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The determination of minority-carrier lifetimes and surface recombination velocities is essential for the development of semiconductor technologies such as solar cells. The recent development of two-photon time-resolved microscopy allows for better measurements of bulk and subsurface interfaces properties. Here, we analyze the diffusion problem related to this optical technique. Our three-dimensional treatment enables us to separate lifetime (recombination) from transport effects (diffusion) in the photoluminescence intensity. It also allows us to consider surface recombination occurring at a variety of geometries: a single plane (representing an isolated exposed or buried interface), a two parallel planes (representing two inequivalent interfaces), and a spherical surface (representing the enclosing surface of a grain boundary). We provide fully analytical results and scalings directly amenable to data fitting and apply those to experimental data collected on heteroepitaxial CdTe/ZnTe/Si. [ABSTRACT FROM AUTHOR]

Temperature-dependent measurements of carrier recombination rates using a time-resolved optical pump-probe technique are reported for mid-wave infrared InAs/InAs1–xSbx type-2 superlattices (T2SLs). By engineering the layer widths and alloy compositions, a 16K band-gap of ~235±10 meV was achieved for five unintentionally and four intentionally doped T2SLs. Carrier lifetimes were determined by fitting lifetime models based on Shockley-Read-Hall (SRH), radiative, and Auger recombination processes to the temperature and excess carrier density dependent data. The minority carrier (MC), radiative, and Auger lifetimes were observed to generally increase with increasing antimony content and decreasing layer thickness for the unintentionally doped T2SLs. The MC lifetime is limited by SRH processes at temperatures below 200K in the unintentionally doped T2SLs. The extracted SRH defect energy levels were found to be near mid-bandgap. Also, it is observed that the MC lifetime is limited by Auger recombination in the intentionally doped T2SLs with doping levels greater than n~1016 cm–3. [ABSTRACT FROM AUTHOR]

A photoluminescence (PL) spectroscopy study of the bulk quaternary alloy InAlAsSb is presented. Samples were grown lattice-matched to InP by molecular beam epitaxy and two different growth temperatures of 450 °C and 325 °C were compared. Interpolated bandgap energies suggest that the development of this alloy would extend the range of available direct bandgaps attainable in materials lattice-matched to InP to energies as high as 1.81 eV. However, the peak energy of the observed PL emission is anomalously low for samples grown at both temperatures, with the 450 °C sample showing larger deviation from the expected bandgap. A fit of the integrated PL intensity (I) to an I ∞ Pk dependence, where P is the incident power density, yields characteristic coefficients k=1.05 and 1.18 for the 450 °C and 325 °C samples, respectively. This indicates that the PL from both samples is dominated by excitonic recombination. A blue-shift in the peak emission energy as a function of P, along with an S-shaped temperature dependence, is observed. These trends are characteristic of spatially-indirect recombination associated with compositional variations. The energy depth of the confining potential, as derived from the thermal quenching of the photoluminescence, is 0.14 eV for the 325 °C sample, which is consistent with the red-shift of the PL emission peak relative to the expected bandgap energy. This suggests that compositional variation is the primary cause of the anomalously low PL emission peak energy. The higher energy PL emission of the 325 °C sample, relative to the 450 °C sample, is consistent with a reduction of the compositional fluctuations. The lower growth temperature is therefore considered more favorable for further growth optimization. [ABSTRACT FROM AUTHOR]

Although the long-term stability of organic light-emitting diodes (OLEDs) under electrical operation made significant progress in recent years, the fundamental underlying mechanisms of the efficiency decrease during operation are not well understood. Hence, we present a comprehensive degradation study of an OLED structure comprising the well-known green phosphorescent emitter Ir(ppy)3. We use transient methods to analyze both electrical and optical changes during an accelerated aging protocol. Combining the results of displacement current measurements with time-resolved investigation of the excited states lifetimes of the emitter allows for a correlation of electrical (e.g., increase of the driving voltage due to trap formation) and optical (e.g., decrease of light-output) changes induced by degradation. Therewith, it is possible to identify two mechanisms resulting in the drop of the luminance: a decrease of the radiative quantum efficiency of the emitting system due to triplet-polaron-quenching at trapped charge carriers and a modified charge carrier injection and transport, as well as trap-assisted non-radiative recombination resulting in a deterioration of the charge carrier balance of the device. [ABSTRACT FROM AUTHOR]

Excitation correlation photoluminescence (ECPL) measurements are often analyzed in the approximation of a cross correlation of charge carrier populations generated by the two delayed pulses. In semiconductors, this approach is valid for a linear non-radiative recombination path, but not for a non-linear recombination rate as in the general Shockley-Read-Hall recombination scenario. Here, the evolution of the ECPL signal was studied for deep trap recombination following Shockley-Read-Hall statistics. Analytic solutions can be obtained for a fast minority trapping regime and steady state recombination. For the steady state case, our results show that the quadratic radiative term plays only a minor role, and that the shape of the measured signal is mostly determined by the non-linearity of the recombination itself. We find that measurements with unbalanced intense pump and probe pulses can directly provide information about the dominant non-radiative recombination mechanism. The signal traces follow the charge carrier concentrations, despite the complex origins of the signal, thus showing that ECPL can be applied to study charge carrier dynamics in semiconductors without requiring elaborate calculations. The model is compared with measurements on a reference sample with alternating layers of InGaAs/InAlAs that were additionally cross-checked with time resolved optical pump terahertz probe measurements and found to be in excellent agreement. [ABSTRACT FROM AUTHOR]

The charge carrier transport in thin film hybrid solar cells is analyzed and correlated with device performance and the mechanisms responsible for recombination loss. The hybrid bulk heterojunction consisted of a blend of poly(3-hexylthiophene) (P3HT) and small size (2.4 nm) PbS quantum dots (QDs). The charge transport in the P3HT:PbS blends was determined by measuring the space-charge limited current in hole-only and electron-only devices. When the loading of PbS QDs exceeds the percolation threshold, a significant increase of the electron mobility is observed in the blend with PbS QDs. The hole mobility, on the other hand, only slightly decreased upon increasing the loading of PbS QDs. We also showed that the photocurrent is limited by the low shunt resistance rather than by space-charge effects. The significant reduction of the fill factor at high light intensity suggests that under these conditions the non-geminate recombination dominates. However, at open-circuit conditions, the trap-assisted recombination dominates over nongeminate recombination. [ABSTRACT FROM AUTHOR]

