Light Harvesting In Solar Cells Research Articles

A comprehensive investigation of the synthesis, spectral, DFT, and optical properties of a novel oxadiazolyl-pyrano[3,2-c]quinoline for photosensor applications

The condensation reaction of pyranoquinoline-3-carbaoxldehyde 1 with benzohydraide afforded hydrazone 2 which upon oxidative cyclization yielded 6-ethyl-4-hydroxy-3-(5-phenyl-1,3,4-oxadiazol-2-yl)-2H-pyrano[3,2-c]quinoline-2,5(6H)-dione (EHPOPQ, 3). The DFT and B3LYP/6-311++G(d,p) basis set were used to compute the optimized molecular geometry. The global reactivity descriptors were examined and showed that hydrazone 2 exhibited high softness while aldehyde 1 had more electronegativity and high global electrophilicity. Subsequently, the reactive sites of the present compounds were located by tracing the MEP map. The GIAO method was used to calculate the 1H and 13C NMR. The current comprehensive investigation of the novel (EHPOPQ) reveals its significant potential for applications in nonlinear optics (NLO) and photovoltaics. Through high-level computational methods, EHPOPQ has an exceptionally high first hyperpolarizability (βtot) of 950 × 10−30 esu, which is substantially higher than that of the conventional NLO material urea. This high βtot value suggests that EHPOPQ could dramatically enhance the efficiency and performance of NLO devices such as frequency converters and optical modulators. In parallel, the detailed spectroscopic analysis of EHPOPQ's optical properties provided critical insights for photovoltaic applications. The optical band gap was measured to be 3.07 eV, indicating a direct band gap transition suitable for efficient light harvesting in solar cells. Additionally, dispersion parameters were carefully analyzed, which are essential for understanding the interaction of light with the material. The experimental characterization of EHPOPQ-based photovoltaic devices showed promising results. Current-voltage (J-V) measurements under varying illumination intensities revealed significant enhancements in the device's short-circuit current (from 1.2 µA to 4.3 µA) and open-circuit voltage (from 0.25 V to 0.47 V) as light intensity increased. These findings demonstrate the material's heightened photoresponsivity and suggest its potential as an efficient light conversion material for solar energy applications. These specific findings underline the importance of EHPOPQ in advancing both NLO and photovoltaic technologies, offering a pathway to more efficient and effective devices.

Cu metal nanoparticles in transparent electrodes for light harvesting in solar cells

We report on copper nanoparticles produced by laser ablation, in acetone and methanol, from a Cu target using a 1064 nm nanosecond pulsed laser. The morphology, size, structure and chemical composition of the nanoparticles are investigated as a function of the solvent employed. Different analyses confirm the metallic nature of the nanoparticles, without amorphous carbon or copper oxides shells. Then, the nanoparticles are embedded between two transparent electrodes, aluminium-doped zinc oxide (AZO) and zirconium-doped indium oxide (IZrO) as top and bottom layers, respectively. The Glass/IZrObott/Cu nanoparticles/AZOtop structures are synthesized and optimized as plasmonic and conductive structure for photovoltaic applications. Optical properties show a strong dependence on the thermal annealing at 200 °C and type of copper nanoparticles embedded in transparent electrodes. The transparent electrode with the lowest Egap limits the Egap to the whole structure. The best structure shows a mean value of transmittance in the visible-NIR range of ∼79% with an Egap of 3.43 eV and, moreover, it shows diffused transmittance between 2.5 and 6% in VIS-NIR range and a sheet resistance of 79 Ω/sq. The performances of the best structure are tested measuring the internal quantum efficiency of a tandem solar cell, getting values as high as 89%.

Crystal Chemistry, Optic and Magnetic Characterizations of a New Copper Based Material Templated by Hexahydrodiazepine.

