A liquid junction photoelectrochemical (PEC) solar cell based on p-type methylammonium lead iodide (p-MeNH3PbI3) perovskite with a large open-circuit voltage is developed. MeNH3PbI3 perovskite is readily soluble or decomposed in many common solvents. However, the solvent dichloromethane (CH2Cl2) can be employed to form stable liquid junctions. These were characterized with photoelectrochemical cells with several redox couples, including I3(-)/I(-), Fc/Fc(+), DMFc/DMFc(+), and BQ/BQ(•-) (where Fc is ferrocene, DMFc is decamethylferrocene, BQ is benzoquinone) in CH2Cl2. The solution-processed MeNH3PbI3 shows cathodic photocurrents and hence p-type behavior. The difference between the photocurrent onset potential and the standard potential for BQ/BQ(•-) is 1.25 V, which is especially large for a semiconductor with a band gap of 1.55 eV. A PEC photovoltaic cell, with a configuration of p-MeNH3PbI3/CH2Cl2, BQ (2 mM), BQ(•-) (2 mM)/carbon, shows an open-circuit photovoltage of 1.05 V and a short-circuit current density of 7.8 mA/cm(2) under 100 mW/cm(2) irradiation. The overall optical-to-electrical energy conversion efficiency is 6.1%. The PEC solar cell shows good stability for 5 h under irradiation.

To investigate the effects of land use and crop management on soybean rhizobial communities, 280 nodule isolates were trapped from 7 fields with different land use and culture histories. Besides the known Bradyrhizobium japonicum, three novel genospecies were isolated from these fields. Grassland (GL) maintained a higher diversity of soybean bradyrhizobia than the other cultivation systems. Two genospecies (Bradyrhizobium spp. I and III) were distributed widely in all treatments, while Bradyrhizobium sp. II was found only in GL treatment. Cultivation with soybeans increased the rhizobial abundance and diversity, except for the soybean monoculture (S-S) treatment. In monoculture systems, soybeans favored Bradyrhizobium sp. I, while maize and wheat favored Bradyrhizobium sp. III. Fertilization decreased the rhizobial diversity indexes but did not change the species composition. The organic carbon (OC) and available phosphorus (AP) contents and pH were the main soil parameters positively correlated with the distribution of Bradyrhizobium spp. I and II and Bradyrhizobium japonicum and negatively correlated with Bradyrhizobium sp. III. These results revealed that different land uses and crop management could not only alter the diversity and abundance of soybean rhizobia, but also change interactions between rhizobia and legume or nonlegume plants, which offered novel information about the biogeography of rhizobia.

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Electrodeposition of Si films from a Si-containing electrolyte is a cost-effective approach for the manufacturing of solar cells. Proposals relying on fluoride-based molten salts have suffered from low product quality due to difficulties in impurity control. Here we demonstrate the successful electrodeposition of high-quality Si films from a CaCl -based molten salt. Soluble Si -O anions generated from solid SiO are electrodeposited onto a graphite substrate to form a dense film of crystalline Si. Impurities in the deposited Si film are controlled at low concentrations (both B and P are less than 1 ppm). In the photoelectrochemical measurements, the film shows p-type semiconductor character and large photocurrent. A p-n junction fabricated from the deposited Si film exhibits clear photovoltaic effects. This study represents the first step to the ultimate goal of developing a cost-effective manufacturing process for Si solar cells based on electrodeposition.

A variety of PbI 2 /MAPbI 3 perovskites were prepared and investigated by a rapid screening technique utilizing a modified scanning electrochemical microscope (SECM) in order to determine how excess PbI 2 affects its photoelectrochemical (PEC) properties. An optimum ratio of 2.5% PbI 2 /MAPbI 3 was found to enhance photocurrent over pristine MAPbI 3 on a spot array electrode under irradiation. With bulk films of various PbI 2 /MAPbI 3 composites prepared by a spin-coating technique of mixed precursors and a one-step annealing process, the 2.5% PbI 2 /MAPbI 3 produced an increased photocurrent density compared to pristine MAPbI 3 for 2 mM benzoquinone (BQ ) reduction at −0.4 V vs Fc/Fc + . As a result of the relatively high quantum yield of MAPbI 3 , a time-resolved photoluminescence quenching experiment could be applied to determine electron−hole diffusion coefficients and diffusion lengths of PbI 2 /MAPbI 3 composites, respectively. The diffusion coefficients combined with the exciton lifetime of the pristine 2.5% PbI 2 /MAPbI 3 (τ PL = 103.3 ns) give the electron and hole exciton diffusion lengths, ∼300 nm. Thus, the 2.5% PbI 2 /MAPbI 3 led to an approximately 3.0-fold increase in the diffusion length compared to a previous report of ∼100 nm for the pristine MAPbI 3 perovskite. We then demonstrated that the efficiency of liquid-junction solar cells for 2.5% excess PbI 2 of p-MAPbI 3 was improved from 6.0% to 7.3%.

This communication presents a novel kind of silicon nanomaterial: freestanding Si nanowire arrays (Si NWAs), which are synthesized facilely by one-step template-free electro-deoxidation of SiO 2 in molten CaCl 2 . The self-assembling growth process of this material is also investigated preliminarily.

Production of silicon film directly by electrodeposition from molten salt would have utility in the manufacturing of photovoltaic and optoelectronic devices owing to the simplicity of the process and the attendant low capital and operating costs. Here, dense and uniform polycrystalline silicon films (thickness up to 60 µm) are electrodeposited on graphite sheet substrates at 650 °C from molten KCl-KF-1 mol% K 2 SiF 6 salt containing 0.020-0.035 wt% tin. The growth of such high-quality tin-doped silicon films is attributable to the mediation effect of tin in the molten salt electrolyte. A four-step mechanism is proposed for the generation of the films: nucleation, island formation, island aggregation, and film formation. The electrodeposited tindoped silicon film exhibits n-type semiconductor behavior. In liquid junction photoelectrochemi cal measurement, this material generates a photocurrent about 38-44% that of a commercial n-type Si wafer.

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