Two-dimensional Perovskitoids Enhance Stability in Perovskite Solar Cells.

Two-dimensional (2D)/three-dimensional (3D) perovskite heterostructures have played a key role in advancing the performance of perovskite solar cells (PSCs)1,2. However, the migration of cations between 2D and 3D layers results in the disruption of octahedral networks that leads to degradation in performance over time3,4. We hypothesized that perovskitoids, with robust organic-inorganic networks enabled by edge- and face-sharing, could impede ion migration. We explored a set of perovskitoids of varying dimensionality, and found that cation migration within perovskitoid/perovskite heterostructures was suppressed compared to the 2D/3D perovskite case. Increasing the dimensionality of perovskitoids improves charge transport when they are interfaced with 3D perovskite surfaces - this the result of enhanced octahedral connectivity and out-of-plane orientation. The 2D perovskitoid (A6BfP)8Pb7I22 (A6BfP: N-aminohexyl-benz[f]-phthalimide) provides efficient passivation of perovskite surfaces and enables uniform large-area perovskite films. Devices based on perovskitoid/perovskite heterostructures achieve a certified quasi-steady-state power conversion efficiency of 24.6% for centimeter-area PSCs. We removed the fragile hole transport layers and showed stable operation of the underlying perovskitoid/perovskite heterostructure at 85°C for 1,250 hours for encapsulated large-area devices in an air ambient.

Regulating surface potential maximizes voltage in all-perovskite tandems.

The open-circuit voltage (VOC) deficit in perovskite solar cells is greater in wide-bandgap (over 1.7 eV) cells than in perovskites of roughly 1.5 eV (refs. 1,2). Quasi-Fermi-level-splitting measurements show VOC-limiting recombination at the electron-transport-layer contact3-5. This, we find, stems from inhomogeneous surface potential and poor perovskite-electron transport layer energetic alignment. Common monoammonium surface treatments fail to address this; as an alternative, we introduce diammonium molecules to modify perovskite surface states and achieve a more uniform spatial distribution of surface potential. Using 1,3-propane diammonium, quasi-Fermi-level splitting increases by 90 meV, enabling 1.79 eV perovskite solar cells with a certified 1.33 V VOC and over 19% power conversion efficiency (PCE). Incorporating this layer into a monolithic all-perovskite tandem, we report a record VOC of 2.19 V (89% of the detailed balance VOC limit) and over 27% PCE (26.3% certified quasi-steady state). These tandems retained more than 86% of their initial PCE after 500 h of operation.

Suppressed phase segregation for triple-junction perovskite solar cells.

The tunable bandgaps and facile fabrication of perovskites make them attractive for multi-junction photovoltaics1,2. However, light-induced phase segregation limits their efficiency and stability3-5: this occurs in wide-bandgap (>1.65 electron volts) iodide/bromide mixed perovskite absorbers, and becomes even more acute in the top cells of triple-junction solar photovoltaics that require a fully 2.0-electron-volt bandgap absorber2,6. Here we report that lattice distortion in iodide/bromide mixed perovskites is correlated with the suppression of phase segregation, generating an increased ion-migration energy barrier arising from the decreased average interatomic distance between the A-site cation and iodide. Using an approximately 2.0-electron-volt rubidium/caesium mixed-cation inorganic perovskite with large lattice distortion in the top subcell, we fabricated all-perovskite triple-junction solar cells and achieved an efficiency of 24.3 per cent (23.3 per cent certified quasi-steady-state efficiency) with an open-circuit voltage of 3.21 volts. This is, to our knowledge, the first reported certified efficiency for perovskite-based triple-junction solar cells. The triple-junction devices retain 80 per cent of their initial efficiency following 420 hours of operation at the maximum power point.

Appropriate livestock grazing alleviates the loss of plant diversity and maintains community resistance in alpine meadows.

