of a-Si, CuInSe₂ or the organic semiconductor MDMO-PPV. A potential for very resource efficient solar energy conversion based on plasmonics is thus demonstrated.

Fundamental limit of light trapping in grating structures

We use a rigorous electromagnetic approach to analyze the fundamental limit of light-trapping enhancement in grating structures. This limit can exceed the bulk limit of 4n², but has significant angular dependency. We explicitly show that 2D gratings provide more enhancement than 1D gratings. We also show the effects of the grating profile's symmetry on the absorption enhancement limit. Numerical simulations are applied to support the theory. Our findings provide general guidance for the design of grating structures for light-trapping solar cells.

Integrating in situ high pressure small and wide angle synchrotron x-ray scattering for exploiting new physics of nanoparticle supercrystals

Combined small and wide angle synchrotron x-ray scattering (SAXS and WAXS) techniques have been developed for in situ high pressure samples, enabling exploration of the atomic structure and nanoscale superstructure phase relations. These studies can then be used to find connections between nanoparticle surfaces and internal atomic arrangements. We developed a four-axis control system for the detector, which we then employed for the study of two supercrystals assembled from 5 nm Fe(3)O(4) and 10 nm Au nanoparticles. We optimized the x-ray energy and the sample-to-detector distance to facilitate simultaneous collection of both SAXS and WAXS. We further performed in situ high pressure SAXS and WAXS on a cubic supercrystal assembled from 4 nm wurtzite-structure CdSe nanoparticles. While wurtzite-structure CdSe nanoparticles transform into a rocksalt structure at 6.2 GPa, the cubic superstructure develops into a lamellarlike mesostructure at 9.6 GPa. Nanoparticle coupling and interaction could be enhanced, thus reducing the compressibility of the interparticle spacing above ∼3 GPa. At ∼6.2 GPa, the wurtzite-to-rocksalt phase transformation results in a noticeable drop of interparticle spacing. Above 6.2 GPa, a combined effect from denser CdSe nanoparticle causes the interparticle spacing to expand. These findings could be related to a series of changes including the surface structure, electronic and mechanical properties, and strain distribution of CdSe under pressure. This technique opens the way for exploring the new physics of nanoparticles and self-assembled superlattices.

Excitation of multiple dipole surface plasmon resonances in spherical silver nanoparticles

We observe the appearance of multiple dipole surface plasmon resonances in spherical Ag nanoparticles when embedded in an organic semiconductor that exhibits a highly dispersive permittivity. Comparing the absorption spectra of thin-films with and without Ag nanoparticles reveals the presence of two plasmon peaks. Numerical simulations and calculations based on an electrostatic model allow us to attribute both peaks to dipole resonances, and show that the strong dispersion of the organic permittivity is responsible for this behavior. The presence of these two plasmon resonances was found to enhance the absorption of the organic semiconductor over a broad wavelength range.

Colloidal quantum dots as probes of excitation field enhancement in photonic antennas

Optical antennas are essential devices to interface light to nanoscale volumes and locally enhance the electromagnetic intensity. Various experimental methods can be used to quantify the antenna amplification on the emission process, yet characterizing the antenna amplification at the excitation frequency solely is a challenging task. Such experimental characterization is highly needed to fully understand and optimize the antenna response. Here, we describe a novel experimental tool to directly measure the antenna amplification on the excitation field independently of the emission process. We monitor the transient emission dynamics of colloidal quantum dots and show that the ratio of doubly to singly excited state photoluminescence decay amplitudes is an accurate tool to quantify the local excitation intensity amplification. This effect is demonstrated on optical antennas made of polystyrene microspheres and gold nanoapertures, and supported by numerical computations. The increased doubly excited state formation on nanoantennas realizes a new demonstration of enhanced light-matter interaction at the nanoscale.

Quantitative analysis of localized surface plasmons based on molecular probing

We report on the quantitative characterization of the plasmonic optical near-field of a single silver nanoparticle. Our approach relies on nanoscale molecular molding of the confined electromagnetic field by photoactivated molecules. We were able to directly image the dipolar profile of the near-field distribution with a resolution better than 10 nm and to quantify the near-field depth and its enhancement factor. A single nanoparticle spectral signature was also assessed. This quantitative characterization constitutes a prerequisite for developing nanophotonic applications.

