The area of thin-film photovoltaics has been overwhelmed by organometal halide perovskites. Unfortunately, serious stability concerns arise with perovskite solar cells. For example, methyl-ammonium lead iodide is known to decompose in the presence of water and, more severely, even under inert conditions at elevated temperatures. Here, we demonstrate inverted perovskite solar cells, in which the decomposition of the perovskite is significantly mitigated even at elevated temperatures. Specifically, we introduce a bilayered electron-extraction interlayer consisting of aluminium-doped zinc oxide and tin oxide. We evidence tin oxide grown by atomic layer deposition does form an outstandingly dense gas permeation barrier that effectively hinders the ingress of moisture towards the perovskite and—more importantly—it prevents the egress of decomposition products of the perovskite. Thereby, the overall decomposition of the perovskite is significantly suppressed, leading to an outstanding device stability.

Semitransparent perovskite solar cells (PSCs) are of interest for application in tandem solar cells and building-integrated photovoltaics. Unfortunately, several perovskites decompose when exposed to moisture or elevated temperatures. Concomitantly, metal electrodes can be degraded by the corrosive decomposition products of the perovskite. This is even the more problematic for semitransparent PSCs, in which the semitransparent top electrode is based on ultrathin metal films. Here, we demonstrate outstandingly robust PSCs with semitransparent top electrodes, where an ultrathin Ag layer is sandwiched between SnO x grown by low-temperature atomic layer deposition. The SnO x forms an electrically conductive permeation barrier, which protects both the perovskite and the ultrathin silver electrode against the detrimental impact of moisture. At the same time, the SnO x cladding layer underneath the ultra-thin Ag layer shields the metal against corrosive halide compounds leaking out of the perovskite. Our semitransparent PSCs show an efficiency higher than 11% along with about 70% average transmittance in the near-infrared region (λ > 800 nm) and an average transmittance of 29% for λ = 400-900 nm. The devices reveal an astonishing stability over more than 4500 hours regardless if they are exposed to ambient atmosphere or to elevated temperatures.

Corrosive precursors used for the preparation of organic-inorganic hybrid perovskite photoactive layers prevent the application of ultrathin metal layers as semitransparent bottom electrodes in perovskite solar cells (PVSCs). This study introduces tin-oxide (SnO ) grown by atomic layer deposition (ALD), whose outstanding permeation barrier properties enable the design of an indium-tin-oxide (ITO)-free semitransparent bottom electrode (SnO /Ag or Cu/SnO ), in which the metal is efficiently protected against corrosion. Simultaneously, SnO functions as an electron extraction layer. We unravel the spontaneous formation of a PbI interfacial layer between SnO and the CH NH PbI perovskite. An interface dipole between SnO and this PbI layer is found, which depends on the oxidant (water, ozone, or oxygen plasma) used for the ALD growth of SnO . An electron extraction barrier between perovskite and PbI is identified, which is the lowest in devices based on SnO grown with ozone. The resulting PVSCs are hysteresis-free with a stable power conversion efficiency (PCE) of 15.3% and a remarkably high open circuit voltage of 1.17 V. The ITO-free analogues still achieve a high PCE of 11%.

In this study, carbon nanodots (C-dots)/WO photocatalysts were prepared via a two-step hydrothermal method. The morphologies and optical properties of the as-prepared materials were investigated. Compared with the prepared WO and C-dots, the C-dots/WO possessed stronger photocatalytic capability and excellent recyclability for photocatalytic elimination of Rhodamine B. For example, the achieved first order reaction rate constant of 0.01942 min for C-dots/WO was ∼7.7 times higher than that of the prepared WO. The enhanced photocatalytic activity of C-dots/WO was attributed to the enhanced light harvesting ability and efficient spatial separation of photo-excited electron-hole pairs resulting from the synergistic effect of WO and C-dots. The high photocatalytic activity of C-dots/WO remained unchanged even after 3 cycles of use. Meanwhile, a possible mechanism of C-dots/WO for the enhanced photocatalytic activity was proposed.

