Broadband Light Harvesting Research Articles

Plasmonic enhancement of betanin-lawsone co-sensitized solar cells via tailored bimodal size distribution of silver nanoparticles

Natural pigment-based photosensitizers are an attractive pathway for realizing low cost and environmentally friendly solar cells. Here, broadband light-harvesting is achieved using two natural pigments, betanin and lawsone, absorbing in the green and blue region of the solar spectrum respectively. The use of bimodal size distribution of AgNPs tailored for each of the pigments to further increase their efficiency is the key feature of this work. This study demonstrates a significant enhancement in current-density, voltage, and efficiency by 20.1%, 5.5%, and 28.6% respectively, in a betanin-lawsone co-sensitized solar cell, via plasmonic enhancement using silver nanoparticles (AgNPs). The optimum sizes of the nanoparticles have been calculated by studying their optical response and electric field profiles using Finite Difference Time Domain (FDTD) simulations, aimed at matching their resonant wavelengths with the absorption bands of the dyes. Simulations show that AgNPs of diameters 20 nm and 60 nm are optimum for enhanced absorption by lawsone and betanin respectively. The FDTD simulations of the plasmonic photoelectrodes demonstrated 30% and 15% enhancement in the power absorption by betanin and lawsone at the LSPR peaks of the 60 nm and 20 nm AgNPs respectively. An optimum overall concentration of 2% (v/v) and a ratio of 4:1 (20 nm:60 nm) of the bimodal distribution of the AgNPs, was determined for incorporation in the photoanodes. An average efficiency of 1.02 ± 0.006% was achieved by the betanin-lawsone co-sensitized solar cell with the bimodal distribution of AgNPs, compared to 0.793 ± 0.006% achieved by the non-plasmonic solar cell of otherwise identical configuration. Electrochemical impedance spectroscopy confirmed that the incorporation of the bimodal distribution of AgNPs in the solar cells also enabled enhanced electron lifetime and reduced recombination compared to the non-plasmonic counterpart, thereby improving the charge transfer. The plasmonic enhancement methodology presented here can be applied to further improve the efficiency of other natural dye-sensitized solar cells.

A broadband aggregation-independent plasmonic absorber for highly efficient solar steam generation

A plasmonic solar absorber, featuring broadband light harvesting by manipulating the structural anisotropy at the single nanoparticle level, enables absorption over the entire solar spectrum.

Broadband Light Harvesting and Unidirectional Electron Flow for Efficient Electron Accumulation for Hydrogen Generation.

The efficiency of solar hydrogen evolution closely depends on the multiple electrons accumulation on the catalytic center for two-electron-involved water reduction. Herein, we report an effective approach to enable broadband light absorption and unidirectional electron flow for efficiently accumulating electrons at active sites for hydrogen evolution by rationally engineering the nanostructure of Pt nanoparticles (NPs), TiO2 , and SiO2 support. In addition to Schottky-junction-driven electron transfer from TiO2 to Pt, Pt NPs also produce hot electrons by recycling the scattered visible and near-infrared (vis-NIR) light of the support. Unidirectional electron flow to active sites is realized by tuning the components spatial distribution. These features collectively accumulate multiple electrons at catalytic Pt sites, thereby affording enhanced activity toward hydrogen evolution under simulated sunlight.

Broadband Light Harvesting and Unidirectional Electron Flow for Efficient Electron Accumulation for Hydrogen Generation

AbstractThe efficiency of solar hydrogen evolution closely depends on the multiple electrons accumulation on the catalytic center for two‐electron‐involved water reduction. Herein, we report an effective approach to enable broadband light absorption and unidirectional electron flow for efficiently accumulating electrons at active sites for hydrogen evolution by rationally engineering the nanostructure of Pt nanoparticles (NPs), TiO2, and SiO2 support. In addition to Schottky‐junction‐driven electron transfer from TiO2 to Pt, Pt NPs also produce hot electrons by recycling the scattered visible and near‐infrared (vis‐NIR) light of the support. Unidirectional electron flow to active sites is realized by tuning the components spatial distribution. These features collectively accumulate multiple electrons at catalytic Pt sites, thereby affording enhanced activity toward hydrogen evolution under simulated sunlight.

