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The inorganic CsPbI3 perovskite has attracted tremendous attention in the photovoltaic fields for its chemical stability and suitable band gap. Generally, CsPbI3 solar cells with decent performances adopted high annealing temperature to form high-quality black-phase perovskite films. The high-temperature process hinders its practical application and further development. Hence, fabricating stable black-phase CsPbI3 at low temperature is imperative and necessary. In this work, a new additive p-xylilenediamine bromide (PhDMADBr) is reported to facilitate the synthesis of solution-processed, high-quality, and stable γ-CsPbI3 films at a surprisingly low temperature of 60 °C. The additive with an appropriate content can effectively improve both the film morphology and crystallinity of γ-CsPbI3 perovskite films. PhDMADBr anchors to the perovskite surface or grain boundaries as a protection through hydrogen bonding between its ammonium cations and CsPbI3. In addition, the Br element introduced by the additive passivates I- vacancies in perovskite films, resulting in the improvement of both phase stability and devices' performance. Finally, the PSCs based on the modified γ-CsPbI3 perovskite film achieve a champion efficiency of 12.71%. Moreover, the device retains 85% of its original efficiency after being kept for 1000 h.

Hydrogen production via water splitting is considered to be one of the most promising technologies in the future hydrogen economy, where the critical challenge in this technology is exploring high-...

Ionic conductors are normally prepared from water-based materials in the solid form and feature a combination of intrinsic transparency and stretchability. The sensitivity toward humidity inevitably leads to dehydration or deliquescence issues, which will limit the long-term use of ionic conductors. Here, a novel ionic conductor based on natural bacterial cellulose (BC) and polymerizable deep eutectic solvents (PDESs) is developed for addressing the abovementioned drawbacks. The superstrong three-dimensional nanofiber network and strong interfacial interaction endow the BC-PDES ionic conductor with significantly enhanced mechanical properties (tensile strength of 8 × 105 Pa and compressive strength of 6.68 × 106 Pa). Furthermore, compared to deliquescent PDESs, BC-PDES composites showed obvious mechanical stability, which maintain good mechanical properties even when exposed to high humidity for 120 days. These materials were demonstrated to possess multiple sensitivity to external stimulus, such as strain, pressure, bend, and temperature. Thus, they can easily serve as supersensitive sensors to recognize physical activity of humans such as limb movements, throat vibrations, and handwriting. Moreover, the BC-PDES ionic conductors can be used in flexible, patterned electroluminescent devices. This work provides an efficient strategy for making cellulose-based sustainable and functional ionic conductors which have broad application in artificial flexible electronics and other products.

Steering the crystallization of two-dimensional (2D) perovskite film is an important strategy to improve the power conversion efficiency (PCE) of 2D perovskite solar cells (PVSCs). In this paper, the deionized water (H2O) additive is introduced into the perovskite precursor solution to prepare high-quality 2D perovskite films. The 2D perovskite film treated with 3% H2O shows a good surface morphology, increased crystal size, enhanced crystallinity, preferred orientation, and low defect density. The fabricated 2D PVSC with 3% H2O exhibits a higher PCE compared with that without H2O (12.15% vs 2.29%). Furthermore, the shelf stability of unsealed devices with 3% H2O under ambient environment is significantly improved. This work provides a simple method to prepare high-quality 2D perovskite films for efficient and stable 2D PVSCs.

The trap-state density in perovskite films largely determines the photovoltaic performance of perovskite solar cells (PSCs). Increasing the crystal grain size in perovskite films is an effective method to reduce the trap-state density. Here, we have added NH4SCN into perovskite precursor solution to obtain perovskite films with an increased crystal grain size. The perovskite with increased crystal grain size shows a much lower trap-state density compared with reference perovskite films, resulting in an improved photovoltaic performance in PSCs. The champion photovoltaic device has achieved a power conversion efficiency of 19.36%. The proposed method may also impact other optoelectronic devices based on perovskite films.

