An enhancement of efficiency of a solid-state dye-sensitized solar cell due to cocktail effect of N719 and black dye

The solar cell performance of the black dye, N719 dye and the cocktail of two dyes on TiO₂ films were studied by mean of the utilization as light harvesting electrodes in solid-state FTO|TiO₂|dye|CuI|Cr–FTO cells. The power conversion efficiencies of 3.8% and 3.0% are obtained when N719 and black dye were used. When the mixture of 1:1 of two dyes was used, the conversion efficiency rises to 4.6%. In the mixture of N719 and black dye, the N719 dye acts as the aggregation preventer and a co-absorber on TiO₂ surfaces. The increased absorption of light by the two dyes results in increase of electron injection thus enhancing both the short-circuit current density and the open circuit voltage contributing to increased power conversion efficiency of the cell.     

Optimization of F-doped SnO2 electrodes for organic photovoltaic devices

Fluorine-doped tin oxide (FTO) thin films have been investigated as an alternative to indium tin oxide anodes in organic photovoltaic devices. The structural, electrical, and optical properties of the FTO films grown by pulsed laser deposition were studied as a function of oxygen deposition pressure. For 400 nm thick FTO films deposited at 300°C and 6.7 Pa of oxygen, an electrical resistivity of 5×10⁻⁴ Ω-cm, sheet resistance of 12.5 Ω/□, average transmittance of 87% in the visible range, and optical band gap of 4.25 eV were obtained. Organic photovoltaic (OPV) cells based on poly(3-hexylthiophene)/[6,6]-phenyl-C₆₁-butyric acid methyl ester bulk heterojunctions were prepared on FTO/glass electrodes and the device performance was investigated as a function of FTO film thickness. OPV cells fabricated on the optimum FTO anodes (∼300–600 nm thick) exhibited power conversion efficiencies of ∼3%, which is comparable to the same device made on commercial ITO/glass electrodes (3.4%).     

Nanostructured ZnO thin films by chemical bath deposition in basic aqueous ammonia solutions for photovoltaic applications

This paper presents further insights and observations of the chemical bath deposition (CBD) of ZnS thin films using an aqueous medium involving Zn-salt, ammonium sulfate, aqueous ammonia, and thioure. Results on physical and chemical properties of the grown layers as a function of ammonia concentration are reported. Physical and chemical properties were analyzed using scanning electron microscopy (SEM), X-ray energy dispersive (EDX), and X-ray diffraction (XRD). Rapid growth of nanostructured ZnO films on fluorine-doped SnO₂ (FTO) glass substrates was developed. ZnO films crystallized in a wurtzite hexagonal structure and with a very small quantity of Zn(OH)₂ and ZnS phases were obtained for the ammonia concentration ranging from 0.75 to 2.0 M. Flower-like and columnar nanostrucured ZnO films were deposited in two ammonia concentration ranges, respectively: one between 0.75 and 1.0 M and the other between 1.4 and 2.0 M. ZnS films were formed with a high ammonia concentration of 3.0 M. The formation mechanisms of ZnO, Zn(OH)₂, and ZnS phases were discussed in the CBD process. The developed technique can be used to directly and rapidly grow nanostructured ZnO film photoanodes. Annealed ZnO nanoflower and columnar nanoparticle films on FTO substrates were used as electrodes to fabricate the dye sensitized solar cells (DSSCs). The DSSC based on ZnO-nanoflower film showed an energy conversion efficiency of 0.84%, which is higher compared to that (0.45%) of the cell being constructed using a photoanode of columnar nanoparticle ZnO film. The results have demonstrated the potential applications of CBD nanostructured ZnO films for photovoltaic cells.     

Enhanced photoelectrochemical performance of ZnO photoanode with scattering hollow cavities

Abstract ZnO nanoparticles with average diameter of 12 nm were used to fabricate ZnO photoanodes by electrohydrodynamic (EHD) technique for dye-sensitized solar cells (DSSCs). To enhance the light scattering and conversion efficiency, the ZnO film with scattering hollow cavities (HCs) was realized by calcining polystyrene spheres (PSs) in the film. The films had strong light scattering ability and the overall light to electricity conversion efficiency (η) was improved and reached 5.5% under illumination of simulated solar light (AM-1.5, 100 mW/cm²).     

