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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.

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.

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.].

Perovskite oxides have been considered as ideal electrocatalysts for water electrolysis since they are eco-friendly, abundant, and easy to be fabricated. However, their application in hydrogen evolution reaction (HER) is still limited because of relatively poor efficiency and stability. Herein, we report that a facile fabrication method, pulsed laser deposition, is employed to fabricate nanoscale LaCoO3−δ on nickel foam as an active electrocatalyst for HER. We find that in-situ surface reconstruction takes place in HER cycles, which enhances the HER activity greatly. By depositing additional NiO layer and annealing in H2 atmosphere, the catalytic performance and long-term stability of LaCoO3−δ can be further improved. As a result, the catalyst demonstrates a remarkable HER activity with a low overpotential of 180 mV at 10 mA cm−2 and superb stability up to 50 h in alkaline media. Our work uncovers that the underlying phase transition in an alkaline medium and the interface engineering play critical roles in the improved HER activity of perovskite oxides. This work may provide insightful guidance to engineer perovskite oxides as electrocatalysts in the electrolysis of water.

Low processing temperature of tin dioxide (SnO2) is essential for flexible perovskite solar cells (f-PSCs). However, the low processing temperature of SnO2 results in an inferior photovoltaic performance due to compromised carrier transport capacity in devices. The deteriorated carrier transport mainly results from the suppressed interfacial charge transfer. To overcome these issues, we used ionic liquid to modify the interface between perovskite films and SnO2 in f-PSCs. Density Function Theory calculations were implemented to demonstrate the ionic liquid modification induced the formation of interfacial dipolar layer (IDL) and defect passivation in perovskites. The IDL and defect passivation improves the interfacial charge transfer and intra-perovskite charge transport, respectively. As a result, the f-PSCs based on ionic liquid modified SnO2 yield the champion power conversion efficiency (PCE) of 19.0%. This work provides a method to effectively improve the performance of f-PSCs using low-temperature processed SnO2 ESLs using affordable materials and a facile approach.

In this work, an anti-solvent process was used to fabricate a perovskite-PCBM bulk heterojunction, in which PCBM diffused in CH3NH3PbI3 and passivated grain boundary defects. Different concentrations of PCBM were studied in this paper. When a low concentration (5 mg/ml, 10 mg/ml or 15 mg/ml) of PCBM was used, the PCBM-CH3NH3PbI3 transition layer provided efficient electron collection. With the increase of the concentration of PCBM, a thicker PCBM layer was formed in the bulk heterojunction. Such a thick PCBM resulted in rough perovskite morphology and low photo-carrier collection efficiency. SEM images and metallographic microscope images confirmed that the PCBM upper layer gradually covered grain boundaries of perovskite films with the increase of the PCBM concentration. On the other hand, low concentrations of PCBM improved the light absorption and crystallinity of CH3NH3PbI3 films. The PCBM/perovskite heterojunction exhibited a high UV responsivity of 0.18 AW-1 and a response time less than 123 ms. This research provides a way to improve the quality of perovskite films and the performance of perovskite photodetectors.

In this study, we investigated the nucleation mechanism of perovskite films by employing isopropanol (IPA), a weakly coordinating solvent, to anneal both PbI2 and CH3NH3PbI3 in the sequential deposition and CsPbI3 in the one-step deposition. IPA solvent annealing (IPA SA) of PbI2 films was carried out at different temperatures. The grain size, compactness, roughness and morphology of PbI2 and CH3NH3PbI3 films were seriously affected by annealing methods. Similarly, weakly coordinating solvent annealing process was also employed to anneal all inorganic CsPbI3 perovskite in a one-step method. A continuous and dense CsPbI3 film with uniform grain size was obtained. We recognized that weakly coordinating solvent annealing for perovskite could regulate the dissolution-recrystallization process via controlling the volume of residual solvent in perovskite intermediate films. The power conversion efficiency (PCE) of conventional CH3NH3PbI3 perovskite solar cells (PSCs) reached 17.4% and that of CsPbI3 PSCs reached 2.5% based on this sequential IPA SA process.

