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Among 2D Transition Metal Dichalcogenides (TMDs), ultrathin molybdenum disulfide (MoS2) nanosheets are well researched in terms of synthesis, characterization and applications owing to its unique properties in contrast to the bulk material. Here, 2D MoS2 suspensions are prepared via grinding-assisted liquid phase exfoliation. The processing parameters like initial concentration of MoS2 powder, grinding hours, solvent and high-power sonication are optimized for efficient and scalable production of MoS2 nanosheets. The suspensions are characterized for their optical and structural properties and are compared to analyze the effect of synthesis conditions on the properties of the obtained samples. The bandgap of the synthesized MoS2 lies above 2.0 eV in contrast with a bandgap of 1.57 eV for bulk sample. The difference between the peaks corresponding to in-plane and out-of-plane vibration modes is lower than bulk sample depicting the formation of mono to few-layered MoS2. It is found that grinding-assisted sonication in NMP solvent is the most efficient method to produce low-dimensional nanosheets. The well dispersed MoS2 nanoflakes can be blended with other nanomaterials to prepare hybrid dispersions and can thus be explored for optoelectronic applications.

The present work focuses on studying the optical properties of the pristine PEDOT:PSS and the PEDOT:PSS modified with de-ionized water, ethylene glycol and MWCNT. The effect of various additives on the absorption, the refractive index, and the dielectric constant has been inspected. The refractive index dispersion has been analyzed using the single oscillator model developed by Wemple and DiDomenico. The optical constants, such as the dispersion energy, the single oscillator energy, the average oscillator strength, the average interband oscillator strength, the long wavelength refractive index, and the plasma resonance frequency have been determined. The energy bandgap was found reduced with the addition of EG and MWCNT representing a red shift and a conformational change in the PEDOT:PSS from a benzoid to a quinoid structure. The UV-visible absorption spectrum indicates the creation of free charges. The increase in the refractive index with doping suggests the formation of localized energy states within the energy bandgap. These localized states act as recombination centers and increase the low energy electronic transitions. The dielectric constant was also found increased in the modified samples, exhibiting advantages for the formation of conducting thin films. A phase segregated morphology was obtained for the solvent treated PEDOT:PSS, and the MWCNTs were observed to be uniformly distributed throughout the polymer. Furthermore, the optical conductivity has been calculated to give comprehensive information about material properties and their systematic selection for desired applications. Keywords: PEDOT:PSS, Optical properties, Refractive index, Ethylene glycol, MWCNT, Optical conductivity

Metal-Insulator-Metal type devices based on poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM) have been examined to understand the effect of degradation on the charge injection and transport phenomena. The Fowler Nordheim (FN) plots with time have been investigated to analyze the behavior of charge tunneling through the potential barrier at the interfaces. A clear transition from thermionic emission to tunneling is observed, and the transition voltage at which this occurs reduces with time. Furthermore, there is appearance of multiple inflexion points with time in the FN plots, and this is explained on the basis of recombination and majority charge carriers within the device. To validate the observations, comparative studies have been carried out on multi-walled carbon nanotube doped samples, which indicate similar behavior for fresh and degraded samples. It is, thus, ascertained that defect states, recombination of charge carriers and the mobility plays a significant role in governing the device behavior.

The perovskite materials based photovoltaic cells play a crucial role in the conversion of sunlight into electric energy. The commonly used perovskite materials are CH3NH3Pbl3 and CH3NH3Snl3. ln the present manuscript, a theoretical comparison is done by simulating the structures lTO/TiO2/CH3NH3Pbl3/p-Gr/Ag and lTO/TiO2/CH3NH3Snl3/p-Gr/Ag structures in AFORS-HET software under the illumination condition of AM 1.5G. Here, TiO2 and p-Graphene (p-Gr) play the role of electron transporting material and hole transporting material respectively with lTO and Ag as front and back contacts. The thickness of layers is directly related to the cost of the cells. Therefore, we optimized the CH3NH3Pbl3 and CH3NH3Snl3 layers thickness to observe the performance of the device. The power conversion efficiency of 10.62% is obtained for CH3NH3Snl3 based solar cell at optimized thickness of 800 nm as compared to 9.74% efficiency for CH3NH3Pbl3 based solar cell at an optimized thickness of 700 nm. The textured nature of front surface also enhances the efficiency 10.56% and 12.38% for CH3NH3Pbl3 and CH3NH3Snl3 respectively.

