Tin sulfide (SnS), as a promising absorber material in thin-film photovoltaic devices, is described. Here, it is confirmed that SnS evaporates congruently, which provides facile composition control akin to cadmium telluride. A SnS heterojunction solar cell is demons trated, which has a power conversion efficiency of 3.88% (certified), and an empirical loss analysis is presented to guide further performance improvements.

For most metals, increasing temperature (T) or disorder hastens electron scattering. The electronic conductivity (σ ) decreases as T rises because electrons are more rapidly scattered by lattice vibrations. The value of σ decreases as disorder increases because electrons are more rapidly scattered by imperfections in the material. This is the scattering rate hypothesis, which has guided our understanding of metal conductivity for over a century. However, for so-called bad metals with very low σ this hypothesis predicts scattering rates so high as to conflict with Heisenberg's uncertainty principle 1,2 . Bad-metal conductivity has remained a puzzle since its initial discovery in the 1980s in high-temperature superconductors. Here we introduce the rare-earth nickelates (RNiO 3 , R = rare-earth) as a class of bad metals. We study SmNiO 3 thin films using infrared spectroscopy while varying T and disorder. We show that the interaction between lattice distortions and Ni-O covalence explains bad-metal conductivity and the insulator-metal transition. This interaction shifts spectral weight over the large energy scale established by the Ni-O orbital interaction, thus enabling very low σ without violating the uncertainty principle.The Drude model describes the dependence of σ on the lifetime (τ ) between scattering events, the free carrier concentration (n), the carrier effective mass (m * ), and the elementary charge (q): σ = nq 2 τ /m * . For metals the electron-phonon scattering rate increases with T , producing a linear dependence σ∝ T at sufficiently high T . Elementary quantum theory dictates that this relationship cannot continue indefinitely. According to Heisenberg's uncertainty principle the uncertainty E of a particle's energy is inversely proportional to its lifetime: E = h/τ . Therefore there exists a minimum τ below which the concept of a welldefined quasiparticle energy becomes unphysical. This lower bound on τ implies a minimum metallic conductivity (σ MIR ), which is called the Mott-Ioffe-Regel (MIR) limit 1,2 . Most metals reach their melting temperature well before the MIR limit. There are some so-called 'saturating' metals for which σ (T ) approaches σ MIR and saturates, thus validating the MIR limit. However, in bad metals the relationship σ −1 ∝ T continues unabated through the MIR limit. According to the Drude model these metals have lifetimes so short that the quasiparticles should be unstable (that is, decohere), producing an insulating state, and yet the transport properties remain metallic. Bad-metal conductivity is often found in strongly correlated materials such as the high-T superconductors and the Mott insulator-metal transition (IMT) system VO 2 . The phenomenon of bad-metal conductivity is a central problem in condensed matter physics 1-3 .Here we study bad-metal conductivity and the insulator-metal transition in the nickelates. The nickelate phase diagram features an antiferromagnetic insulator at low T and a paramagnetic metal (PM) at high T . For R = Sm and heavier there is also an in...

Measurements of magnetic noise emanating from ferromagnets due to domain motion

Thin‐film solar cells consisting of earth‐abundant and non‐toxic materials were made from pulsed chemical vapor deposition (pulsed‐CVD) of SnS as the p‐type absorber layer and atomic layer deposition (ALD) of Zn(O,S) as the n‐type buffer layer. The effects of deposition temperature and annealing conditions of the SnS absorber layer were studied for solar cells with a structure of Mo/SnS/Zn(O,S)/ZnO/ITO. Solar cells were further optimized by varying the stoichiometry of Zn(O,S) and the annealing conditions of SnS. Post‐deposition annealing in pure hydrogen sulfide improved crystallinity and increased the carrier mobility by one order of magnitude, and a power conversion efficiency up to 2.9% was achieved. Copyright © 2014 John Wiley & Sons, Ltd.

