Slow Organic‐to‐Inorganic Sub‐Lattice Thermalization in Methylammonium Lead Halide Perovskites Observed by Ultrafast Photoluminescence

Carrier dynamics in methylammonium lead halide (CH₃NH₃PbI_3–xCl_x) perovskite thin films, of differing crystal morphology, are examined as functions of temperature and excitation wavelength. At room temperature, long‐lived (>nanosecond) transient absorption signals indicate negligible carrier trapping. However, in measurements of ultrafast photoluminescence excited at 400 nm, a heretofore unexplained, large amplitude (50%–60%), 45 ps decay process is observed. This feature persists for temperatures down to the orthorhombic phase transition. Varying pump photon energy reveals that the fast, band‐edge photoluminescence (PL) decay only appears for excitation ≥2.38 eV (520 nm), with larger amplitudes for higher pump energies. Lower photon‐energy excitation yields slow dynamics consistent with negligible carrier trapping. Further, sub‐bandgap two‐photon pumping yields identical PL dynamics as direct absorption, signifying sensitivity to the total deposited energy and insensitivity to interfacial effects. Together with first principles electronic structure and ab initio molecular dynamics calculations, the results suggest the fast PL decay stems from excitation of high energy phonon modes associated with the organic sub‐lattice that temporarily enhance wavefunction overlap within the inorganic component owing to atomic displacement, thereby transiently changing the PL radiative rate during thermalization. Hence, the fast PL decay relates a characteristic organic‐to‐inorganic sub‐lattice equilibration timescale at optoelectronic‐relevant excitation energies.     

Efficient Passivation with Lead Pyridine‐2‐Carboxylic for High‐Performance and Stable Perovskite Solar Cells

Stability has become the main obstacle for the commercialization of perovskite solar cells (PSCs) despite the impressive power conversion efficiency (PCE). Poor crystallization and ion migration of perovskite are the major origins of its degradation under working condition. Here, high‐performance PSCs incorporated with pyridine‐2‐carboxylic lead salt (PbPyA₂) are fabricated. The pyridine and carboxyl groups on PbPyA₂ can not only control crystallization but also passivate grain boundaries (GBs), which result in the high‐quality perovskite film with larger grains and fewer defects. In addition, the strong interaction among the hydrophobic PbPyA₂ molecules and perovskite GBs acts as barriers to ion migration and component volatilization when exposed to external stresses. Consequently, superior optoelectronic perovskite films with improved thermal and moisture stability are obtained. The resulting device shows a champion efficiency of 19.96% with negligible hysteresis. Furthermore, thermal (90 °C) and moisture (RH 40–60%) stability are improved threefold, maintaining 80% of initial efficiency after aging for 480 h. More importantly, the doped device exhibits extraordinary improvement of operational stability and remains 93% of initial efficiency under maximum power point (MPP) tracking for 540 h.     

Reducing Saturation‐Current Density to Realize High‐Efficiency Low‐Bandgap Mixed Tin–Lead Halide Perovskite Solar Cells

The unsatisfactory performance of low‐bandgap mixed tin (Sn)–lead (Pb) halide perovskite subcells has been one of the major obstacles hindering the progress of the power conversion efficiencies (PCEs) of all‐perovskite tandem solar cells. By analyzing dark‐current density and distribution, it is identified that charge recombination at grain boundaries is a key factor limiting the performance of low‐bandgap mixed Sn–Pb halide perovskite subcells. It is further found that bromine (Br) incorporation can effectively passivate grain boundaries and lower the dark current density by two–three orders of magnitude. By optimizing the Br concentration, low‐bandgap (1.272 eV) mixed Sn–Pb halide perovskite solar cells are fabricated with open‐circuit voltage deficits as low as 0.384 V and fill factors as high as 75%. The best‐performing device demonstrates a PCE of >19%. The results suggest an important direction for improving the performance of low‐bandgap mixed Sn–Pb halide perovskite solar cells.     

Metal‐Oxide‐Free Methylammonium Lead Iodide Perovskite‐Based Solar Cells: the Influence of Organic Charge Transport Layers

Metal‐oxide‐free methylammonium lead iodide perovskite‐based solar cells are prepared using a dual‐source thermal evaporation method. This method leads to high quality reproducible films with large crystal domain sizes allowing for an in depth study of the effect of perovskite film thickness and the nature of the electron and hole blocking layers on the device performance. The power conversion efficiency increases from 4.7% for a device with only an organic electron blocking layer to almost 15% when an organic hole blocking layer is also employed. In addition to the in depth study on small area cells, larger area cells (approx. 1 cm^?2) are prepared and exhibit efficiencies in excess of 10%.     

