Photovoltaic applications of perovskite semiconductor material systems have generated considerable interest in part because of predictions that primary defect energy levels reside outside the bandgap. We present experimental evidence that this enabling material property is present in the halide-lead perovskite, CH 3 NH 3 PbI 3 (MAPbI 3 ), consistent with theoretical predictions. By performing X-ray photoemission spectroscopy, we induce and track dynamic chemical and electronic transformations in the perovskite. These data show compositional changes that begin immediately with exposure to X-ray irradiation, whereas the predominant electronic structure of the thin film on compact TiO 2 appears tolerant to the formation of compensating defect pairs of V I and V MA and for a large range of I/Pb ratios. Changing film composition is correlated with a shift of the valence-band maximum only as the halide−lead ratio drops below 2.5. This delay is attributed to the invariance of MAPbI 3 electronic structure to distributed defects that can significantly transform the electronic density of states only when in high concentrations.

The characterization and implementation of solution-processed, wide bandgap nickel oxide (NiO x ) holeselective interlayer materials used in bulk-heterojunction (BHJ) organic photovoltaics (OPVs) are discussed. The surface electrical properties and charge selectivity of these thin films are strongly dependent upon the surface chemistry, band edge energies, and midgap state concentrations, as dictated by the ambient conditions and film pretreatments. Surface states were correlated with standards for nickel oxide, hydroxide, and oxyhydroxide components, as determined using monochromatic X-ray photoelectron spectroscopy. Ultraviolet and inverse photoemission spectroscopy measurements show changes in the surface chemistries directly impact the valence band energies. O 2 -plasma treatment of the asdeposited NiO x films was found to introduce the dipolar surface species nickel oxyhydroxide (NiOOH), rather than the p-dopant Ni 2 O 3 , resulting in an increase of the electrical band gap energy for the near-surface region from 3.1 to 3.6 eV via a vacuum level shift. Electron blocking properties of the as-deposited and O 2 -plasma treated NiO x films are compared using both electron-only and BHJ devices. O 2 -plasma-treated NiO x interlayers produce electron-only devices with lower leakage current and increased turn on voltages. The differences in behavior of the different pretreated interlayers appears to arise from differences in local density of states that comprise the valence band of the NiO x interlayers and changes to the band gap energy, which influence their hole-selectivity. The presence of NiOOH states in these NiO x films and the resultant chemical reactions at the oxide/ organic interfaces in OPVs is predicted to play a significant role in controlling OPV device efficiency and lifetime.

Magnesium-based batteries possess potential advantages over their lithium counterparts. However, reversible Mg chemistry requires a thermodynamically stable electrolyte at low potential, which is usually achieved with corrosive components and at the expense of stability against oxidation. In lithium-ion batteries the conflict between the cathodic and anodic stabilities of the electrolytes is resolved by forming an anode interphase that shields the electrolyte from being reduced. This strategy cannot be applied to Mg batteries because divalent Mg cannot penetrate such interphases. Here, we engineer an artificial Mg-conductive interphase on the Mg anode surface, which successfully decouples the anodic and cathodic requirements for electrolytes and demonstrate highly reversible Mg chemistry in oxidation-resistant electrolytes. The artificial interphase enables the reversible cycling of a Mg/VO full-cell in the water-containing, carbonate-based electrolyte. This approach provides a new avenue not only for Mg but also for other multivalent-cation batteries facing the same problems, taking a step towards their use in energy-storage applications.

molecule based OPVs these gains arise primarily from enhanced short-circuit photocurrent ( J sc ), due to the enhanced dispersion and molecular organization of the donor and acceptor phases, and through the use of new donor polymers with higher ionization potentials (IP) and lower band-gaps than the original poly(thiophene) donors, simultaneously extending the spectral response of the OPV and increasing the open-circuit voltage ( V oc ). [3][4][5] Increasing IP in the donor poly mer increases the frontier orbital energy differences which is known to control the V OC followingwhere E HOMO and E LUMO are the transport energy levels for active layer materials minus what has been an observed offset of 0.3 V [ 5 ] which is related to the polaron pair binding energy. [ 6 ] It has been shown that increasing the frontier orbital energy difference also lowers the probability for dark charge transfer at the D/A inter face, decreasing the reverse saturation current density ( J sat ) which helps V oc to reach its maximum obtainable value. [7][8][9] Full dispersion of the donor and acceptor materials in these devices also increases the probability for charge recombination at the contact electrodes since both donor and acceptor

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