Alpine meadows constitute one of the major ecosystems on the Qinghai-Tibetan Plateau, with livestock grazing exerting a considerable impact on their biodiversity. However, the degree to which plant diversity influences community stability under different grazing intensities remains unclear in this region. This study conducted controlled grazing experiments across four levels of grazing intensity (no-, low-, medium-, and high-grazing) based on herbage utilization rate to assess the influence of grazing intensities on plant community structure and diversity-stability relationships. We discovered that high-grazing reduced plant diversity and attenuated the temporal stability and resistance of above-ground biomass. No- and low-grazing could alleviate plant biomass loss, with community resistance being optimal under low-grazing. The direct effects of livestock grazing on temporal stability were found to be negligible. Plant characteristics and diversity accounted for a substantial proportion of livestock grazing effects on community resistance (R2 = 0.46), as revealed by piecewise structural equation model analysis. The presence of plant diversity enhances the resistance of alpine meadows against disturbance and accelerates the recovery after grazing. Our results suggest that low-grazing intensity may represent a judicious option for preserving species diversity and community stability on the Qinghai-Tibetan Plateau.

Atomic Layer Deposition of ZnO on CuO Enables Selective and Efficient Electroreduction of Carbon Dioxide to Liquid Fuels.

Electrochemical reduction of carbon dioxide, if powered by renewable electricity, could serve as a sustainable technology for carbon recycling and energy storage. Among all the products, ethanol is an attractive liquid fuel. However, the maximum faradaic efficiency of ethanol is only ≈10 % on polycrystalline Cu. Here, CuZn bimetallic catalysts were synthesized by in situ electrochemical reduction of ZnO-shell/CuO-core bi-metal-oxide. Dynamic evolution of catalyst was revealed by STEM-EDS mapping, showing the migration of Zn atom and blending between Cu and Zn. CuZn bimetallic catalysts showed preference towards ethanol formation, with the ratio of ethanol/ethylene increasing over five times regardless of applied potential. We achieved 41 % faradaic efficiency for C2+ liquids with this catalyst. Transitioning from H-cell to an electrochemical flow cell, we achieved 48.6 % faradaic efficiency and -97 mA cm-2 partial current density for C2+ liquids at only -0.68 V versus reversible hydrogen electrode in 1 m KOH. Operando Raman spectroscopy showed that CO binding on Cu sites was modified by Zn. Free CO and adsorbed *CH3 are believed to combine and form *COCH3 intermediate, which is exclusively reduced to ethanol.

A Scalable Methylamine Gas Healing Strategy for High-Efficiency Inorganic Perovskite Solar Cells.

An easy and scalable methylamine (MA) gas healing method was realized for inorganic cesium-based perovskite (CsPbX3 ) layers by incorporating a certain amount of MAX (X=I or Br) initiators into the raw film. It was found that the excess MAX accelerated the absorption of the MA gas into the CsPbX3 film and quickly turned it into a liquid intermediate phase. Through the healing process, a highly uniform and highly crystalline CsPbX3 film with enhanced photovoltaic performance was obtained. Moreover, the chemical interactions between a series of halides and MA gas molecules were studied, and the results could offer guidance in further optimizations of the healing strategy.

Transformative Evolution of Organolead Triiodide Perovskite Thin Films from Strong Room-Temperature Solid-Gas Interaction between HPbI3-CH3NH2 Precursor Pair.

We demonstrate the feasibility of a nonsalt-based precursor pair--inorganic HPbI3 solid and organic CH3NH2 gas--for the deposition of uniform CH3NH3PbI3 perovskite thin films. The strong room-temperature solid-gas interaction between HPbI3 and CH3NH2 induces transformative evolution of ultrasmooth, full-coverage perovskite thin films at a rapid rate (in seconds) from nominally processed rough, partial-coverage HPbI3 thin films. The chemical origin of this behavior is elucidated via in situ experiments. Perovskite solar cells, fabricated using MAPbI3 thin films thus deposited, deliver power conversion efficiencies up to 18.2%, attesting to the high quality of the perovskite thin films deposited using this transformative process.

Gga-miR-101-3p Plays a Key Role in Mycoplasma gallisepticum (HS Strain) Infection of Chicken.