Does N‐Terminal Protein Acetylation Lead to Protein Degradation?

The N‐end rule denotes the relationship between the identity of the amino‐terminal residue of a protein and its in vivo half‐life. Since its discovery in 1986, the N‐end rule has generally been described by a defined set of rules for determining whether an amino‐terminal residue is stabilizing or not. However, recent studies are revealing that this N‐end rule (or N‐degron concept) is less straightforward than previously appreciated. For instance, it is unveiled that N‐terminal acetylation of N‐terminal residues may create a degradation signal (Ac‐degron) that promotes the degradation of target proteins. A recent high‐throughput dissection of degrons in yeast proteins amino termini intriguingly suggested that the hydrophobicity of amino‐terminal residues—but not the N‐terminal acetylation status—may be the indispensable feature of amino‐terminal degrons. Herein, these recent advances in N‐terminal acetylation and the complexity of N‐terminal degradation signals in the context of the N‐degron pathway are analyzed.     

Functional Graded Germanium–Lead Chalcogenide‐Based Thermoelectric Module for Renewable Energy Applications

High thermoelectric conversion efficiencies can be achieved by making use of materials with, as high as possible, figure of merit, ZT, values. Moreover, even higher performance is possible with appropriate geometrical optimization including the use of functionally graded materials (FGM) technology. Here, an advanced n‐type functionally graded thermoelectric material based on a phase‐separated (PbSn_0.05Te)_0.92(PbS)_0.08 matrix is reported. For assessment of the thermoelectric potential of this material, combined with the previously reported p‐type Ge_0.87Pb_0.13Te showing a remarkable dimensionless figure of merit of 2.2, a finite‐element thermoelectric model is developed. The results predict, for the investigated thermoelectric couple, a very impressive thermoelectric efficiency of 14%, which is more than 20% higher than previously reported values for operating under cold and hot junction temperatures of 50 °C and 500 °C, respectively. Validation of the model prediction is done by a thermoelectric couple fabricated according to the model's geometrical optimization conditions, showing a good agreement to the theoretically calculated results, hence approaching a higher technology readiness level.     

Mixed 3D–2D Passivation Treatment for Mixed‐Cation Lead Mixed‐Halide Perovskite Solar Cells for Higher Efficiency and Better Stability

Layered low‐dimensional perovskite structures employing bulky organic ammonium cations have shown significant improvement on stability but poorer performance generally compared to their 3D counterparts. Here, a mixed passivation (MP) treatment is reported that uses a mixture of bulky organic ammonium iodide (iso‐butylammonium iodide, iBAI) and formammidinium iodide (FAI), enhancing both power conversion efficiency and stability. Through a combination of inactivation of the interfacial trap sites, characterized by photoluminescence measurement, and formation of an interfacial energetic barrier by which ionic transport is reduced, demonstrated by Kelvin probe force microscopy, MP treatment of the perovskite/hole transport layer interface significantly suppresses photocurrent hysteresis. Using this MP treatment, the champion mixed‐halide perovskite cell achieves a reverse scan and stabilized power conversion efficiency of 21.7%. Without encapsulation, the devices show excellent moisture stability, sustaining over 87% of the original performance after 38 d storage in ambient environment under 75 ± 20% relative humidity. This work shows that FAI/ i BAI, is a new and promising material combination for passivating perovskite/selective‐contact interfaces.     

Photophysics of Methylammonium Lead Tribromide Perovskite: Free Carriers,Excitons, and Sub‐Bandgap States

Methylammonium lead tribromide perovskite, one of the first artificially synthesized perovskites, can be used in multijunction solar cells and for light‐emitting applications. Its structure leads to a wide direct bandgap, a high extinction coefficient for absorption, and an exciton binding energy that is higher than the thermal energy at room temperature. The broad range of studies performed on the optical phenomena in this material has revealed the contribution of free carriers, excitons, and defect states to its photoluminescence properties. The present report aims to highlight the role played by the different primary photoexcitations, by defects and a variety of optical phenomena (dual emission, reabsorption, photon‐recycling, Rashba‐splitting) on the observed excited‐state properties of this semiconductor. Focus is given to the manifestation of these properties in different spectroscopic measurements.     