Crystals of the new organic-inorganic material (DAP-H2)[CuBr4] (1); (DAP = hexahydrodiazepine (C5H14N2)) were successfully synthesized by slow evaporation and characterized by single-crystal X-ray diffraction, infrared spectroscopy, thermal analysis, UV-Vis-NIR diffuse reflectance spectroscopy, and magnetic measurements. X-ray investigation demonstrates that 1 crystallizes in the monoclinic space group C2/c. The supramolecular crystal structure of 1 is guided by several types of hydrogen bonding which connect anions and cations together into a three-dimensional network. The optical band gap was determined by diffuse reflectance spectroscopy to be 1.78 eV for a direct allowed transition, implying that it is suitable for light harvesting in solar cells. The vibrational properties of this compound were studied by infrared spectroscopy, while its thermal stability was established by simultaneous TGA-DTA from ambient temperature to 600 °C. The study of the photoresponse behavior of an optoelectronic device, based on (C5H14N2)[CuBr4], has shown a power conversion efficiency (PCE) of 0.0017%, with J sc = 0.0208 mA/cm2, V oc = 313.7 mV, and FF = 25.46. Temperature dependent magnetic susceptibility measurements in the temperature range 1.8-310 K reveal weak antiferromagnetic interactions via the two-halide superexchange pathway [2J/k B = -8.4(3) K].

Selenium-containing bodipy dyes as photosensitizers

“Boron-dipyrromethenes or BF2dipyrrins (BODIPY)“ are high fluorescent dyes and it is applicable in many fields for their attractive photochemical and photophysical properties. BODIPY has different sites of potential for its functional groups, where these groups can be functionalized and introduced. BODIPY can help in building blocks for the synthesization of the desired derivatives of BODIPY. The paper presents a series of existing literature on the given topic to obtain the required information for further studies. It presents that BODIPY could be utilized to wash the living cells for sensing the temperature and fluorescence imaging, in addition to that it also presents an increase of water solubility for increasing the efficiency. Different methods are utilized for the preparation of Selenium BODIPY, 2–1 pot procedure that follows the DDQ oxidation process. One of the most commonly used approaches for synthesis is the pyrrole condensation with aldehydes and the reaction within it is performed with the help of chromatography. BODIPY dyes are able to note their absorption band and stoke shifts for functionalized polymers for systems for light harvesting in solar cells. The dyes holds fluorescence molecules with relevant chemical and physical characteristics for both thermal and chemical stabilities. The substance possess low polarity and pH elements with low sensitivity and PDT as a photosensitizer. The applications of BODIPY hold sharp absorption and visible fluorescence, easy to use synthetization, ”high absorption coefficient“, and stable chemical and thermal properties. Lastly, it can be seen that BODIPY are able to produce dyes quickly and easily.

Thioacetamide-derived nitrogen and sulfur co-doped carbon quantum dots for “green” quantum dot solar cells

To make quantum dot sensitized solar cells (QDSCs) competitive, a power conversion efficiency (PCE) comparable to other developing solar cells is required. Significant attention has been paid to undoped or nitrogen (N) doped carbon quantum dots (N-CQDs) for use as sensitizers or light harvesters in solar cells. However, to our knowledge, the nitrogen and sulfur (S) co-doped CQDs (N, S-CQDs) have never been used as the absorbing layer alone. In the present work, we synthesize nitrogen and sulfur co-doped carbon quantum dots (N, S-CQDs) from a single precursor thioacetamide (TA), via a hydrothermal method. The as-prepared N, S-CQDs were employed as a “green” photoactive layer in TiO2 film, as photoanode. The solar cell delivered an open-circuit voltage (Voc) of 0.43 V, short-circuit current (Jsc) of 0.61 mA/cm−2, fill factor (FF) of 52 %, and PCE of 1.36%; highest among all the carbon-based QDSCs. Moreover, Device-NS showed more stability over 48 h compared to Device-C and Device-N. Undeniably, the achieved PCE is not satisfactory; however, the upgraded device fabrication and structural design may improve PCE and current densities while sustaining the high open-circuit voltage. This study demonstrated the potential application of N, S-CQDs for low-cost, “green” quantum dot solar cell applications.

