For highly efficient and stable perovskite solar cells (PSCs), small molecular hole transporting materials (HTMs) with high glass transition temperature, hydrophobicity, excellent film-formation and excellent hole mobility is highly desireable. However, developing a single molecule, which could meet all the above mention properties, is challenging. Herein, novel small molecules were design and synthesized, which show a suitable HOMO energy level and fulfill the above metioned properties simultaneously. For this purpose, we incorporate a hydrophobic trifluoropropoxy-terminal group to diphenylamine in SGT-405(3,6), a carbazole-based promising non-spiro-type small molecular HTM with excellent performance and low-cost, leading to two new HTMs (SGT-405s(C-2 ,CF3) and SGT-405d(C-2 ,CF3)). Among them SGT-405s(C-2 ,CF3) showed an excellent hole mobility of 3.32 x 10(-4) cm(2) V-1 s(-1) , a remarkable high T-g of 183 celcius and increased water contact angle of 87 degrees compared to that of spiro OMeTAD (77.7 degrees). Due to these superior properties, compared to those of spiro-OMeTAD, PSCs based on SGT-405s(C-2 ,CF3) showed a remarkable power conversion efficiency (PCE) of 20.14%, which is higher than that of spiro-OMeTAD (18.97%), together with enhanced long-term and thermal stability. Our work revealed for the first time that trifluoropropoxy is a potential terminal group and an effective strategy for the design of new HTMs possessing superior properties in terms of glass transition temperature, hydrophobicity and film formation, for realizing efficient PSCs with enhanced moisture and thermal stability, simultaneously.

Tellurium-doped mesoporous carbon composite materials (Te/NMC) have been prepared by a facile intercalation method in the presence of nitrogen-doped mesoporous carbon (NMC) with tellurium powder, for the first time. The effects of the co-doped N and Te in the mesoporous carbon matrix on the physical/chemical properties and capacitance performances were investigated via the use of various characterization methods and electrochemical studies. The as-prepared NMC and Te/NMC materials were found to mainly be composed of mesopores and maintained the 3D hierarchical graphite-like structure with lots of defect sites. By intercalation of Te atoms into the NMC materials, 2.12 at% (atom%) of Te was doped into NMC and the specific surface area of Te/NMC (261.07 m(2) g(-1)) decreased by about 1.5 times compared to that of NMC (437.96 m(2) g(-1)). In electrochemical measurements as a supercapacitor (SC) electrode, the Te/NMC based electrode, even with its lower porosity parameters, exhibited a higher capacitive performance compared to the NMC-based electrode. These results for Te/NMC arise due to the pseudo-capacitive effect of doped Te and the increase in the capacitive area available from the formation of interconnections in the mesoporous carbons through Te-O bonds. As a result, the synergetic effect of the Te and N atoms enables Te/NMC to exhibit the highest specific capacitance of 197 F g(-1) at a current density of 0.5 A g(-1). Moreover, remarkable long-term cycling stability with the retention of more than 95% of the initial capacitance is observed for Te/NMC at a current density of 5 A g(-1) and also for 1000 charge-discharge cycles.

The halide perovskite solar cells nowadays have emerged as a potential candidate for photovoltaic technology because of their high efficiency, low-cost, and facile fabrication process. In this study, the structural, elastic, electronic, and optical properties of pure and metal (Fe) doping lead-free perovskite CsSnCl3 and lead halide perovskite CsPbCl3 have been calculated by using density functional theory. The present study shows that the metal doping exhibits high absorption and high conductivity than the pure counterpart due to reducing the bandgap. The bandgap of Fe-doped CsSnCl3 is narrowing more than Fe-doped CsPbCl3. The Fe-doped CsSnCl3 reveals a more enhanced optical nature than the Fe-doped CsPbCl3 owing to the greater shipment of absorption peaks toward the lower energy region and the narrowing bandgap. The mechanical parameters show that the pure and Fe-doped samples are mechanically stable. The failure mode indicates that the Fe-doped perovskites are highly ductile in nature as pristine samples, which makes them suitable for use in thin films. The electronic band structure of doped samples exhibited the intermediate state (donor level) in the bandgap. The creation of intermediate states helps the excited photoelectron to easily transfer from the valence to the conduction band. A combined analysis of metal doping in lead halide and lead-free halide demonstrated that Fe-doped CsSnCl3 is more promising to use in solar cells and other optoelectronic applications.

