Flexible Cellulose Paper‐based Asymmetrical Thin Film Supercapacitors with High‐Performance for Electrochemical Energy Storage

Cellulose paper (CP)‐based asymmetrical thin film supercapacitors (ATFSCs) have been considered to be a novel platform for inexpensive and portable devices as the CP is low‐cost, lightweight, and can be rolled or folded into 3D configurations. However, the low energy density and poor cycle stability are serious bottlenecks for the development of CP‐based ATFSCs. Here, sandwich‐structured graphite/Ni/Co₂NiO₄‐CP is developed as positive electrode and the graphite/Ni/AC‐CP as negative electrode for flexible and high‐performance ATFSCs. The fabricated graphite/Ni/Co₂NiO₄‐CP positive electrode shows a superior areal capacitance (734 mF/cm² at 5 mV/s) and excellent cycling performance with ≈97.6% C_sp retention after 15 000 cycles. The fabricated graphite/Ni/AC‐CP negative electrode also exhibits large areal capacitance (180 mF/cm² at 5 mV/s) and excellent cycling performance with ≈98% C_sp retention after 15 000 cycles. The assembled ATFSCs based on the sandwich‐structured graphite/Ni/Co₂NiO₄‐CP as positive electrode and graphite/Ni/AC‐CP as negative electrode exhibit large volumetric C_sp (7.6 F/cm³ at 5 mV/s), high volumetric energy density (2.48 mWh/cm³, 80 Wh/kg), high volumetric power density (0.79 W/cm³, 25.6 kW/kg) and excellent cycle stability (less 4% C_sp loss after 20 000 cycles). This study shows an important breakthrough in the design and fabrication of high‐performance and flexible CP‐based electrodes and ATFSCs.     

Flexible and Semi‐Transparent Ultra‐Thin CIGSe Solar Cells Prepared on Ultra‐Thin Glass Substrate: A Key to Flexible Bifacial Photovoltaic Applications

For applications to semi‐transparent and/or bifacial solar cells in building‐integrated photovoltaics and building‐applied photovoltaics, studies are underway to reduce the processing cost and time by decreasing the thickness of Cu(In_1?x,Ga_x)Se₂ (CIGSe) absorber to the ultra‐thin scale (≤500 nm). To dynamically and affordably meet the growing demand for electric power, daylighting, and architectural aesthetics of buildings in urban area, flexible semi‐transparent ultra‐thin (F‐STUT) CIGSe solar cells are proposed on flexible ultra‐thin glass (UTG) and compared with rigid semi‐transparent ultra‐thin (STUT) CIGSe solar cells fabricated on soda‐lime glass (SLG). At all the tested deposition temperatures of CIGSe, the F‐STUT CIGSe solar cells exhibit superior performance compared to the rigid STUT CIGSe solar cells. Furthermore, through realistic measurement under ≈1.3‐sun illumination, maximum bifacial power conversion efficiency of 11.90% and 13.23% are obtained for SLG and UTG, respectively. The major advantages of using UTG instead of SLG are not only the intrinsic characteristics of UTG, such as flexibility and high transmittance, but also collateral benefits such as the larger CIGSe grain size at the deposition temperature, better CIGSe crystalline quality, more precise controllability of the alkali element, and reduced thickness of the interfacial GaO_x layer, which enhance the photovoltaic parameters.     

Samarium-Doped Nickel Oxide for Superior Inverted Perovskite Solar Cells: Insight into Doping Effect for Electronic Applications

Hole transport layers (HTLs) play a key role in perovskite solar cells (PSCs), particularly in the inverted PSCs (IPSCs) that demand more in its stability. In this study, samarium-doped nickel oxide (Sm:NiO_x) nanoparticles are synthesized via a chemical precipitation method and deposited as a hole transport layer in the IPSCs. Sm³⁺ doping can reduce the formation energy of Ni vacancy and naturally increase the density of Ni vacancies, thereby rendering increased hole density. Thenceforth, the electronic conductivity is enhanced significantly, and work function enlarged in the Sm:NiO_x film in favor of extracting holes and suppressing charge recombination. Consequently, the Sm:NiO_x-based IPSCs attain outstanding power conversion efficiencies as high as 20.71%. Even when it is applied in flexible solar cells, it still outputs efficiency as high as 17.95%. More importantly, the Sm:NiO_x is compatible with large-scale processing whereby the large area IPSCs of 1.0 cm² and 40 × 40 mm² deliver high efficiencies of 18.51% and 15.27%, respectively, all are among the highest for the inorganic HTLs based IPSCs. This research demonstrates that, while revealing the doping effect in depth, Sm:NiO_x can be a promising hole transport material for fabricating efficient, large-area, and flexible IPSCs in the future.     

