This work investigates the creation of nanostructured glass surfaces through the solid-state thermal dewetting of gold (Au) thin films, followed by the removal of the resulting Au nanoisland (AuNI) to form craters on the glass substrate. By varying the nominal thickness of the Au film and the annealing time, we controlled the size, density, and distribution of the AuNI, which in turn affected the dimensions of the resulting craters. Characterization of these nanostructured surfaces was performed using SEM and AFM analyses, revealing significant variations in the lateral and vertical characteristics. Experimental reflectivity measurements showed up to a 20% reduction, demonstrating the tunability of the nanostructured surfaces. The Maxwell-Garnett model (MGM) was employed to theoretically model the optical properties of these surfaces, treating the craters as air-filled cylinders. The MGM parameters, including the thickness of the nanostructured layer and the filling fraction of the cylinders, were derived to match experimental data. Further theoretical optimization indicated that achieving craters with a depth of approximately 100nm could further reduce reflectivity. This tunability in nanostructuring enables the design of glass surfaces with specific optical properties, making the findings promising for applications such as solar cells, where minimizing Fresnel losses is crucial.
This work investigates the reflectance properties of nanostructured glass surfaces modeled as random monolayers of air spheres embedded in a glass matrix. The study employs three analytical models: the Maxwell-Garnett Model (MGM), the 2D Dipole Model (2-DMM), and the Coherent Scattering Model (CSM). All models predicted a decrease in reflectance due to the nanostructuring of the glass surface. This decrease in reflectance is particularly significant, reaching up to almost 20% across the entire visible spectrum, for nanostructures with 15% surface coverage and crater radii of 50nm. Each model’s suitability, advantages, and limitations are discussed in the context of varying particle sizes and surface coverages.
This investigation assesses the effect of different encapsulation materials and environmental conditions on ionic currents in methylammonium lead iodide (MAPI) thin films, which are essential for the stability of perovskite solar cells. Encapsulation types such as PMMA, MgF2, and SiO2 were examined under both air and vacuum conditions, complemented by an epoxy-sealed glass cover for extra protection. Employing the photo-electromotive force technique to analyze ion dynamics, findings indicate that environmental exposure and layer interaction profoundly influence ionic activity. While a single encapsulation layer falls short in protecting against environmental factors, combining SiO2 with an epoxy-sealed glass significantly improves MAPI film stability, albeit the epoxy layer alters ionic responses, underscoring the complexity in optimizing encapsulation for enhanced solar cell performance.
In this work, we investigate the plasmonic response of a random metasurface based on gold nano-islands (AuNI) in an attenuated total reflectance (ATR) configuration. AuNI structures were obtained by thermal annealing of an ultrathin gold film deposited on a glass substrate. The samples exhibited a wide range of sizes and particle densities, varying the nominal gold thickness. For p polarization, a well-defined localized surface plasmon resonance (LSPR) dip was observed in all samples, while for s polarization, only AuNI with the smallest radii showed this dip. Some samples exhibited nearly zero reflection at the resonance wavelength. The highest sensitivity among all tested samples was achieved in these samples, providing potential for optimizing LSPR transducers in sensing applications. Notably, the resonance wavelength exhibited a nonlinear dependence on the refractive index in sensitivity measurements displaying a blue shift.
In this work, we have developed a refractive index change sensing system utilizing localized surface plasmon resonance (LSPR) transduction, combined with a position-sensitive photodetector (PSPD). As the transducers, we utilized gold nano-islands formed through thermal annealing of an Au film with a nominal thickness of 13 nm. The LSPR was excited by evanescent wave in an attenuated total reflectance configuration. Refractive index changes result in modifications across the angular spectrum of LSPR, giving rise to variations in the differential signal detected between the two quadrants of the photodetector. We determined the refractive index resolution of our sensing system at different wavelengths and performed a comparative analysis with traditional surface plasmon resonance (SPR) transducers and available literature data. While LSPR transducers demonstrate a lower refractive index resolution (RIR) compared to SPR, the approach presented in this work stands out when compared to other LSPR sensing methods. Notably, at a wavelength of 785 nm, it achieves a remarkable RIR of 1.4 × 10−6 RIU.