Enhancing Optical,Electronic, Crystalline,and Morphological Properties of Cesium Lead Halide by Mn Substitution for High‐Stability All‐Inorganic Perovskite Solar Cells with Carbon Electrodes

In this work all‐inorganic perovskite CsPbIBr₂ are doped with Mn to compensate their shortcomings in band structure for the application of perovskite solar cells (PSCs). The novel Mn‐doped all‐inorganic perovskites, CsPb_1?xMn_xI_1+2xBr_2?2x, are prepared in ambient atmosphere. As the concentration of Mn²⁺ ions increases, the bandgaps of CsPb_1?xMn_xI_1+2xBr_2?2x decrease from 1.89 to 1.75 eV. Additionally, when the concentration of Mn dopants is appropriate, this novel Mn‐doped all‐inorganic perovskite film shows better crystallinity and morphology than its undoped counterpart. These advantages alleviate the energy loss in hole transfer and facilitate the charge‐transfer in perovskites, therefore, PSCs based on these novel CsPb_1?xMn_xI_1+2xBr_2?2x perovskite films display better photovoltaic performance than the undoped CsPbIBr₂ perovskite films. The reference CsPbIBr₂ cell reaches a power conversion efficiency (PCE) of 6.14%, comparable with the previous reports. The CsPb_1?xMn_xI_1+2xBr_2?2x cells reach the highest PCE of 7.36% (when x = 0.005), an increase of 19.9% in PCE. Furthermore, the encapsulated CsPb_0.995Mn_0.005I_1.01Br_1.99 cells exhibit good stability in ambient atmosphere. The storage stability measurements on the encapsulated PSCs reveal that PCE is dropped by only 8% of the initial value after >300 h in ambient. Such improved efficiency and stability are achieved using low‐cost carbon electrodes (without expensive hole transport materials and Au electrodes).     

Addressing Toxicity of Lead: Progress and Applications of Low‐Toxic Metal Halide Perovskites and Their Derivatives

Metal halide perovskites have been brought to the forefront of research focus in solution‐processable photovoltaics, with the device efficiency swiftly surging to over 22% over the past few years. The state‐of‐the‐art metal halide perovskites that have been intensively investigated include toxic lead, which potentially hampers their commercialization process. To address this toxicity issue, intensive recent research effort has been devoted to developing low‐toxic metal halide perovskites and their derivatives for photovoltaic applications. Herein, the recent research progress achieved so far in addressing the toxicity issue of lead halide perovskites in photovoltaics is summarized. By comparing the merits and drawbacks of different low‐toxic metal halide systems, the current challenges and opportunities in the photovoltaic field are highlighted. Potential low‐toxic metal halide perovskites and their derivatives are also discussed from the perspective of theoretical calculations. Furthermore, promising applications of low‐toxic metal halide perovskites beyond the photovoltaic sector are briefly discussed.     

Examination of Changes in Enzyme Activities of Erythrocyte Glucose 6‐Phosphate Dehydrogenase and 6‐Phosphogluconate Dehydrogenase in Rats Given Naringenin and Lead Acetate

In our study, controlled experimental groups were performed by giving substances Lead acetate, Naringenin and Naringenin + Lead acetate to rats in vivo conditions Changes in the glucose 6‐phosphate dehydrogenase (G6PD) and 6‐phosphogluconate dehydrogenase (6PGD) enzyme activities in erythrocytes of rats in these groups were compared to the Control group. An inhibition significant degree for G6PD enzyme activity was observed in all groups when compared to the Control group (p < 0.001). While inhibition significant degree for 6PGD enzyme activity was observed in Lead acetate groups (p < 0.001), no significant effect was observed in the Naringenin and Naringenin + Lead acetate groups (p > 0.05). In addition, lead levels in the groups of rats were determined using an inductively coupled plasma mass spectrometer (ICP‐MS) device. As a result of measurements by the ICP‐MS device, lead levels were found as an average of 42.9 ± 2.51, 36.71 ± 1.13, 172.16 ± 9.63, and 95.07 ± 5.87 ppm in the Control, Naringenin, Lead acetate and Naringenin + Lead acetate groups, respectively. Our results were shown that Naringenin has protective effects on the Lead acetate induced oxidative stress erythrocytes in rat.     