Despite the high power conversion efficiency, the severe performance degradation of organic-inorganic lead halide perovskite solar cells caused by moisture and thermal phase transition is an obstacle to commercialization of the perovskite solar cells. We propose the theoretical lifetime extraction of perovskite solar cells with a mixed-cations lead halide perovskite absorber containing CH3NH3+, CH3(NH2)2+ and Cs+. The estimated mean time to failure (MTTF) of the triple cation perovskite solar cells is up to 180 days in ambient. Compared with the perovskite solar cells based on CH3NH3PbI3, the triple-cation perovskite solar cells, whose power conversion efficiency reaches 18.2% in this study, have a much better performance in terms of thermal stability and humidity stability. Improvements of both performance and stability pave the way for commercialization of perovskite solar cells.

The thin flexible film heater made of carbon fibers is widely considered to be an ideal material for the use as self-heating devices because of its safe, low-cost, no noises, small size and fast heating as well as energy saving. Presently thin flexible film heater is mostly fabricated by mixing method using the long cellulose fibers as film-forming materials and carbon fibers as self-heating materials, which mostly suffer from opaque or uneven heating field. In this work, we firstly reported a flexible and transparent thin film heater (FTFH) composed of carbon fibers and regenerated cellulose. The use of regenerated cellulose for membrane materials brings high transmittance, strong adhesion, fast temperature response and high generated temperature. More importantly, the FTFH using novel carbon fibers as self-heating materials and regenerated cellulose as membrane materials show a rapid heating response (12 s), higher power density (2577 w/m2) and long-term stability of generated temperature (162.3 °C).

Presently flexibly transparent film or nanopaper from all cellulose was mostly fabricated by assembling cellulose nanofibers disintegrated from macroscopic wood fibers which mostly suffers from potential environmental toxicity or high cost. In this work, we firstly reported an all-cellulose transparent film fabricated by a novel microwave-assisted ionic liquids technology (MILT). The use of MILT for treating the original all-cellulose paper brings nearly 2.6 fold-increases in optical transmission, and 2.0 fold-increases in tensile property compared to those without microwave assistance. More importantly, by contrast with the partial dissolution of cellulose in typical DMAC/LiCl, ILs, NaOH/urea, the MILT is extremely time-saved with responding to the highest increase in mechanical property because the high efficient surface dissolution and welding bind individual sheets together under a micro environment.

With the rapid development of organic-inorganic lead halide perovskite photovoltaics, increasingly more attentions are paid to explore the growth mechanism and precisely control the quality of perovskite films. In this study, we propose a “stitching effect” to fabricate high quality perovskite films by using chlorobenzene (CB) as an anti-solvent and isopropyl alcohol (IPA) as an additive into this anti-solvent. Because of the existence of IPA, CB can be efficiently released from the gaps of perovskite precursors and the perovskite film formation can be slightly modified in a controlled manner. More homogeneous surface morphology and larger grain size of perovskite films were achieved via this process. The reduced grain boundaries ensure low surface defect density and good carrier transport in the perovskite layer. Meanwhile, we also performed the Fourier transform infrared (FTIR) spectroscopy to investigate the film growth mechanism of unannealed and annealed perovskite films. Solar cells fabricated by using the “stitching effect” exhibited a best efficiency of 19.2%. Our results show that solvent and solvent additives dramatically influenced the formation and crystallization processes for perovskite materials due to their different coordination and extraction capabilities. This method presents a new path towards controlling the growth and morphology of perovskite films.