In this study, we investigate the phenomenon of nearly zero reflectance and associated phase singularity in a random array of gold nanoislands (Au NI) both theoretically and experimentally. The Au NI were produced via solid-state thermal dewetting of ultrathin gold films, which were magnetron sputtered onto a glass substrate. The morphology of the nanoislands was characterized using scanning electron microscopy and atomic force microscopy. To understand the plasmonic response of the random array of Au NI, we conducted reflectance measurements for both s and p polarized beams demonstrating the p. These measurements were performed using the attenuated total internal reflectance configuration. A partial state of topological darkness in a random array of Au NI was demonstrated by showing nearly zero reflection for the p polarization component. Additionally, we employed a common path spectral interferometer to measure the differential phase spectra. Our findings revealed that the differential phase spectra exhibited abrupt ±π phase jumps, indicating the presence of a phase singularity regime. Moreover, we demonstrated high bulk reflectance index sensitivity (RIS) within this regime. To validate our experimental results, we compared them with analytical reflectance and phase spectra obtained through the application of island film theory. The agreement between the experimental and theoretical predictions provided strong confirmation of our measurement technique.
We have demonstrated theoretically and experimentally that the current induced by an interference pattern moving at constant velocity can be used to determine the ion mobility and activation energy in perovskite semiconductors. The frequency dependence of the signal has features predicted by theory: the high-frequency peak corresponds to the electron/hole photoconductivity relaxation process, and the low-frequency peak occurs when the velocity of the interference pattern synchronizes with the ion motion; by determining the peak’s position, it becomes possible to estimate the ion mobility. The values of ion mobility and activation energy agree with the data reported in the literature.
The study of unstable interfaces in perovskite semiconductors requires crucial information on interfacial composition, chemical gradients, and impurity distribution. A versatile technique called TOF-SIMS can provide this information effectively. Solar cells employing methylammonium lead triiodide as the photoactive layer were fabricated, utilizing PEDOT:PSS or NiOx thin film as the hole transporting layer, and PCBM plus ZnO as the electron transporting layer. These inorganic and organic layers were deposited through magnetron sputtering and solution processing, respectively. To comprehensively examine each interface within the device structure, a detailed TOF-SIMS study was conducted.
Organic materials have become very important in recent years due to their potential use for photovoltaic applications. Among the main advantages of organic semiconductors are their functional and mechanical flexibility, as well as fabrication simplicity. However, these materials usually afford moderate efficiency in organic photovoltaic devices. On the other hand, hydrogenated amorphous silicon (a-Si:H) is a widely known inorganic semiconductor that compared to their organic counterparts has excellent photogeneration and transport properties and it is suitable for large area fabrication of flexible devices. The idea of combining organic semiconductors and amorphous silicon films in hybrid photovoltaic devices is very attractive due to the possibility to complement the useful properties of both material systems. The photovoltaic devices that we study in this work consist of a p-i-n structure, which is also commonly used in inorganic solar cells. In such kind of structures, the light is mainly absorbed in the intrinsic silicon film and the p- and ntype films are used to create an electric field that separates electrons and holes to produce a photocurrent. In this work, we use an organic material (PEDOT:PSS) to replace the p-type inorganic film in amorphous silicon p-i-n structure. It is widely known, that PEDOT:PSS based organic film is highly transparent and its conductivity can be modified e.g. immerse in a solvent type. Here we present the results of experimental investigation of the effect of isopropanol (IPA) treatments in p-type (PEDOT:PSS) organic layer on characteristics of hybrid solar cell structure.
In this work, we present the results of investigation of thin film hybrid organic-inorganic photovoltaic structures based on flat heterojunction hydrogenated silicon (a-Si:H) and poly(3,4 ethylene dioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) fabricated on polyethylene naphthalate (PEN). Different thicknesses of transparent AL doped Zn:O (AZO) electrodes have been tested on PEN substrate and studied by atomic force microscopy (AFM). The AZO films on PEN substrate were statistically processed to obtain surface morphological characteristics, such as root mean square roughness RQ, skewness SK and kurtosis KU. Performance characteristics of fabricated photovoltaic structures have been measured and analyzed for different thicknesses of the transparent electrodes under standard illumination (AM 1.5 I0= 100mW/cm2). Structures on flexible substrates show reproducible performance characteristic as their glass substrate counterpart with values of JSC= 6 mA/cm2, VOC= 0.535 V, FF= 43 % and PCE= 1.41%.