Broadband optical transmission through sandwich-shaped multilayer tapered metallic slit arrays

The non-resonant extraordinary optical transmission (EOT) can achieve broadband transmission, which is significant for broadband light harvesting devices. A metallic single slit nanostructure or slit array structure, due to simple structure and easy-to integration, has been used to construct a light source in the nanostructures based on the surface plasmon polaritons (SPPs). To obtain broadband transmission, in this paper, we propose a sandwich-shaped multilayer tapered metallic slit arrays. The transmission properties of the multilayer tapered metallic slit arrays were investigated using the finite element method (FEM). Results show that, compared with monolayer tapered metallic slit arrays structure, multilayer tapered metallic slit arrays can achieve more transmission peaks in the spectra and leading to broadband transmission in the infrared; the tapered provides a gradual impedance variation from the entrance to the exit of the slits, the light is strongly localized and enhanced at the slit exits and the dielectric layer, in contrast with straight slits. In addition, the effects of the thickness of the dielectric layer, the position of dielectric layer, the period of the arrays and the width of the slit entrance on the transmission property were also studied. These results would be helpful for designing the broadband transmission properties of multilayer structures and may be applied value in the fields of nano-light source design, photonic integrated circuits and optoelectronic circuits and so on.

High performance n+p-Si/Ti/NiS O photocathode for photoelectrochemical hydrogen evolution in alkaline solution

Abstract Silicon, as a promising semiconductor for fabricating photocathode toward photoelectrochemical hydrogen evolution reaction (PEC-HER), should be improved in light harvesting ability and catalytic kinetics to obtain high PEC performance. Herein, a novel amorphous Nickel Oxysulfide (NiSxOy) film is effectively integrated with a Ti protected n+p-Si micropyramid photocathode by the electrodeposition method. The fabricated n+p-Si/Ti/NiSxOy photocathode exhibits excellent PEC-HER performance with an onset potential of 0.5 V (at J = −0.1 mA/cm2), a photocurrent density of −26 mA/cm2 at 0 V vs. RHE, and long term stability of six hours in alkaline solution (pH ≈ 14). The synergy of unique n+p-Si micropyramid architectures (omnidirectional broadband light harvesting ability), novel amorphous NiSxOy catalyst (high HER electrocatalytic activity and good optical transparency) results in the high performance of n+p-Si/Ti/NiSxOy. This work offers a novel strategy for effectively integrating electrocatalysts with semiconductor to design efficient photoelectrode toward PEC water splitting.

Polymer Solar Cells with 90% External Quantum Efficiency Featuring an Ideal Light- and Charge-Manipulation Layer.

Rapid progress in the power conversion efficiency (PCE) of polymer solar cells (PSEs) is beneficial from the factors that match the irradiated solar spectrum, maximize incident light absorption, and reduce photogenerated charge recombination. To optimize the device efficiency, a nanopatterned ZnO:Al2 O3 composite film is presented as an efficient light- and charge-manipulation layer (LCML). The Al2 O3 shells on the ZnO nanoparticles offer the passivation effect that allows optimal electron collection by suppressing charge-recombination loss. Both the increased refractive index and the patterned deterministic aperiodic nanostructure in the ZnO:Al2 O3 LCML cause broadband light harvesting. Highly efficient single-junction PSCs for different binary blends are obtained with a peak external quantum efficiency of up to 90%, showing certified PCEs of 9.69% and 13.03% for a fullerene blend of PTB7:PC71 BM and a nonfullerene blend, FTAZ:IDIC, respectively. Because of the substantial increase in efficiency, this method unlocks the full potential of the ZnO:Al2 O3 LCML toward future photovoltaic applications.

Three-dimensional TiO2/Au nanoparticles for plasmon enhanced photocatalysis

The mechanisms of plasmonic nanostructures assisted photocatalytic processes are fundamental and of great importance and interest for decades. Therefore, we adopt a unique porous structure of three-dimensional TiO2/Au nanoparticles to experimentally explore the potential mechanisms of rhodamine B (RhB) based photocatalytic degradation. The highly efficient absorbance measured across the entire ultraviolet and infrared regions shows the broadband light harvesting capability and photocatalytic activity, in which the direct bandgap transition, plasmon sensitization as well as the plasmonic photothermal effect can be beneficial for the photocatalytic reaction. The RhB photocatalytic degradation experiments were conducted systematically under solar irradiance with finely chosen optical filters. Apart from the ultraviolet-driven degradation of TiO2, the plasmon assisted photocatalytic rate of our TiO2/Au structure can be enhanced by >30% as compared to the referenced TiO2 structure (equivalent to 2–4 times promotion with respect to the same quantity of the active material TiO2). Detailed wavelength-dependent analyses have revealed that the visible-driven degradation rate can be enhanced by 10 times because of the plasmon sensitization effect; while infrared-driven degradation rate is enhanced by 4 times as well for the plasmonic photothermal effect, respectively. Our experimental results may provide a clear understanding for the wavelength-dependent plasmon enhanced photocatalytic processes.