Maximized optical absorption in ultrathin films and its application to plasmon-based two-dimensional photovoltaics

For ultrathin films of a given material, light absorption is proportional to the film thickness. However, if the optical constants of the film are chosen in an optimal way, light absorption can be high even for extremely thin films and optical path length. We derive the optimal conditions and show how the maximized absorptance depends on film thickness. It is then shown that the optimal situation can be emulated by tuning of the geometric parameters in feasible nanocomposites combining plasmonic materials with semiconductors. Useful design criteria and estimates for the spatial absorption-distribution over the composite materials are provided. On the basis of efficient exchange of oscillator strength between the plasmonic and semiconductor constituents, a high quantum yield for semiconductor absorption can be achieved. The results are far-reaching with particularly promising opportunities for plasmonic solar cells.

Tailoring light-matter-spin interactions in colloidal hetero-nanostructures

The interplay between light and matter is the basis of many fundamental processes and various applications. Harnessing light-matter interactions in principle allows operation of solid state devices under new physical principles: for example, the a.c. optical Stark effect (OSE) has enabled coherent quantum control schemes of spins in semiconductors, with the potential for realizing quantum devices based on spin qubits. However, as the dimension of semiconductors is reduced, light-matter coupling is typically weakened, thus limiting applications at the nanoscale. Recent experiments have demonstrated significant enhancement of nanoscale light-matter interactions, albeit with the need for a high-finesse cavity, ultimately preventing device down-scaling and integration. Here we report that a sizable OSE can be achieved at substantial energy detuning in a cavity-free colloidal metal-semiconductor core-shell hetero-nanostructure, in which the metal surface plasmon is tuned to resonate spectrally with a semiconductor exciton transition. We further demonstrate that this resonantly enhanced OSE exhibits polarization dependence and provides a viable mechanism for coherent ultrafast spin manipulation within colloidal nanostructures. The plasmon-exciton resonant nature further enables tailoring of both OSE and spin manipulation by tuning plasmon resonance intensity and frequency. These results open a pathway for tailoring light-matter-spin interactions through plasmon-exciton resonant coupling in a judiciously engineered nanostructure, and offer a basis for future applications in quantum information processing at the nanoscale. More generally, integrated nanostructures with resonantly enhanced light-matter interactions should serve as a test bed for other emerging fields, including nano-biophotonics and nano-energy.

Periodic nanotemplating by selective deposition of electroless gold island films on particle-lithographed dimethyldichlorosilane layers

Uniform hexagonal arrays of diverse nanotemplated metal structures were formed via selective electroless gold plating on particle-lithographed dimethyldichlorosilane layers. Surface-associated water at silica bead interstices was shown to correlate with the formation of silane rings with outer ring diameters ranging from 522.5+/-29.7 to 1116.9+/-52.6 nm and/or spherical gold nanoparticles with diameters from 145.5+/-20.2 to 389.1+/-51.1 nm in the array. Reproducibility and millimeter-size scalability of the array were achieved without the need for expensive and sophisticated lithography or metal deposition equipment. The formation of each structure was explained on the basis of the silanization mechanism and microscopic characterization, as well as dimensional analysis of the nanostructures. This new, facile, and versatile method enables fine fabrication of regular metal nanoparticle array platforms to improve optical and plasmonic features in nanoelectronics and nanophotonic devices.