Lead halide perovskite solar cells (PSCs) appear to be the ideal future candidate for photovoltaic applications owing to the rapid development in recent years. The electron transport layers (ETLs) prepared by low-temperature process are essential for widespread implementation and large-scale commercialization of PSCs. Here, we report an effective approach for producing planar PSCs with Al3+ doped SnO2 ETLs prepared by using a low-temperature solution-processed method. The Al dopant in SnO2 enhanced the charge transport behavior of planar PSCs and increased the current density of the devices, compared with the undoped SnO2 ETLs. Moreover, the enhanced electrical property also improved the fill factors (FF) and power conversion efficiency (PCE) of the solar cells. This study has indicated that the low-temperature solution-processed Al-SnO2 is a promising ETL for commercialization of planar PSCs.

Perovskite solar cells (PSCs) have attracted great attention due to their low cost and high power conversion efficiency (PCE). However, the defects and grain boundaries in perovskite films dramatically degrade their performance. Here, we show a two-step annealing method to produce mesoporous PbI2 films for growth of continuous, pinhole-free perovskite films with large grains, followed by additional ethanol vapor annealing of perovskite films to reduce the defects and grain boundaries. The large perovskite grains dramatically suppress the carrier recombination, and consequently we obtain ZnO-nanorod-based PSCs that exhibit the best efficiency of 17.3%, with high reproducibility.

The environmental instability of perovskite solar cells caused by the ultraviolet photocatalytic effect of metal oxide layers is a critical issue that must be solved. In this paper, we report improved environmental stability of ZnO film-based planar heterojunction perovskite solar cells, by suppressing photocatalytic activities induced by the ZnO electron transfer layer. The photovoltaic performance and stability in an ambient environment under continuous illumination are effectively improved by applying an aluminum oxide interlayer on the ZnO film to suppress the photocatalytic degradation of perovskites. The highest efficiency of solar cells has increased from 14.62% to 17.17%, and after 250 h of continuous exposure under full spectrum simulated sunlight in air, the efficiency remains as high as 15.03%. The results suggest that effective suppression of photocatalytic degradation of perovskites with a modified electron transfer layer is a new solution to improve the long-term environmental stability of perovskite solar cells.

Perovskite solar cells (PSCs) have been developed rapidly in recent time, and efficient planar PSCs are regarded as the most promising alternative to the Si solar cells. In this study, we demonstrated that Li-doping of compact TiO2 can reduce the density of electron traps and increase the conductivity of the electron transport layer (ETL) of PSCs. Due to the improved electronic property of ETL, the Li-doped compact TiO2 based planar heterojunction PSCs exhibit negligible hysteretic J-V behavior. Comparing with the undoped compact TiO2 based PSCs, the power conversion efficiency (PCE) of the Li-doped compact TiO2 film based PSCs is improved from 14.2% to 17.1%. Fabrication of highly efficient planar PSCs provides a pathway for commercialization of PSCs.

Oxygen vacancies in non-stoichiometric TiO2 electron transport layers can capture injected electrons and act as recombination centers. In this study, the compact TiO2 electron transport layers of perovskite solar cells (PSCs) are doped with different molar ratios of Fe3+ in order to passivate such defects and improve their electron transport properties. The electrical conductivity, absorption, crystal structure, and the performance of the PSCs are systematically studied. It shows that Fe3+-doping improves the conductivity of TiO2 compact layers compared with the pristine TiO2, boosting the photovoltaic performance of PSCs. The reduced trap-filled limit voltage (VTFL) of the Fe3+-doped TiO2 compact layers suggests that trap density in the Fe3+-TiO2 films is much lower than that of a pristine TiO2 film. With the optimized doping concentration (1 mol%) of Fe3+, the best power conversion efficiency of PSCs is improved from 16.02% to 18.60%.

