A comprehensive theoretical study of halide perovskites ABX3

Solar cells based on halide perovskites have recently been attractive due to their excellent power conversion efficiency (PCE), lower cost and simple manufacture. Here, a series of halide perovskites (ABX₃: A = CH₃NH₃, CH(NH₂)₂, Cs, Rb; B = Pb, Sn, Ge; X = I, Br, Cl, F) were investigated by Density Functional Theory (DFT) calculations, together with Shockley-Queisser Maximum Solar Cell Efficiency (S-Q) and Spectroscopic Limited Maximum Efficiency (SLME) mathematical models. The results indicate that: the electronic structure of germanium perovskites bears a close similarity to that of lead perovskites with a small energy difference between the nonbonding orbital and antibonding orbitals, but with a large energy difference comparing with that of tin perovskites (0.6–1.7 eV for CsGeI₃ at Z point of the Brillouin zone, 0.7–1.4 eV for CH₃NH₃PbI₃ and 1.4–2.2 eV for CH₃NH₃SnI₃ at R point of the Brillouin zone), which is attributable to the atomic level, where the 4s orbital energy of Ge (−11.5 eV) is close to the 6s orbital energy of Pb (−11.6 eV), but the 5s orbital energy of Sn (−10.1 eV) is significantly high. Therefore, germanium perovskites possess as high absorption coefficient around solar spectrum as lead perovskites, while tin perovskites only have low absorption coefficient, which makes the short-circuit current of CsGeI₃ and CH₃NH₃PbI₃ (0.017 Acm⁻² and 0.016 Acm⁻², simulated by SLME with a 200 nm absorber under AM1.5G) are higher than that of CH₃NH₃SnI₃ (0.015 Acm⁻²) even if the bandgap of CsGeI₃ and CH₃NH₃PbI₃ (1.51 eV and 1.55 eV) are larger than that of CH₃NH₃SnI₃ (1.21 eV). Meanwhile, the effective mass of electrons and holes are approximate for germanium perovskites and lead perovskites (0.14:0.19 for CsGeI₃ and 0.12:0.12 for CH₃NH₃PbI₃), indicating a balanced electrons and holes transport, whereas the electrons transport is much slower than the holes transport for tin perovskites due to the effective mass of electron is much larger than that of hole (0.17:0.04 for CH₃NH₃SnI₃). As a result, the PCE of CsGeI₃ (27.9%) and CH₃NH₃PbI₃ (26.7%) is higher than that of CH₃NH₃SnI₃ (19.9%).     

Large oscillator strength excitons in PbGa2S4 crystals

Exciton states with a large oscillator strength (transverse-longitudinal splitting of 50 meV) and binding energy of 290 meV have been observed in PbGa₂S₄ crystals. The ground exciton states are stable up to the room temperature. The ground (n = 1) exciton state and two excited (n = 2 and n = 3) states of the short-wavelength B-excitons series were observed at low temperature (T = 10 K). The ground (n = 1) and the excited (n = 2) states of the long-wavelength A-exciton series were also revealed. The exciton Bohr radius of the ground exciton state was determined to be 70 Å for the A-exciton and 10 Å for the B-exciton. The band splitting and the main parameters of excitons have been determined from the calculation of the reflectivity spectra contours. The group theory analysis of the band symmetry was performed and the scheme of bands responsible for exciton transitions in the center of the Brillouin zone was proposed.     