Fabrication and replication of arrays of single- or multicomponent nanostructures by replica molding and mechanical sectioning

This paper describes the fabrication of arrays of nanostructures (rings, crescents, counterfacing split rings, cylinders, coaxial cylinders, and other structures) by a four-step process: (i) molding an array of epoxy posts by soft lithography, (ii) depositing thin films on the posts, (iii) embedding the posts in epoxy, and (iv) sectioning in a plane parallel to the plane defined by the array of posts, into slabs, with an ultramicrotome ("nanoskiving"). This work demonstrates the combination of four capabilities: (i) formation of structures that are submicrometer in all dimensions; (ii) fabrication of 3D structures, and arrays of structures, with gradients of height; (iii) patterning of arrays containing two or more materials, including metals, semiconductors, oxides, and polymers; and (iv) generation of as many as 60 consecutive slabs bearing contiguous arrays of nanostructures. These arrays can be transferred to different substrates, and arrays of gold rings exhibit plasmonic resonances in the range of wavelengths spanning 2-5 microm.

High-throughput nanofabrication of infrared plasmonic nanoantenna arrays for vibrational nanospectroscopy

The introduction of high-throughput and high-resolution nanofabrication techniques operating at low cost and low complexity is essential for the advancement of nanoplasmonic and nanophotonic fields. In this paper, we demonstrate a novel fabrication approach based on nanostencil lithography for high-throughput fabrication of engineered infrared plasmonic nanorod antenna arrays. The technique relying on deposition of materials through a shadow mask enables plasmonic substrates supporting spectrally sharp collective resonances. We show that reflectance spectra of these antenna arrays are comparable to that of arrays fabricated by electron beam lithography. We also show that nanostencils can be reused multiple times to fabricate a series of infrared nanoantenna arrays with identical optical responses. Finally, we demonstrate fabrication of plasmonic nanostructures in a variety of shapes with a single metal deposition step on different substrates, including nonconducting ones. Our approach, by enabling the reusability of the stencil and offering flexibility on the substrate choice and nanopattern design, could facilitate the transition of plasmonic technologies to the real-world applications.

Light trapping in ultrathin plasmonic solar cells

We report on the design, fabrication, and measurement of ultrathin film a-Si:H solar cells with nanostructured plasmonic back contacts, which demonstrate enhanced short circuit current densities compared to cells having flat or randomly textured back contacts. The primary photocurrent enhancement occurs in the spectral range from 550 nm to 800 nm. We use angle-resolved photocurrent spectroscopy to confirm that the enhanced absorption is due to coupling to guided modes supported by the cell. Full-field electromagnetic simulation of the absorption in the active a-Si:H layer agrees well with the experimental results. Furthermore, the nanopatterns were fabricated via an inexpensive, scalable, and precise nanopatterning method. These results should guide design of optimized, non-random nanostructured back reflectors for thin film solar cells.

Enhanced absorption in optically thin solar cells by scattering from embedded dielectric nanoparticles

We present a concept for improving the efficiency of thin-film solar cells via scattering from dielectric particles. The particles are embedded directly within the semiconductor absorber material with sizes on the order of one wavelength. Importantly, this geometry is fully compatible with the use of an anti-reflective coating (ARC) to maximize light capture. The concept is demonstrated through finite-difference time domain (FDTD) simulations of spherical SiO(2) particles embedded within a 1.0 microm layer of crystalline silicon (c-Si) utilizing a 75 nm ARC of Si(3)N(4). Several geometries are presented, with gains in absorbed photon flux occurring in the red end of the spectrum where silicon absorption is weak. The total integrated absorption of incident photon flux across the visible AM-1.5 spectrum is on the order of 5-10% greater than the same geometry without any dielectric scatterers.

Enhanced light trapping in thin-film solar cells by a directionally selective filter

A directionally selective multilayer filter is applied to a hydrogenated amorphous silicon solar cell to improve the light trapping. The filter prevents non-absorbed long-wavelength photons from leaving the cell under oblique angles leading to an enhancement of the total optical path length for weakly absorbed light within the device by a factor of kappa(r) = 3.5. Parasitic absorption in the contact layers limits the effective path length improvement for the photovoltaic quantum efficiency to a factor of kappa(EQE) = 1.5. The total short-circuit current density increases by DeltaJ(sc) = 0.2 mAcm(-2) due to the directional selectivity of the Bragg-like filter.

