Low-temperature planar organic−inorganic lead halide perovskite solar cells have been at the center of attraction as power conversion efficiencies go beyond 20%. Here, we investigate Nb doping of SnO 2 deposited by a lowcost, scalable chemical bath deposition (CBD) method. We study the effects of doping on compositional, structural, morphological, and device performance when these layers are employed as electron-selective layers (ESLs) in planarstructured PSCs. We use doping concentrations of 0, 1, 5, and 10 mol % Nb to Sn in solution. The ESLs were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy, and ultraviolet−visible spectroscopy. ESLs with an optimum 5 mol % Nb doping yielded, on average, an improvement of all the device photovoltaic parameters with a champion power conversion efficiency of 20.5% (20.1% stabilized).

Electrochemical deposition of ZnOThe working electrode is kept at a potential negative to the reduction potential of O 2 , which causes oxygen gas near the electrode to be reduced to hydroxide ions. The hydroxide ions react with the zinc ions and forms zinc hydroxide, zinc oxyhydroxide or zinc oxide (depending on temperature).

Zinc oxide is a well-known metal oxide semiconductor with a wide direct band gap that offers a promising alternative to titanium oxide in photocatalytic applications. ZnO is studied here as quantum dots (QDs) in colloidal suspensions, where ultrasmall nanoparticles of ZnO show optical quantum confinement with a band gap opening for particles below 9 nm in diameter from the shift of the band edge energies. The optical properties of growing ZnO QDs are determined with Tauc analysis, and a system of QDs for the treatment and degradation of distributed threats is analyzed using an organic probe molecule, methylene blue, whose UV/vis spectrum is analyzed in some detail. The effect of optical properties of the QDs and the kinetics of dye degradation are quantified for low-dimensional ZnO materials in the range of 3−8 nm and show a substantial increase in photocatalytic activity compared to larger ZnO particles. This is attributed to a combined effect from the increased surface area as well as a quantum confinement effect that goes beyond the increased surface area. The results show a significantly higher photocatalytic activity for the QDs between 3 and 6 nm with a complete decolorization of the organic probe molecule, while QDs from 6 nm and upward in diameter show signs of competing reduction reactions. Our study shows that ultrasmall ZnO particles have a reactivity beyond that which is expected because of their increased surface area and also demonstrates size-dependent reaction pathways, which introduces the possibility for size-selective catalysis.

No abstract

In this study, the photocatalytic activity of TiO 2 nanofibers toward ammonia borane hydrolysis has been strongly modified by doping the nanostructure by ZnO and Fe 2 O 3 oxides.Due to the differences in the work function and band gap energy among the three semiconductors (TiO 2 , ZnO and Fe 2 O 3 ), illumination of TiO 2 leads to accumulate the electrons and holes on the conduction and valance bands of Fe 2 O 3 and ZnO, respectively. Accordingly, the experimental results indicated that the surface of the obtained nanofibers is very active which results in an instant hydrolysis of ammonia borane molecules reaching the active zone Downloaded by [New York University] at 04:01 19 February 2015A c c e p t e d M a n u s c r i p t 2 surrounding the nanofibers. Moreover, negative activation energy was determined as increasing the temperature led to decrease the photocatalytic performance. Furthermore, kinetic studies indicated that the heterogeneous catalytic reaction describing the ammonia borane hydrolysis process is zero order which additionally supports the super activity of the introduced nanofibers.It was also observed that Fe 2 O 3 content in the introduced nanofibers has distinct influence as the best performance was obtained at 1 wt%. The modified TiO 2 nanofibers were prepared by calcination of electrospun nanofibers composed of titanium isopropoxide, zinc acetate and iron acetate in air at 700 o C for 1 h. Overall, the present study opens a new avenue to overcome the fast electrons/holes recombination dilemma facing TiO 2 -based nanostructures.