Stability of Halide Perovskite Solar Cell Devices: In Situ Observation of Oxygen Diffusion under Biasing

Using in situ electrical biasing transmission electron microscopy, structural and chemical modification to n–i–p‐type MAPbI₃ solar cells are examined with a TiO₂ electron‐transporting layer caused by bias in the absence of other stimuli known to affect the physical integrity of MAPbI₃ such as moisture, oxygen, light, and thermal stress. Electron energy loss spectroscopy (EELS) measurements reveal that oxygen ions are released from the TiO₂ and migrate into the MAPbI₃ under a forward bias. The injection of oxygen is accompanied by significant structural transformation; a single‐crystalline MAPbI₃ grain becomes amorphous with the appearance of PbI₂. Withdrawal of oxygen back to the TiO₂, and some restoration of the crystallinity of the MAPbI₃, is observed after the storage in dark under no bias. A subsequent application of a reverse bias further removes more oxygen ions from the MAPbI₃. Light current–voltage measurements of perovskite solar cells exhibit poorer performance after elongated forward biasing; recovery of the performance, though not complete, is achieved by subsequently applying a negative bias. The results indicate negative impacts on the device performance caused by the oxygen migration to the MAPbI₃ under a forward bias. This study identifies a new degradation mechanism intrinsic to n–i–p MAPbI₃ devices with TiO₂.     

Improved Thermal Stability and Film Uniformity of Halide Perovskite by Confinement Effect brought by Polymer Chains of Polyvinyl Pyrrolidone

Polyvinyl pyrrolidone (PVP) is doped to PbI₂ and organic salt during two-step growth of halideperovskite. It is observed that PVP molecules can interact with both PbI₂ and organic salt, reduce the aggregation and crystallization of the two, and then slow down the coarsening rate of perovskite. As doping concentration increases from 0 to 1 mM in organic salt, average crystallite size of perovskite decreases monotonously from 90 to 34 nm; Surface fluctuation reduces from 259.9 to 179.8 nm at first, and then increases; Similarly, surface roughness decreases from 45.55 to 26.64 nm at first, and then rises. Accordingly, a kind of “confinement effect” is resolved to crystallite growth and surface fluctuation/roughness, which helps to build compact and uniform perovskite film. Density of trap states (t-DOS) is cut down by ≈60% at moderate doping  (0.2 mM). Due to the “confinement effect”, power conversion efficiency of perovskite solar cells is improved from 19.46 (±2.80) % to 21.50 (±0.99) %, and further improved to 24.11% after surface modification. Meanwhile, “confinement effect” strengthens crystallite/grain boundaries and improves thermal stability of both film and device. T₈₀ of device increases to 120 h, compared to 50 h for reference ones.     

In Situ Formation of Compact PbI2 Shell Boosts the Efficiency and Thermostability of Perovskite Solar Cells

Judicious tailoring of a robust interlayer is central to maintain the durable operation of optoelectronic devices. In this paper, an ultrathin, compact, and uniform PbI₂ shell on the surface of perovskite via the method of ZnI₂ aided in situ transformation is produced. The resultant PbI₂ interlayer can prolong the excited‐state lifetime of perovskite and attenuate the recombination kinetics of separated charges, leading to an improvement of power conversion efficiency up to 22.5% for perovskite solar cells (PSCs) at the AM 1.5G conditions. Moreover, the PSC with PbI₂ interlayer exhibits an enhanced thermostability, retaining 87% of initial efficiency after aging at 60 °C for 1000 h.     

In Situ Construction of Stable Tissue‐Directed/Reinforced Bifunctional Separator/Protection Film on Lithium Anode for Lithium–Oxygen Batteries

To achieve a high reversibility and long cycle life for Li–O₂ battery system, the stable tissue‐directed/reinforced bifunctional separator/protection film (TBF) is in situ fabricated on the surface of metallic lithium anode. It is shown that a Li–O₂ cell composed of the TBF‐modified lithium anodes exhibits an excellent anodic reversibility (300 cycles) and effectively improved cathodic long lifetime (106 cycles). The improvement is attributed to the ability of the TBF, which has chemical, electrochemical, and mechanical stability, to effectively prevent direct contact between the surface of the lithium anode and the highly reactive reduced oxygen species (Li₂O₂ or its intermediate LiO₂) in cell. It is believed that the protection strategy describes here can be easily extended to other next‐generation high energy density batteries using metal as anode including Li–S and Na–O₂ batteries.     

乙腈对环己烷单体溶液中沉降聚合聚3,4-乙撑二氧噻吩涂层结构与光电性能的影响EI北大核心CSCD

为利用溶剂化效应来优化液相沉降聚合聚3,4-乙撑二氧噻吩(PEDOT)的结构和光电性能,将吸附Fe(OTs)3的聚对苯二甲酸乙二醇酯(PET)膜悬于含乙腈的EDOT环己烷溶液中,于60℃原位合成PEDOT涂层。以紫外-可见吸收光谱、X射线光电子能谱分析所合成PEDOT的共轭链结构和掺杂度,以四探针测量表面电阻,研究乙腈含量对合成PEDOT结构与性能的影响。当乙腈体积分数为0.05%时,添加的乙腈能抑制短共轭链的生成,提高掺杂度,在降低表面电阻的同时,改善透光率。乙腈体积分数在0.24%以内时,PEDOT的导电性随乙腈体积分数的上升而增加。当乙腈体积分数超过0.7%时,PEDOT中短共轭链数目增加,光电性能下降。当乙腈体积分数为8%时,由于吸附的Fe(OTs)_3溶解太快,无法在PET表面合成导电PEDOT膜。乙腈体积分数为0.24%时,获得的PEDOT膜的表面电阻可达174Ω,透光率80%,粘附力为5B级。     