vHere, we consider the possibility of involving the photo-EMF detectors in registration of the parameters peculiar to ultrashort
optical pulses, and it is compared whit the recently triple correlator via Direct and Cascade Third Harmonic
Generation. Knowledge of triple auto-correlation function, whose Fourier transformation shapes the corresponding
bispectrum, makes possible recovering such train-average parameters as, for instance, the pulse width and frequency
chirp as well as revealing asymmetry of ultra-short pulse envelope. The main advantage of applying the photo-EMF
detectors lies in an opportunity to detect triple correlations directly, without any intermediate frequency conversion with
optical nonlinear processes in additional crystals. Then, the theory of three-beam-correlations at photosensitive layer of
the photo-EMF detector is developed, so that principal possibility of registering the high-order-correlations is
demonstrated. It can be done within schematic arrangement including the three-beam Michelson interferometer, so that
the obtained high-order-correlations have non-traditional form and need rather specific algorithm for their further
processing. Also, the experimental characterizations are presented for gallium arsenide (GaAs) semiconductor and the
poly-fluoren 6-co-triphenyldiamine (PF6-TPD) photo-conductor-polymer, which both exhibit the photo-EMF-effect.
They both exhibit high-pass transfer functions that give us high vibration stability. This novel approach provides more
reliable analyzing train-average parameters of picosecond pulses due to significantly higher level of the output optical
signals under processing.
The results on characterization of the main photoelectric properties of the polymer:fulleren based composite
material by using the non-steady-state photo-electromotive force (p-EMF) and modulated photocurrent technique are
presented. By measuring this current under different experimental conditions, important material photoelectric
parameters such as drift L0 and diffusion length LD, photocarrier's lifetime τ ; quantum efficiency of charge
generation φ can be determined. The 50% of the composite weight consists of a mixture of the hole-conducting
polymer PF6:TPD (poly-hexyle-triophene:N,N'-bis(4-methylphenyl)-N,N'-bis-(phenyl)-benzidine) sensitized with the
highly soluble C60 derivative PCBM (phenyl-C61-butyric acid methyl ester) . Seven samples with varied
polymer:sensitizer weight ratio (49:1wt.-%, 45:5wt.-%, 40:10wt.-%, 15:35wt.-%, 25:25wt.-%, 10:40wt.-%, 5:45wt.-%)
where prepared. The remaining 50% were two azo-dyes 2,5-dimethyl-(4-p-nitrophenylazo)-anisole (DMNPAA) and 3-
methoxy-(4-p-nitrophenylazo)-anisole (MNPAA) (25wt.-% each). Photoconductive composite film was sandwiched
between two glass plates covered by transparent ITO electrodes. Two counter-propagating beams derived from a cw
HeNe laser (λ = 633nm) intersected inside the detector creating an interference pattern. The output photo-EMF
current (SEE MANUSCRIPT FOR EQUATION) was detected as a voltage drop by a lock-in amplifier.
At polymer sensitizer ratio 25:25wt.-% the signal sign changes to the opposite revealing that the majority
carriers at this and higher concentration of sensitizer are electrons. Our results show that the majority carrier's lifetime
τ is only slightly affected by the variations of sensitizer concentration. Mobility-lifetime product μhτh of holes, on its
turn decreases at the increasing sensitizer concentration, while μeτe of electrons keeps increasing. All this indicates that
the carrier's mobility is strongly influenced by the changes on sensitizer concentrations.
Organic semiconductors with bipolar (electron and hole) transport capability play a crucial role in electronic and
optoelectronic devices such as organic light-emitting diodes (OLEDs), bipolar transistors and photovoltaic cells.