Control over the dimensions of nanoscale patterns on macroscopic areas of solid surfaces by varying ion beam parameters has been useful in electronic, optic and optoelectronic applications. This work presents a comparative study on projectile’s (Ar and Kr) mass-dependent growth of ripples as a function of the incidence angle. Oblique implantation produces ripples between 50°-70° with highest ordering at ∼60°. Heavy mass implantation (Kr+) produces higher amplitude of ripples with shorter wavelength as compared to lighter Ar+ ion, and vice versa. Compositional study shows that the broader near surface damage for Ar+ under higher penetration range produces longer ripple wavelength as compared to Kr+.

Metal-organic framework (MOF)-based materials are recognized as potential media for photo-reductive demineralization of heavy and radioactive metal(loid) pollutants. In this review, the recent progress achieved in the development of MOF-based photocatalysts is highlighted for the photocatalytic reduction of Cr(VI)) and U(VI) metal(loid)s in water based on three key performance metrics such as quantum yield (QE), space–time yield (STY), and figures of merit (FOMs). For such evaluation, particular emphasis has been placed on the effect of modification strategies and inorganic nodes (e.g., Zn, Ti, Zr, Fe, In, Cd, and Cr metal sites). Among the surveyed MOFs, flower-like Zn-MOF/BUC-21@titanate nanotube/Ag@Ag3PO4@MIL-125-NH2 and MOF-derived g-C3N4 nanosheets were identified as the best performers to detoxify chromium and uranium, respectively. The superiority of these MOF-photocatalysts is attributable to their superior capabilities for photoreduction process (e.g., in terms of electron-hole pair separation mechanisms, metals adsorption, and UV-visible light harvesting). The overall results of this review will help open a new room for the development of the next-generation MOF-based photocatalytic systems (in terms of catalytic activity, upscalability, and photocatalytic stability/reusability) for the efficient reduction of heavy and radioactive metal ions in water under solar light.

The perovskite solar cell structures: FTO/SnO2/(CH3NH3PbI3 or CH3NH3SnI3)/CuInSe2/Ag have been proposed and numerically analyzed using SCAPS-1D software. The performance of the designed cell structures are optimized by studying the effect of layers’ thickness, the electron affinity of transporting layers, and the bandgap of the hole transporting layer. The optimized power conversion efficiency of 20.36% and 18.89% are obtained for solar cells based on CH3NH3PbI3 and CH3NH3SnI3 absorbers, respectively. In addition, the effect of defect density in the perovskite layer and at the interfaces between different layers are investigated. The manuscript findings revealed that CuInSe2 nanocrystals act as an efficient inorganic HTL, and the defect density is a critical factor for affecting the performance of the cells.

In this paper, the degradation of fill factor with time of organic bulk heterojunction solar cells has been investigated up to 312 h. The experimental data of P3HT:PCBM solar cells has been analyzed theoretically to determine the parameters which affect the FF. The existing empirical formula has been applied to degradation data, and it was found to deviate drastically as the cell degrades, indicating that the correct behavior of solar cell is not imitated using the current FF formula. In view of the discrepancy, the expression for fill factor has been modified taking into account the material and device properties, which directly influence the working of a solar cell. All the values can be determined experimentally. The results of the modified expression gives better theoretical fit of FF with time. The results highlight the parameters which should be targeted in order to overcome the short lifetime of organic solar cells.

