The abundant-metal-based polyoxometalate complex [Co(4)(H(2)O)(2)(PW(9)O(34))(2)](10-) is a hydrolytically and oxidatively stable, homogeneous, and efficient molecular catalyst for the visible-light-driven catalytic oxidation of water. Using a sacrificial electron acceptor and photosensitizer, it exhibits a high (30%) photon-to-O(2) yield and a large turnover number (>220, limited solely by depletion of the sacrificial electron acceptor) at pH 8. The photocatalytic performance of this catalyst is superior to that of the previously reported precious-metal-based polyoxometalate water oxidation catalyst [{Ru(4)O(4)(OH)(2)(H(2)O)(4)}(γ-SiW(10)O(36))(2)](10-).

A totally homogeneous, molecular, visible-light-driven water oxidation system is reported. The three system components are (i) a water oxidation catalyst, 1 (a Ru(IV)(4)O(4) cluster stabilized by oxidatively resistant [SiW(10)O(32)](8-) ligands); (ii) a photosensitizer, [Ru(bpy)(3)](2+); and (iii) a sacrificial electron acceptor, S(2)O(8)(2-). Dioxygen is formed rapidly with an initial turnover frequency of approximately 8 x 10(-2) s(-1) and an estimated quantum yield (defined as the number of O(2) molecules formed per two photons absorbed) of approximately 9%.

A postsynthesis assembly approach, an ex situ ligand exchange route, was developed for fast (within 2 h) and high loading (34% coverage) deposition of CdSe QDs on TiO(2) films. With the combination of high-quality QD sensitizers and the effective deposition technique, a record photovoltaic performance with an efficiency of 5.4% was observed for the resulting cell device.

Dye-sensitized solar cells have attracted intense research attention owing to their ease of fabrication, cost-effectiveness and high efficiency in converting solar energy. Noble platinum is generally used as catalytic counter electrode for redox mediators in electrolyte solution. Unfortunately, platinum is expensive and non-sustainable for long-term applications. Therefore, researchers are facing with the challenge of developing low-cost and earthabundant alternatives. So far, rational screening of non-platinum counter electrodes has been hamstrung by the lack of understanding about the electrocatalytic process of redox mediators on various counter electrodes. Here, using first-principle quantum chemical calculations, we studied the electrocatalytic process of redox mediators and predicted electrocatalytic activity of potential semiconductor counter electrodes. On the basis of theoretical predictions, we successfully used rust (a-Fe 2 O 3 ) as a new counter electrode catalyst, which demonstrates promising electrocatalytic activity towards triiodide reduction at a rate comparable to platinum.

Several key properties of the water oxidation catalyst Rb(8)K(2)[{Ru(IV)(4)O(4)(OH)(2)(H(2)O)(4)}(gamma-SiW(10)O(36))(2)] and its mechanism of water oxidation are given. The one-electron oxidized analogue [{Ru(V)Ru(IV)(3)O(6)(OH(2))(4)}(gamma-SiW(10)O(36))(2)](11-) has been prepared and thoroughly characterized. The voltammetric rest potentials, X-ray structures, elemental analysis, magnetism, and requirement of an oxidant (O(2)) indicate these two complexes contain [Ru(IV)(4)O(6)] and [Ru(V)Ru(IV)(3)O(6)] cores, respectively. Voltammetry and potentiometric titrations establish the potentials of several couples of the catalyst in aqueous solution, and a speciation diagram (versus electrochemical potential) is calculated. The potentials depend on the nature and concentration of counterions. The catalyst exhibits four reversible couples spanning only ca. 0.5 V in the H(2)O/O(2) potential region, keys to efficient water oxidation at low overpotential and consistent with DFT calculations showing very small energy differences between all adjacent frontier orbitals. The voltammetric potentials of the catalyst are evenly spaced (a Coulomb staircase), more consistent with bulk-like properties than molecular ones. Catalysis of water oxidation by [Ru(bpy)(3)](3+) has been examined in detail. There is a hyperbolic dependence of O(2) yield on catalyst concentration in accord with competing water and ligand (bpy) oxidations. O(2) yields, turnover numbers, and extensive kinetics data reveal several features and lead to a mechanism involving rapid oxidation of the catalyst in four one-electron steps followed by rate-limiting H(2)O oxidation/O(2) evolution. Six spectroscopic, scattering, and chemical experiments indicate that the catalyst is stable in solution and under catalytic turnover conditions. However, it decomposes slowly in acidic aqueous solutions (pH < 1.5).

To date, the formation mechanism of organolead halide CH 3 NH 3 PbI 3 perovskites based on the efficient sequential reaction route has remained virtually unexplored. Such a synthetic method usually yields high-performance solar cells with an efficiency over 15%, and the identification of the crystal growth mechanism is crucial for understanding the chemical reaction process and further improving the light converting efficiency. Herein, we develop a versatile and facile approach based on sequential reaction to produce freestanding CH 3 NH 3 PbI 3 crystals as a model for crystal growth mechanism studies. It was found that the in situ transformation and dissolution−crystallization mechanisms play competing roles in determining the characteristics of products that are largely depend on the chemical reaction kinetics. Such a method can also be readily used for synthesis of freestanding CH 3 NH 3 PbI 3 crystals with controllable morphological characteristics, such as cuboids, rods, wires, and plates. The synthetic strategy as well as the crystal growth mechanisms exemplified here can also serve in the design and development of more sophisticated organolead halide perovskites as well as further optimization across a range of possible domains of applications.

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Recently, a hot casting technique was developed to prepare pinhole free perovskite thin films with millimeter-scale grains. However, its intrinsic formation mechanism has not been studied in the literature up to now. Here, we demonstrate a Volmer−Weber growth mechanism during the hot casting, a process that typically involves the formation of island shaped grains and the following integration into dense perovskite films. It was found that such crystal growth was determined by the multiple effect of thermal energy and force centrifugal field. Particularly, the thermal energy can facilitate the formation of CH 3 NH 3 PbI 3 and overcome the energy barriers of the precursor solutions on the substrates. The detailed morphologies of CH 3 NH 3 PbI 3 films can be optimized by regulating deposition parameters including casting temperature and rotate speed. Solar cells constructed with these thin films achieve an average power conversion efficiency of 12.6 ± 0.3% under standard AM 1.5 G conditions.