Mycoplasma gallisepticum (MG), one of the most pathogenic Mycoplasma, has caused tremendous economic loss in the poultry industry. Recently, increasing evidence has suggested that micro ribonucleic acids (miRNAs) are involved in microbial pathogenesis. However, little is known about potential roles of miRNAs in MG infection of chicken. In the present study, using miRNA Solexa sequencing we have found that gga-miR-101-3p was up-regulated in the lungs of MG-infected chicken embryos. Moreover, gga-miR-101-3p regulated expression of the host enhancer of zeste homolog 2 (EZH2) through binding to the 3' un-translated region (3'-UTR) of EZH2 gene. Over-expression of gga-miR-101-3p significantly inhibited EZH2 expression and hence inhibited proliferation of chicken embryonic fibroblast (DF-1 cells) by blocking the G1-to-S phase transition. Similar results were obtained in MG-infected chicken embryos and DF-1 cells, where gga-miR-101-3p was significantly up-regulated, while EZH2 was significantly down-regulated. This study reveals that gga-miR-101-3p plays an important role in MG infection through regulation of EZH2 expression and provides a new insight into the mechanisms of MG pathogenesis.

Methylamine-Gas-Induced Defect-Healing Behavior of CH3NH3PbI3 Thin Films for Perovskite Solar Cells.

We report herein the discovery of methylamine (CH3NH2) induced defect-healing (MIDH) of CH3NH3PbI3 perovskite thin films based on their ultrafast (seconds), reversible chemical reaction with CH3NH2 gas at room temperature. The key to this healing behavior is the formation and spreading of an intermediate CH3NH3PbI3⋅xCH3NH2 liquid phase during this unusual perovskite-gas interaction. We demonstrate the versatility and scalability of the MIDH process, and show dramatic enhancement in the performance of perovskite solar cells (PSCs) with MIDH. This study represents a new direction in the formation of defect-free films of hybrid perovskites.

Alpine grassland degradation intensifies the burrowing behavior of small mammals: evidence for a negative feedback loop.

Globally, grassland degradation is an acute ecological problem. In alpine grassland on the Tibetan Plateau, increased densities of various small mammals in degraded grassland are assumed to intensify the degradation process and these mammals are subject to lethal control. However, whether the negative impact of small mammals is solely a result of population size or also a result of activity and behavior has not been tested. In this study, we use plateau pika as a model to compare population size, core area of colony, and the number of burrow entrances and latrines between lightly and severely degraded grassland. We test whether the alleged contribution of pika to grassland degradation is a result of increased population size or increased burrowing activities of individuals in response to lower food abundance. We found that grassland degradation resulted in lower plant species richness, plant height, and biomass. Furthermore, the overall population size of pika was not significantly affected by location in lightly and severely degraded grassland. However, pika core areas in severely grassland degradation were significantly larger and had significantly higher densities of burrows and latrines. Our study provides convincing evidence that habitat-induced changes in the behavior of small, burrowing mammals, such as pika, can exacerbate grassland degradation. This finding has significant implications for managing small mammals and restoring degraded grassland ecosystems.

The effects of grassland degradation on the genetic structure of a small mammal.

Grassland degradation is challenging the health of grassland ecosystems globally and causing biodiversity decline. Previous studies have demonstrated the impact of grassland degradation on the abundance and behavior of small mammals. Little is known about how it affects the genetic structure of gregarious mammals in the wild. This study explores the effects of grassland degradation on the genetic structure of a small burrowing mammal, plateau pika (Ochotona curzoniae). We used nine microsatellite loci to analyze the genetic diversity and genetic differentiation between colonies and genetic relatedness between individuals within the colony. We found that pikas in severely degraded grasslands had a significantly higher genetic diversity within colonies, a higher level of gene flow between colonies, and a lower genetic differentiation between colonies compared to pikas in less degraded grasslands. Individuals within colonies had a significantly lower genetic relatedness in severely degraded grasslands than in less degraded grasslands. This study has provided potential evidence of a significant impact of grassland degradation on the genetic structure of pikas, which has caused a breakdown of their kin-selected colony structure.

Improved charge extraction in inverted perovskite solar cells with dual-site-binding ligands.

