Abstract: In this paper, Cu 2 ZnSnS 4 (CZTS) thin films were directly formed on FTO glass substrates by a simple ethanol-thermal method, and the films were annealed at 550 o C under different atmospheric environments. Field emission scanning electron microscopy, energy dispersive spectroscopy, X-ray powder diffraction, and photoelectrical measurements were conducted to investigate effects of annealing parameters on surface morphology, chemical compositions, crystal structures, and photoelectrical properties of the thin films. All the thin films were smooth and compact, but their color and micro-topography were different through different annealing atmospheres. The addition of sulfur during the annealing process is necessary to tailor sulfur concentration in the films and the crystallization of CZTS phase.

Abstract: In this paper, we propose a new kind of nanostructure solar cell involving perovskite CH 3 NH 3 PbI 2 Cl and metal-oxide semiconductor TiO 2 . Taking advantage of the promising properties of this solution-processed perovskite material such as good light absorption and ambipolar transport of charge carriers, we choose CH 3 NH 3 PbI 2 Cl as both a light absorber for TiO 2 nanoparticle sensitization and hole transport material, which helps to constitute a solid-state sensitized solar cell with much simpler construction. Specifically, the cell fabrication and characterization are reported; the analysis based on small-signal electrochemical measurements is in particular provided, in order to investigate internal mechanisms of this photovoltaic device, mainly including charge accumulation, recombination and transport through it.

Abstract: Organic-inorganic lead halide perovskite, initially applied as active layer in light-emitting diode (LED) and field-effect transistor ( FET) devices [1] , has been gradually introduced into the development of solar cells and plays such critical role as either light absorber or hole conducting material (HCM). This kind of hybrid layer structure makes perovskite as a promising candidate in photovoltaic applications, mainly due to its attractive chemical versatility that can readily tune the electronic coupling between inorganic sheets, and eventually tailor its optical/electronic properties [2] . In order to understand the performance of a photovoltaic device especially involving such novel material for its further optimization consideration, exploring the photogenerated charge accumulation and transport is imperative to be highlighted. Here we report the work on perovskite (CH 3 NH 3 PbI 2 Cl [3] )-based nanostructure solar cell, including the cell fabrication and characterization, and particularly provide the analysis on charge carrier properties on the basis of dynamic electrochemical measurements. In this research stage, we targets more than achieving relatively fair energy conversion efficiency, instead we hope to uncover internal mechanisms of charge carrier movement and subsequently the substantial function of perovskite in photovoltaic device. The stack structure of the mesoscopic solar cell we developed for this investigation is shown in Fig. 1(a). The nanoporous semiconductor oxide membrane was fabricated by screen-printing technique on fluorine doped tin oxide (FTO) glass substrate with terpineol-based paste made by commercial-available TiO 2 powder (Aldrich, d=25nm). The work electrode coated with the TiO 2 paste was sintered under airflow at 550 o C for 3 h. Iodide-chloride mixed-halide perovskite was synthesized from a N,N-Dimethylformamide solution of CH 3 NH 3 I and PbCl 2 (3:1 molar ratio) [3] . The precursor solution was deposited on porous TiO 2 surface via spin-coating or dipping process, and then was dried at 100 o C. After drying, obvious color variation indicated the formation of perovskite layer. The function of the perovskite layer in nanostructure solar cells strongly depends on the deposition method. In particular, the shape of nanocrystalline CH 3 NH 3 PbI 2 Cl infiltrating into TiO 2 porous membrane, probably with quantum-dot structure, is confirmed by electron microscopy micrographs. One thing should be noted is that, combining the band diagram shown in Fig.1(b), the extremely thin CsSnI 2.95 F 0.05 layer (referring our previous work for its synthesis [4] ) deposited on counter electrode performs more like energy ‘staircase’ for hole transport rather than pure hole conducting material. Meanwhile, a heterojunction-like cell (called ‘blank’ cell) containing only CH 3 NH 3 PbI 2 Cl layer on the TiO 2 film is produced for comparison. In order to thoroughly understand the decisive mechanisms of charge accumulation and transport behaviors on photovoltaic conversion, a systematic characterizations including photocurrent transient, open-circuit voltage decay (OCVD) and electrochemical impedance spectroscopy (EIS) were carried out under different operation conditions. Correspondingly the effective lifetime and diffusivity of charge carriers are extracted to investigate the transport properties of photon-generated electrons. Particularly, chemical capacitance (C μ ) is examined since it assists to monitor the Fermi level of electrons and density of states (DoS) in perovskite absorber, which significantly differentiates from conventional dye (e.g. N719) sensitized solar cells on the aspect of charge generation and accumulation in light absorber material. Consequently, our research demonstrates the promising HCM-free nanostructure solar cells involving solution-processed perovskite material. Fair light absorption and charge accumulation capability make self-assembled CH 3 NH 3 PbI 2 Cl behave as both sensitizer and charge transport material, which helps to constitute new kind of solid-state sensitized solar cells with a much simpler configuration. Reference 1. D. B. Mitzi, K. Chondroudis, and C.R. Kagan, Organic–inorganic electronics. IBM J. Res. & Dev. , 2001. 45 (1): p. 29-45. 2. Etgar, L., Semiconductor Nanocrystals as Light Harvesters in Solar Cells. Materials 2013. 6 : p. 445--59. 3. Lee, M.M., et al., Efficient hybrid solar cells based on meso-superstructured organometal halide perovskites. Science, 2012. 338 ( 6107): p. 643-647. 4. Sun, X., et al., Effects of calcination treatment on the morphology, crystallinity, and photoelectric properties of all-solid-state dye-sensitized solar cells assembled by TiO2 nanorod arrays. Phys. Chem. Chem. Phys., 2013. 15 : p. 18716-18720.

Abstract: In this study, Cu 2 ZnSnS 4 (CZTS) thin films were directly formed on FTO glass substrates by a simple ethanol-thermal method, and the films were annealed at 823K under different atmosphere environments. Field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), X-ray powder diffraction (XRD), and photoelectrical measurements were used to investigate effects of annealing parameters in surface morphology, chemical compositions, and crystal structures of the thin films as well as photoelectrical properties, respectively. All the thin films were smooth and compact, but their color and micro-topography were different through different annealing atmosphere. The addition of sulfur during the annealing process is necessary to tailor sulfur concentration in the films and the crystallization of CZTS phase. Furthermore, the films exhibited p-type semiconductor characteristics, which is desirable for their applications in thin films solar cells.

Abstract: In recent years, energy converting and storage systems have been playing a crucial role in alleviating the pressure of energy crisis. Oxygen reduction reactions (ORRs) play an important role in energy converting and storage systems, such as fuel cells and metal air batteries. Herein, it is critical important to develop high efficient and stable electrocatalysts for ORRs to replace platinum-based catalytic materials. In this work, nickel-cobalt bimetallic metal-organic framework (NiCo-MOF-74) and its derivatives (oxides, phosphide and sulfide) were synthesized and their electrochemical performances for ORRs were evaluated. It was found that the series of NiCo-MOF-74 products with rod-like structure show excellent electrochemical performance, especially the sulfide. The sulfide exhibits the onset potential of -0.14V vs Ag/AgCl. Therefore, the series of NiCo-MOF-74 derivatives have great potential in ORRs as highly active, stable, low-cost catalysts.