Analysis of multilayer convective flow of a hybrid nanofluid in porous medium sandwiched between the layers of nanofluid

AbstractAgBr acts as a good sensitizer for titanium oxide, hence TiO2–AgBr nanoparticles exhibit high photocatalytic activity which helps decompose methyl orange under visible light irradiation. Methyl orange is a chemical compound that is hard to degrade and has high stability. It is photoreactive and can capture photons from the sun and is highly used as a light harvester in solar cells, hence, it is used in solar applications. In view of this, the present article deals with the analysis of heat transfer in a multilayer flow of two immiscible nanofluids in a vertical channel that finds application in the fields of solar reactors, electronic cooling, and so on. The mathematical model involving the effect of thermal radiation and the presence of heat source is in the form of a system of ordinary differential equations. This system of equations is simplified using the differential transform method‐Padé approximant and the resulting equations are solved algebraically. It is observed that the temperature of the coolant does not reach its saturation point faster due to the presence of different base fluids that differ in their thermal conductivity. This helps in maintaining the optimum temperature of the system.

Fabrication of Perovskite Solar Cells with Digital Control of Transparency by Inkjet Printing.

Semitransparency is an attractive and important property in solar cells since it opens new possibilities in a variety of applications such as tandem cell configuration and building-integrated photovoltaics. Metal halide perovskite has the optimal properties to function as the light harvester in solar cells and can be made as a thin film, while its chemical composition can change its band gap. However, achieving high transparency usually compromises the solar cell's efficiency. Here we report on a unique approach to fabricating semitransparent perovskite solar cells that does not rely on their composition or their thickness. The approach is based on a scalable process, inkjet printing of arrays of transparent pillars, which are composed of inert photopolymerizable liquid compositions and are partly covered by the perovskite. This material can be printed at specific locations and array densities, thus providing a digital control of both the transparency and efficiency of the solar cells. The new semitransparent device structure shows 11.2% efficiency with 24% average transparency without a top metal contact. Further development including deposition of a transparent contact enabled the fabrication of fully semitransparent devices with an efficiency of 10.6% and average transparency of 19%.

Optical studies of semiconductor perovskite nanocrystals for classical optoelectronic applications and quantum information technologies: a review

Semiconductor perovskite films are now being widely investigated as light harvesters in solar cells with ever-increasing power conversion efficiencies, which have motivated the fabrication of other optoelectronic devices, such as light-emitting diodes, lasers, and photodetectors. Their superior material and optical properties are shared by the counterpart colloidal nanocrystals (NCs), with the additional advantage of quantum confinement that can yield size-dependent optical emission ranging from the near-UV to near-infrared wavelengths. So far, intensive research efforts have been devoted to the optical characterization of perovskite NC ensembles, revealing not only fundamental exciton relaxation and recombination dynamics but also low-threshold amplified spontaneous emission and novel superfluorescence effects. Meanwhile, the application of single-particle spectroscopy techniques to perovskite NCs has helped to resolve a variety of optical properties for which there are few equivalents in traditional colloidal NCs, mainly including nonblinking photoluminescence, suppressed spectral diffusion, stable exciton fine structures, and coherent single-photon emission. While the main purpose of ensemble optical studies is to guide the smooth development of perovskite NCs in classical optoelectronic applications, the rich observations from single-particle optical studies mark the emergence of a potential platform that can be exploited for quantum information technologies.