Growth of nanocrystalline TiO2 films by pulsed-laser-induced liquid-deposition method and preliminary applications for dye-sensitized solar cells

A novel technique, the pulsed-laser-induced liquid-deposition (PLLD) method, has been employed to grow nanocrystalline TiO₂ films on fluorine-doped tin-oxide-coated (FTO) glass substrates at room temperature. The PLLD method was implemented by directing a pulsed laser into a liquid precursor and depositing the photosynthesized nanocrystalline TiO₂ on an FTO glass substrate immersed in the liquid precursor. The as-grown nanocrystalline TiO₂ films were found to have a rutile crystal structure and consist of a number of flower-like TiO₂ crystal units arrayed together on the FTO glass substrate. Each of the flower-like TiO₂ crystal units was composed of many nanostructured TiO₂ whiskers, and their building blocks were found to be bundles of TiO₂ nanorods with diameter of about 5 nm. The growth of these TiO₂ nanorods is highly anisotropic, with the preferential growth direction along [001]. As-grown nanocrystalline TiO₂ films were annealed at 450°C in air for 30 min for the applications of dye-sensitized solar cells, and the nanostructured characteristics with good porosity were preserved after annealing. A preliminary dye-sensitized solar cell was built based on the annealed nanocrystalline TiO₂ film. The results suggest that the PLLD method is a promising technique for growing nanocrystalline TiO₂ films for photovoltaic applications.     

Entropy function approach to charged BTZ black hole

We find solution to the metric function f(r) = 0 of charged BTZ black hole making use of the Lambert function. The condition of extremal charged BTZ black hole is determined by a non-linear relation of M _e (Q) = Q ²(1 − ln Q ²). Then, we study the entropy of extremal charged BTZ black hole using the entropy function approach. It is shown that this formalism works with a proper normalization of charge Q for charged BTZ black hole because AdS₂ × S¹ represents near-horizon geometry of the extremal charged BTZ black hole. Finally, we introduce the Wald’s Noether formalism to reproduce the entropy of the extremal charged BTZ black hole without normalization when using the dilaton gravity approach.     

Simple solar cells of 3.5% efficiency with antimony sulfide‐selenide thin films

Thin films of antimony sulfide‐selenide solid solutions (Sb₂S_x Se_3–x) were prepared by chemical bath deposition and thermal evaporation to constitute solar cells of a transparent conductive oxide (FTO)/CdS/Sb₂S_x Se_3–x/C–Ag. The cell parameters vary depending on the sulfide‐selenide composition in the films. The best solar cell efficiency of 3.6% was obtained with a solid solution Sb₂S_1.5Se_1.5 prepared by thermal evaporation of the precipitate for which the open circuit voltage is 0.52 V and short circuit current density, 15.7 mA/cm²under AM 1.5G (1000 W/m²) solar radiation. For all‐chemically deposited solar cells of Sb₂S_1.1Se_1.9 absorber, these values are: 2.7%, 0.44 V, and 15.8 mA/cm², and for Sb₂S_0.8Se_2.2, they are: 2.5%, 0.38 V and 18 mA/cm². (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Hawking radiation of scalar and Dirac quanta from a Kerr black hole

Unruh’s technique of replacing collapse by boundary conditions on the past horizon (theξ-quantisation scheme) for the derivation of the well-known Hawking radiation is extended to the Kerr black hole for the scalar and especially for the spin half field. The expectation value of the energy momentum tensor is evaluated asymptotically in theξ-vacuum state yielding explicitly the net Hawking flux of scalar and spin half quanta. The appropriate statistical distribution that emerges naturally for Dirac quanta validates the ξ-scheme for fermions and confirms the association of temperature with a Kerr black hole.     

Moduli and (un)attractor black hole thermodynamics

We investigate four-dimensional spherically symmetric black hole solutions in gravity theories with massless, neutral scalars non-minimally coupled to gauge fields. In the non-extremal case, we explicitly show that, under the variation of the moduli, the scalar charges appear in the first law of black hole thermodynamics. In the extremal limit, the near horizon geometry is AdS ₂ × S ² and the entropy does not depend on the values of moduli at infinity. We discuss the attractor behaviour by using Sen’s entropy function formalism as well as the effective potential approach and their relation with the results previously obtained through special geometry method. We also argue that the attractor mechanism is at the basis of the matching between the microscopic and macroscopic entropies for the extremal non-BPS Kaluza–Klein black hole.     

Effects of hydrogen plasma treatment on SnO2:F substrates for amorphous Si thin film solar cells

We investigated the effects of hydrogen plasma treatment on the physical and electrical properties of fluorine-doped tin oxide (FTO) films used for amorphous silicon (a-Si) thin film solar cells. A slight increase in carrier concentration by the hydrogen doping effect was observed for the FTO film exposed to the hydrogen plasma for 5 min. For further exposure to the plasma, the chemical reduction became prominent and resulted in deterioration of the electrical and optical properties of the film. XPS analysis revealed that the chemical reduction of SnO₂ to Sn metallic state occurs on the surface region. It was found that the defects formed by hydrogen plasma act as recombination centers at the interface between FTO electrode and p-layer of a-Si solar cells. This phenomenon resulted in the deterioration of the cell performance. The averaged conversion efficiency (6.82%) of the cells on pristine FTO hydrogen substrate was decreased to 5.81% for the cells on FTO treated for 5 min, which is mainly attributed to the decrease in short-circuit current density.     