The rational design of high-performance, flexible, transparent, electrically conducting sensor attracts considerable attention. However, these designed devices predominantly utilize glass and plastic substrates, which are expensive and not environmentally friendly. Here, novel transparent and conductive woods (TCWs) were fabricated by using renewable wood substrates and low-cost conductive polymers. Polymerizable deep eutectic solvents (PDES), acrylic-acid (AA)/choline chloride (ChCl), were used as backfilling agents and in situ photopolymerized in the delignified wood, which endowed the materials with high transparency (transmittance of 90%), good stretchability (strain up to 80%), and high electrical conductivity (0.16 S m-1). The retained cellulose orientation and strong interactions between the cellulose-rich template and poly(PDES) endow TCWs with excellent mechanical properties. Moreover, TCWs exhibited excellent sensing behaviors to strain/touch, even at low strain. Therefore, these materials can be used to detect weak pressure such as human being's subtle bending-release activities. This work provides a new route to fabricate functional composite materials and devices which have promising potential for electronics applications in flexible displays, tactile skin sensors, and other fields.

Despite the considerably improved efficiency of inorganic–organic metal hybrid perovskite solar cells (PSCs), electron transport is still a challenging issue. In this paper, we report the use of ZnO nanorods prepared by hydrothermal self-assembly as the electron transport layer in perovskite solar cells. The efficiency of the perovskite solar cells is significantly enhanced by passivating the interfacial defects via atomic layer deposition of Al2O3 monolayers on the ZnO nanorods. By employing the Al2O3 monolayers, the average power conversion efficiency of methylammonium lead iodide PSCs was increased from 10.33% to 15.06%, and the highest efficiency obtained was 16.08%. We suggest that the passivation of defects using the atomic layer deposition of monolayers might provide a new pathway for the improvement of all types of PSCs..

While most work carried out to date has focused on the solvent annealing of perovskite, in the present work, we focused on the solvent annealing of lead iodide. Based on the two-step spin-coating method, we designed a screening method to search for an effective solvent annealing process for PbI2. PbI2 films were annealed in diverse solvent atmospheres, including DMF, DMSO, acetone, and isopropanol (IPA). We found that the solvent annealing of PbI2 in the DMF, acetone, and IPA atmospheres resulted in dense PbI2 films, which impeded the complete conversion of PbI2 to CH3NH3PbI3. Surprisingly, employing the DMSO solvent annealing process for PbI2 led to porous PbI2, which facilitated the complete conversion of PbI2 to perovskite with larger grain sizes. Solar cells fabricated using the DMSO solvent annealing process exhibited the best efficiency of 18.5%, with a fill factor of 76.5%. This unique solvent annealing method presents a new way of controlling the perovskite film quality for highly efficient solar cells.

The potential toxic issue of lead content is still a problem for prohibiting the commercialization of lead halide perovskite solar cells (PSCs). As an element of group 14 metals, tin (Sn) is the most likely substitute for lead element in perovskites. However, Sn-based PSCs still suffer from the low power conversion efficiency (PCE) because Sn2+ in tin-based perovskites is easily oxidized into Sn4+ once exposed to air. To fabricate stable and efficient Sn-based PSCs, herein we incorporate large ethylammonium (EA+) cation into CH3NH3SnI3 (MASnI3) abided by the Goldschmidt tolerance factor to fabricate vertically oriented 2D/3D mixed perovskite films. The vertically oriented structure provides a direct pathway for electron and hole transport. As a result, the PCE is highly improved to 9.24% and the corresponding PSC still retains 95% of the initial efficiency after being kept for 30 days without encapsulation in the glovebox. Therefore, our results suggest a promising strategy to develop highly efficient and stable Sn-based PSCs.