The crystal structure of Z‐Gly‐Aib‐Gly‐Aib‐OtBu

The synthetic peptide Z‐Gly‐Aib‐Gly‐Aib‐OtBu was dissolved in methanol and crystallized in a mixture of ethyl acetate and petroleum ether. The crystals belong to the centrosymmetric space group P4/n that is observed less than 0.3% in the Cambridge Structural Database. The first Gly residue assumes a semi‐extended conformation (φ ±62°, ψ ?131°). The right‐handed peptide folds in two consecutive β‐turns of type II' and type I or an incipient 3₁₀‐helix, and the left‐handed counterpart folds accordingly in the opposite configuration. In the crystal lattice, one molecule is linked to four neighbors in the ab‐plane via hydrogen bonds. These bonds form a continuous network of left‐ and right‐handed molecules. The successive ab‐planes stack via apolar contacts in the c‐direction. An ethyl acetate molecule is situated on and close to the fourfold axis. Copyright © 2015 European Peptide Society and John Wiley & Sons, Ltd.     

Application of NMR spectroscopy for assignment of the absolute configuration of 8‐tert‐butyl‐2‐hydroxy‐7‐methoxy‐8‐methyl‐9‐oxa‐6‐azaspiro[4.5]dec‐6‐en‐10‐one

In order to assign the absolute configurations of 8‐tert‐butyl‐2‐hydroxy‐7‐methoxy‐8‐methyl‐9‐oxa‐6‐azaspiro[4.5]dec‐6‐en‐10‐one ( 2a , 2b ), their esters ( 5a , 5b , 5c , 5d ) with (R)‐ or (S)‐2‐methoxyphenylacetic acid ( 4a , 4b ) have been synthesized. The absolute configurations of these compounds have been determined on the basis of NOESY correlations between the protons of the tert‐butyl group and the cyclopentane fragment of the molecules. The crucial part of this analysis was assignment of the absolute configuration at C‐5. Additionally, by calculation of the chemical shift anisotropy, δ^RS, for the relevant protons, it was also possible to confirm the absolute configurations at the C‐2 centres of compounds 2a , 2b and 5a , 5b , 5c , 5d . Chirality, 25:422–426, 2013.© 2013 Wiley Periodicals, Inc.     

Homo‐C‐nucleoside analogs IV. Synthesis of 4‐(2,5‐anhydro‐D‐altro‐pentitol‐1‐yl)‐2‐phenyl‐2H‐1,2,3‐triazole homo‐C‐nucleoside. CD assignment of the absolute configuration of the carbon bridge

Dehydrative cyclization of 4‐(D‐altro ‐pentitol‐1‐yl)2‐phenyl‐2H ‐1,2,3‐triazole in basic medium with one moler equivalent of p‐toluene sulfonyl chloride in pyridine solution gave the homo‐C‐ nucleoside 4‐(2,5‐anhydro‐D‐altro ‐1‐yl)‐2‐phenyl‐2H ‐1,2,3‐triazole. The structure and anomeric configuration was determined by acylation, nuclear magnetic resonance (NMR), and mass spectroscopy. The stereochemistry at the carbon bridge of homo‐C‐ nucleoside 2‐phenyl‐2H ‐1,2,3‐triazoles was determined by circular dichroism (CD) spectroscopy.     

Crystal structure of D‐glycero‐Β‐D‐manno‐heptose‐1‐phosphate adenylyltransferase from Burkholderia pseudomallei

The crystal structure of HldC from B. pseudomallei (BpHldC), the fourth enzyme of the heptose biosynthesis pathway, has been determined. BpHldC converts ATP and d ‐glycero‐β‐d ‐manno‐heptose‐1‐phosphate into ADP‐d ‐glycero‐β‐d ‐manno‐heptose and pyrophosphate. The crystal structure of BpHldC belongs to the nucleotidyltransferase α/β phosphodiesterase superfamily sharing a common Rossmann‐like α/β fold with a conserved T/HXGH sequence motif. The invariant catalytic key residues of BpHldC indicate that the core catalytic mechanism of BpHldC may be similar to that of other closest homologues. Intriguingly, a reorientation of the C‐terminal helix seems to guide open and close states of the active site for the catalytic reaction.