No abstract

Organometallic halide perovskite solar cells (PSCs) have unique photovoltaic properties for use in next-generation solar energy harvesting systems. The highest efficiency of PSCs reached 22.1% on a laboratory scale of <0.1 cm device area. Thus, scaling up is the next step toward commercialization, but the difficulty in controlling the quality of large-area perovskite thin films remains a fundamental challenge. It has also been frequently reported that the J- V hysteresis is intensified in PSCs with areas larger than 1 cm. In this study, we have fabricated a large-area perovskite layer using PbICl films, providing an intrinsic porous layer and enhancing the uniformity of the perovskite layer at areas larger than 1 cm. Furthermore, we have investigated the polymeric properties of the prevalent hole-transporting material poly(triarylamine) (PTAA) with its photovoltaic performance. Two types of PTAAs, poly[bis(4-phenyl)(2,4-dimethylphenyl)amine] and poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine], were compared. A series of PTAAs with different molecular weights ( M) and polydispersity indices were studied, as the molecular weight of the PTAA is a key factor in determining the electrical properties and photovoltaic performance of the system. The fabricated PSCs with an aperture area of 1 cm based on a high-molecular-weight PTAA achieved a power conversion efficiency of 16.47% with negligible hysteresis and excellent reproducibility.

Planar perovskite solar cells (PSCs) incorporating n‐type SnO2 have attracted significant interest because of their excellent photovoltaic performance. However, the film fabrication of SnO2 is limited by self‐aggregation and inhomogeneous growth of the intermediate phase, which produces poor morphology and properties. In this study, a self‐controlled SnO2 layer is fabricated directly on a fluorine‐doped tin oxide (FTO) surface through simple and rapid chemical bath deposition. The PSCs based on this hydrolyzed SnO2 layer exhibit an excellent power conversion efficiency of 20.21 % with negligible hysteresis. Analysis of the electrochemical impedance spectroscopy on the charge transport dynamics indicates that the bias voltage influences both interfacial charge transportation and the ionic double layer under illumination. The hydrolyzed SnO2‐based PSCs demonstrate a faster ionic charge response time of 2.5 ms in comparison with 100.5 ms for the hydrolyzed TiO2‐based hysteretic PSCs. The results of quasi‐steady‐state carrier transportation indicate that a dynamic hysteresis in the J–V curves can be explained by complex ionic‐electronic kinetics owing to the slow ionic charge redistribution and hole accumulation caused by electrode polarization, which causes an increase in charge recombination. This study reveals that SnO2‐based PSCs lead to a stabilized dark depolarization process compared with TiO2‐based PSCs, which is relevant to the charge transport dynamics in the high‐performing planar SnO2‐based PSCs.

Glucose isomerases produced by Thermoanaerobacter strain B6A and Clostridium thermosulfurogenes strain 4B were purified 10-11-fold to homogeneity and their physicochemical and catalytic properties were determined. Both purified enzymes displayed very similar properties (native Mr 200000, tetrameric subunit composition, and apparent pH optima 7.0-7.5). The enzymes were stable at pH 5.5-12.0, and maintained more than 90% activity after incubation at high temperature (85°C) for 1 h in the presence of metal ions. The N-terminal amino acid sequences of both thermostable glucose isomerases were Met-Asn-Lys-Tyr-Phe-Glu-Asn and were not similar to that of the thermolabile Bacillus subtilis enzyme. The glucose isomerase from C. thermosulfurogenes and Thermoanaerobacter displayed pI values of 4.9 and 4.8, and their k,,t and Km values for D-glucose at 65°C were 1040 and 1260 min-' and 140 and 120 mm respectively. Both enzymes displayed higher kc.t and lower Km values for D-xylose than for D-glucose. The C. thermosulfurogenes enzyme required Co2+ or Mg2+ for thermal stability and glucose isomerase activity, and Mn2+ or these metals for xylose isomerase activity. Crystals of C. thermosulfurogenes glucose isomerase were formed at room temperature by the hanging-drop method using 16-180% poly(ethylene glycol) (PEG) 4000 in 0.1 M-citrate buffer.

The substrate specificity of thermophilic xylose isomerase from Clostridium thenmosulfurogenes was examined by using predictions from the known crystal structure of the Arthrobacter enzyme and site-directed mutagenesis of the thermophilexylA gene. The orientation ofglucose as a substrate in the active site of the thermophilic enzyme was modeled to position the C-6 end of hexose toward His-101 in the substratebinding pocket. The locations of which (kCt/Kl,) for glucose than the wild-type enzyme of 5-and 2-fold, respectively. They also exhibited 1.5-and 3-fold higher catalytic efficiency for D-glucose than for D-xylose, respectively. These results provide evidence that alteration in substrate specificity of factitious thermophilic xylose isomerases can be achieved by designing reduced steric constraints and enhanced hydrogenbonding capacity for glucose in the substrate-binding pocket of the active site.Specificity of enzymes toward their substrates is determined in part by molecular residues that provide for binding of the substrate and that maintain substrate steric configuration in the active site. A variety of factors influence enzymesubstrate complementarity and catalytic efficiency including steric fit, charge interactions, hydrogen bonding, and hydrophobic interactions (1). Until recently, the main strategy to reveal and study the molecular basis of these factors was to determine the tertiary structure of the enzyme-substrate complexes by x-ray crystallography. Redesigning proteins by engineering of their genes is now a viable approach that complements structural studies and enables determination of amino acid substitution effects on mutant enzyme function. Thus, substrate specificity has been altered by redesigning the structural frame of an enzyme (1-4), its electrostatic network (5-8), or its hydrophobic interaction with the substrate (9). Catalytic function of an enzyme can also be changed and regulated by modifications of the physical microenvironment of its catalytic site (10, 11).Xylose isomerase (D-xylose ketol-isomerase; EC 5.3.1.5) converts D-xylose to D-xylulose during xylose metabolism in various microorganisms (12). This enzyme also catalyzes the conversion of D-glucose to D-fructose in vitro and has been used as an industrial biocatalyst for production of high fructose corn syrup (13). Xylose isomerase displays lower kcat and higher Km values for glucose than those for xylose, and it requires different metal ions for enzyme catalysis on these substrates (i.e., Mn2+ for xylose and Co2+ for glucose) (14-16).The catalytic mechanism for xylose isomerase was originally believed to involve histidine-directed general base catalysis (17). Currently, an alternative mechanism of catalysis has been proposed based on results of x-ray crystallographic studies on Arthrobacter or Streptomyces enzymes (18-21) and biochemical properties exhibited by thermophilic enzymes obtained by site-directed mutagenesis of the xylA gene from Clostridium thermosulfurogenes (22).The enzymatic interconversion of...