Hybrid lead halide perovskite solar cells (PSCs) are amongst those efficient solar cell technologies which are developing rapidly. The rapid advancement in PSCs technology is because of favorable properties of perovskite materials and addition of charge selective layers. Here, we report lithium-doped SnO $_{2}$ electron transport layer (ETL) to improve electrons extraction from the perovskite absorbing layer. The lithium-doped SnO $_{2}$ not only shows relatively higher conductivity, reduced oxygen-deficient regions, improved oxidation state, but also induces a larger grain size of perovskite films. This leads to an improvement in all related photovoltaic parameters of the methylammonium lead iodide (MAPbI3) planar heterojunction PSCs. The champion device yields a power conversion efficiency of 19.09%. The simple solution and lower annealing processed ETLs are compatible with almost all substrates used in PSCs and other perovskite-based devices.

Both value-added utilization of low-rank renewable feedstocks to prepare catalytic materials and selective transformation of bioderived aldehydes are very attractive topics. Herein, lignosulfonate, a waste by-product from the paper industry, was simply assembled with ZrCl4 under non-toxic hydrothermal conditions for scalable preparation of Zr-containing polyphenolic biopolymer catalysts (Zr LS). Systematic characterizations indicated that the strong coordination between Zr4+ and phenolic hydroxyl groups in lignosulfonate led to the formation of strong Lewis acid-base couple sites (Zr4+−O2−) and porous inorganic-organic framework structure (mesopores centered at 6.1 nm), while the inherent sulfonic groups in lignosulphonate could serve as Bronsted acidic sites. The cooperative role of these versatile acid−base sites in Zr LS afforded excellent catalytic performance for Meerwein-Ponndorf-Verley (MPV) reaction of a broad range of bioderived platform chemicals under mild conditions (80 °C), especially of furfural (FF) to furfuryl alcohol (FA), in quantitative yields (96%) with high FA formation rate of 9600 μmol g−1 h−1 and TOF of 4.37 h−1. Kinetic studies revealed that the activation energy of the MPV reduction of FF was as low as 52.25 kJ/mol, accounting for the high reaction rate. Isotopic labelling experiments demonstrated direct hydrogen transfer from the α-C of 2-PrOH to the α-C of FF on acid-base sites was the rate-determining step. Moreover, Zr LS showed good recyclability for at least seven reaction cycles.

The stability issue of perovskite solar cells is the greatest bottleneck on the way to commercialization. Here, we report the degradation mechanism of perovskite solar cells (PSCs) with inverted structure of fluorine-doped tin oxide (FTO)/Cu:NiOx/MAPbI3/PC61BM/Ag. The oxidative degradation of PC61BM electron transport layer forms pinholes and leads to the water-catalyzed decomposition of perovskites. The formation of silver iodide confirms the iodine is from decomposition of perovskites. The instability of inverted PSCs based on Cu:NiOx is owing to corrosive behavior of silver electrode. In addition, we find that a small amount of bromine doping in the perovskite material can delay the corrosion of the silver electrode. This paper demonstrates it is essential to deeply understand the degradation mechanism of the devices and a small amount of bromine doping is a feasible strategy to suppress the corrosion of the silver electrodes.

The rapid development of modern electronics and high-frequency and high-speed circuits sets stringent requirements of low dielectric permittivity and efficient heat removal of thermal-management materials to reduce the time delay of signal propagation and ensure the long lifetime of the electronics. In this work, we report a novel thermally conductive and minimally dielectric nanocomposite film by vacuum filtering aramid nanofibers (ANFs) on nylon filter with boron nitride nanosheets (BNNSs). To obtain a continuous, uniform, freestanding composite film with both low dielectric permittivity and strong thermal conductivity, ANF suspensions were dialyzed and then absorbed into a BNNSs/Isopropanol (IPA) dispersion by bath-sonication. The advantage of the nanocomposite film lies in that it possesses an out-plane thermal conductivity up to 0.6156 (w·m−1·k−1) at BNNSs mass percent of 50 wt%, a conductivity that is almost 5 times that of the pure nano-aramid film. The nanocomposite film also boasts a low dielectric permittivity (∼2.4 at 108 Hz) along with excellent mechanical flexibility and strength (∼62 MPa).