In this work, BiVO 4 composites, containing the tetragonal zircon phase (tz -BiVO 4), and monoclinic scheelite phase (ms -BiVO 4), were synthesized using the microemulsion method. The effect of pH on phase composition and photocatalytic activity were investigated. Based on X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), a ms/tz -BiVO 4 composite forms at pH = 1.0 and pure ms -BiVO 4 is obtained in the pH range 4.0–10.0. The three primary steps in preparing BiVO 4 were monitored by optical microscopy and the role played by the microemulsion on the phase composition of BiVO 4 is explained. Photoluminescence spectroscopy (PL), UV–visible diffuse reflectance spectroscopy (UV-DRS), Brunauer-Emmett-Teller (BET), linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) were employed to characterize the physical and chemical properties of BiVO 4 composites. The composite formed at pH = 1 exhibited the lowest hole-electron (h + - e - ) recombination rate, resulting in the highest photocatalytic activity towards microcystin-LR (MC-LR), with near 100% removal of MC-LR in 5 h. ESR and trapping experiments indicated that MC-LR degradation was mediated primarily by hydroxyl radicals (•OH), superoxide radicals (O 2 •−) and photogenerated holes (h + ). [ABSTRACT FROM AUTHOR]

Surface recombination in GaN and ZnO crystals was comparatively investigated using steady-state and time-resolved photoluminescence (PL) measurements. The measurements were performed for various surface orientations (+c, -c, and m-plane surfaces), and the measured PL intensity and lifetime showed distinct dependence on the surface orientation. The dependence clearly indicates that the surface recombination rate is modified by the effects of surface band bending. The results were also verified by numerical analysis using a rate equation model considering the diffusion of photoexcited carriers and their recombination processes on the surface and inside the crystal. [ABSTRACT FROM AUTHOR]

With the appearance of new near-field optical microscope, people's field of vision has been broadened to less than one tenth of the wavelength, that is, nanometer scale. In the near-field optical microscope, a probe with an aperture much smaller than the wavelength of light is used instead of an optical lens. When such a sub wavelength probe is placed within a wavelength from the surface of the object, that is, the near-field area, rich sub micron optical information can be detected by detecting the non radiation field bound to the surface of the object. In this paper, the near-field optical properties of hexagonal star and hexagonal petal MoS2 crystals are studied by near-field optical microscopy. The experimental results show that the grain boundaries of single MoS2 crystal can be distinguished in AFM and fluorescence images, but not in near-field optical images and Raman surface scanning. The near-field signal increases with the increase of sample thickness, which can be understood as the higher charge concentration in the thicker region. The grain boundary and edge of multi-layer MoS2 crystal can be distinguished in the near-field optical chart. The superposition growth of multi-layer MoS2 crystal often leads to the complex interaction between the atomic position and electronic structure. As a result, the structural and electronic recombination has taken place at the edge and the grain boundary of the atomic level. [ABSTRACT FROM AUTHOR]

Abstract In this study, we have demonstrated an inversion in the efficiency of TiO 2 and ZnO based dye sensitized solar cells for an organic sensitizer C343 and another Ru based sensitizer N719. Despite of faster electron injection from sensitizer C343 to TiO 2 than ZnO, the later shows a better photovoltaic efficiency. The higher photocurrent in C343-ZnO has been mechanistically justified by slower back electron recombination and higher dye loading obtained from open circuit potential decay, electrochemical impedance spectroscopy and absorption spectra of the sensitized photoanodes. The similar positive features are there for N719-ZnO system also. Still TiO 2 -N719 performs much better than ZnO-N719 in terms of device efficiency. We have found a signature of H-type aggregate formation of N719 dye on the ZnO photoanode surface which shows a higher energy absorption peak than the monomeric form of the dye in the diffuse reflectance mode absorption spectra of the photoanodes. These type of aggregates are unable to inject electrons into the semiconductor rather the dye aggregates can pull back the electrons from the CB of the ZnO and eventually undergoes ground state recombination. Ultrafast transient absorption spectroscopy and wavelength dependent photo-current spectra provide further insight into the effect of the dye aggregates on the photo-excited carrier dynamics which essentially reduces the light harvesting efficiency. Graphical abstract Inversion in efficiency of TiO 2 and ZnO photo-anode based DSSC depending on the choice of sensitizer. fx1 [ABSTRACT FROM AUTHOR]

A tetraaryl‐1,4‐dihydropyrrolo‐[3,2‐b]pyrroles (TAPP) moiety with the combination of two pyrrole rings and four phenyl moieties demonstrated strong electron‐donating ability and nonplanar configuration simultaneously. Once incorporated into the organic dyes as a novel electron donor, it was beneficial for the enhancement of light‐harvesting ability and suppression of electron recombination in the photovoltaic and photocatalysis systems. With the linkage of tunable conjugated bridges and electron acceptor, the corresponding organic dyes exhibited improved photovoltaic performance in dye‐sensitized solar cells and facilitated photocatalytic hydrogen generation with a highest turnover number (TON) of 4337. Through the detailed investigation of relationship between molecular structures and photovoltaic/photocatalysis property, the connection and difference in molecular design for these two systems are well explained, with the aim to promote the application of dye‐sensitized technology in various fields. TAPP dance: With the incorporation of tetraaryl‐1,4‐dihydropyrrolo‐[3,2‐b]pyrroles (TAPP) derivatives into organic dyes as novel electron donors, the optimized photovoltaic and photocatalysis performance is achieved by the efficient suppression of electron recombination in different conditions. [ABSTRACT FROM AUTHOR]