Heteroleptic Tin-Antimony Sulfoiodide for Stable and Lead-free Solar Cells

Summary The quaternary chalcogenide halides of group IV and V elements have attracted much attention due to their interesting semiconducting properties as well as a suitable band gap for solar cells. Here, for the first time, we report on solar cells using tin-antimony sulfoiodide (Sn2SbS2I3). Sn2SbS2I3 solar cells were fabricated using a chemical single-step deposition process with a solution containing a SbCl3-thiourea complex and SnI2 with the configuration of TiO2 and poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b′]dithiophene)-alt-4,7-(2,1,3-enzothiadiazole)] as the electron- and hole-transporting layers, respectively. The best-performing cell exhibits a power conversion efficiency of 4.04% under the illumination of standard AM 1.5G conditions (100 mW cm−2). These unencapsulated cells exhibited good stabilities at 80% relative humidity, 85°C in air, and under illumination, respectively. These results provide guidelines for fabrication of lead-free heteroleptic perovskite solar cells by hosting divalent or combinations of monovalent and trivalent metal cations.

Analysis of highly efficient perovskite solar cells with inorganic hole transport material

Organo-halide perovskites in planar heterojunction architecture have shown considerable promise as efficient light harvesters in solar cells. We carry out a numerical modeling of a planar lead based perovskite solar cell (PSC) with Cu2ZnSnS4 (CZTS) as the hole transporting material (HTM) using the one-dimensional solar cell capacitance simulator (SCAPS-1D). The effects of numerous parameters such as defect density, thickness, and doping density of the absorber layer on the device performance are investigated. The doping densities and electron affinities of the electron transporting material (ETM) and the HTM are also varied to optimize the PSC performance. It has been observed that a thinner absorber layer of ∼220 nm with a defect density of 1014 cm−3 compared to the reference structure improves the device performance. When doping density of the absorber layer increases beyond 2 × 1016 cm−3, the power conversion efficiency (PCE) reduces due to enhanced recombination rate. The defect density at the absorber/ETM interface reduces the PCE as well. Considering a series resistance of 5 Ω · cm2 and all the optimum parameters of absorber, ETM and HTM layers simultaneously, the overall PCE of the device increases significantly. In comparison with the reference structure, the PCE of the optimized device has been increased from 12.76% to 22.7%, and hence the optimized CZTS based PSC is highly efficient.

Ab Initio Study of Optoelectronic and Magnetic Properties of Ternary Chromium Chalcogenides

Using first-principles calculations, we investigate the magnetic order in the ground state of several ternary chromium chalcogenide compounds. Electronic band structure calculations indicate that these compounds are either metallic or semiconductors with relatively low bandgap energies. The large optical absorption coefficients, predicted by our calculations, suggest that some of these compounds may be useful as light harvesters in solar cells or as infrared detectors.

Nanostructured ZnO - its challenging properties and potential for device applications

Nanostructured ZnO possessing interesting structural and optical properties offers challenging opportunities for innovative applications. In this lecture the review of the optical and structural properties of ZnO nanostructured layers is presented. It is shown that they have a direct impact on the parameters of devices involving ZnO. An analysis of current trends in the photovoltaic (PV) field shows that improved light harvesting and efficiency of solar cells can be obtained by implementing nanostructured ZnO layers to process advanced solar cell structures. Because of amenability to doping, high chemical stability, sensitivity to different adsorbed gases, nontoxicity and low cost ZnO attracted much attention for application as gas sensors. The sensitivity of nano-grain ZnO gas elements is comparatively high because of the grain-size effect. Application of nanostructured ZnO for gas sensors and for increasing of light harvesting in solar cells is demonstrated.

Reduced Ensemble Plasmon Line Widths and Enhanced Two-Photon Luminescence in Anodically Formed High Surface Area Au-TiO2 3D Nanocomposites.