No abstract

Determination of the variation of the fluorescence line positions of ruby, strontium tetraborate, alexandrite, and samarium-doped yttrium aluminum garnet with pressure and temperature J. Appl. Phys. 110, 023521 (2011) Condensed matter experiments at high pressure accentuate the need for accurate pressure scales over a broad range of temperatures, as well as placing a premium on a homogeneous pressure environment. However, challenges remain in diamond anvil cell technology, including both the quality of various pressure transmitting media and the accuracy of secondary pressure scales at low temperature. We directly calibrate the ruby fluorescence R1 line shift with pressure at T = 4.5 K using high-resolution x-ray powder diffraction measurements of the silver lattice constant and its known equation of state up to P = 16 GPa. Our results reveal a ruby pressure scale at low temperatures that differs by 6% from the best available ruby scale at room T. We also use ruby fluorescence to characterize the pressure inhomogeneity and anisotropy in two representative and commonly used pressure media, helium and methanol:ethanol 4:1, under the same preparation conditions for pressures up to 20 GPa at T = 5 K. Contrary to the accepted wisdom, both media show equal levels of pressure inhomogeneity measured over the same area, with a consistent ⌬P / P per unit area of Ϯ1.8 % / ͑10 4 m 2 ͒ from 0 to 20 GPa. The helium medium shows an essentially constant deviatoric stress of 0.021Ϯ 0.011 GPa up to 16 GPa, while the methanol:ethanol mixture shows a similar level of anisotropy up to 10 GPa, above which the anisotropy increases. The quality of both pressure media is further examined under the more stringent requirements of single crystal x-ray diffraction at cryogenic temperature. For such experiments we conclude that the ratio of sample-to-pressure chamber volume is a critical parameter in maintaining sample quality at high pressure, and may affect the choice of pressure medium.

Quantum criticality is a central concept in condensed matter physics, but the direct observation of quantum critical fluctuations has remained elusive. Here we present an X-ray diffraction study of the charge density wave (CDW) in 2H-NbSe 2 at high pressure and low temperature, where we observe a broad regime of order parameter fluctuations that are controlled by proximity to a quantum critical point. X-rays can track the CDW despite the fact that the quantum critical regime is shrouded inside a superconducting phase; and in contrast to transport probes, allow direct measurement of the critical fluctuations of the charge order. Concurrent measurements of the crystal lattice point to a critical transition that is continuous in nature. Our results confirm the long-standing expectations of enhanced quantum fluctuations in low-dimensional systems, and may help to constrain theories of the quantum critical Fermi surface.incommensurate electronic state | transition metal dichalcogenides | diffraction line shapes | diamond anvil cell A continuous change of phase often involves critical fluctuations that destabilize one phase in favor of another. These fluctuations characterize the nature of the phase transition, but can be difficult to measure directly. This difficulty is especially acute in broad classes of materials with quantum phase transitions (1, 2), from colossal magnetoresistance manganites (3) to heavy fermion and cuprate superconductors (4, 5) to archetypal, metallic ferromagnets (6, 7), where strong interactions can cut off the critical behavior via a structural instability, or competing ground states can shroud the quantum critical point.Charge and spin density wave (CDW/SDW) systems have been shown to be good candidates for experimental studies of quantum critical behavior, where fluctuations disrupt electron pairing and restore the metallic Fermi surface (8, 9). In these systems the interaction strengths are weaker than in strongly correlated materials, reducing the likelihood of strong first-order transitions and allowing experimental access to the quantum critical point. Recent low-temperature studies of the SDW transition in bulk, elemental Cr under pressure demonstrated a continuous quantum phase transition in an antiferromagnetic metal (10, 11), but the quantum fluctuation regime deduced via transport measurements was very narrow. Stronger fluctuations over a broader range are expected in systems with lower electronic dimensionality. Moreover, quantum criticality in two-dimensional layered systems with predilections for density wave distortions has received sustained interest due to the observation of density wave pairing in the high-T C superconductors (12-14). Here we present a low-temperature and high-pressure synchrotron X-ray diffraction study of the two-dimensional CDW system 2H-NbSe 2 , where scattering from the incommensurate charge order is possible even deep within the coexisting superconducting ground state. Our results demonstrate a wide regime of spatial fluctuations of the CDW order par...

Transition metal perovskite chalcogenides (TMPCs) are explored as stable, environmentally friendly semiconductors for solar energy conversion. They can be viewed as the inorganic alternatives to hybrid halide perovskites, and chalcogenide counterparts of perovskite oxides with desirable optoelectronic properties in the visible -infrared part of the electromagnetic spectrum. Past theoretical studies have predicted large absorption coefficient, desirable defect characteristics, and bulk photovoltaic effect in TMPCs. Despite recent progresses in polycrystalline synthesis and measurements of their optical properties, it is necessary to grow these materials in high crystalline quality to develop a fundamental understanding of their optical properties and evaluate their suitability for photovoltaic application. Here, we report the growth of single crystals of a two-dimensional (2D) perovskite chalcogenide, Ba 3 Zr 2 S 7 , with a natural superlattice-like structure of alternating double-layer perovskite blocks and single-layer rock salt structure. The material demonstrated a bright photoluminescence peak at 1.28 eV with a large external luminescence efficiency of up to 0.15%. We performed time-resolved photoluminescence spectroscopy on these crystals and obtained an effective recombination time of ~65 ns. These results clearly show that 2D Ruddlesden-Popper phases of perovskite chalcogenides are promising materials to achieve single-junction solar cells.