Effect of 10 MeV electron irradiation on dye-sensitized solar cells

The effect of 10?MeV electrons’ irradiation on dye-sensitized solar cells (DSSCs) has been studied in this paper. J–V characteristics measurements were carried out in order to investigate the degradation of the cells in electron radiation environments. The short-circuit current (J_sc) and maximum power density (P_max) of cells decrease significantly after the electron irradiation. When the irradiation dose increases to 10?kGy, the initial maximum power decreases nearly by 50%. The influences of the electron irradiation on FTO, dye sensitizer and anode were studied to investigate the degradation mechanism of DSSC, respectively. The ultraviolet–visible spectra of FTO show that the absorption peaks of dye decrease, resulting in a decline of the FTO transmittance. According to the X-ray diffraction measurement results, it was found that the particle size of nano-crystalline TiO₂ had changed after the electron irradiation. With the help of SEM, the conglomeration of TiO₂ nano-particles appears after the electron irradiation.     

The volume inside a black hole

The horizon (the surface) of a black hole is a null surface, defined by those hypothetical “outgoing” light rays that just hover under the influence of the strong gravity at the surface. Because the light rays are orthogonal to the spatial two-dimensional surface at one instant of time, the surface area of the black hole is the same for all observers (i.e. the same for all coordinate definitions of “instant of time”). This value is 4π(2Gm/c ²)² for nonspinning black holes, with G = Newton’s constant, c = speed of light, and m = mass of the black hole. The three-dimensional spatial volume inside a black hole, in contrast, depends explicitly on the definition of time, and can even be time dependent, or zero. We give examples of the volume found inside a standard, nonspinning spherical black hole, for several different standard time-coordinate definitions. Elucidating these results for the volume provides a new pedagogical resource of facts already known in principle to the relativity community, but rarely worked out.     

Effects of various solar indices on accuracy of Earth’s thermospheric neutral density models

Four kinds of solar indices F10.7, E10.7, S10, Mg10 and four thermospheric neutral density models, i.e., CIRA72, DTM94, NRLMSISE00 and JB2006, are discussed. The CHAMP accelerometer data are used to calculate thermospheric total mass density. Based on the comparison of the model densities with CHAMP observations, the effects of various indices on the model accuracy are detected. It is found that under quiet and moderate solar conditions (F10.7<160), all of the models’ errors are reduced about 15% by using E...     

Photovoltaic effect of TiO2 thick films with an ultrathin BiFeO3 as buffer layer

The photovoltaic (PV) effect of a bilayer anatase TiO₂/BiFeO₃ (BFO) film has been studied. The 20-nm ultrathin BFO layers were deposited on the fluorine-doped tin oxide (FTO) glass substrates by the chemical solution deposition method. An anatase TiO₂ layer is deposited subsequently on the BFO surface via a screen-printing technique. It is found that the FTO/TiO₂/Au cell exhibits negligible PV effect under solar exposure, while the one after introducing an ultrathin BFO film between TiO₂ and FTO leads to a considerable PV effect with an open-circuit voltage of ?0.58 V and a photocurrent density of 18.27 µA/cm². The FTO/BiVO₄ (BVO)/TiO₂/Au cell was constructed to investigate the underlying mechanism for the observed effect. A negligible PV effect of the FTO/BVO/TiO₂/Au cell indicates that the PV effect of the FTO/BFO/TiO₂/Au cell arises mainly from a built-in electric field in the BFO film induced by the self-polarization. Our work opens up a new path to utilize TiO₂ and may influence the future design of solar cells.     

Passivation of black silicon boron emitters with atomic layer deposited aluminum oxide

The nanostructured surface – also called black silicon (b‐Si) – is a promising texture for solar cells because of its extremely low reflectance combined with low surface recombination obtained with atomic layer deposited (ALD) thin films. However, the challenges in keeping the excellent optical properties and passivation in further processing have not been addressed before. Here we study especially the applicability of the ALD passivation on highly boron doped emitters that is present in crystalline silicon solar cells. The results show that the nanostructured boron emitters can be passivated efficiently using ALD Al₂O₃ reaching emitter saturation current densities as low as 51 fA/cm². Furthermore, reflectance values less than 0.5% after processing show that the different process steps are not detrimental for the low reflectance of b‐Si. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Photoelectric properties of ITO/p +-p −-InP solar cells in linearly polarized light