Localized surface plasmon resonances (LSPR) in TiO2 nanorod and nanotube arrays decorated by gold nanoparticles can be exploited to improve photocatalytic activity, enhance nonlinear optical coefficients, and increase light harvesting in solar cells. However, the LSPR typically has a low quality factor, and the resonance is often obscured by the Urbach tail of the TiO2 band gap absorption. Attempts to increase the LSPR extinction intensity by increasing the density of gold nanoparticles on the surface of the TiO2 nanostructures invariably produce peak broadening due to the effects of either agglomeration or polydispersity. We present a new class of hybrid nanostructures containing gold nanoparticles (NPs) partially embedded in nanoporous/nanotubular TiO2 by performing the anodization of cosputtered Ti-Au thin films containing a relatively high ratio of Au:Ti. Our method of anodizing thin film stacks containing alternate layers of Ti and TiAu results in very distinctive LSPR peaks with quality factors as high as 6.9 and ensemble line widths as small as 0.33 eV even in the presence of an Urbach tail. Unusual features in the anodization of such films are observed and explained, including oscillatory current transients and the observation of coherent heterointerfaces between the Au NPs and anatase TiO2. We further show that such a plasmonic NP-embedded nanotube structure dramatically outperforms a plasmonic NP-decorated anodic nanotube structure in terms of the extinction coefficient, and achieves a strongly enhanced two-photon fluorescence due to the high density of gold nanoparticles in the composite film and the plasmonic local field enhancement.

Controlling the intensity of light in large areas at the interfaces of a scattering medium

The recent advent of wave-shaping methods has demonstrated the focusing of light through and inside even the most strongly scattering materials. Typically in wavefront shaping, light is focused in an area with the size of one speckle spot. It has been shown that the intensity is not only increased in the target speckle spot, but also in an area outside the optimized speckle spot. Consequently, the total transmission is enhanced, even though only the intensity in a single speckle spot is controlled. Here, we experimentally study how the intensity enhancement on both interfaces of a scattering medium depends on the optimization area on the transmission side. We observe that as the optimization radius increases, the enhancement of the total transmitted intensity increases. We find a concomitant decrease of the total reflected intensity, which implies an energy redistribution between transmission and reflection channels. In addition, we find qualitative evidence of a long-range reflection-transmission correlation. Our result is useful for efficient light harvesting in solar cells, multichannel quantum secure communications, imaging, and complex beam delivery through a scattering medium.

Mapping the energy density of shaped waves in scattering media onto a complete set of diffusion modes.

We study the energy density of shaped waves inside a quasi-1D disordered waveguide. We find that the spatial energy density of optimally shaped waves, when expanded in the complete set of eigenfunctions of the diffusion equation, is well described by considering only a few of the lowest eigenfunctions. Taking into account only the fundamental eigenfunction, the total internal energy inside the sample is underestimated by only 2%. The spatial distribution of the shaped energy density is very similar to the fundamental eigenfunction, up to a cosine distance of about 0.01. We obtain the energy density of transmission eigenchannels inside the sample by numerical simulation of the scattering matrix. Computing the transmission-averaged energy density over all transmission channels yields the ensemble averaged energy density of shaped waves. From the averaged energy density, we reconstruct its spatial distribution using the eigenfunctions of the diffusion equation. The results of our study have exciting applications in controlled biomedical imaging, efficient light harvesting in solar cells, enhanced energy conversion in solid-state lighting, and low threshold random lasers.

Modified Becke-Johnson exchange potential: improved modeling of lead halides for solar cell applications

We report first-principles calculations, within density functional theory, on the lead halide compounds PbCl 2 , PbBr 2 , and CH 3 NH 3 PbBr 3−x Clx, taking into account spin-orbit coupling. We show that, when the modified Becke-Johnson exchange potential is used with a suitable choice of defining parameters, excellent agreement between calculations and experiment is obtained. The computational model is then used to study the effect of replacing the methylammonium cation in CH 3 NH 3 PbI 3 and CH 3 NH 3 PbBr 3 with either N 2 H 5 + or N 2 H 3 + , which have slightly smaller ionic radii than methylammonium. We predict that a considerable downshift in the values of the band gaps occurs with this replacement. The resulting compounds would extend optical absorption down to the near-infrared region, creating excellent light harvesters for solar cells.

Bifunctional Polymer Nanocomposites as Hole-Transport Layers for Efficient Light Harvesting: Application to Perovskite Solar Cells.