In this work, we reported a gradient structure that can significantly improve the mechanical strength of aramid paper by depositing a layer of nano-aramid fibers (ANFs) on both sides. The introduction of Dimethyl Diallyl Ammonium Chloride (DMDAAC) in the fabrication of nanostructured aramid-composites dramatically promotes the dewatering efficiency of the aramid nanofibers slurry, and also accelerates the formation of gradient structural of the composites. The gradient deposition of ANFs in the porous aramid paper matrix yields the highly pilotaxitic textures and stiff structures of the aramid composite paper. The results indicated that the tensile strength, specific strength, and fracture energy increased respectively 36.7 times, 14.1 times and 78.0 times from the original aramid paper. The method reported in this work gives a good case for designing the structure composites with low density and high strength in aerospace and car manufacturing applications.

Perovskite solar cells (PSCs) have been developed rapidly recently and regarded as one of the most promising solar cells. It is still a challenge to fabricate PSCs with long-time stability. The main threat to the long-time stability of PSCs is the water molecules in air that can decompose the perovskite film. It is reported that blocking the contact between moisture and perovskite is an effective way to mitigate the decomposition of perovskite and stabilize the performance of the solar cells. So in this study, we improved the moisture resistance of the hole transport layer (HTL) by using hydrophobic additive, 2,2′,7,7′-tetrakis(N,N-di-p-methoxy phenyl amine)-9,9′-spiro bifluorenedi[bis-(trifluoromethanesulfonyl)imide] (Spiro-(TFSI)2), to substitute the lithium bis(trifluoromethylsulphonyl)imide (Li-TFSI) with hygroscopic nature. Pinholes in the HTL also have been eliminated dramatically after the Spiro-(TFSI)2 has been introduced into the HTL, which contributes to the further enhancement of the moisture resistance. The champion solar cell based on the Spiro-(TFSI)2 with a power conversion efficiency (PCE) of 19.1% has been obtained, and the results demonstrate that the performance stability has been improved dramatically via introducing the hydrophobic additive into the HTL. This work has provided an effective method to improve the performance stability of PSCs.

In the past few decades, the preparation of cellulose nanofibers (CNF) has been restricting its application in industrialization. A fast and green preparation method is urgently needed to promote t...

Although SnO2 is widely used in perovskite solar cells (PSCs) as the electron transport layer, there is still a need for a detailed investigation regarding the impact of physisorption on the performance of PSCs. Here, we report the role of physisorption of oxygen species from the ambient atmosphere in the oxidation states and defective oxides at the surface of SnO2 nanoparticles for the performance of PSCs. The SnO2 nanoparticle's thin film shows a higher oxidation state (Sn–O) and lower charge trap sites at an annealing temperature of 100 °C, and the SnO2 film based PSCs yield an efficiency of 18.04%. The annealing process results in the gradual desorption of physically adsorbed oxygen species. Therefore, the annealing process of SnO2 nanoparticle thin films in atmosphere is the key factor to control the oxidation states and defective oxides at the surface of SnO2 nanoparticle thin films.

The fabrication of perovskite solar cells in ambient air is of significant economic benefit. However, to date, there is no satisfactory solution to achieve this, and the reported results of solar cells fabricated in ambient air vary significantly. It has been observed through studies of the “turbid point”, a time point at which the appearance of the precursor film changes from transparent to turbid, that the crystallization of methylammonium lead iodide (MAPbI3) precursor films is strongly affected by humidity. A theoretical model based on the dependence of crystallization on evaporation was developed. We further designed a “humidity-insensitive antisolvent method” based on the turbid point and its tuning to control the fabrication of high-quality MAPbI3 films and solar cells irrespective of the ambient humidity levels. Note that a champion device prepared in ambient air at 90% RH exhibits the efficiency of 19.5%, which is highest among those of the devices prepared in ambient air with over 30% RH. Our study may also impact other perovskite devices and inspire other researchers to perform innovative experiments.