Recently, a considerable amount of work has been devoted to the characterization of ambipolar transport in organic
materials, allowing for a better understanding of their properties as well as the physical processes, which take place in
materials and devices [1-4]. The experimental methods used to obtain information about charge transport in organic
semiconductors - time-of-flight (TOF) transient photoconductivity [5], charge extraction by linearly increasing voltage
(CELIV) [6], current-voltage measurements in space charge limited current regime [7], and field effect transistor (FET)
measurements [8, 9] are mostly focused on determination of charge carrier mobility. On the other hand, for many devices
(e.g. organic photovoltaic solar cells or light emitting diodes) the knowledge of the transport and recombination
characteristics of both carriers (electron and hole), and specifically their diffusion LD = the square root of Dτ (here D is the diffusion
coefficient and τ is the photocarriers lifetime) and drift lengths L0 = μτE0 (here μ is the carrier's mobility and E0 is
the electric dc field) is important.
We present an advanced approach to describing low-power trains of bright picosecond optical dissipative solitary
pulses with an internal frequency modulation in practically important case of exploiting semiconductor heterolaser
operating in near-infrared range in the active mode-locking regime. In the chosen schematic arrangement, process of
the active mode-locking is caused by a hybrid nonlinear cavity consisting of this heterolaser and an external rather long
single-mode optical fiber exhibiting square-law dispersion, cubic Kerr nonlinearity, and small linear optical losses. Our
analysis of shaping dissipative solitary pulses includes three principal contributions associated with the modulated
gain, total optical losses, as well as with linear and nonlinear phase shifts. In fact, various trains of the non-interacting
to one another optical dissipative solitons appear within simultaneous balance between the second-order dispersion and
cubic-law Kerr nonlinearity as well as between active medium gain and linear optical losses in a hybrid cavity. Our
specific approach makes possible taking the modulating signals providing non-conventional composite regimes of a
multi-pulse active mode-locking. Within our model, a contribution of the appearing nonlinear Ginzburg-Landau
operator to the parameters of dissipative solitary pulses is described via exploiting an approximate variational
procedure involving the technique of trial functions.
We discuss specifically elaborated approach for characterizing the train-average parameters of low-power picosecond
optical pulses with the frequency chirp, arranged in high-repetition-frequency trains, in both time and frequency
domains. This approach had been previously applied to rather important case of pulse generation when a single-mode
semiconductor heterolaser operates in a multi-pulse regime of the active mode-locking with an external single-mode
fiber cavity. In fact, the trains of optical dissipative solitary pulses, which appear under a double balance between
mutually compensating actions of dispersion and nonlinearity as well as gain and optical losses, are under
characterization. However, in the contrast with the previous studies, now we touch an opportunity of describing two
chirped optical pulses together. The main reason of involving just a pair of pulses is caused by the simplest opportunity
for simulating the properties of just a sequence of pulses rather then an isolated pulse. However, this step leads to a set
of specific difficulty inherent generally in applying joint time-frequency distributions to groups of signals and
consisting in manifestation of various false signals or artefacts. This is why the joint Chio-Williams time-frequency
distribution and the technique of smoothing are under preliminary consideration here.
Talbot self-images localization is important in many optical applications such as interferometry, metrology
and nanolithography. Usually, the problem of self-images localization is reduced to the finding the planes of
maximal light pattern visibility. There are several conventional techniques that determine the contrast of an intensity
distribution generated by a periodical object, such as root mean square (RMS) method, and variogram-based method.
In all these cases, a CCD camera is used to record the light patterns that are processed and analyzed in order to find
the self-image position. Recently, it has been proposed the use an adaptive photo-detector based on the non-steadystate
photo-electromotive force (photo-EMF) effect, which uses periodically oscillating light pattern to induce
alternating current through the short-circuited photoconductive sample. Here we perform the theoretical analysis of
the technique based on the photo-EMF effect against the conventional methods for the localization of the Talbot
patterns.
We present the experimental study of a new method that uses an adaptive photodetector based on the nonsteady-
state photoelectromotive force (photo-EMF) effect for measuring the visibility of the Talbot patterns generated by a Ronchi grating. It was demonstrated that the photo-EMF based detector could be used for efficient localization of planes with minimal and maximal visibility in real time, with high spatial resolution and without any
signal processing. The possibility for localization of self-images in turbid media was also investigated. Finally, the
performance of our method was compared against conventionally used method based on analysis of images obtained by CCD camera.