P3HT:PCBM is a popular material used for the fabrication of organic solar cells. However, the rapid degradation of these devices restricts their commercialization. It is, therefore, necessary to study the charge conduction mechanism in these materials with time. The Fowler-Nordheim (FN) plots of P3HT:PCBM based MIM devices show nonlinear behavior. As the device degrades, voltage at which substantial tunnelling is observed shifts to lower voltage, indicating the effect of diffused impurities. A clear transition from thermionic emission to field emission is observed. Interestingly, the degraded device shows multiple minima in the FN plots, indicating conversion of hole-only device into electron-only device at high voltages. The potential barrier at the interfaces has been estimated. Thus, by restricting the formation of interface states due to impurities, devices with higher lifetimes can be achieved.

Metal-organic frameworks (MOFs) have drawn a great deal of attention due to a diverse range of advantageous properties (e.g., large surface area, favorable pore-size distribution, structural tunability, versatility, and facile functionalization). The bimetallic MOFs (BMOFs) formed through the incorporation of bimetals in MOF structure are useful to enhance the intrinsic properties of frameworks, as they can favorably introduce defects and high porosity through combinational effects between different metals. As such, the utility of BMOFs can be expanded greatly in diverse applications such as supercapacitor (SC) electrode. In this review, we describe different methods of preparing BMOFs and their derivatives for the construction of diverse BMOF-based SCs. The recent advances achieved in the design and production of pristine BMOFs and their derived nanostructures (e.g., bimetal oxides, sulfides, phosphides, and carbonaceous products) in SC applications are also addressed in association with the evaluation of their electrochemical performance. The present review is thus expected to help establish a technology roadmap for the fabrication and commercialization of novel SC products.

The current density-voltage ( J-V ) characteristics were measured for poly [N-9″-heptadeca-nyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzo-thiadiazole)]:[6,6]-phenyl-C71-butyric acid methyl ester (PCDTBT:PC 71 BM) solar cells and studied for degradation analysis up to 150 h of fabrication. It was observed that the dark J-V characteristics in the degraded cell could be explained using both drift-diffusion (D-D) model and space charge limited current (SCLC) model. The D-D model could explain the J-V characteristics at initial voltage region, while SCLC model fitted well in the later part. By comparing the experimental data with theoretical curves, it was found that the transition from D-D model to SCLC model depends on the span of degradation. The results indicated an increase of traps and decrease of charge carrier mobility which may lead to degradation of organic solar cells. This work gave an insight into the degradation mechanism influencing the performance of organic solar cells.

The use of multilayer p-graphene as hole transporting layer has been successfully shown to improve the performance of perovskite solar cell. The structure of p-graphene/CH3NH3PbI3/n-cSi is designed and simulated in AFORS-HET software. We optimized the parameters of single layer p-graphene and obtained power conversion efficiency (PCE) of 12.21% under an illumination of AM 1.5G. With an increase in the number of p-graphene layers, the PCE falls down to 10.01%. The optimization of active layer parameters increases the PCE up to 12.27%. Further optimization of n-cSi parameters lead to the highest PCE of 16.75%. A significant effect of the operating temperature on the solar cell performance is observed. The effect of textured front surface on the solar cell performance is also studied and a PCE of 17.90% is obtained for textured surface as compared to 16.75% for planar surface. Our studies indicated that p-graphene may act as an efficient hole transporting layer in perovskite solar cell.

The current development of efficient solar cells based on perovskite materials as active layer promises to transform the field of thin film solar cells. A substantial progress in terms of efficiency has been achieved. However, the unstable nature of the device is a major drawback. The study of perovskite solar cells is still at dawn and considerable fundamental research is needed for commercial viability. In the present work, theoretical studies have been carried out to understand the working procedure of perovskite materials for solar cell applications. Based on the diode model, an efficiency of 11.25% is obtained for a cell with CH3NH3PbI3 as the active layer. The diode model has been employed to investigate the current density-voltage (J-V) characteristics and power-voltage (P-V) characteristics under illumination. We also analyzed the efficiency (η) variation for different values of series resistance (RS) keeping the shunt resistance (RP) constant and vice versa. From the above calculations, the fill factor (FF) of the solar cells has been deduced. It is observed that our numerical results are in good agreement with the experimental as well as theoretical results existing in literature.

