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.

Measurements of magnetic noise emanating from ferromagnets due to domain motion

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...

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.