Abstract The longitudinal dynamics of electron-cooled and radio-frequency (RF)-bunched 12 C 6 + and 16 O 8 + ion beams have been investigated at a heavy-ion experimental cooler storage ring CSRe. An rf-buncher was employed to longitudinally modulate the ion beams. A new resonant Schottky pick-up was applied to monitor the intensities and longitudinal dynamics of stored and electron-cooled ion beams. Using electron-cooling, the separated Schottky noise signals of the 12 C 6 + and 16 O 8 + ions were clearly observed in the Schottky spectrum. The storage times and the particle numbers of both ion beams were measured by Schottky noise, which demonstrated the ability to perform Schottky mass spectrometry measurements and also the measurement of highly charged ions at the CSRe. In addition, an enhancement of the Schottky noise signals was observed for rf-bunched ion beams, which could be used to diagnose the intensity ion beams at storage rings. Finally, a broadly longitudinal manipulation of the ion beams by scanning the bunching frequency was realized. The investigation of electron–ion recombination experiment at ultra-low collision energies by scanning the bunching frequency of the ion beams at the storage ring CSRe is proposed. Highlights • The individual lifetimes and numbers of the 12 C 6 + and 16 O 8 + ions were measured. • An enhancement of the Schottky noise signals was observed for rf-bunched ion beams. • A broadly longitudinal manipulation of the ion beams was realized. [ABSTRACT FROM AUTHOR]

Abstract: The steady-state, spatially periodic, structures generated by the evolution of the nonlinear stage of recombination instability in dusty plasma of a non-self-sustained discharge are studied. The research has revealed two types of structures typical for this kind of discharge; they differ in the rates of the increment of recombination instability. The features of each type of structure are described, and the mechanism of their formation is presented. It is shown that the calculation results qualitatively and, with a small variation of discharge parameters, quantitatively agree with the experimental data. [ABSTRACT FROM AUTHOR]

An electromagnetic wave impinging on a gold nanosponge coherently excites many electromagnetic hot-spots inside the nanosponge, yielding a polarization-dependent scattering spectrum. In contrast, a hole, recombining with an electron, can locally excite plasmonic hot-spots only within a horizon given by the lifetime of localized plasmons and the speed carrying the information that a plasmon has been created. This horizon is about 57 nm, decreasing with increasing size of the nanosponge. Consequently, photoluminescence from large gold nanosponges appears unpolarized. [ABSTRACT FROM AUTHOR]

Constructing heterojunction is one of the methods to restrain the hole-electron recombination and thus improve the photoelectric property. In this work, PbS nanoparticles were grown directly on ultra thin MoS 2 nanosheets to fabricate 2D MoS 2 /PbS nanocomposites via a facile one-pot solvothermal route. PbS nanoparticles anchored on MoS 2 sheets exhibited high crystallinity and uniformity. The particle size can be controlled by varying the precursor concentration. The nanocomposites displayed higher photocurrent compared with pristine MoS 2 , due to the improved light harvesting and the construction of p-n heterojunction structure. [ABSTRACT FROM AUTHOR]

The construction of a plasmonic photocatalyst is an efficient way to suppress detrimental electrons-holes recombination and extend the spectral range of light absorption in semiconductors. However, the facilitation effect in the aspect of electrons-holes separation is great limited as the lack of a driving force compelled the electrons or holes migration to surface catalytic sites makes them flow randomly in semiconductors. In this work, we confirm that the integration of MoS 2 nanosheets formed two dimensional (2D) layered heterojunction with C 3 N 4 with Au-C 3 N 4 plasmonic photocatalyst can further enhance electrons-holes separation through the formation of Au-C 3 N 4 -MoS 2 nanostructure by a facile ultrasonic chemical method. The integrated MoS 2 nanosheets extract the electrons not only from C 3 N 4 due to a building up of 2D layered heterojunction but also from plasmonic Au via a “pipe” played by C 3 N 4 . The electrons “pump” role of the 2D MoS 2 nanosheets makes electrons flow randomly turn into the well-organized migration direction, promoting the electrons-holes more efficient separation and lifetime prolongation. Meanwhile, MoS 2 nanosheets also increase the light absorption of the photocatalyst owing to its inherent strength of the narrower band gap. Enabled by integration of 2D MoS 2 nanosheets, the hydrogen production rate is 2.08 times higher than that of its counterpart Au-C 3 N 4. This work highlights a new window to employ 2D layered heterojunction for enhanced photocatalytic hydrogen evolution performance. [ABSTRACT FROM AUTHOR]

The concept of negatively charged electrostatic blocking barrier is demonstrated using benzotriazole (btzH) as ancillary ligands in a new ruthenium-dicarboxybipyridine photosensitizer, [Ru(dcbpyH) 2 (btzH) 2 ], which was deprotonated in a stepwise manner generating the (Bu 4 N) 2 [Ru(dcbpy) 2 (btzH) 2 ], (Bu 4 N) 3 [Ru(dcbpy) 2 (btzH)(btz)] and (Bu 4 N) 4 [Ru(dcbpy) 2 (btz) 2 ] acid-base conjugates. All compounds were isolated as solids and used for the preparation of DSSCs with structurally similar TiO 2 /dye interface but distinct electric charge properties. The results revealed that the negative charges at the TiO 2 surface, generated by deprotonation of the dcbpyH ligands, are less effective than those generated by deprotonation of the ancillary ligands located much farther from the surface. This peripheral electrostatic field probably is more effective in inhibiting the approach of the negatively charged hole transporter I 3 − , and consequently the electron recombination, thus enhancing the overall cell performance. This hypothesis was confirmed by measuring the interfacial resistance and capacitance of running cells, and simulating the respective impedance spectroscopy data using the transmission line model. [ABSTRACT FROM AUTHOR]

We discuss some aspects important for interpretation of the Ps formation process in liquids and molecular media: (1) inhomogeneity of intratrack reactions and parameters of the e+ track, (2) final states of e+, its solvation in polar and nonpolar liquids, relation to e+ mobility, (3) quasi-neutrality of the e+ blob and its ambipolar outdiffusion, (4) appearance of the "in-blob" and "out-of-the-blob" positron fractions, and (5) electric field effect on Ps formation. [ABSTRACT FROM AUTHOR]

