Pronounced, Reversible, and in Situ Modification of the Electronic Structure of Graphene Oxide via Buckling below 160 K

We have shown that the electronic structure of graphene oxide is strongly, but reversibly, affected by temperature. Below 160 K, graphene oxide is much more completely oxidized, removing any last remaining π-conjugated network. Through DFT simulations, we have shown that this is due to buckling-induced oxidation. As temperature is reduced, the lightly oxidized, graphene-like zones attempt to expand due to a negative thermal expansion coefficient (TEC), but the heavily oxidized zones, with a TEC that is near zero, prevent this from happening. This contributes to localized buckling. The deformed regions oxidize much more readily, and the 1,2-epoxide groups form a new type of functional group never before seen: a triply bonded oxygen, bonded at the 1,3,5 sites of the hexagonal carbon rings. We have called this group TB-epoxide. Stable only under buckling, the TB-epoxide groups revert back to 1,2-epoxides once the lattice relaxes to a flatter profile. We have shown that one can alter the electronic structure of graphene oxide to induce temporary, but more complete, oxidation via strain

ITO Modification for Efficient Inverted Organic Solar Cells

We demonstrate a facile approach to designing transparent electron-collecting electrodes by depositing thin layers of medium and low work function metals on top of transparent conductive metal oxides (TCOs) such as ITO and FTO. The modified electrodes were fairly stable for months under ambient conditions and maintained their electrical characteristics. XPS spectroscopy data strongly suggested integration of the deposited metal in the TCO structure resulting in additional doping of the conducting oxide at the interface. Kelvin probe microscopy measurements revealed a significant decrease in the ITO work function after modification. Organic solar cells based on three different conjugated polymers have demonstrated state of the art performances in inverted device geometry using Mg- or Yb-modified ITO as electron collecting electrode. The simplicity of the proposed approach and the excellent ambient stability of the modified ITO electrodes allows one to expect their wide utilization in research laboratories and electronic industry

Probing the Intrinsic Thermal and Photochemical Stability of Hybrid and Inorganic Lead Halide Perovskites

We report a careful and systematic study of thermal and photochemical degradation of a series of complex haloplumbates APbX₃ (X = I, Br) with hybrid organic (A⁺ = CH₃NH₃) and inorganic (A⁺ = Cs⁺) cations under anoxic conditions (i.e., without exposure to oxygen and moisture by testing in an inert glovebox environment). We show that the most common hybrid materials (e.g., MAPbI₃) are intrinsically unstable with respect to the heat- and light-induced stress and, therefore, can hardly sustain the real solar cell operation conditions. On the contrary, the cesium-based all-inorganic complex lead halides revealed far superior stability and, therefore, provide an impetus for creation of highly efficient and stable perovskite solar cells that can potentially achieve pragmatic operational benchmarks