Inverted (pin) perovskite solar cells (PSCs) afford improved operating stability in comparison to their nip counterparts but have lagged in power conversion efficiency (PCE). The energetic losses responsible for this PCE deficit in pin PSCs occur primarily at the interfaces between the perovskite and the charge-transport layers. Additive and surface treatments that use passivating ligands usually bind to a single active binding site: This dense packing of electrically resistive passivants perpendicular to the surface may limit the fill factor in pin PSCs. We identified ligands that bind two neighboring lead(II) ion (Pb2+) defect sites in a planar ligand orientation on the perovskite. We fabricated pin PSCs and report a certified quasi-steady state PCE of 26.15 and 24.74% for 0.05- and 1.04-square centimeter illuminated areas, respectively. The devices retain 95% of their initial PCE after 1200 hours of continuous 1 sun maximum power point operation at 65°C.

Altitude-dependent metabolite biomarkers reveal the mechanism of plateau pika adaptation to high altitudes.

The harsh environment in the Tibetan plateau, the highest place in the world, poses thermoregulatory challenges and hypoxic stress to animals. The impacts of plateau environment on animal physiology and reproduction include external factors such as strong ultraviolet radiation and low temperature, and internal factors such as animal metabolites and gut microbiota. However, it remains unclear how plateau pika adapt to high altitudes through the combination of serum metabolites and gut microbiota. To this end, we captured 24 wild plateau pikas at the altitudes of 3400, 3600, or 3800 m a.s.l. in a Tibetan alpine grassland. Using the machine learning algorithms (random forest), we identified five biomarkers of serum metabolites indicative of the altitudes, that is, dihydrotestosterone, homo-l-arginine, alpha-ketoglutaric-acid, serotonin, and threonine, which were related to body weight, reproduction, and energy metabolism of pika. Those metabolic biomarkers were positively correlated with Lachnospiraceae_ Agathobacter, Ruminococcaceae, or Prevotellaceae_Prevotella, suggesting the close relationship between metabolites and gut microbiota. By identifying the metabolic biomarkers and gut microbiota analysis, we reveal the mechanisms of adaptation to high altitudes in plateau pika.

Refining Perovskite Heterojunctions for Effective Light-Emitting Solar Cells.

Solar cells capable of light-harvesting during daytime and light-emission at night are multifunctional semiconductor devices with many potential applications. Here, it is reported that halide perovskite heterojunction interfaces can be refined to yield stable and efficient solar cells. The cell can also operate effectively as an ultralow-voltage light-emitting diode (LED) with a peak external quantum efficiency of electroluminescence (EQEEL ) of 3.3%. Spectroscopic and microscopic studies reveal that double-heterojunction refinement with wide-bandgap salts is key to densifying the packing of perovskite grains and enlarging the bandgaps of the perovskite surfaces that are in contact with charge-transport semiconductors. The refined perovskite enables a simple device with dual actions of solar cells and LEDs. This type of all-in-one device has the potential to be used in multifunctional harvesting-storage-utilization (HSU) systems.

Rational design of Lewis base molecules for stable and efficient inverted perovskite solar cells.

Lewis base molecules that bind undercoordinated lead atoms at interfaces and grain boundaries (GBs) are known to enhance the durability of metal halide perovskite solar cells (PSCs). Using density functional theory calculations, we found that phosphine-containing molecules have the strongest binding energy among members of a library of Lewis base molecules studied herein. Experimentally, we found that the best inverted PSC treated with 1,3-bis(diphenylphosphino)propane (DPPP), a diphosphine Lewis base that passivates, binds, and bridges interfaces and GBs, retained a power conversion efficiency (PCE) slightly higher than its initial PCE of ~23% after continuous operation under simulated AM1.5 illumination at the maximum power point and at ~40°C for >3500 hours. DPPP-treated devices showed a similar increase in PCE after being kept under open-circuit conditions at 85°C for >1500 hours.

Engineering ligand reactivity enables high-temperature operation of stable perovskite solar cells.