A new approach to largely enhancing light harvesting of solar cells by employing bifunctional polymer nanocomposites as hole-transport layers (HTLs) is proposed. To illustrate our working principle, CH3NH3PbI3-xClx perovskite solar cells are used as examples. Gold nanoparticles (Au-NPs) are added into a conjugated poly(3-hexylthiophene-2,5-diyl) (P3HT) matrix, resulting in a ∼4-fold enhancement in the electrical conductivity and carrier mobility of the native P3HT film. The improved electrical properties are attributed to enhanced polymer chain ordering caused by Au-NPs. By integration of those P3HT:Au-NP films with an optimum loading concentration of 20% into perovskite solar cells as HTLs, this leads to a more than 25% enhancement in the power conversion efficiency (PCE) compared with that of the NP-free one. In addition to the modulated electrical properties of the HTL, the improved performance can also be attributed to the scattering effect from the incorporated Au-NPs, which effectively extends the optical pathway to amplify photon absorption of the photoactive layer. The design principle shown here can be generalized to other organic materials as well, which should be very useful for the further development of high-performance optoelectronic devices.

Schottky Solar Cells with CuInS2 Nanocrystals as Absorber Material

Abstract Colloidal semiconductor nanocrystals with tunable optical properties are promising materials for light harvesting in solar cells. So far, in particular cadmium and lead chalcogenide nanocrystals were intensively studied in this respect, and the device performance has made rapid progress in recent years. In contrast, less research efforts were undertaken to develop solar cells based on Cd- and Pb-free nanoparticles as absorber material. In the present work, we report on Schottky solar cells with the absorber layer made of colloidal copper indium disulfide nanocrystals. Absorber films with up to ∼ 500 nm thickness were realized by a solution-based layer-by-layer deposition technique. The device performance was systematically studied dependent on the absorber layer thickness. Decreasing photocurrent densities with increasing thickness revealed charge transport to be a limiting factor for the device performance.

Research on Charge Accumulation and Transport in Hole-Conductor-Free Perovskite (CH3NH3PbI2Cl) -based Nanostructure Solar Cells