The research for highly selective catalytic transfer hydrogenation (CTH) of 5-hydroxymethylfurfural (5-HMF) into 2,5-bis(hydroxymethyl)furan (BHMF) is an extremely important pathway for biomass valorization. Herein, we use lignosulfonate, a waste by-product from the paper industry, as a building block to coordinate with different metal ions (Hf4+, Zr4+, Fe3+, Al3+, Zn2+) and thus a series of inorganic-biopolymer hybrids (M–LigS) were prepared by a hydrothermal self-assembly method. The resulting Hf–LigS hybrid with strong Lewis acid–base couple sites and moderate Bronsted acidic sites from the inherent sulfonic groups in LigS exhibited the best catalytic activity for CTH of 5-HMF with 2-propanol (2-PrOH) in high yields (90%) under mild reaction conditions (100 °C in 2 h). This robust bifunctional acid–base Hf–LigS is also demonstrated to be effective in one-step reductive etherification of 5-HMF to 5-[(1-methylethoxy)methyl]-2-furanmethanol (MEFA), a potential biomass-derived fuel additive, with 95% yield. Kinetic studies revealed that the activation energy for CTH of 5-HMF was 62.25 kJ mol−1, accounting for the high reaction rate. Isotopic labelling experiments demonstrated that intermolecular hydrogen transfer from the α-C of 2-PrOH to the α-C of 5-HMF was the dominant reaction pathway and the direct hydride transfer on acid–base sites was the rate-determining step. Due to the strong interactions between Hf4+ and phenolic hydroxyl groups, Hf–LigS was highly stable and could be reused without a significant decline in activity.

Exploring both high-performance catalytic materials from non-edible lignocellulosic biomass and selective hydrodeoxygenation of bioderived molecules will enable value-added utilization of renewable feedstocks to replace rapidly diminishing fossil resources. Herein, we developed a scale-up and sustainable method to fabricate gram-quantities of highly dispersed cobalt nanocatalysts sheathed in multilayered N-doped graphene (Co@NG) by using a biomacromolecule carboxymethyl cellulose (CMC) as a raw material. The ionic gelation of CMC, urea and Co2+ ions leads to uniform dispersion and chelation of different species, consequently resulting in the formation of highly distributed Co nanoparticles (NPs) (10.91 nm) with N-enriched graphene shells in the solid-state thermolysis process. The usage of urea as a non-corrosive activation agent can introduce a porous belt-like nanostructure and abundant doped nitrogen. Among all the prepared catalysts in this work, the optimized Co@NG-6 with the largest specific surface area (627 m2 g−1), the most and strongest basic sites, and the highest proportion of pyridinic-N (37.6%) and mesopores exhibited excellent catalytic activity (99% yield of 2-methoxy-p-cresol) for base-free transfer hydrodeoxygenation (THD) of vanillin using bioderived formic acid (FA) as a H source at 160 °C for 6 h. The poisoning tests and electron paramagnetic resonance (EPR) spectra verified that the strong interaction between N atoms and encapsulated Co NPs provided synergistic effects, which were essential for the outstanding catalytic performance of Co@NG-6. The deuterium kinetic isotope effect study clearly demonstrated that the formation of Co-H−via β-hydride elimination and protonation was the rate-determining step, and protic N–H+ and hydridic Co-H− were considered to be active intermediate species in the THD reaction. Furthermore, Co@NG-6 was highly stable for recycling owing to the graphene shells preventing Co NPs from corrosion and aggregation.