Broadband Enhancement of PbS Quantum Dot Solar Cells by the Synergistic Effect of Plasmonic Gold Nanobipyramids and Nanospheres

AbstractFor the first time, the plasmonic gold bipyramids (Au BPs) are introduced to the PbS colloidal quantum dot (CQD) solar cells for improved infrared light harvesting. The localized surface plasmon resonance peaks of Au BPs matches perfectly with the absorption peaks of conventional PbS CQDs. Owing to the geometrical novelty of Au BPs, they exhibit significantly stronger far‐field scattering effect and near‐field enhancement than conventional plasmonic Au nanospheres (NSs). Consequently, device open‐circuit voltage (Voc) and short‐circuit current (Jsc) are simultaneously enhanced, while plasmonic photovoltaic devices based on Au NSs only achieve improved Jsc. The different effects and working mechanisms of these two Au nanoparticles are systematically investigated. Moreover, to realize effective broadband light harvesting, Au BPs and Au NSs are used together to simultaneously enhance the device optical and electrical properties. As a result, a significantly increased power conversion efficiency (PCE) of 9.58% is obtained compared to the PCE of 8.09% for the control devices due to the synergistic effect of the two plasmonic Au nanoparticles. Thus, this work reveals the intriguing plasmonic effect of Au BPs in CQD solar cells and may provide insight into the future plasmonic enhancement for solution‐processed new‐generation solar cells.

Photocatalytic Water-Splitting Enhancement by Sub-Bandgap Photon Harvesting.

Upconversion is a photon-management process especially suited to water-splitting cells that exploit wide-bandgap photocatalysts. Currently, such catalysts cannot utilize 95% of the available solar photons. We demonstrate here that the energy-conversion yield for a standard photocatalytic water-splitting device can be enhanced under solar irradiance by using a low-power upconversion system that recovers part of the unutilized incident sub-bandgap photons. The upconverter is based on a sensitized triplet-triplet annihilation mechanism (sTTA-UC) obtained in a dye-doped elastomer and boosted by a fluorescent nanocrystal/polymer composite that allows for broadband light harvesting. The complementary and tailored optical properties of these materials enable efficient upconversion at subsolar irradiance, allowing the realization of the first prototype water-splitting cell assisted by solid-state upconversion. In our proof-of concept device the increase of the performance is 3.5%, which grows to 6.3% if concentrated sunlight (10 sun) is used. Our experiments show how the sTTA-UC materials can be successfully implemented in technologically relevant devices while matching the strict requirements of clean-energy production.

Broadband Light Absorption and Efficient Charge Separation Using a Light Scattering Layer with Mixed Cavities for High-Performance Perovskite Photovoltaic Cells with Stability.

CH3 NH3 PbI3 is one of the promising light sensitizers for perovskite photovoltaic cells, but a thick layer is required to enhance light absorption in the long-wavelength regime ranging from PbI2 absorption edge (500 nm) to its optical band-gap edge (780 nm) in visible light. Meanwhile, the thick perovskite layer suppresses visible-light absorption in the short wavelengths below 500 nm and charge extraction capability of electron-hole pairs produced upon light absorption. Herein, we find that a new light scattering layer with the mixed cavities of sizes in 100 and 200 nm between transparent fluorine-doped tin oxide and mesoporous titanium dioxide electron transport layer enables full absorption of short-wavelength photons (λ < 500 nm) to the perovskite along with enhanced absorption of long-wavelength photons (500 nm < λ < 780 nm). Moreover, the light-driven electric field is proven to allow efficient charge extraction upon light absorption, thereby leading to the increased photocurrent density as well as the fill factor prompted by the slow recombination rate. Additionally, the photocurrent density of the cell with a light scattering layer of mixed cavities is stabilized due to suppressed charge accumulation. Consequently, this work provides a new route to realize broadband light harvesting of visible light for high-performance perovskite photovoltaic cells.