This perspective thoroughly explores the energy loss factors in DSSCs and estimates the feasible efficiency of DSSCs under outdoor and indoor conditions, and compares it with the SQ limit of an ideal solar cell.

Lead-free metal halide perovskites have nowadays become familiar owing to their potential use in solar cells and other optoelectronic applications. In this study, we carried out the structural, elastic, electronic, and optical properties of pure and metal (Mo/Tc) doped CsSnBr3 by using the density functional theory. The metal doping CsSnBr3 displays a narrowing band gap and as a result the optical functions exhibit high absorption and high conductivity in the visible region. Metal doping samples also reveal a high dielectric constant which indicates a low charge-carrier recombination rate and hence enhances the device performance. The optical absorption spectra of metal doped samples greatly shifted (red-shift) towards the lower energy region compared with the pure sample which creates a high-intensity peak in the visible region. The mechanical parameter reveals a highly ductile, soft, and flexible nature which indicates the suitability for use in thin films. The electronic band structure of metal-doped CsSnBr3 shows an intermediate state that assists the excited electron to pass on from valence band to conduction band. The overall study suggests that lead-free CsSn0.875Tc0.125Br3 perovskite is a promising candidate for solar cells and other optoelectronic applications.

The structural and elastic properties of Y2C3 have been studied under ambient to 160 GPa pressure using first principles method based on density functional theory. New bond formation of C-C and Y-Y were observed at 50 GPa and 140 GPa, respectively. Bond lengths of C-C, C-Y, and Y-Y are decreased with increase of pressure and maximum value was found to be 0.39093 angstrom for C-Y-2 bond. Anisotropy of bond lengths was observed due to displacement of Y and C atoms along the different directions. Y2C3 was found to be mechanically stable up to 130 GPa. Elastic constants and moduli showed anomaly at 50 GPa which may be due to pressure induced structural phase change. Poor/non-metallic behavior of Y2C3 was changed to metallic under external pressure. Anisotropic nature was observed below and above 80 GPa. The Vickers hardness HBV = 40.80 GPa at 70 GPa implies that Y2C3 becomes superhard material.

Due to the ever-increasing energy demand, fuel depletion and global climate change, investigation and development of renewable energy conversion and storage devices have increased round the world. Dyesensitized solar cells and supercapacitors are considered clean and environmentally friendly energy conversion and storage devices, thanks to their simple fabrication process and low cost. During this study, in place Ru nanoparticles (Ru-NPs) are prepared on the N-doped template-free mesoporous carbon through the stabilization and carbonization of poly (butyl acrylate)-b-polyacrylonitrile (PBA-b-PAN) block copolymer with Ru (acac)3. Ru-NPs and N-doped porous carbon are formed simultaneously, where PBA-block act as a porous template, while PANblock and Ru (acac)3 acts as semi-graphitic carbon and Ru source, respectively. The resulting Ru-NPs on N-doped mesoporous carbon shows a really high specific gravimetric capacitance of 656.25 F g−1 at a scan rate of 10 mV s−1, good rate capability, and excellent long-term cycling stability (almost 100% retention after 5000 cycles) when applied because the electrode in supercapacitors. Furthermore, it shows excellent catalytic activity toward the cobalt reduction reaction in DSSC, and optical transmittance properties within the visible wavelength (AVT, 42.25%). When Ru-NPs on N-doped mesoporous carbon were employed as CEs during a bifacial DSSC using SGT-021 sensitizer, an interesting power conversion efficiency of 10.13 % and 8.64% from the front and rear illumination, respectively, were obtained. Also, a typical DSSC with the resulting CEs shows a PCE of 11.42%.