This paper presents a model of sublinearity of thermoluminescence (TL) dose response, based on the competitive interaction between active electron trapping centers and deep hole centers during excitation and heating of a phosphor. It is shown by analytical and numerical calculations that the sublinear response is observed at low doses, when the trap occupancy is far from saturation. It is found that the linearity index of TL dose response depends on the concentration of the deep hole traps, and on the coefficient of non-radiative electron recombination. The TL dose response is derived in parametric form. A new analytical expression is derived for the threshold doses, at which the TL response changes from a sublinear growth to an almost linear behavior. This phenomenon of a sublinear TL response changing into a linear behavior, is explained by the deep traps filling up to saturation. The dependence of the linearity index on the model parameters is found by numerical methods. [ABSTRACT FROM AUTHOR]

Recurring problems of titanium dioxide (TiO 2 ) for needing UV light to be activated and high electron-hole recombination rate limit the application of TiO 2 as a prolific photocatalyst. By modifying the morphology and introducing electron trapping species into TiO 2 , the photocatalytic activity of TiO 2 could be improved. Solvents of two different kinds; distilled water and Zamzam water were used in peroxotitanic acid synthesis of TiO 2 and the photocatalyst was utilized to degrade Reactive Blue 19 (RB19) dye under blue light irradiation (475 nm) to assess the visible light activity of synthesized TiO 2. Fluorine was incorporated to control the morphology while gold nanoparticles (GNP) stabilized by arabic gum were deposited to trap electrons. The morphology of F-TiO 2 which appeared to be in ovoid shape was confirmed by Field Emission-Scanning Electron Microscope (FE-SEM) and Transmission Electron Microscope (TEM). Brunauer-Emmett-Teller (BET) surface area and crystallite size estimated from X-ray Diffraction (XRD) data revealed that F-TiO 2 modified using HF was smaller in size and exhibited single anatase phase. The band gap of Au-TiO 2 synthesized by distilled and Zamzam water was 2.78 eV and 2.89 eV respectively; shifted from 3.08 eV in blank TiO 2 . Peroxo Au/F-TiO 2 synthesized with the incorporation of arabic gum as GNP stabilizer and HF as fluorine modifier degraded up to 49.23% of RB19 within two hours of reaction. The addition of fluorine and gold demonstrated high ability to enhance visible light activity of TiO 2 with distilled water used as solvent displayed higher photocatalytic performance compared to Zamzam water. [ABSTRACT FROM AUTHOR]

Sensitizer loading level is one of the key factors determined the performance of sensitized solar cells. In this work, we systemically studied the influence of photo-anode thicknesses on the performance of the quantum-dot sensitized solar cells. It is found that the photo-to-current conversion efficiency enhances with increased film thickness and peaks at around 20 μm. The optimal value is about twice as large as the dye counterparts. Here, we also uncover the underlying mechanism about the influence of film thickness over the photovoltaic performance of QDSSCs from the light harvesting and charge recombination viewpoint. [ABSTRACT FROM AUTHOR]

The presence of copper contamination is known to severely degrade the minority carrier lifetime of p-type silicon upon exposure to illumination. In this contribution, we have analyzed the recombination activity of light-activated copper defects in deliberately Cu-contaminated p-type silicon by means of a recombination model that quantitatively defines the effect of metallic precipitates on minority carrier lifetime. The excellent agreement between the model and the experimental data indicates that (i) the formation of Cu precipitates is the probable root-cause behind Cu-LID and (ii) in the samples examined in this work, the precipitate radius varies between few to several tens of nm with corresponding densities estimated to be in the range of 108-1010 cm−3. Further evidence of these results was obtained from the analysis of temperature-dependent lifetime data. While applied here to light-activated copper defects, the procedure described in this article can be applied for characterizing lifetime-limiting precipitates originated by other transition metals (e.g., Fe or Ni). [ABSTRACT FROM AUTHOR]

The move toward lower cost sources of solar silicon has intensified the efforts to investigate the possibilities of passivating or reducing the recombination activity caused by deep states associated with transition metals. This is particularly important for the case of the slow diffusing metals early in the periodic sequence which are not removed by conventional gettering. In this paper, we examine reactions between hydrogen and transition metals and discuss the possibility of such reactions during cell processing. We analyse the case of hydrogenation of iron in p-type Si and show that FeH can form under non-equilibrium conditions. We consider the electrical activity of the slow diffusing metals Ti, V, and Mo, how this is affected in the presence of hydrogen, and the stability of TM-H complexes formed. Finally, we discuss recent experiments which indicate that re-siting of some transition metals from the interstitial to substitutional site is possible in the presence of excess vacancies, leading to a reduction in recombination activity. Periodic ordering of the 3d, 4d, and 5d transition metals with adjacent columns of the periodic table. The metals with hydrogen complexes which have had their electronic properties reported in the literature or in this paper are highlighted in green. [ABSTRACT FROM AUTHOR]

We have recently found that in-diffusion of hydrogen into n-type Si crystals containing oxygen and carbon impurities can result in the formation of powerful recombination centers (M. Vaqueiro-Contreras et al., to appear in PSS RRL). Here, we describe a combination of first-principles calculations and electrical measurements to investigate the composition, structure, electrical activity and recombination mechanism of a carbon-oxygen-hydrogen complex (COH) in Si. We found a defect comprising a carbon-oxygen complex connected to an H atom whose location depends on the charge state of the complex, and showing a calculated acceptor level at Ev + 0.3 eV, a few meV away from the observations. Bistable carbon-oxygen-hydrogen complex in silicon. Carbon, oxygen, hydrogen, and silicon atoms are shown in gray, red, black, and white, respectively. [ABSTRACT FROM AUTHOR]