Bulk-heterojunction (BHJ) organic solar cells (OSCs) were fabricated with various active layer materials. Solar cells of configuration ITO/PEDOT:PSS/P3HT:PC61BM/Al, ITO/PEDOT:PSS/P3HT:PC71BM/Al and ITO/PEDOT:PSS/ PCDTBT:PC71BM/Al were fabricated. Current density-voltage (J-V) characteristics were measured in the dark and under illumination in ambient conditions. A single theoretical model was able to explain the J-V characteristics of all freshly prepared cells using realistic parameters. Copyright © 2015 VBRI Press.

(1-x) Ba 0.95 Sr 0.05 TiO 3 – (x) Ni 0.7 Zn 0.2 Co 0.1 Fe 2 O 4 magnetoelectric composites are synthesized by the standard solid state reaction method and are investigated in detail. X-ray diffraction (XRD) analysis confirms the successful formation of the composites. The results of scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) reveal that NZCF phase is well dispersed in the BST matrix and has larger average grain size. The dielectric constant variation with frequency demonstrates dispersion in the low frequency region which may be ascribed to the Maxwell–Wagner interfacial polarization. Besides, the dielectric constant vs. Temperature plots of the composites exhibit ferroelectric to paraelectric phase transition, which is dependent on the NZCF content. A sharp transition peak is observed for low ferrite content, whereas for higher ferrite content, it seems to be suppressed. The maximum value of the piezoelectric coefficient ( d 33 ) obtained for the composites is 25 pC/N. With increasing NZCF content in the composites, the ferromagnetic properties get stronger while, ferroelectric behavior is gradually weakens. The observed behavior of magnetoelectric coefficient (α E ) is explained in terms of variation of the resistivity of the composites and the ferrite concentration and maximum α E achieved is 2.58 mV/cm Oe for the composite with 70% BST + 30% NZCF.

Multiferroic composites have been prepared by submerging of barium strontium titanate (Ba0.95Sr0.05TiO3) (BST) pellets (sintered at different temperatures) in nickel cobalt ferrite (Ni0.8Co0.2Fe2O4) (NCF) Sol followed by sintering. This method resulted into uniform distribution of small amount of NCF nanoparticles in BST matrix. The presence of NCF within BST pellets has been confirmed by magnetization versus magnetic field loops and energy dispersive X-ray spectroscopy (EDS) measurements. Smaller content of NCF in composite samples prepared from submerging method significantly affected dielectric, piezoelectric, and ferroelectric properties. Magnetodielectric effect in composite samples confirmed the presence of magnetoelectric coupling.

The effect of multi-walled carbon nanotubes on the properties of P3HT:PCBM based solar cells has been studied. The concentration of MWCNT was optimized at 0.2% and the concentration of P3HT:PCBM was increased from 20 mg / ml to 30 mg / ml to obtain highest efficiency. An increase in charge carrier mobility was also observed, which is attributed to high charge transport properties of MWCNT. The active layer was optically stable with respect to absorption, whereas the emission spectra revealed an increase in charge recombination with time. The solar cells doped with MWCNT exhibited increased stability as compared to undoped cells.

Degradation and short shelf life have been observed experimentally in poly(3-hexylthiophene) (P3HT): 6,6-phenyl C61-butyric acid methyl ester (PCBM) based blend solar cells. Both dark and illuminated current–voltage characteristics could be explained quantitatively with a proposed single model for a typical degraded organic solar cell-glass/ITO/PEDOT:PSS/P3HT:PCBM/Al. It has been found that surface state density, interface thickness, tunneling coefficient and occupation probabilities of the interface states becomes important with the passage of time. To look into the problem the activity at ITO/PEDOT:PSS and P3HT:PCBM/Al interfaces are studied using realistic values of the interfaces. The experimental J–V characteristics is well explained with the inclusion of tunneling current through these surface states and becomes the dominant current component for the degraded cell. It is also found that surface state density increases to 1012–1013 cm−2 eV−1, which has been verified with C–V measurements and also is in agreement with our proposed model for BHJ solar cell after 150 h of fabrication.