Indium phosphide heterostructures and transparent conducting films of wide-gap oxides have previously been used in the development of highly efficient solar cells, making it possible to bring their efficiencies up to 18% [M. M. Koltun, Optics and Metrology of Solar Cells [in Russian], Nauka, Moscow (1985); V. M. Botnaryuk, L. S. Gagara, L. V. Gorchak et al., Geliotekhnika 23, 37 (1990); V. Botnariuc, L. Gagara, E. Negru et al., Solar Energy in Romania 2(1), 53 (1993)]. In the present paper results are reported from the first studies of the photoelectric properties, in linearly polarized light, of solar cells consisting of a heterojunction between single crystal indium phosphide and a mixed indium and tin oxide film (ITO film, E _g ≅3.6 eV [G. Check and A. Genis, Solid State Techol. 23(1), 102 (1980)]). Zh. Tekh. Fiz. 68, 72–76 (May 1998)     

A facile two-step preparation of compact and crystalline Sb2S3 thin film for efficient solar cells

The two-step preparation of compact and crystalline Sb₂S₃ thin films was firstly reported using the pyrolysis of the Sb-butyldithiocarbamate complex solution in DMF. The porous and amorphous Sb₂S₃ thin films were successfully prepared at 170 °C for 30 min, and then can be converted to compact and crystalline Sb₂S₃ thin films at 200 °C for 30 min or 300 °C for 2 min. The corresponding solar cells with the architecture of FTO/TiO₂ compact layer/Sb₂S₃/spiro-OMeTAD/Au achieved the photoelectric conversion efficiency of 4.16% at 200 °C and 5.05% at 300 °C. The two-step preparation of the compact and crystalline Sb₂S₃ thin films can provide the feasible approach for the fabrication of various microstructure thin film solar cells and the low preparation temperature of 200 °C was also attractive to assemble the flexible Sb₂S₃ thin film solar cells.     

Black holes,AdS, and CFTs

This brief conference proceeding attempts to explain the implications of the anti-de Sitter/conformal field theory (AdS/CFT) correspondence for black hole entropy in a language accessible to relativists and other non-string theorists. The main conclusion is that the Bekenstein–Hawking entropy S _BH is the density of states associated with certain superselections sectors, defined by what may be called the algebra of boundary observables. Interestingly while there is a valid context in which this result can be restated as “S _BH counts all states inside the black hole,” there may also be another in which it may be restated as “S _BH does not count all states inside the black hole, but only those that are distinguishable from the outside.” The arguments and conclusions represent the author’s translation of the community’s collective wisdom, combined with a few recent results.     

Growth of TiO2 nanosheet-array thin films by quick chemical bath deposition for dye-sensitized solar cells

Rutile TiO₂ nanofilms, which were composed of many nanosheet-array domains with different orientations, were synthesized directly on fluorine-doped SnO₂ conductive glass (FTO) substrates by a chemical deposition method in a short time in this paper. The average thickness of the nanosheets is about 10 nm; the nanosheets in each domain were parallel to each other and perpendicular to the substrate. The size and profile of the domains have a good correspondence to those of the FTO grains of the substrate, indicating a coherent nucleating and epitaxial growing nature of the films. The nanosheets split gradually and finally developed into nanofibers on prolonging the growing time to 20 h. Dye-sensitized solar cells, which were fabricated with the films, present an open-circuit voltage of 0.63 V and a short-circuit current of 7.02 mA/cm², respectively.     

Optical parameters of nanostructured thin films of?electromagnetite Pb1? x Sr x (Fe0.012Ti0.988)O3

Polycrystalline Pb_1−x Sr _x (Fe_0.012Ti_0.988)O₃ (0.2≤x≤0.4) (PSFT) thin films have been grown on fused quartz substrates by metallo-organic decomposition technique. The grown films were characterized using X-ray diffraction (XRD), atomic force microscopy (AFM), source meter and UV–Vis–NIR spectrophotometer to determine the structural, microstructural, dc resistivity and optical properties. The XRD pattern confirmed that the PSFT films has distorted tetragonal single phase, which close to cubic at higher Sr concentration. AFM analysis revealed that the grains size reduces with increasing Sr concentration and their average values lies in the range of 26–9 nm. The higher values of dc resistivity of PSFT nano grains indicate that the transmission of light occurs within these grains up to short wavelength. The refractive index and the extinction coefficient were determined from the optical transmission spectrum in the wavelength range of 200–1100 nm and compared with that theoretically calculated, when fitted to a single oscillator model. The values of optical band gap were determined from Tauc’s extrapolation fitting and suggests that the transformation of electrons during transmission of light through local states within Fermi gap.