Dye-sensitized solar cells (DSSCs) and perovskite solar cells (PSCs) favor minimal environmental impact and low processing costs, factors that have prompted intensive research and development. In both cases, rare, expensive, and less stable metals (Pt and Au) are used as counter/back electrodes; this design increases the overall fabrication cost of commercial DSSC and PSC devices. Therefore, significant attempts have been made to identify possible substitutes. Carbon-based materials seem to be a favorable candidate for DSSCs and PSCs due to their excellent catalytic ability, easy scalability, low cost, and long-term stability. However, different carbon materials, including carbon black, graphene, and carbon nanotubes, among others, have distinct properties, which have a significant role in device efficiency. Herein, we summarize the recent advancement of carbon-based materials and review their synthetic approaches, structure-function relationship, surface modification, heteroatoms/metal/metal oxide incorporation, fabrication process of counter/back electrodes, and their effects on photovoltaic efficiency, based on previous studies. Finally, we highlight the advantages, disadvantages, and design criteria of carbon materials and fabrication challenges that inspire researchers to find low cost, efficient and stable counter/back electrodes for DSSCs and PSCs.

In this work, we have investigated the structural, mechanical, electronic, thermal, vibrational, and optical properties of a new MAB phase Cr4AlB4 for the first time within the framework of density functional theory (DFT) and compared with other MAB phases, Cr2AlB2 and Cr4AlB6. The computed lattice constants are in excellent agreement with the available experimental as well as theoretical values. The new compound is found to be mechanically and dynamically stable as evident from the calculated elastic properties and phonon dispersion spectra. From the theoretical analysis of Pugh’s ratio, Poisson’s ratio, and Cauchy pressure, all the MAB compounds studied here are brittle in nature. The calculated hardness of the studied MAB compounds shows good agreement with the available measured values for other MAB phases. The synthesized Cr4AlB4 is expected to be a material of high potentials for use in hypersonic vehicles, scramjet engines, and thermal management electronics as it possesses high bulk modulus, high stiffness constants, high Debye temperature, as well as high thermal conductivity. The calculated electronic band structures reveal the metallic characteristics of the studied MAB phases. The electron density of states suggests that the chemical bonding is a mixture of covalent, metallic and polar covalent in nature. The optical reflectivity suggests that the studied MAB compounds are promising materials for protection against solar heating. Temperature and pressure dependent thermal properties are investigated through quasi-harmonic Debye model for the first time. The present results might be complementary data for future experimental and theoretical works.

Ru-NPs-embedded self-templated mesoporous carbons were successfully prepared by a facile route. They show excellent electrochemical performance with very high specific gravimetric capacitance, good rate capability, and excellent long-term cycling stability.

The development of a highly active, long-lasting, and cost-effective electrocatalyst as an alternative to platinum (Pt) is a vital issue for the commercialization of dye-sensitized solar cells. In this study, Ru-N-doped template-free mesoporous carbon (Ru-N-TMC) was prepared by the direct stabilization and carbonization of the poly(butyl acrylate)-b-polyacrylonitrile (PBA-b-PAN) block copolymer and ruthenium(iii) acetylacetonate [Ru(acac)3]. During the stabilization process, microphase separation occurred in the PBA-b-PAN block copolymer due to the incompatibility between the two blocks, and the PAN block transformed to N-doped semi-graphitic carbon. In the carbonization step, the PBA block was eliminated as a porous template, creating hierarchal mesopores/micropores. Meanwhile, Ru(acac)3 was decomposed to Ru, which was homogeneously distributed over the carbon substrate and anchored through N and O heteroatoms. The resulting Ru-N-TMC showed ultra-low charge transfer resistance (Rct = 0.034 Ω cm2) in the Co(bipyridine)33+/2+ reduction reaction, indicating very high electrocatalytic ability. Even though it is a transparent counter electrode (CE, average visible transmittance of 42.25%), covering a small fraction of the fluorine doped tin oxide (FTO)/glass substrate with Ru-N-TMC, it led to lower charge transfer resistance (Rct = 0.55 Ω cm2) compared to Pt (Rct = 1.00 Ω cm2). The Ru-N-TMC counter electrode exhibited a superior power conversion efficiency (PCE) of 11.42% compared to Pt (11.16%) when employed in SGT-021/Co(bpy)33+/2+ based dye-sensitized solar cells (DSSCs). Furthermore, a remarkable PCE of 10.13% and 8.64% from front and rear illumination, respectively, was obtained when the Ru-N-TMC counter electrode was employed in a bifacial DSSC. The outstanding catalytic activity and PCE of Ru-N-TMC were due to the high surface area of Ru-N-TMC, which contained numerous active species (Ru and N), easily facilitated to redox ions through the hierarchical microporous/mesoporous structure.