Films of PEDOT:PSS and doped PEDOT:PSS, used as hole extracting layer in organic solar cells, have been studied using scanning electron microscopy, Kelvin probe work function measurement, Col-Cole plots, and conductivity measurements and current voltage (I–V) characteristics with time. A change in morphology is observed in PEDOT:PSS films doped with ethylene glycol and multi-walled carbon nanotubes. The doped films have rougher morphology as compared to the pristine films. The work function increases for doped sample thus improving the charge transfer. Further, the analyses of Cole-Cole plots show that the resistance of doped film is lower than pristine film. The change in conductivity with time has been measured, and the I–V characteristics of fresh and degraded samples indicates that fall in conductivity of HEL is one of the reasons for the decrease in device performance.

We have investigated the degradation of P3HT:PCBM (poly(3-hexylthiophene):6,6-phenylC61 butyric acid methyl ester) solar cell beyond 150 h of fabrication in continuation to our earlier reported work up to 150 h of fabrication. The current- voltage characteristics of degraded Indium tin oxide/poly(3,4-ethylenedioxythiopene):poly(styrenesulfonate)/poly(3-hexylthiophene):6,6-phenylC61 butyric acid methyl ester/Aluminum (ITO/PEDOT:PSS/P3HT:PCBM/Al) solar cell can be explained by considering the tunneling current through electrode interfaces, increase in both the interface states density and the thickness of interface with time for150-200 h. Beyond 200 h of fabrication, a significant reduction in the occupation probability at the electrode interfaces explains the experimental results up to 300 h fairly well. Calculations based on realistic parameters and activity at both the electrode interfaces (ITO/PEDOT:PSS and P3HT:PCBM/Al) confirm that degradation at P3HT:PCBM/Al interface is more prominent than that at ITO/PEDOT:PSS interface.

The present work is a detailed study of the optical, morphological and electrical properties of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate), PEDOT:PSS, films doped with ethylene glycol (EG) and multi-walled carbon nanotubes (MWCNT). The conductivity of PEDOT:PSS films doped with EG and MWCNT is higher than pristine PEDOT:PSS film. The optical transparency of PEDOT:PSS film decreases insignificantly after addition of MWCNT and EG. The films were further studied using atomic force microscopy, ?x-ray diffraction, Raman spectroscopy and Kelvin probe work function measurement, after which films of PEDOT:PSS with EG and MWCNT were optimized for the fabrication of solar cells. The optimized film was used as a hole extracting layer in a typical ITO/PEDOT:PSS/P3HT:PCBM/Al solar cell. The suitable concentration for an optimized film was found to be 4% MWCNT and 1:4 ratio of EG to PEDOT:PSS. The performance of the device with doped PEDOT:PSS was found to improve in terms of short circuit current density (JSC) and efficiency (?). The solar cell with a doped PEDOT:PSS layer showed higher JSC?and ? due to the increase in the interchains among PEDOT chains along with the introduction of MWCNT channels in PEDOT:PSS matrix. The degradation behavior of the cells was studied and it was found that both pristine and doped PEDOT:PSS cells showed similar trends of degradation. The performance degradation with time was also studied under variable environmental conditions, which showed different aging rates for the two devices.

Mobility and lifetime of the carriers are two very crucial parameters, which can account for the aging of a photovoltaic device, because changes in morphology, electrode/polymer interfaces, etc., will finally result in decrease of mobility and lifetime of carriers. In the present work, we have tried to explain our experimental data with the help of theoretical analysis based on our earlier model in which we have incorporated the activity at electrode interfaces in terms of density of surface states, thickness of interface layer, and tunneling probability. Calculations show that decrease in mobility for a cell under illumination is much faster than in a dark cell. Photoinduced oxidation plays a dominant role in fast degradation of the mobility. The lifetime is also seen to decrease because of modification of parameters such as interface thickness, density of interface states, and roughness.