4-Stilbenecarboxaldehyde (4SCA) at pH 3 was added to TiO2 anatase to form a new catalyst where the aldehyde carbonyl group reacts with the TiO2-OH to form the corresponding acetal (4SCA-TiO2). 4SCA-TiO2 significantly retards the electron recombination when it is illuminated with ultraviolet B light because of the formation of a stable radical anion·−4SCA-TiO2 that we have detected spectroelectrochemically. The light excited electron on the catalysis is transferred relatively slow to solution. Therefore, the electron transfer to solution is the rate-limiting step for water-dissolved organic compound degradation when 4SCA-TiO2 is used as photocatalyst. For instance, degradation rate constants using naphthalene (Naph) and p-nitrophenol (PNP) in an ample pH range support the proposal. Accordingly, rate constants are faster when the standard redox potential of the involved electron acceptor in the solution increases. In fact, this condition can be tuned to promote reactivity. The affinity between the organics being degraded and 4SCA-TiO2 also influences on the degradation rate constants. [ABSTRACT FROM AUTHOR]

Mesoporous TiO 2 films were modified with Sm(NO 3 ) 3 ·6H 2 O and TiCl 4 mixture solution in dye-sensitized solar cells. Samarium oxide was formed after modification according to UV–vis absorption spectra and X-ray photoelectron spectra (XPS) analyses, and acted as energy barrier on TiO 2 surface. The electron recombination reaction with I 3 − can be suppressed when samples are treated using Sm 3+ /TiCl 4 solutions via electrochemical impedance spectroscopy (EIS) and open circuit voltage decay (OCVD) analyses. With the mesoporous TiO 2 film modified by the TiCl 4 mixture solution contained 0.07 M samarium trinitrate, the power conversion efficiency of the dye-sensitized solar cell is increased from 6.91% to 8.23%. The enhanced performance is ascribed to the increase of dye loading, the reduce of surface state density, and the energy barrier created on TiO 2 surface. It is a effective method to improve the power conversion efficiency without requiring a tedious synthesis pathway. [ABSTRACT FROM AUTHOR]

A study of the dynamics of the positive charges in liquid argon has been carried out in the context of the future massive time projection chambers proposed for dark matter and neutrino physics. Given their small mobility coefficient in liquid argon, the ions spend a considerably longer time in the active volume with respect to the electrons. The positive charge density can be additionally increased by the injection, in the liquid volume, of the ions produced by the electron multiplying devices located in gas argon. The impact of the ion current on the uniformity of the field has been evaluated as well as the probability of the charge signal quenching due to the electron–ion recombination along the drift. The study results show some potential concerns for massive detectors with drift of many meters operated on surface. [ABSTRACT FROM AUTHOR]

Recent advances in dye-sensitized solar cells (DSSC), including the use of nanocarbons, resulted in breakthroughs relevant to both the academic and industrial sectors. Their relevance encompasses, on one hand, the development and integration of novel nanocarbon/dye hybrids for superior light-harvesting and improved charge injection properties and, on the other hand, the integration of nanocarbons into each part of DSSCs for enhancing the charge collection efficiency as well as the dye and electrolyte regeneration processes. In the context of the earlier, control over the electron injection and recombination rates is realized on the molecular level. In the context of the latter, i) the charge transport and charge collection efficiencies in the photoelectrode are increased, ii) the charge recombination processes are reduced, when used as a nanocarbon-based buffer layer, iii) the ion diffusion and catalytic effects into (quasi) solid-state electrolytes are improved, and iv) devices using Pt-free counter electrodes with similar device efficiencies are realized. Leading examples of nanocarbons are graphene, carbon black, multi-walled carbon nanotubes, and single-walled carbon nanotubes. In this review, the focus is on a novel carbon allotrope, namely single-walled carbon nanohorns (SWCNH), which is discussed in depth and in comparison with other nanocarbons. [ABSTRACT FROM AUTHOR]

Three dithiafulvene-based metal-free organic sensitizers all using pyridine as the acceptor but with different π-bridges of phenyl ( DTF-Py1 ), thienyl ( DTF-Py2 ) and phenyl-thienyl ( DTF-Py3 ) have been designed, synthesized and used as photosensitizers for dye-sensitized solar cells (DSCs). Introducing thienyl unit into the π-bridge, as well as extension of the π-bridge can dramatically improve their light harvesting ability and suppress the electron recombination, thus uplifting the performance of DSCs. The overall power conversion efficiency of DSC based on DTF-Py3 shows the highest efficiency of 2.61% with a short-circuit photocurrent density of 7.99 mA cm −2 , an open-circuit photovoltage of 630 mV, and a fill factor of 0.52, under standard global AM 1.5 solar light condition. More importantly, the long-term stability of the DTF-Py3 based DSCs under 500 h light-soaking has been demonstrated. [ABSTRACT FROM AUTHOR]

In most cases, the combination of both anatase (up to 80%) and rutile (up to 20%) structures in a mixedphase TiO2 semiconductor results in a better photocatalytic performance compared to the pure phase. The improvement from anatase to rutile is brought about by the enhanced transportation of photogenerated electrons. This consequently results in improved efficiency of the photoelectric and photocurrent conversion. This review highlights the effects of the morphology, particle size, and crystal structure of mixed-phase TiO2 toward the photodegradation of water pollutants. It was demonstrated that the synergistic effect between anatase and rutile TiO2 due to the interfacial electron transfer from rutile to anatase improved the photocurrent as well as the overall conversion efficiency of the anatase photoanodes. The morphologies of mixed-phase TiO2 also contributed to the final photodegradation properties. The charge and electron transfer of mixed-phase TiO2 improved the 1D structure. This consequently enables photodegradation at the visible light range. [ABSTRACT FROM AUTHOR]