The structural, elastic, electronic, Vickers-Hardness, vibrational, Optical and thermo dynamical properties of potentially technologically important superconductors BaRh2P2 and SrIr2As2 are calculated using density functional theory (DFT) with CASTEP code for the first time. The structural and other physical properties of BaRh2P2 and SrIr2As2 are compared with the results where available and show well accord. The phonon dispersion curve is calculated and the dynamical stability of this compound is investigated. Both the compounds show mechanically stable under the Born stability conditions. For the above condition BaRh2P2 behaves ductile nature and SrIr2As2 indicates the brittle nature. The Mulliken dislocation bonding population and charge density maps show stronger bond between As-Ir compared with Ir-Ir bond. The overall superior conversation reflects that the chemical bonding in BaRh2P2 and SrIr2As2 superconductors can be denominated as an extremely anisotropic connection between ionic, covalent and metallic interactions. At the Fermi level valence band and conduction bands overlapped, so the compounds are metal. From the Fermi surface and charge density map it is observed that both ionic and covalent bond exist. Vickers hardness reveals the both superconductors relatively soft with compare to Diamond. The optical and acoustic modes are observed clearly. We calculate the Helmholtz free energy (F), internal energy (E), entropy (S), and specific heat capacity (C-v) from the phonon density of states. Various optical parameters are also calculated. The reflectance spectrum shows that this compound has the potential to be used as an efficient solar reflector. Debye temperature of BaRh2P2 and SrIr2As2 superconductors are 273.91 K and 341.03 K calculated by using present elastic constants data. The superconducting parameter indicates the phonon-mediated medium coupled BCS superconductors. The acquired results in present investigation could provide a great spur for future studies. (C) 2017 Published by Elsevier B.V.

Edge-functionalized graphene nanoplatelets (GnPs) were synthesized by a simple ball-milling process of graphite in the presence of halogen (F, I), metalloids (Se, Te and Sb) and subsequently applied to dye-sensitized solar cells (DSSCs) as counter electrodes (CEs). In our previous works, a series of edge-functionalized GnPs were thoroughly studied and successfully utilized as CEs in DSSCs, with the aim of finding possible alternatives to the noble and expensive Pt metal as CE. However, in each study, the GnP-CEs were not only fabricated with different dyes and electrolytes but were also evaluated on different occasions, and thus, it was difficult to identify which type of edge-functionalized GnPs was the best. Herein, DSSCs with different edge-functionalized GnP-CEs were fabricated under the same environmental conditions, photovoltaic performances were then evaluated employing both I-/I-3(-) and Co(bpy)(3)(2+/3+) (bpy = 2,2'-bipyridine) redox couples with three different sensitizers to assess the electrocatalytic activity of the different GnP-CEs. Photovoltaic performances of edge-halogenated GnP-CEs with N719 dye employing the I-/I-3(-) redox couple were lower than those of the metalloid-doped GnP-CEs and were even inferior to Pt-CE, which was consistent with the R-ct values. Conversely, among the metalloid-doped GnP-CEs, SbGnP-CE exhibited a higher R-ct value and lower power conversion efficiency (PCE) value of 8.70% and 6.60% with N719 and SGT-130 dyes, respectively. However, when the devices were fabricated with the Co(bpy)(3)(2+/3+) redox couple, the opposite occurred and SbGnPs displayed the highest PCE of 10.42% with SGT-130 dye and 12.08% with SGT-021 dye. Furthermore, SeGnP-CE and TeGnP-CE showed superior compared to the Pt-CE with both I-/I-3(-) and Co(bpy)(3)(2+/3+) electrolyte solutions. (C) 2018 Elsevier Ltd. All rights reserved.