影响中国铅精矿进出口的风险因素分析

对我国过去4a铅精矿进出口状况进行了回顾,分析影响中国铅精矿进出口的风险因素,并预测我国在未来一段时期内铅精矿净进口量将呈现持续增加的态势。     

Stabilisation/solidification of lead-contaminated soil by using ladle furnace slag and carbon dioxide

Global sustainable development faces challenges in greenhouse gas emission, consumption of non-renewable resource and energy, waste landfilling, and environmental pollution. Geotechnical engineering also faces similar challenges; for example, the use of cement and lime for stabilisation/solidification (S/S) of contaminated soil is associated with carbon dioxide (CO₂) emission and consumption of limestone and energy. In this context, this study introduces a sustainable S/S method by using an industrial waste, ladle furnace slag (LFS), and a greenhouse gas, CO₂, to replace common additives for S/S of lead (Pb)-contaminated soil. LFS was first mixed with Pb-contaminated soils and then CO₂ was introduced into the soil for carbonation. The results showed that LFS-stabilised Pb-contaminated soils could achieve CO₂ uptake up to 18% of LFS mass. After carbonation, the concentration of leached Pb from contaminated soils was reduced by three orders of magnitude than that without carbonation, demonstrating higher S/S efficacy than cement, lime, and magnesia. Additionally, this method can improve soil strength, as well as reduce non-renewable resource consumption, energy use, LFS landfilling, and additive cost.     

Self-template synthesis of PbS nanodendrites and its photocatalytic performance

PbS nanodendrites were prepared by a simple hydrothermal process from Pb(NO₃)₂ and thiourea (NH₂CSNH₂) at 120 °C without any additives. The structure and morphology of obtained-samples were characterized by X-ray powder diffraction (XRD) and field-emission scanning electron microscopy (SEM). The effect of Pb and S source, the ratio of Pb/S or CTAB/EDA and pH value on the morphologies of the products were investigated. A possible formation mechanism of PbS nanocrystals was discussed based on their shape evolutions. The photocatalytic property of PbS dendrites was also investigated. It was found that the novel nanocrystals have high catalytic efficiency for the degradation of Rhodamine B (RhB) under visible irradiation.     

易切削黄铜的研究现状及其机理浅析

传统的易切削铅黄铜中含有的铅元素对环境和人都有极大的危害,所以急需寻找一种或者多种元素来替代易切削铅黄铜中的铅.本文介绍了易切削黄铜的发展现状,并经过对比分析其性能了解几种有发展前景的易切削黄铜.从易切削黄铜的切削特点出发研究其易切削的本质,并通过添加微量元素如Ni、P、Ca等,以及稀土元素Ce来改善黄铜的切削性能,达到易切削黄铜低铅或者无铅的目的.     

中国领先美国的七大技术及对于制造技术重要意义的再认识

本文详尽地介绍了中国领先美国的七大技术的意义、特点、国际水平、发展趋势和领先美国及世界的具体情况,并加以评论,目的是为中国战略性新兴产业的发展提供参考。本文的第二部分着重阐述了对于制造技术重要意义的再认识,分列了10个问题加以论述:1)美国依靠什么成为世界第一强国;2)产业革命使资本主义国家崛起;3)技术革命推动产业革命;4)依靠什么中国才能崛起;5)中国不重视技术有历史根源;6)诺贝尔奖越来越重视应用科学研究;7)NBICM汇聚技术将可能引发一场新的技术革命;8)制造业的重要意义;9)制造技术是所有科学技术的实现技术;10)发展战略性新兴产业。     

回收铅锌冶炼废渣中铜的研究

针对某公司铅锌冶炼废弃炉渣嵌布粒度细、解离度低等特点,在细磨至-0.074 mm占85%的条件下,通过两次粗选,一次扫选,选铜粗精矿二段再磨,二次精选后,再磨细度-0.049 mm占90%,得到了含铜20.36%,含银478.87g/t的铜精矿,铜和银的回收率也分别达到64.86%和59.79%。     

SMT生产线制程工艺控制细则

从符合RoHS指令及无铅产品可靠性方面考虑,EMS企业最好把无铅制程与有铅制程划分区域、分线进行,但由于资金缺少或有铅产品还占有很大市场份额等种种原因,部分中小型EMS企业不得不采用无铅有铅制程共线的方案.在这种复杂的情况下,为防止有铅产品及其材料对无铅产品造成污染,必须要严格对无铅产品生产过程中的各个工序进行有效控制...