Broadband and omnidirectional light harvesting enhancement in photovoltaic devices with aperiodic TiO2 nanotube photonic crystal

Design of more effective broadband light-trapping elements to improve the light harvesting efficiency under both normal and tilted light for solar cells and other photonic devices is highly desirable. Herein we present a theoretical analysis on the optical properties of a novel TiO2 nanotube aperiodic photonic crystal (NT APC) following an aperiodic sequences and its photocurrent enhancement effect for dye-sensitized solar cells (DSSCs) under various incidence angles. It is found that, compared to regular PC, the designed TiO2 NT APC owns broader reflection region and a desired omnidirectional reflection (ODR) bandgaps, leading to considerable and stable photocurrent enhancement under both normal and oblique light. The effects of the structural parameters of the TiO2 NT APC, including the average lattice constant and the common sequence difference, on the optical properties, ODR bandgaps and absorption magnification of the integrated DSSCs are investigated in detail. Moreover, the angular dependence of photocurrent enhancement and angular compensation effect of such TiO2 NT APCs are also provided to offer a guidance on the optimum structural parameters design under different engineering application conditions.

Exceptionally omnidirectional broadband light harvesting scheme for multi-junction concentrator solar cells achieved via ZnO nanoneedles.

GaInP/GaAs/Ge triple-junction concentrator solar cells with significant efficiency enhancement were demonstrated with antireflective ZnO nanoneedles. The novel nanostructure was attained with a Zn(NO3)2-based solution containing vitamin C. Under one sun AM 1.5G solar spectrum, conversion efficiency of the triple-junction device was improved by 23.7% via broadband improvement in short-circuit currents of 3 sub-cells after the coverage by the nanoneedles with a graded refractive index profile. The efficiency enhancement further went up to 45.8% at 100 suns. The performance boost through the nanoneedles also became increasingly pronounced in the conditions of high incident angles and the cloudy weather, e.g. 220.0% of efficiency enhancement was observed at the incident angle of 60°. These results were attributed to the exceptional broadband omnidirectionality of the antireflective nanoneedles.

Enhancing absorption in coated semiconductor nanowire/nanorod core–shell arrays using active host matrices

In the present work, we investigated theoretically and experimentally the interaction of radiation field phenomena interacting with arrays of nanowire/nanorod core–shell embedded in active host matrices. The optical properties of composites are explored including the case when the absorption of propagating wave by dissipative component is completely compensated by amplification in active (lasing) medium. On the basis of more elaborated modeling approach and extended effective medium theory, the effective polarizability and the refractive index of electromagnetic mode dispersion of the core–shell nanowire arrays are derived. ZnS(shell)-coated by sulphidation process on ZnO(shell) nanorod arrays grown on (100) silicon substrate by chemical bath deposition (CBD) has been used for theoretical comparison. Compared with the bare ZnO nanorods, ZnS-coated core/shell nanorods exhibit a strongly reduced ultraviolet (UV) emission and a dramatically enhanced deep level (DL) emission. Obviously, the UV and DL emission peaks are attributed to the emissions of ZnO nanorods within ZnO/ZnS core/shell nanorods. The reduction of UV emission after ZnS coating seems to agree with the charge separation mechanism of type-II band alignment that holes transfer from the core to shell, which would quench the UV emission to a certain extent. Our theoretical calculations and numerical simulation demonstrate that the use of active host (amplifying) medium to compensate absorption at metallic inclusions. Moreover the core–shell nanorod/nanowire arrays create the opportunity for broad band absorption and light harvesting applications.

Broadband and wide-angle light harvesting by ultra-thin silicon solar cells with partially embedded dielectric spheres.

We propose a design of crystalline silicon thin-film solar cells (c-Si TFSCs, 2 μm-thick) configured with partially embedded dielectric spheres on the light-injecting side. The intrinsic light trapping and photoconversion are simulated by the complete optoelectronic simulation. It shows that the embedding depth of the spheres provides an effective way to modulate and significantly enhance the optical absorption. Compared to the conventional planar and front sphere systems, the optimized partially embedded sphere design enables a broadband, wide-angle, and strong optical absorption and efficient carrier transportation. Optoelectronic simulation predicts that a 2 μm-thick c-Si TFSC with half-embedded spheres shows an increment of more than 10 mA/cm2 in short-circuit current density and an enhancement ratio of more than 56% in light-conversion efficiency, compared to the conventional planar counterparts.