Thermal instability of hybrid perovskite thin films is one of the important issues that must be overcome on the way to commercialization of perovskite solar cells, and it is also essential to deeply understand the degradation mechanism of perovskite thin films caused by thermal instability. In this paper, we demonstrate that the CH3NH3PbI3 film with larger grain sizes and fewer grain boundaries exhibits a higher thermal stability and the solar cell device exhibits improved photovoltaic performance. The grain size is well controlled by employing isopropanol solvent annealing on CH3NH3PbI3 films, and the highest efficiency of perovskite solar cells increases from 16.87% to 18.56% with the increase in the grain size. The results demonstrate that the reduction of grain boundaries is a feasible strategy to solve the thermal instability issue of perovskite thin films.

The world is currently transitioning from a fossil-fuel-driven energy economy to one that is supplied by more renewable and sustainable materials. Trees as the most abundant renewable bioresource have attracted significant attention for advanced materials and manufacturing in this epochal transition. Trees are composed with complex structures and components such as trunk (stem and bark), leaf, flower, seed, and root. Although many excellent reviews have been published regarding advanced applications of wood and wood-derived biopolymers in different fields, such as energy, electronics, biomedical, and water treatment, no reviews have revisited and systematically discussed functional materials and even devices derived from trees in a full scope yet. Therefore, a timely summary of the recent development of materials and structures derived from different parts of trees for sustainability is prsented here. A concise introduction to the different parts of the trees is given first, which is followed by the corresponding chemistry and preparation of functional materials using various biopolymers from trees. The most promising applications of biopolymer-based materials are discussed subsequently. A comprehensive review of the different parts of trees as sustainable functional materials and devices for critical applications is thus provided.

Aramid fibers exhibit impressive mechanical properties, electrical insulation properties, and chemical stability. However, physical properties of the aramid paper are poor because of the chemical inertness and smooth surface of aramid fibers. This study reports a simple and efficient method for substantially improving the performance of the para-aramid/meta-aramid composite paper by introducing the N,N-dimethylacetamide (DMAc)/LiCl solution to induce partial dissolution or by adding the DMAc/LiCl/para-aramid solution to induce regeneration. Experimental results state that the tensile strength, specific strength, folding resistance, and interlayer bonding strength of the aramid paper are increased by 2.17, 2.13, 34.7, and 9.39 times, respectively, because of the dense and compact structure of the paper. Furthermore, the water resistance of the paper was also considerably improved. After immersing the paper samples in water for 24 h, their moisture absorption rate decreased to approximately 54% from approximately 143% for the original paper. Results indicate that partial dissolution/regeneration welding is a viable method for the efficient reinforcement of the aramid composite paper, providing additional possibilities for manufacturing the high-performance aramid paper-based materials. Keywords: Aramid composites, Partial dissolution, Regeneration welding, Mechanical properties, Reinforcement

© 2020, Tsinghua University Press and Springer-Verlag GmbH Germany, part of Springer Nature. The unique physical and chemical properties of metal halide perovskites predestine the devices to achieve high performance in optoelectronic field. Among the numerous high qualities of perovskites, their different low-temperature synthesis methods and preparation processes make them impressive and popular materials for flexible optoelectronic devices. Mainstream perovskite devices, for instance, solar cells, photodetectors and light-emitting diodes, have been fabricated on flexible substrates and show outstanding flexibility as well as high performance. For soft wearable electronic systems, mechanical flexibility is the premier condition. Compared to common devices based on rigid substrates, flexible perovskite devices are more practical and see widespread applications in energy, detection, display, and other fields. This review summarizes the recent progress of flexible perovskite solar cells, photodetectors and light-emitting diodes. The design and fabrication of different high-performance flexible perovskite devices are introduced. Various low-dimensional perovskite materials and configurations for flexible perovskite devices are presented. In addition, the limitations and challenges for further application are also briefly discussed. [Figure not available: see fulltext.].