Carrier and spin recombination are investigated in p-type GaAs of acceptor concentration NA=1.5 × 1017 cm-3 using time-resolved photoluminescence spectroscopy at 15 K. At low photocarrier concentration, acceptors are mostly neutral and photoelectrons can either recombine with holes bound to acceptors (e-A0 line) or form excitons which are mostly trapped on neutral acceptors forming the (A0X) complex. It is found that the spin relaxation is faster for free electrons that recombine through the e-A0 transition due to exchange scattering with either trapped or free holes, whereas spin flip processes are less likely to occur once the electron forms with a free hole an exciton bound to a neutral acceptor. An increase in the photocarrier concentration induces a cross-over to a regime where the bimolecular band-to-band (b-b) emission becomes more favorable due to screening of the electron-hole Coulomb interaction and ionization of excitonic complexes and free excitons. Then, the formation of excitons is no longer possible, the carrier recombination lifetime increases and the spin lifetime is found to decrease dramatically with a concentration due to fast spin relaxation with free photoholes. In this high density regime, both the electrons that recombine through the e-A0 transition and through the b-b transition have the same spin relaxation time. [ABSTRACT FROM AUTHOR]

The influence of non-radiative exciton recombination (NRER) on the photoconversion efficiency in silicon solar cells with short Shockley-Read-Hall lifetimes tSRH has been studied. It has been shown that the efficiency reduction due to this effect is the stronger the shorter tSRH. The influence of NRER is most evident when the NRER time becomes shorter than tSRH. At sufficiently short tSRH, NRER substantially limits the optimal base doping levels of silicon solar cells, at which the photoconversion efficiency is maximal. [ABSTRACT FROM AUTHOR]

A newly planar dithiafulvene sensitizer ( DTF-C4 ) trending to form J -aggregates on the surface of mesoporous TiO 2 by simply rinsing with a poor solvent acetonitrile was synthesized. We further show that the self-assembled J -aggregates optimized the TiO 2 surface utilization, enhanced the light harvesting ability by broadening and red-shifting the absorption, and suppressed the electron recombination, thereby significantly promoting the solar cell efficiency. Compared to the photoanode surface modified with DTF-C4 and the classical coadsorbent chenodeoxycholic acid (CDCA), the DSC based the DTF-C4 compact J -aggregates exhibited a dramatically improved performance without the loss of adsorbed dyes, uplifting the power conversion efficiency from 4.68% to 7.48% alongside with a high open-circuit voltage of above 850 mV, which is higher than that of the commercial N719-based cell (770 mv). [ABSTRACT FROM AUTHOR]

We theoretically investigate the high-order harmonic generation (HHG) and the spatial distribution in HHG of the H 2 + molecule by introducing a time-delayed two-color laser field which consists of the mid-infrared and near-infrared laser field. For the different time delays of the two-color laser fields, the pulse shapes are changed which result in the variation of the electron recombined with the nuclei along the positive- or negative- z direction. When the time delay is 0 fs (1.34 fs), a smooth harmonic plateau from the electron recombined with the nuclei along the negative (positive)- z direction can be achieved. An isolated attosecond pulse with a duration of about 99 as is generated when the time delay is 1.34 fs. We perform the classical analysis which is consistent with the numerical results from the one-dimensional non-Born-Oppenheimer time dependent Schrödinger equation (TDSE). We also investigate emission time of harmonics in terms of a time-frequency analysis to further understand the underlying physical mechanism. [ABSTRACT FROM AUTHOR]

We present observations of H Ly- α and H 2 emissions on the body of Jupiter obtained during the Cassini flyby in late 2000 and early 2001. The H Ly- α emission is highly organised by System III longitude and latitude, peaking at a brightness of 22 kR between 90 and 120° longitude. This is known as the H Ly- α ‘bulge’. These observations add to a number of previous studies, showing that the feature is very long-lived, present over several decades. We show that there is a strong correlation between the prevailing solar H Ly- α flux (measured at Earth) and the peak brightness of the H Ly- α bulge at Jupiter, which supports the notion that it is primarily driven by solar resonance scatter. The H Ly- α brightness distribution is not aligned with the jovigraphic equator, but is approximately aligned with the particle drift equator of some, but not all, major Jupiter magnetic field models. On the time scale of days, the bulge region appears twice as variable as the non-bulge region. We propose that the electron recombination of H 3 + is an important reaction for the generation of the H Ly- α bulge, which requires an enhancement of soft electrons at the location of the bulge. We derive an equatorial H 3 + lifetime of 1.6 ± 0.4 h and a corresponding column averaged electron density of 1.7 × 10 9 m − 3 . [ABSTRACT FROM AUTHOR]

ZnO, plasmonic gold nanoparticles and conductive carbon nanotubes were combined by in situ growing to improve the light absorption and the electron mobility and the performance of polymer solar cells. Gold nanoparticles decorated carboxylic CNT (CNT-Au) was prepared by simple dehydration-condensation reaction. While CNT provides the template for the in situ growth of ZnO to form homogeneous film with less defects and higher conductivity, gold nanoparticles induce the surface plasmon effect to increase the light absorption. Compared to the bare ZnO, ZnO@CNT-Au nanohybrids could increase photo-generated excitons, decrease the charge recombination and facilitate the electron collection. In consequence, the power conversion efficiency of inverted polymer solar cell based on thieno [3,4-b]thiophene/benzodithiophene (PTB7) [6,6]:– phenyl C 71 -butyric acid methyl ester (PC 71 BM) was improved to 7.9% by adopting ZnO@CNT-Au as cathode buffer layer. [ABSTRACT FROM AUTHOR]

In this study, ultrasmall and ultrafine TiO 2 quantum dots (QDs) were prepared and used as a high-performance compact layer (CL) in dye-sensitized solar cells (DSCs). We systematically investigated the performance of TiO 2 CL under both low-intensity light and indoor fluorescent light illumination and found that the efficiency of DSCs with the insertion of optimal TiO 2 QDs-CL was increased up to 18.3% under indoor T5 fluorescent light illumination (7000 lux). We clarified the controversy over the blocking effect of TiO 2 CL for the efficiency increment and confirmed that the TiO 2 QDs-CL performed significantly better under low-intensity illumination due to the efficient suppression of electron recombination at the FTO/electrolyte interface. We, for the first time, demonstrate this potential for the application of the DSCs with TiO 2 QDs-CL in the low-intensity light and indoor fluorescent light illumination. [ABSTRACT FROM AUTHOR]