Beyond the demonstration of single-molecule (or singleatom) and organic-thin-film transistors, [1±4] a reliable electrode contact remains one of the most critical challenges in the development of molecular and organic electronics. Except for the tip of a scanning tunneling microscope, [5±7] more practical connections often involve a metal/ insulator(semiconductor)/metal thin-film structure, either through a gate thin-film dielectric assembly below the source±drain, [1±4] or a insulating thin-film separator which runs parallel to the molecular path. [8,9] To achieve practical applications, not only does one need ohmic contacts so that any nonlinearity can be correctly attributed, but also a much more insulating medium to minimize the influence from the surroundings.[10] However, one often encounters unexpected current±voltage characteristics which do not arise from the given atoms or molecules. For example, negative differential resistance (NDR) [11±15] and the memory effect (hysteresis) [16±21] were found not only in singlemolecule devices, but also in organic thin-film transistors, organic light-emitting devices, and metal/inorganic insulator/ metal systems.[22±26] Despite many years of effort, the precise origin of the phenomena remains unknown, which has become a major obstacle in the research and development of new electronic devices. In this report, we try to reveal the origin of such phenomena, based on new experiment results from various metals and both organic and polymeric thin films. The answer is surprisingly found to be two-dimensional (2D) single-electron tunneling due to nanometer-sized metal islands, which were manifested unexpectedly through a wellknown process where some nuclei were blocked from further growth by the sealing of electrode outside crevices. The results not only provide a satisfactory explanation of the anomalous phenomena, but also open a new door to the construction and fabrication of molecular electronic and memory devices.The widespread nature of the phenomena is shown by its easy duplication, using any metal electrode and any organic or inorganic thin-film insulator, or even semiconductors, since the anomalous current is usually several orders of magnitude higher than that of the nominal conductance. The typical current±voltage (I±V) curve showing NDR and a memory effect has two distinctive features. One is a local current maximum (when V = V max ), followed by a region of NDR. The other feature is the dual states for V < V max , where the ªonº state is obtained by reaching the V max first, and the ªoffº state is recovered by visiting a voltage beyond NDR before rapidly setting back to zero.[21] In addition, there are intermediate states available, [21,22] and the phenomena could be removed by exposure to oxygen gas. [13] Many models have been proposed, but so far none offers a satisfactory explanation. The arbitrary choice of metals and insulators of various energies immediately rejects any speculation related to, for example, a particular type of insulating or semiconduc...

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Ternary NiCoFe mixed-metal oxides (NCF-MMOs) with different Ni/Co/Fe ratios were successfully synthesized through a hydrotalcite-like precursor route by co-precipitation of appropriate amounts of metal salts from homogeneous solution, followed by calcination at 600 °C. X-ray diffraction (XRD) patterns revealed the formation of well crystalline layered double hydroxides (LDHs), particularly at the M2+/M3+ ratio of 3 : 1. Brunauer-Emmett-Teller (BET) analysis revealed that the resulting NiCoFe LDHs possessed large specific surface areas (66.9-93.8 m2 g-1). The NCF-MMO (1 : 2 : 1) samples were demonstrated to be formed by the aggregation of regular cubes with an edge length of about 2 μm, and each cube was accumulated with many fine particles with a size of ∼130 nm. UV-vis diffuse reflection spectroscopy (DRS) confirmed that the samples showed a broad absorption in the visible-light region (450-750 nm), with a low band gap of 2.33-2.77 eV. The calcined samples with a Ni/Co/Fe molar ratio of 1 : 2 : 1 possessed the best photocatalytic activity with 96.8% degradation of methylene blue (MB) dye under visible light irradiation for 4 h, which exceeded those of commercial P25 TiO2, binary NiFe mixed-metal oxides and pure Fe2O3, CoO and NiO particles under the same conditions. NCF-MMO (1 : 2 : 1) also had a strong degradation effect on the non-dye pollutant phenol as well. Kinetic studies suggested that the degradation of MB followed a pseudo-first-order kinetic behavior. The photodegradation mechanism of NCF-MMOs was also discussed.

Both porous and scale-like wall zirconia (ZrO2) hollow microspheres were successfully prepared through a facile and mild microwave solvothermal method using the rape pollen as biotemplates. The formation mechanisms were discussed for both ZrO2 hollow microspheres fabricated using pollen biotemplate with different pollen treatments. The porous ZrO2 hollow microspheres had a specific surface area of 40.92 m2·g–1, significantly higher than scale-like wall ZrO2 hollow microspheres (24.79 m2·g–1) and ZrO2 particles (27.99 m2·g–1). The adsorption test results showed that porous ZrO2 hollow microspheres had a higher adsorption capability (96.98 g·mg–1) than scale-like wall ZrO2 hollow microspheres (38.55 g·mg–1) and ZrO2 particles (32.03 g·mg–1) for Congo red. The adsorption followed pseudo-second-order kinetics, and the adsorption process was homogeneous adsorption of monolayer.