Highly conductive poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) films as stand‐alone electrodes for organic solar cells have been optimized using a solvent post‐treatment method. The treated PEDOT:PSS films show enhanced conductivities up to 1418 S cm−1, accompanied by structural and chemical changes. The effect of the solvent treatment on PEDOT:PSS has been investigated in detail and is shown to cause a reduction of insulating PSS in the conductive polymer layer. Using these optimized electrodes, ITO‐free, small molecule organic solar cells with a zinc phthalocyanine (ZnPc):fullerene C60 bulk heterojunction have been produced on glass and PET substrates. The system was further improved by pre‐heating the PEDOT:PSS electrodes, which enhanced the power conversion efficiency to the values obtained for solar cells on ITO electrodes. The results show that optimized PEDOT:PSS with solvent and thermal post‐treatment can be a very promising electrode material for highly efficient flexible ITO‐free organic solar cells.

Transition metal (TM) atoms bound to fullerenes are proposed as adsorbents for high density, room temperature, ambient pressure storage of hydrogen. C60 or C48B12 disperses TMs by charge transfer interactions to produce stable organometallic buckyballs (OBBs). A particular scandium OBB can bind as many as 11 hydrogen atoms per TM, ten of which are in the form of dihydrogen that can be adsorbed and desorbed reversibly. In this case, the calculated binding energy is about 0.3 eV/H(2), which is ideal for use on board vehicles. The theoretical maximum retrievable H2 storage density is approximately 9 wt %.

We studied electrochemical nitrogen reduction reactions (NRR) to ammonia on single atom catalysts (SACs) anchored on defective graphene derivatives by density functional calculations. We find significantly improved NRR selectivity on SACs compared to that on the existing bulk metal surface due to the great suppression of the hydrogen evolution reaction (HER) on SACs with the help of the ensemble effect. In addition, several SACs, including Ti@N4 (0.69 eV) and V@N4 (0.87 eV), are shown to exhibit lower free energy for NRR than that of the Ru(0001) stepped surface (0.98 eV) due to a strong back-bonding between the hybridized d-orbital metal atom in SAC and π* orbital in *N2. Formation energies as a function of nitrogen chemical potential suggest that Ti@N4 and V@N4 are also synthesizable under experimental conditions.

Ambient stability of colloidal nanocrystal quantum dots (QDs) is imperative for low-cost, high-efficiency QD photovoltaics. We synthesized air-stable, ultrasmall PbS QDs with diameter (D) down to 1.5 nm, and found an abrupt transition at D ≈ 4 nm in the air stability as the QD size was varied from 1.5 to 7.5 nm. X-ray photoemission spectroscopy measurements and density functional theory calculations reveal that the stability transition is closely associated with the shape transition of oleate-capped QDs from octahedron to cuboctahedron, driven by steric hindrance and thus size-dependent surface energy of oleate-passivated Pb-rich QD facets. This microscopic understanding of the surface chemistry on ultrasmall QDs, up to a few nanometers, should be very useful for precisely and accurately controlling physicochemical properties of colloidal QDs such as doping polarity, carrier mobility, air stability, and hot-carrier dynamics for solar cell applications.

We present a comprehensive study of the optical and electrical properties of transparent conductive films made from precisely tuned ratios of metallic and semiconducting single-wall carbon nanotubes. The conductivity and transparency of the SWNT films are controlled by an interplay between localized and delocalized carriers, as determined by the SWNT electronic structure, tube-tube junctions, and intentional and unintentional redox dopants. The results suggest that the main resistance in the SWNT thin films is the resistance associated with tube-tube junctions. Redox dopants are found to increase the delocalized carrier density and transmission probability through intertube junctions more effectively for semiconductor-enriched films than for metal-enriched films. As a result, redox-doped semiconductor-enriched films are more conductive than either intrinsic or redox-doped metal-enriched films.

We propose the great potential of single atom catalysts (SACs) for CO2 electroreduction with high activity and selectivity predictions over a competitive H2 evolution reaction. We find the lack of an atomic ensemble for adsorbate binding and unique electronic structure of the single atom catalysts play an important role.

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Lithium-ion batteries are current power sources of choice for portable electronics, offering high energy density and longer lifespan than comparable technologies. Significant improvements in rate and durability for inexpensive, safe and non-toxic electrode materials may enable utilization in hybrid electric or plug-in hybrid electric vehicles (PHEVs). Furthermore, recent efforts for hybrid electric vehicle applications have been focused on new anode materials with slightly more positive insertion voltages with respect to Li/Li þ to minimize any risks of high-surface-area Li plating while charging at high rates, a major safety concern.[1] In hybrid electric vehicles, batteries are cycled with $10% charge/discharge from the point where the cell is at 50% capacity. when cycled in a voltage window of 3.0-0.005 V, but this material suffered from poor cycling stability, with the capacity degrading to 400 mA h g À1 in $100 cycles. [8] By increasing the cut-off potential to 0.2 V and employing a slow rate (discharge and charge at C/15 and C/20, respectively), the cycling was more stable, ranging from 600-400 mA h g À1 in 100 cycles.[8] A tin-doped MoO 3 system was also explored, and the average charge potential was lowered, but at the expense of capacity fading.[9] Here we report on anodes fabricated from crystalline MoO 3 nanoparticles that display both a durable reversible capacity of 630 mA h g À1 and durable high rate capability.The nanoparticle anodes show no capacity degradation for 150 cycles between 3.5 to 0.005 V with both charge and discharge at C/2, compared to micrometer-sized particles where the capacity quickly fades. (Typically both decreased capacity and rapid degradation are observed when deep cycles are employed at higher rates.) Upon cycling, long-range order in the MoO 3 nanostructures is lost. First-principle calculations are employed in order to explain the nanoparticle durability despite the loss of structural order. The crystalline molybdenum oxide nanoparticles are grown at high density by a previously described economical hot-wire chemical vapor deposition (HWCVD) technique.[10] Figure 1a shows a representative transmission electron microscopy (TEM) image of the as-synthesized nanoparticles. Extensive TEM analyses reveal that the bulk powder contains almost exclusively nanospheroids with diameters of 5-20 nm, thus providing a short solid-state Li-ion diffusion path. A highresolution TEM image of a nanoparticle where the lattice fringes are visible is shown in Figure 1b. A simple electrophoresis deposition process [11] is employed to fabricate high-surface area porous nanoparticle films on a stainless steel electrode with a thickness of $2 mm. Figure 1c displays a scanning electron microscopy (SEM) image of an electrophoresis-deposited film. The mass density of the nanoparticle film was found to be $3.3 g cm À3 from mass and thickness data compared to 4.7 g cm À3 for the bulk material. Furthermore, the electrode is comprised of entirely COMMUNICATION