An attempt has been made to fabricate methyl ammonium tin chloride (CHNHSnCl) perovskite-sensitized TiO nanostructure photoanode solar cell with hole transport material (HTM) spiro-MeOTAD and graphite-coated counter electrode (CE). The TiO nanoparticles (TNPs), TiO nanoleaves (TNLs), and TNLs with MgO core/shell photoanodes were prepared to fabricate perovskite-sensitized solar cells (PSSCs). The prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The photovoltaic characteristics of the PSSCs, photocurrent density ( J ), open-circuit voltage ( V ), fill factor (FF), and power conversion efficiency (PCE) were determined under illumination of AM 1.5 G. Electrochemical impedance spectroscopy (EIS) analysis was carried out to study the charge transport and lifetime of charge carriers at the photoanode-sensitizer-electrolyte interface of the PSSCs. The PSSC made with CHNHSnCl perovskite-sensitized TNL-MgO core/shell photoanode and spiro-MeOTAD HTM shows an impressive photovoltaic performance, with J = 17.24 mA/cm, V = 800 mV, FF = 73 %, and PCE = 9.98 % under 100 mW/cm light intensity. The advent of such simple solution-processed mesoscopic heterojunction solar cells paves the way to realize low-cost and high-efficiency solar cells. By the aid of electrochemical impedance spectroscopy, it is revealed that the core/shell structure can increase an interfacial resistance of the photoanode-CHNHSnCl interface and retard an electron recombination process in the photoanode-sensitizer-HTM interface. [ABSTRACT FROM AUTHOR]

Understanding recombination processes in organic semiconductors is fundamental in modeling solar cells and lighting diodes. However, recognition on recombination processes is still controversial. In this work, the trap-assisted Shockley–Read–Hall (SRH) recombination proposed by Kuik et al. (2011) is modified by considering three factors. The first one is the density of state (DOS) for recombination centers in SRH process, the second one is the trapped charges of recombination centers in Poisson equation, the third one is the density dependence of mobility. The modified model is applied to typical devices with experimental data about open circuit voltage ( V oc ) with light intensity ( P in ) which having been used to distinguish recombination processes. These V oc − log( P in ) data previously were explained by using the Langevin recombination, or SRH recombination, or mixing of both recombinations. The results show that these experimental data can be uniformly well fitted and explained by using the modified SRH model. The DOS for recombination centers is not important, but the density dependence of mobility is very important in arriving good fittings. The influence of Langevin recombination is compared, and is shown not enough to explain the saturation effects in V oc − log( P in ) curves at high light strength, if neglecting the density dependence of mobility. [ABSTRACT FROM AUTHOR]

Hierarchical rutile/anatase TiO 2 heterogeneous film for photoelectrochemical application is reported in the work. The TiO 2 heterogeneous film is fabricated by two-step hydrothermal method and possesses high light harvesting property. The heterojunction formed at the interface between anatase and rutile facilitates photogenerated charge carrier separation, resulting in reduced electron recombination with holes in the electrolyte. The optimal photocurrent density of bare TiO 2 heterogeneous film was 0.90 mA/cm 2 at a potential of 0 V versus Ag/AgCl. In addition, the TiO 2 heterogeneous film offers a large surface area for quantum dots anchoring and exhibits a significant improvement in photoelectrochemical performance. The photocurrent density of PbS/CdS co-sensitized TiO 2 heterogeneous film was enhanced to 7.72 mA/cm 2 . The results indicate that the designed TiO 2 heterogeneous structure possesses superior charge separation efficiency and photoelectrochemical properties. [ABSTRACT FROM AUTHOR]

Time-resolved infrared-stimulated luminescence (TR-IRSL) from feldspar samples is of importance in the field of luminescence dating, since it provides information on the luminescence mechanism in these materials. In this paper we present new analytical equations which can be used to analyze TR-IRSL signals, both during and after short infrared stimulation pulses. The equations are developed using a recently proposed kinetic model, which describes localized electronic recombination via tunneling between trapped electrons and recombination centers in luminescent materials. Recombination is assumed to take place from the excited state of the trapped electron to the nearest-neighbor center within a random distribution of luminescence recombination centers. Different possibilities are examined within the model, depending on the relative importance of electron de-excitation and recombination. The equations are applied to experimental TR-IRSL data of natural feldspars, and good agreement is found between experimental and modeling results. [ABSTRACT FROM AUTHOR]

To make quantum dot-sensitized solar cells (QDSSCs) more attractive, it is necessary for the power conversion efficiency (PCE) to be comparable to those of other emerging solar cells. Currently, copper sulfide (CuS) and nickel sulfide (NiS) are commonly used counter electrodes (CEs) in high-efficiency QDSSCs because of their low toxicity, environmental compatibility, and superior electrocatalytic activity in the presence of polysulfide electrolyte. For the first time, novel CuS/NiS electrodes were prepared by facile chemical bath deposition method. This article describes the effect of NiS layer on CuS film for preventing the recombination process to enhance the performance of QDSSCs. Under one sun illumination, the CE with the optimized CuS/NiS composite film exhibits higher short-circuit current density (J sc ), open-circuit voltage (V oc ), and PCE of 12.47 mA cm − 2 , 0.599 V, and 4.19%, respectively. These values are much higher than those of bare CuS (2.73%), NiS (1.82%), and Pt CEs (1.16%). This enhancement is mainly attributed to the improved surface morphology, higher sulfur atomic percentage with Cu vacancies, rapid electron transport, and lower electron recombination rate for the polysulfide electrolyte. Characterization with, cyclic voltammetry, and Tafel polarization was performed to study the reasons for efficient CE performance. [ABSTRACT FROM AUTHOR]

We investigate experimentally the plasma dynamics of a centimeter-scale, laser filamentation-guided spark discharge. Using electrical and optical diagnostics to study monopolar discharges with varying current pulses, we show that plasma decay is dominated by free electron recombination if the current decay time is shorter than the recombination characteristic time. In the opposite case, the plasma electron density closely follows the current evolution. We demonstrate that this criterion holds true in the case of damped alternating current sparks, and that alternative current is the best option to achieve a long plasma lifetime for a given peak current. [ABSTRACT FROM AUTHOR]