Broad Band-Pass and Band-Stop Transmissions Through the Hybrid Gratings of Rectangle and Triangle

Silver gratings of hybrid structures are proposed, and their optical transmission properties are simulated by finite element method. The proposed structure is found to facilitate a broadband-enhanced transmission in the infrared region and exerts a band-stop effect in the visible region. The effects of structural parameters on transmission characteristics are also studied. Results reveal promising applications in broadband light harvesting and filtering devices.

A light-trapping strategy for nanocrystalline silicon thin-film solar cells using three-dimensionally assembled nanoparticle structures

We report three-dimensionally assembled nanoparticle structures inducing multiple plasmon resonances for broadband light harvesting in nanocrystalline silicon (nc-Si:H) thin-film solar cells. A three-dimensional multiscale (3DM) assembly of nanoparticles generated using a multi-pin spark discharge method has been accomplished over a large area under atmospheric conditions via ion-assisted aerosol lithography. The multiscale features of the sophisticated 3DM structures exhibit surface plasmon resonances at multiple frequencies, which increase light scattering and absorption efficiency over a wide spectral range from 350–1100 nm. The multiple plasmon resonances, together with the antireflection functionality arising from the conformally deposited top surface of the 3D solar cell, lead to a 22% and an 11% improvement in power conversion efficiency of the nc-Si:H thin-film solar cells compared to flat cells and cells employing nanoparticle clusters, respectively. Finite-difference time-domain simulations were also carried out to confirm that the improved device performance mainly originates from the multiple plasmon resonances generated from three-dimensionally assembled nanoparticle structures.

Plasmonic nanopillar coupled two-dimensional random medium for broadband light trapping and harvesting

Random textures have proven to be a better option for light localization and energy harvesting in solar cells. On the other hand, plasmonic structures are significant in localizing the fields into submicron domains. We propose a layered structure design that contains the random dielectric medium with a plasmonic nanopillars array as a back reflector, followed by demon- strating its efficient light trapping ability through simulation means. This structure has shown significant enhancement in the broadband absorption of the light spectrum in the wavelength range UV-IR and a higher extinction in the near-infrared wavelengths. The structure also shows the dependence of reflection on the nanopillar height as well as localization in the nano- pillar region. The broadened and red shifted plasmonic nanopillar resonances (transverse and longitudinal) in a high-index medium are shown as the reasons for enhanced broadband absorption. © 2015 Society of Photo-Optical Instrumentation Engineers (SPIE) (DOI: 10.1117/1. JNP.9.093061)

Unraveling the Janus Role of Mie Resonances and Leaky/Guided Modes in Semiconductor Nanowire Absorption for Enhanced Light Harvesting

Light absorption from finite semiconductor nanowires is investigated through a unified theoretical picture and numerical simulations. We first show theoretically from the electromagnetic mode dispersion relation and the Mie extinction cross sections for infinite nanowires that formally equivalent (Janus) formulas yield both leaky/guided modes and Mie resonances as, respectively, complex wave vector or complex frequency solutions that, in turn, overlap only at grazing angles with respect to the nanowire axis. For finite semiconductor nanowires, the angle of incidence becomes critical: absorption is dominated by Mie resonances at incident angles perpendicular (and oblique) to the nanowire axis; by contrast, guided mode excitation (if spectrally available) governs and enhances absorption at grazing incidence. Such theoretical prediction can be exploited to optimize nanowire designs for broad band and broad angle light harvesting applications.

Broadband Light Harvesting and Fast Charge Separation in Ordered Self-Assemblies of Electron Donor–Acceptor-Functionalized Graphene Oxide Layers for Effective Solar Energy Conversion

Three-dimensionally (3D) ordered assemblies of GO layers functionalized with tetrakis(1-methylpyridinium-4-yl)porphyrin p-toluenesulfonate (Por), N,N′-di(2-(trimethylammonium iodide)ethylene) perylenediimide (PDI), and Zn(II) phthalocyanine tetrasulfonic acid (ZnPc) were obtained in water. Proper molar ratio is essential between the cationic dyes, Por and PDI, acting as the “glue” molecules to combine the GO layers and the anionic ZnPc, acting as dispersant of GO layers to (i) construct the 3D assemblies and (ii) the proportional absorption distribution of dye-functionalized GO assemblies. Resulting 3D structures effectively harvest the light from ultraviolet to near-infrared (NIR) regions. Dye molecules are arranged in mainly lateral order on the GO layers with partial stacking, which allows direct interactions with the π-conjugations of the GO surface in 3D architecture. Ultrafast charge separation upon the photoexcitation of the dyes at various wavelengths in the visible/NIR region was observed in thes...