Scalable coating and properties of transparent, flexible, silver nanowire electrodes

We report a comprehensive study of transparent and conductive silver nanowire (Ag NW) electrodes, including a scalable fabrication process, morphologies, and optical, mechanical adhesion, and flexibility properties, and various routes to improve the performance. We utilized a synthesis specifically designed for long and thin wires for improved performance in terms of sheet resistance and optical transmittance. Twenty Omega/sq and approximately 80% specular transmittance, and 8 ohms/sq and 80% diffusive transmittance in the visible range are achieved, which fall in the same range as the best indium tin oxide (ITO) samples on plastic substrates for flexible electronics and solar cells. The Ag NW electrodes show optical transparencies superior to ITO for near-infrared wavelengths (2-fold higher transmission). Owing to light scattering effects, the Ag NW network has the largest difference between diffusive transmittance and specular transmittance when compared with ITO and carbon nanotube electrodes, a property which could greatly enhance solar cell performance. A mechanical study shows that Ag NW electrodes on flexible substrates show excellent robustness when subjected to bending. We also study the electrical conductance of Ag nanowires and their junctions and report a facile electrochemical method for a Au coating to reduce the wire-to-wire junction resistance for better overall film conductance. Simple mechanical pressing was also found to increase the NW film conductance due to the reduction of junction resistance. The overall properties of transparent Ag NW electrodes meet the requirements of transparent electrodes for many applications and could be an immediate ITO replacement for flexible electronics and solar cells.

Perforated semishells: far-field directional control and optical frequency magnetic response

Reduced-symmetry plasmonic nanostructures can be designed to support a range of novel optical phenomena, such as nanoscale control of the far-field scattering profile and magnetic resonances at optical frequencies. A family of reduced-symmetry nanostructures--plasmonic semishells with specifically shaped and oriented perforations introduced into the metallic shell layer--can be tailored to control these effects. Unlike core-shell nanoparticles, perforated semishells can be fabricated using a combination of clean-room techniques. For a semishell with a single spherical perforation positioned on its symmetry axis, we examine how the resonant modes of the structure depend on hole size and shape. Placing the perforation off the symmetry axis allows a family of higher-order modes to be excited in the nanostructure, along with complex near-field charge distributions for the various resonant modes. This reduced-symmetry case provides a platform for optical studies, which agree quite well with theoretical analysis. Our study also examines two important variations of this structure: a semishell with multiple perforations in the shell layer, and a semishell with a wedge-like "slice" in the shell layer. A semishell with a wedge-like perforation can be thought of as a three-dimensional analogue of a split-ring resonator (SRR), an important nanoscale component in metamaterial design. Here we show that the dimensions of the wedge-like perforation, which control the effective optical frequency resistance, inductance, and capacitance of this structure, determine the frequency of the magnetic mode.

Plasmonics for improved photovoltaic devices

The emerging field of plasmonics has yielded methods for guiding and localizing light at the nanoscale, well below the scale of the wavelength of light in free space. Now plasmonics researchers are turning their attention to photovoltaics, where design approaches based on plasmonics can be used to improve absorption in photovoltaic devices, permitting a considerable reduction in the physical thickness of solar photovoltaic absorber layers, and yielding new options for solar-cell design. In this review, we survey recent advances at the intersection of plasmonics and photovoltaics and offer an outlook on the future of solar cells based on these principles.

Plasmonics for extreme light concentration and manipulation

The unprecedented ability of nanometallic (that is, plasmonic) structures to concentrate light into deep-subwavelength volumes has propelled their use in a vast array of nanophotonics technologies and research endeavours. Plasmonic light concentrators can elegantly interface diffraction-limited dielectric optical components with nanophotonic structures. Passive and active plasmonic devices provide new pathways to generate, guide, modulate and detect light with structures that are similar in size to state-of-the-art electronic devices. With the ability to produce highly confined optical fields, the conventional rules for light-matter interactions need to be re-examined, and researchers are venturing into new regimes of optical physics. In this review we will discuss the basic concepts behind plasmonics-enabled light concentration and manipulation, make an attempt to capture the wide range of activities and excitement in this area, and speculate on possible future directions.