Perovskite solar cells (PSCs) consisting of interfacial two- and three-dimensional heterostructures that incorporate ammonium ligand intercalation have enabled rapid progress toward the goal of uniting performance with stability. However, as the field continues to seek ever-higher durability, additional tools that avoid progressive ligand intercalation are needed to minimize degradation at high temperatures. We used ammonium ligands that are nonreactive with the bulk of perovskites and investigated a library that varies ligand molecular structure systematically. We found that fluorinated aniliniums offer interfacial passivation and simultaneously minimize reactivity with perovskites. Using this approach, we report a certified quasi-steady-state power-conversion efficiency of 24.09% for inverted-structure PSCs. In an encapsulated device operating at 85°C and 50% relative humidity, we document a 1560-hour T85 at maximum power point under 1-sun illumination.

Ammonia for post-healing of formamidinium-based Perovskite films.

Solvents employed for perovskite film fabrication not only play important roles in dissolving the precursors but also participate in crystallization process. High boiling point aprotic solvents with O-donor ligands have been extensively studied, but the formation of a highly uniform halide perovskite film still requires the participation of additives or an additional step to accelerate the nucleation rate. The volatile aliphatic methylamine with both coordinating ligands and hydrogen protons as solvent or post-healing gas facilitates the process of methylamine-based perovskite films with high crystallinity, few defects, and easy large-scale fabrication as well. However, the attempt in formamidinium-containing perovskites is challenged heretofore. Here, we reveal that the degradation of formamidinium-containing perovskites in aliphatic amines environment results from the transimination reaction of formamidinium cation and aliphatic amines along with the formation of ammonia. Based on this mechanism, ammonia is selected as a post-healing gas for a highly uniform, compact formamidinium-based perovskite films. In particular, low temperature is proved to be crucial to enable formamidinium-based perovskite materials to absorb enough ammonia molecules and form a liquid intermediate state which is the key to eliminating voids in raw films. As a result, the champion perovskite solar cell based on ammonia post-healing achieves a power conversion efficiency of 23.21% with excellent reproducibility. Especially the module power conversion efficiency with 14 cm2 active area is over 20%. This ammonia post-healing treatment potentially makes it easier to upscale fabrication of highly efficient formamidinium-based devices.

Multimodal host-guest complexation for efficient and stable perovskite photovoltaics.

Formamidinium lead iodide perovskites are promising light-harvesting materials, yet stabilizing them under operating conditions without compromising optimal optoelectronic properties remains challenging. We report a multimodal host-guest complexation strategy to overcome this challenge using a crown ether, dibenzo-21-crown-7, which acts as a vehicle that assembles at the interface and delivers Cs+ ions into the interior while modulating the material. This provides a local gradient of doping at the nanoscale that assists in photoinduced charge separation while passivating surface and bulk defects, stabilizing the perovskite phase through a synergistic effect of the host, guest, and host-guest complex. The resulting solar cells show power conversion efficiencies exceeding 24% and enhanced operational stability, maintaining over 95% of their performance without encapsulation for 500 h under continuous operation. Moreover, the host contributes to binding lead ions, reducing their environmental impact. This supramolecular strategy illustrates the broad implications of host-guest chemistry in photovoltaics.

Ligand-Modulated Excess PbI2 Nanosheets for Highly Efficient and Stable Perovskite Solar Cells.

Excess lead iodide (PbI2 ), as a defect passivation material in perovskite films, contributes to the longer carrier lifetime and reduced halide vacancies for high-efficiency perovskite solar cells. However, the random distribution of excess PbI2 also leads to accelerated degradation of the perovskite layer. Inspired by nanocrystal synthesis, here, a universal ligand-modulation technology is developed to modulate the shape and distribution of excess PbI2 in perovskite films. By adding certain ligands, perovskite films with vertically distributed PbI2 nanosheets between the grain boundaries are successfully achieved, which reduces the nonradiative recombination and trap density of the perovskite layer. Thus, the power conversion efficiency of the modulated device increases from 20% to 22% compared to the control device. In addition, benefiting from the vertical distribution of excess PbI2 and the hydrophobic nature of the surface ligands, the modulated devices exhibit much longer stability, retaining 72% of their initial efficiency after 360 h constant illumination under maximum power point tracking measurement.