ZnSnP2 is a promising candidate for solar absorber materials from the viewpoint of high absorption and earth‐abundant constitution elements. In this paper, we fabricated ZnSnP2 crystals by flux method based on the phase diagram of Sn‐ZnP2 pseudo‐binary system and investigated their properties for an application to photovoltaics. The crystal growth experiments with the cooling rate of 0.7 and 12 °C/h were carried out and we successfully obtained ZnSnP2 crystals with the diameter of 8mm and the thickness of a few mm by a slow cooling rate. The structure of grown crystals studied by X‐ray diffraction was indicated to be chalcopyrite‐type ZnSnP2. In addition, the decrease of the degree of order was observed with the increase of cooling rate. The lattice constants of a and c axes are 5.649 and 11.295 Å, respectively. The composition of grown crystals is a near stoichiometric ratio of ZnSnP2 by EDX analysis. The bandgaps of ZnSnP2 crystals obtained by cooling rate of 0.7 and 12 °C/h were estimated to be 1.61 and 1.48 eV, respectively, which is caused by the difference of the degree of order. The hall‐resistivity measurement showed that ZnSnP2 crystals with a slow cooling rate has a p‐type conduction. The resistivity, the hole concentration and the mobility are 10∼70 Ωcm, 6·1016∼2·1017 cm‐3, and 1∼3 cm2V‐1s‐1. The obtained properties are suitable for an absorber of photovoltaics. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

We report on current density–voltage (J–V) characteristics of solar cells using bulk crystals of ZnSnP2 obtained by solution growth, where Sn was used as a solvent. The minority carrier lifetimes of fast and slow components in bulk crystals of ZnSnP2 were 0.442 and 37.8 ns, respectively, which were obtained by analysis using double exponential function in time‐resolved photoluminescence (TRPL) under the excitation power of 5.05 mW with the beam area of 0.5 mm2. The lifetime is close to that of CIGS, which is as high as to achieve the conversion efficiency of over 16%. TRPL also revealed that the recombination at the surface was dominant since the intensity of fast component was much larger than that of slow component. The well‐known structure Al/Al‐doped ZnO/ZnO/CdS/ZnSnP2/Mo was adopted for solar cells. The short‐circuit current density and the open‐circuit voltage are 1.99 mA cm−2 and 0.172 V, respectively. The wavelength at the absorption edge in external quantum efficiency is consistent with the bandgap of ZnSnP2. However, the conversion efficiency is 0.087%. The J–V curve suggests that the reduction of series resistance is required because it is higher than the value expected from the resistivity of bulk ZnSnP2. The improvement of conduction band offset is also necessary considering from our previous works.

We report on the optimization of interface structure in ZnSnP solar cells. The effects of back electrode materials and related interface on photovoltaic performance were investigated. It was clarified that a conventional structure Mo/ZnSnP showed a Schottky-behavior, while an ohmic-behavior was observed in the Cu/ZnSnP structure annealed at 300 °C. STEM-EDX analysis suggested that Cu-Sn-P ternary compound was formed at the interface. This compound is considered to play an important role to obtain the ohmic contact between ZnSnP and Cu. In addition, it was clarified that the aqua regia etching of ZnSnP bulk crystals before chemical bath deposition process for the preparation of buffer layer was effective to remove the layer including lattice defects introduced by mechanical-polishing, which was supported by TEM observations and photoluminescence measurements. This means that the carrier transport across the interface was improved because of the reduced defect at the interface. Consequently, the conversion efficiency of approximately 2% was achieved with the structure of Al/ZnO;Al/ZnO/CdS/ZnSnP/Cu, where the values of short circuit current density, J, open circuit voltage, V, and fill factor, FF, were 8.2 mA cm, 0.452 V, and 0.533, respectively. However, the value of V was largely low considering the bandgap value of ZnSnP. To improve the conversion efficiency, the optimization of buffer layer material is considered to be essential in the viewpoint of band alignment.

We collected 1,353 strains of beta-hemolytic streptococci of groups A, B, C, and G (1,176 strains of which were group A) isolated in 26 institutions throughout Japan in 1972-1974. The strains were grouped and T-typed by our specific group-and T-factor sera, and the minimal inhibitory concentrations of 10 antibiotics were assayed by the standard method. Resistant strains from the above collection were classified according to group, T-type, and drug resistance pattern. Our data on T-types for 1964-1971 and on drug resistance for 1966-1971 were used to interpret the detected long-term variations in T-type and drug resistance. The stepwise acquisition of multiple drug resistance, the difference in resistance pattern between predominant T-types, and the rarity of single-macrolide resistance were demonstrated.

a b s t r a c tZnSnP 2 is a promising candidate as a solar absorbing material consisting of earth-abundant and low-toxic elements. In this study, the phosphidation method, where co-sputtered Zn-Sn thin films react with phosphorus gas, was adopted for fabricating ZnSnP 2 thin films. To establish the conditions for producing ZnSnP 2 thin films, we investigated the influence of phosphidation temperature on the product phases, and interpreted the experimental results using chemical potential diagrams of the Zn-Sn-P system. ZnSnP 2 thin films with a single phase were obtained by phosphidation at 500°C under a phosphorus vapor pressure of 10 −2 atm. However, formation of ZnSnP 2 protrusions was observed on the surface of the thin films. Based on the experimental results and the chemical potential diagrams, it is indicated that un-reacted liquid Sn particles reacted with Zn and phosphorus gas to form ZnSnP 2 protrusions in a manner similar to the vapor-Liquid-Solid growth mode.