Improving the stability of hybrid organic-inorganic halide perovskite materials is urgent and essential for their applications in optoelectronic devices. Here, we introduce n-butylammonium iodide (BAI) into lead-iodide crystals as guest molecules. As a result of guest effect, only a small amount BA2PbI4 two-dimensional (2D) perovskite (n = 1) is formed in PbI2-BAI films. Most of BAI crystals efficiently cut and squeeze the lattice network of lead iodide. The better orientation of 2D lead iodide crystals is obtained via this guest effect. In the following sequential deposition process, that BAI re-dissolve in MAI isopropanol (IPA) solution leads to a mesoporous structure of PbI2 and introduces a 2D perovskite (n = 2) protect layer in 3D MAPbI3 after annealing. Finally, the morphology, crystallization and stability of CH3NH3PbI3 are simultaneously improved by the insertion of BAI guest molecules. Consequently, CH3NH3PbI3 PSCs with an optimized cutting behavior exhibited a power conversion efficiency of 18% and significantly improved the stability.

Recently, two-dimensional (2D) organic-inorganic hybrid perovskites have attracted tremendous attention due to their excellent environment stability. However, the inhibition of out-of-plane charge transport limits the performance of 2D based perovskite solar cells (PVSCs). To overcome this issue, we prepare the vertical-orientated 2D perovskite film via introducing dimethyl sulfoxide (DMSO) and thio-semicarbazide (TSC) as additives into the precursor solution. High-quality 2D (BA)2(MA)3Pb4I13 (BA = n-butylammonium, MA = methylammonium) films with uniform morphology, increased grain size, intensified crystallinity and vertical orientation are therefore fabricated by a synergistic effect of additives. As a result, the trap-state density in 2D (BA)2(MA)3Pb4I13 films is reduced and the charge transport is remarkably improved. The power conversion efficiency (PCE) of the PVSCs is boosted from the 1.05% to 14.15%. An unsealed device retains 90.3% of its initial PCE after 720 h storage in air atmosphere with relative humidity of 25 ± 5% at 25 °C. The results show the synergistic effect of TSC and DMSO on perovskite films is an effective approach toward efficient and stable 2D PVSC.

Correction for ‘Steering the crystallization of perovskites for high-performance solar cells in ambient air’ by Feng Wang et al., J. Mater. Chem. A, 2019, 7, 12166–12175, DOI: 10.1039/C9TA02566A.

Perovskite solar cells (PSCs) have developed rapidly over the past few years, and the power conversion efficiency of PSCs has exceeded 20%. Such high performance can be attributed to the unique properties of perovskite materials, such as high absorption over the visible range and long diffusion length. Due to the different diffusion lengths of holes and electrons, electron transporting materials (ETMs) used in PSCs play a critical role in PSCs performance. As an alternative to TiO2 ETM, ZnO materials have similar physical properties to TiO2 but with much higher electron mobility. In addition, there are many simple and facile methods to fabricate ZnO nanomaterials with low cost and energy consumption. This review focuses on recent developments in the use of ZnO ETM for PSCs. The fabrication methods of ZnO materials are briefly introduced. The influence of different ZnO ETMs on performance of PSCs is then reviewed. The limitations of ZnO ETM-based PSCs and some solutions to these challenges are also discussed. The review provides a systematic and comprehensive understanding of the influence of different ZnO ETMs on PSCs performance and potentially motivates further development of PSCs by extending the knowledge of ZnO-based PSCs to TiO2 -based PSCs.

Lead-free solution-processed solid-state photovoltaic devices based on formamidinium tin triiodide (FASnI3) and cesium tin triiodide (CsSnI3) perovskite semiconductor as the light harvester are reported. In this letter, we used solvent engineering and anti-solvent dripping method to fabricate perovskite films. SnCl2 was used as an inhibitor of Sn4+ in FASnI3 precursor solution. We obtained the best films under the function of toluene or chlorobenzene in anti-solvent dripping method and monitored the oxidation of FASnI3 films in air. We chose SnF2 as an additive of CsSnI3 precursor solution to prevent the oxidation of the Sn2+, improving the stability of CsSnI3. The experimental results we obtained can pave the way for lead-free tin-based perovskite solar cells (PSCs).