Intrinsic Effect of Nanoparticles on the Mechanical Rupture of Doubled‐Shell Colloidal Capsule via In Situ TEM Mechanical Testing and STEM Interfacial Analysis

The discovery of Pickering emulsion templated assembly enables the design of a hybrid colloidal capsule with engineered properties. However, the underlying mechanisms by which nanoparticles affect the mechanical properties of the shell are poorly understood. Herein, in situ mechanical compression on the transmission electron microscope and aberration‐corrected scanning transmission microscope are unprecedentedly implemented to study the intrinsic effect of nanoparticles on the mechanical properties of the calcium carbonate (CaCO₃)‐decorated silica (SiO₂) colloidal capsule. The stiff and brittle nature of the colloidal capsule is due to the interfacial chemical bonding between the CaCO₃ nanoparticles and SiO₂ inner shell. Such bonding strengthens the mechanical strength of the SiO₂ shell (166 ± 14 nm) from the colloidal capsule compared to the thicker single SiO₂ shell (310 ± 70 nm) from the silica hollow sphere. At elevated temperature, this interfacial bonding accelerates the formation of the single calcium silicate shell, causing shell morphology transformation and yielding significantly enhanced mechanical strength by 30.9% and ductility by 94.7%. The superior thermal durability of the heat‐treated colloidal capsule holds great potential for the fabrication of the functional additives that can be applied in the wide range of applications at elevated temperatures.     

Effect of Hot Rolling on the Properties of In Situ Ti-Aluminide and Alumina-Reinforced Aluminum Matrix Composite

In situ Ti-aluminide and alumina-reinforced aluminium matrix composite were prepared by the melt-cast route by adding 12 µm sized TiO₂ powder particles into molten aluminium at a temperature of 950°C. The effects of hot rolling temperature and percentage deformation on the microstructural architecture and mechanical properties (e.g., hardness and tensile strength) of aluminium matrix composite were studied in detail. Presence of different phases in the composite was identified with the aid of the Energy Dispersive X-Ray Analysis (EDXA). The percentages of reinforcements (Ti-aluminide and alumina) were estimated by image analysis. Fractographic investigations on the fractured surface of tensile specimens were also carried out with the aid of Scanning Electron Microscope (SEM). The composites exhibit fine distribution of reinforcements in the host matrix. It has been found that with the increase in rolling temperature and percentage deformation, hardness values and tensile strength of the composites improve significantly compared to the unreinforced aluminium.     

One‐Step In Situ Growth of Iron–Nickel Sulfide Nanosheets on FeNi Alloy Foils: High‐Performance and Self‐Supported Electrodes for Water Oxidation

Efficient and durable oxygen evolution reaction (OER) catalysts are highly required for the cost‐effective generation of clean energy from water splitting. For the first time, an integrated OER electrode based on one‐step direct growth of metallic iron–nickel sulfide nanosheets on FeNi alloy foils (denoted as Fe? Ni₃S₂/FeNi) is reported, and the origin of the enhanced OER activity is uncovered in combination with theoretical and experimental studies. The obtained Fe? Ni₃S₂/FeNi electrode exhibits highly catalytic activity and long‐term stability toward OER in strong alkaline solution, with a low overpotential of 282 mV at 10 mA cm^?2 and a small Tafel slope of 54 mV dec^?1. The excellent activity and satisfactory stability suggest that the as‐made electrode provides an attractive alternative to noble metal‐based catalysts. Combined with density functional theory calculations, exceptional OER performance of Fe? Ni₃S₂/FeNi results from a combination of efficient electron transfer properties, more active sites, the suitable O₂ evolution kinetics and energetics benefited from Fe doping. This work not only simply constructs an excellent electrode for water oxidation, but also provides a deep understanding of the underlying nature of the enhanced OER performance, which may serve as a guide to develop highly effective and integrated OER electrodes for water splitting.     

Effect of SiC Nanoparticles Content and Mg Addition on the Characteristics of Al/SiC Composite Powders Produced via In Situ Powder Metallurgy Method

In the present study, the effect of the nanosized SiC particles loading and Mg addition on the characteristics of Al/SiC composite powders produced via a relatively new method called “in situ powder metallurgy” (IPM) was investigated. Specified amounts of SiC particles (within a size range of 250 to 600 µm) together with SiC nanoparticles (average size of 60 nm) were preheated and added to aluminum melt. This mixture was stirred via an impeller at a certain temperature for a predetermined time. The liquid droplets created by this process were then subsequently cooled in air and screened through 250 µm sieve to separate micron-sized SiC particles from solidified aluminium powder particles containing nanosized SiC particles. Results of SEM and TEM studies together with microhardness measurements revealed that the commercially pure (CP) Al could not embed as-received SiC particles. However, the nanosized particles were distributed uniformly in the Al-1 wt% Mg powders. The process yield and microhardness of the Al-1Mg composite powders increased with increasing the contributed amount of nanosized SiC particles.