A new single-phase double perovskite superconductor (K-1.00)(Ba-1.00)(3)(Bi0.89Na0.11)(4)O-12 with a T-c similar to 31.5 K has been recently synthesized via the hydrothermal route. In the present study, we employ DFT (density functional theory) calculations to investigate the properties (structural, mechanical, electronic, Fermi surface, charge density) of this new superconductor. The calculated lattice constant is in good agreement with the experimental result. The elastic constants, bulk modulus, shear modulus, Young's modulus, elastic anisotropy of crystal, Peierls stress, and Debye temperature are calculated and used to explain the mechanical behavior of this newly synthesized perovskite. The calculated electron density of states (DOS) indicates strong ionic interactions that are present in the Na-O-Bi planes. Both the electron and hole like bands form the Fermi surface and exhibit the multi-band nature of the compound. The electron charge density map shows the isotropic nature of charge distribution. (C) 2017 Elsevier B.V. All rights reserved.

Static and dynamic heterogeneity of disordered system is one of the current topics in materials science. In disordered ferroelectric materials with random fields, dynamic polar nanoregions (PNRs) appear at Burns temperature and freeze into nanodomain state below Curie temperature ( T C ). This state is very sensitive to external electric field and aging by which it gradually switches into macrodomain state. However, the role of PNRs in such states below T C is still a puzzling issue of materials science. Electric field and aging effects of uniaxial ferroelectric Sr x Ba 1− x Nb 2 O 6 ( x = 0.40, SBN40) single crystals were studied using Brillouin scattering to clarify the critical nature of PNRs in domain states below T C . On field heating, a broad anomaly in longitudinal acoustic (LA) velocity at low temperature region was due to an incomplete alignment of nanodomains caused by the interaction between PNRs. A sharp anomaly near T C was attributed to the complete switching of nanodomain to macrodomain state owing to the lack of interaction among PNRs. After isothermal aging below T C , the noticeable increase of LA velocity was observed. It was unaffected by cyclic temperature measurements up to T C , and recovered to initial state outside of a narrow temperature range above and below aging temperature.

In relaxor ferroelectrics, the role of randomly orientated polar nanoregions (PNRs) with weak random fields (RFs) is one of the most puzzling issues of materials science. The relaxation time of polarization fluctuations of PNRs, which manifests themselves as a central peak (CP) in inelastic light scattering, is the important physical quantity to understand the dynamics of PNRs. Here, the angular and temperature dependences of depolarized and polarized CPs in 0.44Pb(Mg1/3Nb2/3)O3-0.56PbTiO3 single crystals with weak RFs have been studied by Raman and Brillouin scattering, respectively. The CPs observed in Raman scattering show the very clear angular dependence which is consistent with the local tetragonal symmetry. It is different from the well-known local rhombohedral symmetry with strong RFs for Pb(Mg1/3Nb2/3)O3. In Brillouin scattering, depolarized and polarized CPs show two relaxation processes corresponding to transverse and longitudinal fluctuations of PNRs. The remarkable slowing down towards the Curie temperature was observed for transverse fluctuations in local tetragonal symmetry.

A new superconductor (Na0.25K0.45)Ba3Bi4O12, having an A-site-ordered double perovskite structure, with a maximum Tc ∼ 27 K has very recently been discovered through hydrothermal synthesis at 593 K. The structural, elastic, electronic, and thermal properties of the new synthesized compound have been investigated theoretically. Here we have employed the pseudo-potential plane-wave (PP-PW) approach based on the density functional (DFT) theory, within the generalized gradient approximation (GGA). The elastic constants (Cij), Pugh‘s ratio, Cauchy‘s pressure and other elastic parameters are derived first time. We have discussed the bonding nature in the light of the electronic valence charge density. Both electron and hole-like Fermi surfaces are present in the compound under study which indicate the multiple-band nature of (Na0.25K0.45)Ba3Bi4O12. The compound is indicated to be a strongly coupled superconductor which is based on the estimated e-ph coupling constant. The thermodynamic properties at elevated temperature and pressure are calculated and analyzed for the first time by using quasi-harmonic model which includes vibrational term.