Current Advancements in Material Research and Techniques Focusing on Lead-free Perovskite Solar Cells

Organic-inorganic lead halide perovskite solar cells (PSCs) recently achieved a photo-to-electricity conversion efficiency (PCE) of 22.1%. They drew much attention as promising photovoltaic devices. However, the Pb-based PSCs face great challenges for commercial and industrial applications due to the instability and the toxicity of perovskite materials. Herein, we summarize the current development of various types of Pb-free perovskites, such as the Sn-, Bi-, Ge-, Sr-, and Cu-based perovskites and their devices. In addition, we will address some remaining issues and prospects of the Pb-free PSCs

Effects of a novel recombinant somatostatin DNA vaccination on rat fertility and offspring growth

In this study, we investigated the immune effects of a novel somatostatin (SS) DNA vaccine—pVAX- asd-GS/2SS (pGS/2SS), administrated with intramuscular (IM) and subcutaneous (SC) two delivery routes on female rat fertility and offspring growth. Results show that this pGS/2SS DNA vaccine could induce effective  anti-SS immune response in rats (IM group and SC group). The antibody peak of female rats in IM group  occurred later than that in SC group (12th week vs. 10th week), but higher than that in SC group  (OD=1.122±0.273 vs. OD=0.614±0.183). Immunized groups had higher pregnancy rate, litter size, birth  weight of pup and weight gain of pup than the control group (P<0.05). Compared to SC immunization, IM  immunization had better improvement in the pregnancy rate of dam and the weight gain of pup (P<0.05).  However, in litter sizes and birth weight of pups, SC immunization was better than IM immunization. In  conclusion, pGS/2SS as a powerful DNA vaccine improves the fertility of female rats and the growth of pups.Key words: Somatostatin, DNA vaccine, rat, fertility, pup growth

The microstructure and mechanical properties of friction stir welded Ti6Al4V titanium alloy under β transus temperature

Ti6Al4V titanium alloy is friction stir welded using a W-Re rotational tool. The effects of welding speed on the microstructure, tensile strength and fracture properties of weld are investigated. At the rotational velocity of 250 r/min, the peak temperature is lower than β transus temperature, and the weld nugget is made up of fine α phase and transformed β phase. The grain size of shoulder affected zone is bigger than that of weld nugget because of low thermal conductivity of Ti6Al4V titanium alloy. By increasing the welding speed, the grain size of weld nugget, the tensile strength and the ductility of weld all are decreased

Theoretical study of the influence of doped oxygen group elements on the properties of organic semiconductors

Organic semiconductor materials are widely used in the field of organic electronic devices due to their wide variety, low price, and light weight. However, their developments are still restrained by their low stability and carrier mobility. Density functional theory (DFT) was used to study the influence of doped oxygen group elements (O, S, Se, and Te) on the properties of organic semiconductor materials (seven-membered benzothiophene, o-pentacene, thiophene derivatives, and pentacene) in this paper. Based on the calculation of EHOMO, ELUMO, ΔE, and total energy, the performances of organic semiconductor materials without and with doped elements were compared, and it was found that the doping of multi-element Te makes the material have high stability and potential high mobility. For these studied organic semiconductor materials, when the atoms of the doped site change in the order of O, S, Se, and Te, the carrier mobility gradually increases, and the molecules show a tendency of stability. In this paper, promising doping elements and doping methods for these studied molecules are determined through calculations and screening out suitable materials more efficiently and economically without a large amount of repetitive experimental work, which may provide a theoretical basis and guidance for preparing high-performance organic semiconductor materials

Effects of oxidation on fatigue crack initiation and propagation in an advanced disc alloy

Powder metallurgy Ni-based superalloys are widely used for aeroengine turbine disc application due to their exceptional strength properties at elevated temperatures, good fatigue and creep performance as well as excellent corrosion and oxidation resistance. However, oxygen enhanced fatigue crack initiation and intergranular propagation at elevated temperatures in air is commonly observed in aeroengine turbine disc superalloys under dwell fatigue testing conditions [1-7], and this phenomenon is usually ascribed to either decohesion/reduction in cohesion strength of grain boundary (GB) due to dynamic embrittlement [8, 9] or GB oxide cracking caused by stress assisted grain boundary oxidation (SAGBO) [5, 10-12]. Although the influence of oxygen on fatigue crack initiation and propagation has been intensively studied, the underlying mechanism for the oxygen-assisted fatigue failure process is still not clear due to the complex composition of disc alloy and the interaction between environmental attack and mechanical load. In this study, fatigue tests were conducted on the Low Solvus, High Refractory (LSHR) alloy designed by NASA for turbine disc application, with a particular focus on studying the influence of the formation of GB oxides on fatigue crack initiation and propagation processes

Development of a Mixed Halide-chalcogenide Bismuth-based Perovskite MABiI2S with Small Bandgap and Wide Absorption Range

During the last years, lead perovskites have achieved high power conversion efficiency of 23%. However, their long-term stability and toxicity are still crucial issues that required attention. In this study, we are the first to report on the synthesis and characterizations of a new lead-free mixed halide-chalcogenide perovskite MABiI2S (MBIS), and have determined its physical and optical properties by various testing methods. The MBIS has a low bandgap of 1.52 eV, with an extended absorption onset up to over 1000 nm. Solar cells fabricated with the MBIS were inspected and device improvements were applied

Recent Progress in Perovskite Solar Cells Modified by Sulfur Compounds

In the past decade, organic–inorganic hybrid perovskite solar cells (PSCs) have begun to be increasingly studied worldwide owing to the superior properties of perovskite material. However, some issues have delayed their commercialization, such as their long-term stability, cost reduction, scale-up ability, and efficiency. The introduction of sulfur to PSCs can relieve the above issues because sulfur can passivate interfacial trap states, suppress charge recombination, and inhibit ion migration, thereby enhancing the stability of PSCs. Furthermore, Pb-S bonds provide new channels for carrier extraction. Herein, the sulfur-based compounds utilized in PSCs are summarized and classified according to their functions in the different layers of PSCs. The results indicate that these sulfur-based compounds have efficiently promoted the commercialization of PSCs. It is hoped that this review can help others understand the intrinsic phenomena of sulfur-based PSCs and motivate additional investigations

La-doped SnO2 as ETL for efficient planar-structure hybrid perovskite solar cells

SnO2 has attracted considerable attention in perovskite solar cells (PSCs) due to its excellent optical and electrical properties. However, a poor surface morphology, specifically with the presence of pinholes after the annealing process, limits its application in PSCs. To overcome the drawback of tin oxide, lanthanum (La) is herein first to be doped into the SnO2 layer, which is able to alleviate the SnO2 crystal aggregation and produce full-coverage and a uniform film. In addition, La:SnO2 can effectively reduce the band offset of the SnO2 layer, which results in the high Voc of 1.11 V. Systematic analyses revealed that the La:SnO2 layer enhances the electron extraction and suppresses charge recombination, leading to the power conversion efficiency (PCE) enhancement from 14.24% to 17.08%