TiO 2 nanobelts (TiO 2 NBs) were successfully prepared using a solvothermal route via Ti foil as substrate in large scales. The morphology evolution process and formation mechanism of the as-obtained products were investigated in detail. On the basis of this novel structure, chemical sensitive Ag modified TiO 2 NBs nanocomposites (Ag TiO 2 NBs) were fabricated. It was found that Ag TiO 2 NBs exhibit strong light absorption and efficient electron transport. According to Mott-Schottky analysis, Ag TiO 2 NBs show less surface trapping sites compared with TiO 2 NBs. The Ag TiO 2 NBs photoanode fabricated in 0.01 M AgNO 3 demonstrates the best performance with a short-circuit current of 11.9 mA cm −2 corresponding to a photoelectric conversion efficiency of 4.89%, which is higher than that of pure TiO 2 NBs based solar cell by 60%. [ABSTRACT FROM AUTHOR]

Even though SnO 2 has promising electronic properties such as higher election mobility among the high band gap semiconductor nanoparticles that are commonly used in Dye-sensitized Solar Cells (DSCs), the cell efficiency of SnO 2 -based DSCs is considerably low due to high electron recombination; especially through the nanoparticle surface. There have been a few successful attempts in reducing this recombination through the use of very thin insulating layers to cover the surfaces of the nanoparticles in liquid electrolyte-based DSCs. There is enough evidence that this process enhances the efficiency of SnO 2 -based DSCs. Some of the practical limitations associated with the liquid electrolyte-based DSCs’ such as electrolyte leakage, solvent evaporation and sealing imperfections can be suppressed through the use of gel polymer electrolytes. In this study, we have investigated the effect of different coating materials: CaCO 3 , MgO and Al 2 O 3 on the cell performance of DSCs based on gel electrolytes. In all cases, there was a considerable increase in Open Circuit Voltage (V OC ) and Short-Circuit Current Density (J SC ). The enhancement was found to depend on the insulator/SnO 2 molar ratio in all cases. CaCO 3 -coated DSCs gave the best enhancement compared to other systems. The composite system having a molar ratio of 0.12:1 of CaCO 3 to SnO 2 showed 46% increase of V OC , 50% increase of J SC and 233% increase of efficiency compared to the pure SnO 2 -based devices. We have employed several experimental techniques and theories to explain the observed performance of the DSC devices fabricated with the above insulating layers and two different gel electrolytes based on Pr 4 N + I − and LiI salts. [ABSTRACT FROM AUTHOR]

Titanium oxide films were formed by sputtering and then TiWO x films were deposited by bipolar pulsed magnetron sputtering with pure titanium and tungsten metal targets. The sputtering of titanium oxide with tungsten enhanced the orientation of the TiO 2 (1 0 1) plane of the specimen assemblies. The main varying parameter was the tungsten pulse power. Titanium oxide sputtered with tungsten using a pulsing power of 50 W exhibited a superior hydrophilic property, and a contact angle of 13.1°. This fabrication conditions maximized the photocatalytic decomposition of methylene blue solution. The mechanism by which the titanium oxide was sputtered with tungsten involves the photogeneration of holes and electron traps, inhibiting the hole–electron recombination, enhancing hydrophilicity and reducing the contact angle. [ABSTRACT FROM AUTHOR]

In this study, we introduce a new method for the deposition of TiO 2 compact layers which involves the deposition of a wet film of an inorganic titanium (IV) precursor followed by fast hydrolytic conversion to crystalline TiO 2 under near infrared radiative (NIR) treatment. With this, we aim to provide a scalable alternative to methods conventionally employed in laboratories for the fabrication of 3rd generation photovoltaic devices, such as high temperature pyrolysis or spin coating of organic titanium (IV) precursors. Optimization of our solution process is presented in detail. Structural features and crystalline properties of solution processed compact layers are characterized by FEG-SEM imaging and x-ray diffraction analyses and compared to compact layers produced by conventional laboratory techniques. Minimization of electron recombination is evaluated in standard liquid I − / I 3 - dye-sensitized solar cells (DSC). The results show that a compact, homogenous, high coverage yield crystalline TiO 2 anatase layer can be produced by sequential deposition of 2–3 solution processed titanium oxide layers, each in under 30 s. In standard liquid I − / I 3 - DSC the solution processed compact layers strongly increased the electron lifetime, τ n , when compared to cells prepared on a bare FTO substrate. [ABSTRACT FROM AUTHOR]

Four N -fluorenyl indoline sensitizers were designed and synthesized to compare the influence of vinyl bond and aryl ring on the cell efficiency based on the cyanoacrylic acid acceptor. Compared with vinyl bond, the introduction of aryl ring enlarges the conjugation system of the whole molecule and brings out the improvement of the absorption spectra favoring the improvement of J SC . Among three kinds of aryl rings, benzene unit favors the photovoltage due to a reduction of electron recombination while the photocurrent more benefit from thiophene unit. Due to the best J SC , dye with thiophene π-bridge shows the most efficient photoelectricity conversion efficiency and has the maximum η value of 5.89% ( V OC = 650 mV, J SC = 13.88 mA cm −2 , ff = 0.71) under simulated AM 1.5 G irradiation (100 mW cm −2 ). [ABSTRACT FROM AUTHOR]

Using a pneumatic spray gun for a long-distance jet, we coated thioacetamide on the surface of ZnO. Thus, the adsorption capacity of N719 dyes greatly increased. The as-samples were characterised by linear sweep voltammetry and electrochemical impedance spectroscopy analysis. Results showed that the charge recombination resistance increased, which lowered the interface electron recombination rate between ZnO and the electrolyte and between the electrolyte and the dye. Finally, a photoelectric conversion efficiency of 8.28 ± 0.24% for ZnO-based dye-sensitized solar cells was achieved. [ABSTRACT FROM AUTHOR]