The detectors based on non-steady-state photo-electromotive force (p-EMF) effect, induced in a photoconductor by
an oscillating light pattern, have been proposed recently for localization of self-images generated by a periodical
object in real time and without any image processing. Here, we present the detailed theoretical analysis of the p-
EMF effect induced by an arbitrary 1-D periodical light pattern. Analytical expression for p-EMF current density in
a case of light distribution containing only odd harmonics is derived. In order to illustrate our results, axial
dependence of the photo-EMF signal induced by patterns generated in near field by the diffraction on a binary
grating was simulated numerically. Our results demonstrated, that the optimum regime for the localization of selfimages
using the p-EMF based detector is when the fundamental spatial harmonic of the light pattern is smaller than
the inverse of the diffusion length of the charge carriers, being the p-EMF current proportional to the sum of the
squares of the spatial harmonics visibilities.
Practical feasibility of measuring the train-average parameters of picosecond optical pulses being arranged in highfrequency
repetition trains is investigated. For this purpose we consider exploiting the triple auto-correlations, whose
Fourier transformations give the bispectrum of a pulse train. The main merit of similar approach consists in the
capability of recovering signals and revealing asymmetry of pulse envelopes. The triple auto-correlation can be shaped
by a three-beam scanning interferometer with the following one- or two-cascade triple harmonic generation. The
efficiencies of these processes depend on the number of cascades and differ in various modern materials. The key
features of measuring the train-average parameters of pulses with possible frequency chirp are also discussed.
We make an attempt to develop a novel approach to describing the initial stage of the active mode-locking in
semiconductor laser structures based on analyzing the properties of dispersion relations in terms of stability for small
initial perturbations. Nonlinear process of shaping optical pulses is interpreted as manifesting instability of diffusion
type. For the purposes of experimental investigations, the auto-manual opto-electronic measuring system detecting
average time parameters inherent in ultra-short optical pulse trains has been designed. This system is able to register
auto-correlation functions of the second order exploiting the interferometric technique as well as to identify a pulsed
character of the incoming light radiation. Experimental confirmations of appearing the diffusive instability within the
active mode-locking process in semiconductor laser structures operating in the near infrared range are presented.
We report on the use of a photorefractive polymer composite as the active material for a planar photo-
EMF detector suitable for the adaptive detection of optical phase modulated signals in the audio range
(10Hz-10KHz). The composite is based on a conjugated triphenyldiamine- phenylenevinylene polymer
(TPD-PPV) and is sensitized with a highly soluble fullerene derivative (PCBM). We demonstrate
experimentally that the responsitivity of such polymer based detectors can be remarkably enhanced if the
polymer sample is biased by an external dc field. This effect is theoretically explained by the strong
dependence of the charge carrier generation rate on the external dc field, which is an inherent property of
organic photoconductors.
We report on simultaneous characterization of space charge gratings in photorefractive PVK-based polymer films by means of photo-EMF and Two-Wave Mixing (TWM) of periodically phase modulated beams. 100 micron thick samples of a polymer DMNPAA:PVK:ECZ:TNF with chromophore (DMNPAA) concentration of 5 wt% were investigated at (lambda) equals 633 nm in reflectance configuration. The amplitudes of the unshifted (i.e. drift induced) and the shifted (i.e. diffusion or saturation induced) components of the photorefractive space- charge field grating were evaluated directly by detection of the fundamental and the second harmonic of the TWM signal and indirectly from the corresponding harmonics of the photo-EMF current. The unshifted grating component exhibited approximately linear dependence on the externally applied dc field E0 and had an amplitude close to E0, which can be interpreted as absence of any remarkable saturation of trapping centers associated with photorefractive recording. Also growing with E0, the amplitude of the shifted component did not depend on the applied field direction, but was nearly as big as the unshifted component for the external fields of about approximately equals 50 V/micrometers . We interpret these facts as well as an experimentally observed double change of sign fo the fundamental harmonic photo-EMF signal with the external field as a result of dramatic growth of the Einstein ratio D/(mu) (relating diffusion coefficient D and mobility (mu) of the photogenerated carriers) - at least up to 1 V for the external dc field mentioned above. This allows us to address the observed shifted component as an external field enhanced diffusion grating, rather than the result of trapping centers saturation. Additionally, the (mu) (tau) product for dominating photocarriers (holes) was evaluated as approximately equals 0.3*10- 10 cm2/V from the photo-EMF measurements.
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