Biodegradable highly nanostructured paper has received great interest in past years due to its excellent optical properties which facilitate its wide applications in green flexible electronics and devices. However, energy and/or time-consuming procedure during the process of fabricating most nanostructured transparent paper are presently the main obstacle to their scalable production. In this work, we demonstrated a novel nanostructured paper with dually high transparency (∼91%) and high haze (∼89%) that was directly fabricated from original paper with rapid ILs-polishing processes. The whole fabricating time only requires 10 min. Compared to the previously reported nanopaper made of the isolated cellulose nanofibers by pure mechanical and/or chemical approaches, this work presented herein is devoted to use green ILs to polish directly the micrometer-sized fibrous paper into the nanostructured paper. This new method brings a rapid fabrication of transparent nanostructured paper while also retaining dual intriguing properties both in optical transmittance and haze. This work is capable of fabricating next-generation flexible and highly transparent and haze paper by a high-speed roll-to-roll manufacturing process with a much lower cost.

The thermal decomposition of perovskite films on ZnO surfaces is generally believed to originate from specific surface states of ZnO and the impact from the lattice mismatch between ZnO and perovskite films on this process has long been ignored. In this research, the role of lattice mismatch in the thermal degradation process of cesium-containing perovskite films on Al doped ZnO (AZO) is studied. A Ba(OH)2 buffer layer on the surface of AZO is employed to release the lattice mismatch and suppress the thermal degradation of perovskite films resulted from ZnO. Consequently, perovskite films with enhanced thermal stability and crystalline properties are obtained. Meanwhile, the Ba(OH)2 films efficiently passivate the surface trap states and reduce the vacuum level of the AZO surfaces. On this basis, electron transport layer-free perovskite solar cells yield the best efficiency of 18.18% and the thermal stability is obviously improved.

Perovskite solar cells (PSCs) have attracted much attention since the first report. Flexible PSCs are one of the important development orientations due to its light weight. However, a low temperature process is essential to fabricate the flexible PSCs due to the deformation of the plastic substrate. Here, the pre-crystallization SnO2 colloids have been used to deposit the electron transport layer of flexible PSCs. The photovoltaic performance of flexible PSCs has been optimized through controlling the annealing temperature and SnO2 thickness. A moderate annealing temperature reduces the deformation of flexible substrates and protects the conductive layer. A SnO2 film with a suitable thickness not only blocks the direct contact between perovskite and electrode, but also transports the electron from perovskite to anode efficiently. As a result, the power conversion efficiency of the champion PSCs has been improved to 11.61 %.

The photovoltaic performance of perovskite solar cells (PSCs) largely depends on the crystal grain size of perovskite films. Here, we use the mixture of n-octyltrimethoxysilane (OTES) and aminopropyltrimethoxysilane (APTES) to tailor the surface termination state of SnO2 electron transport layer, and demonstrate the crystal grain size of perovskite is remarkably enlarged. The perovskite film with large crystal size shows a lower non-radical recombination density and a longer charge lifetime. The power conversion efficiency of PSCs is eventually improved from 18.21% to 20.3%. The proposed method may also impact other optoelectronic devices based perovskite films.

We report a novel partial dissolution strategy to liberate uniform cellulose nanofibers with diameter of 5–10 nm from macroscopic cellulose fibers and promote separation of nanofibers in an aqueous environment by forming water-soluble sodium carboxymethylcellulose (CMC) through heterogeneous sodium acetoxylation of cellulose. With the obtained cellulose nanofibers, we fabricated nanopapers which exhibit high optical transparency of 90.5% (@550 nm) with promising mechanical properties and high thermal stability. By directly depositing Ag nanowires on a wet nanofiber sheet, we fabricated a flexible transparent electrode with 86.5% (@550 nm) transparency and 26.2 Ω/sq sheet resistance (Rs). Meanwhile, we studied the magnetic properties of sputter deposited thin film of permalloy on nanopaper which exhibited a similar magnetic coercivity and a close saturation magnetization to conventional silicon dioxide-based permalloy.