Organic-inorganic lead halide perovskite, initially applied as active layer in light-emitting diode (LED) and field-effect transistor ( FET) devices[1], has been gradually introduced into the development of solar cells and plays such critical role as either light absorber or hole conducting material (HCM). This kind of hybrid layer structure makes perovskite as a promising candidate in photovoltaic applications, mainly due to its attractive chemical versatility that can readily tune the electronic coupling between inorganic sheets, and eventually tailor its optical/electronic properties[2]. In order to understand the performance of a photovoltaic device especially involving such novel material for its further optimization consideration, exploring the photogenerated charge accumulation and transport is imperative to be highlighted. Here we report the work on perovskite (CH3NH3PbI2Cl[3])-based nanostructure solar cell, including the cell fabrication and characterization, and particularly provide the analysis on charge carrier properties on the basis of dynamic electrochemical measurements. In this research stage, we targets more than achieving relatively fair energy conversion efficiency, instead we hope to uncover internal mechanisms of charge carrier movement and subsequently the substantial function of perovskite in photovoltaic device.The stack structure of the mesoscopic solar cell we developed for this investigation is shown in Fig. 1(a). The nanoporous semiconductor oxide membrane was fabricated by screen-printing technique on fluorine doped tin oxide (FTO) glass substrate with terpineol-based paste made by commercial-available TiO2 powder (Aldrich, d=25nm). The work electrode coated with the TiO2 paste was sintered under airflow at 550oC for 3 h. Iodide-chloride mixed-halide perovskite was synthesized from a N,N-Dimethylformamide solution of CH3NH3I and PbCl2 (3:1 molar ratio) [3]. The precursor solution was deposited on porous TiO2 surface via spin-coating or dipping process, and then was dried at 100oC. After drying, obvious color variation indicated the formation of perovskite layer. The function of the perovskite layer in nanostructure solar cells strongly depends on the deposition method. In particular, the shape of nanocrystalline CH3NH3PbI2Cl infiltrating into TiO2 porous membrane, probably with quantum-dot structure, is confirmed by electron microscopy micrographs. One thing should be noted is that, combining the band diagram shown in Fig.1(b), the extremely thin CsSnI2.95F0.05 layer (referring our previous work for its synthesis[4]) deposited on counter electrode performs more like energy ‘staircase’ for hole transport rather than pure hole conducting material. Meanwhile, a heterojunction-like cell (called ‘blank’ cell) containing only CH3NH3PbI2Cl layer on the TiO2film is produced for comparison.In order to thoroughly understand the decisive mechanisms of charge accumulation and transport behaviors on photovoltaic conversion, a systematic characterizations including photocurrent transient, open-circuit voltage decay (OCVD) and electrochemical impedance spectroscopy (EIS) were carried out under different operation conditions. Correspondingly the effective lifetime and diffusivity of charge carriers are extracted to investigate the transport properties of photon-generated electrons. Particularly, chemical capacitance (Cμ) is examined since it assists to monitor the Fermi level of electrons and density of states (DoS) in perovskite absorber, which significantly differentiates from conventional dye (e.g. N719) sensitized solar cells on the aspect of charge generation and accumulation in light absorber material.Consequently, our research demonstrates the promising HCM-free nanostructure solar cells involving solution-processed perovskite material. Fair light absorption and charge accumulation capability make self-assembled CH3NH3PbI2Cl behave as both sensitizer and charge transport material, which helps to constitute new kind of solid-state sensitized solar cells with a much simpler configuration. Reference 1. D. B. Mitzi, K. Chondroudis, and C.R. Kagan, Organic–inorganic electronics. IBM J. Res. & Dev. , 2001. 45(1): p. 29-45.2. Etgar, L., Semiconductor Nanocrystals as Light Harvesters in Solar Cells. Materials 2013. 6: p. 445--59.3. Lee, M.M., et al., Efficient hybrid solar cells based on meso-superstructured organometal halide perovskites. Science, 2012. 338 ( 6107): p. 643-647.4. Sun, X., et al., Effects of calcination treatment on the morphology, crystallinity, and photoelectric properties of all-solid-state dye-sensitized solar cells assembled by TiO2 nanorod arrays. Phys. Chem. Chem. Phys., 2013. 15: p. 18716-18720.

Quantized structuring of transparent films with femtosecond laser interference

The confinement of laser interactions inside transparent materials assisted by tight optical focusing and short-pulsed nonlinear interactions has driven many high-resolution patterning and probing applications in science and technology. In thin transparent films, laser interactions confined to the film/substrate interface have underpinned blistering and ejection processes for nanofluidic channel fabrication, film patterning and cell catapulting. Here, we harness femtosecond lasers to drive nonlinear interactions within Fabry–Perot interference fringes to define narrow nanolength scale zones for highly resolved internal structuring of a film of refractive index, nfilm, at fringe maxima separated by λ/2nfilm. This novel interaction internally cleaves the film to open subwavelength internal cavities and form thin membranes at single or multiple depths from which follow significant opportunities for writing multilevel nanofluidic channels inside the film, as well as ejecting nanodisks at quantized film depths for coloring and three-dimensional surface patterning that promise new compact types of lab-in-film devices. High-resolution structuring of thin transparent films using a femtosecond laser can aid the fabrication of various devices. Kitty Kumar and co-workers from the University of Toronto in Canada say that interference from reflections at the film’s boundaries causes the laser light to create a series of periodic plasma disks in the dielectric film that eject material. The resulting laser-generated nanovoids could be useful for fabricating miniature cavities and fluidic waveguides or performing nanoscale texturing to improve light harvesting in solar cells or light extraction from LEDs. The researchers tested their scheme with a stream of 200 fs pulses from a 522 nm frequency-doubled fibre laser operating at a repetition rate of 100 kHz. They focused the pulses onto an SiNx film measuring 20–1,545 nm thick.