Reversible Coloration Enhanced by Electrochemical Deposition of an Ultrathin Zinc Layer onto an Anodic Nanoporous Alumina Layer

A productive method is introduced to realize large area color electronic paper (e‐paper) with high UV resistance, heat resistance, and good significant bending properties using a color change triggered by reversible electronic change in the device structure. Reversible coloration and decoloration triggered by electrochemical deposition and desorption, respectively, of an ultra‐thin zinc (Zn) layer on a thin transparent conductive layer coated on anodic nanoporous alumina has been developed. The deposition of the ultra‐thin Zn layer triggers the formation of destructive interference, which leads to coloration. Yellow, magenta, and cyan colors were obtained in the colored state by increasing the NP‐Al₂O₃ layer thickness, based on Bragg diffraction theory. Reflectance of more than 70% and contrast values of more than 7 were obtained, which are nearly equivalent to those of previous e‐papers. The color images in these devices also showed high UV resistance, heat resistance, and repeated significant bending endurance. The devices can be fabricated with large areas using low‐cost manufacturing processes such as anodic oxidation, and use abundantly available materials. Our proposed device provides low‐cost and flexible large area color e‐paper for outdoor use.     

Printable and Homogeneous NiOx Hole Transport Layers Prepared by a Polymer-Network Gel Method for Large-Area and Flexible Perovskite Solar Cells

As one of the most promising hole transport layers (HTLs), nickel oxide (NiO_x) has received extensive attention due to its application in flexible large-area perovskite solar cells (PSCs). However, the poor interface contact caused by inherent easy-agglomeration phenomenon of NiO_x nanoparticles (NPs) is still the bottleneck for achieving high-performance devices. Herein, a general strategy to synthesize NiO_x NPs with high crystallinity and good dispersibility via the polymer network micro-precipitation method is reported. Promisingly, this approach realizes the flow-division of precipitant and the restraint of the NPs motion, thereby effectively alleviating the coagulation phenomenon caused by excessive local concentration and secondary movement adsorption. Furthermore, the addition of ionic liquid not only inhibits the secondary aggregation of NiO_x NPs during the dispersion process, but also significantly enhances the properties of the colloidal solution. Ultimately, the 1.01 cm² PSCs based on the optimized NiO_x HTLs achieve the champion power conversion efficiency of 20.91% and 19.17% on rigid and flexible substrates, respectively. Moreover, the reproducibility and stability of PSCs are also significantly improved, especially for flexible devices. Overall, this strategy provides the possibility for flexible, large-area fabrication of high-quality NiO_x HTLs to promote the development of stable and efficient perovskite devices.     

Flexible,Stretchable, Transparent Conducting Films Made from Superaligned Carbon Nanotubes

A straightforward roll‐to‐roll process for fabricating flexible and stretchable superaligned carbon nanotube films as transparent conducting films is demonstrated. Practical touch panels assembled by using these carbon nanotube conducting films are superior in flexibility and wearability—and comparable in linearity—to touch panels based on indium tin oxide (ITO) films. After suitable laser trimming and deposition of Ni and Au metal, the carbon nanotube film possesses excellent performance with two typical values of sheet resistances and transmittances (208 Ω □^?1, 90% and 24 Ω □^?1, 83.4%), which are comparable to ITO films and better than the present carbon nanotube conducting films in literature. The results provide a route to produce transparent conducting films more easily, effectively, and cheaply, an important step for realizing industrial‐scale applications of carbon nanotubes for transparent conducting films.     

Skin‐Like Oxide Thin‐Film Transistors for Transparent Displays

Flexible transparent display is a promising candidate to visually communicate with each other in the future Internet of Things era. The flexible oxide thin‐film transistors (TFTs) have attracted attention as a component for transparent display by its high performance and high transparency. The critical issue of flexible oxide TFTs for practical display applications, however, is the realization on transparent and flexible substrate without any damage and characteristic degradation. Here, the ultrathin, flexible, and transparent oxide TFTs for skin‐like displays are demonstrated on an ultrathin flexible substrate using an inorganic‐based laser liftoff process. In this way, skin‐like ultrathin oxide TFTs are conformally attached onto various fabrics and human skin surface without any structural damage. Ultrathin flexible transparent oxide TFTs show high optical transparency of 83% and mobility of 40 cm² V^?1 s^?1. The skin‐like oxide TFTs show reliable performance under the electrical/optical stress tests and mechanical bending tests due to advanced device materials and systematic mechanical designs. Moreover, skin‐like oxide logic inverter circuits composed of n‐channel metal oxide semiconductor TFTs on ultrathin, transparent polyethylene terephthalate film have been realized.     

The Remarkable Thermal Stability of Amorphous In‐Zn‐O Transparent Conductors

Transparent conducting oxides (TCOs) are increasingly critical components in photovoltaic cells, low‐e windows, flat panel displays, electrochromic devices, and flexible electronics. The conventional TCOs, such as Sn‐doped In₂O₃, are crystalline single phase materials. Here, we report on In‐Zn‐O (IZO), a compositionally tunable amorphous TCO with some significantly improved properties. Compositionally graded thin film samples were deposited by co‐sputtering from separate In₂O₃ and ZnO targets onto glass substrates at 100 °C. For the metals composition range of 55–84 cation% indium, the as‐deposited IZO thin films are amorphous, smooth (R_RMS < 0.4 nm), conductive (σ ∼ 3000 Ω⁻¹ · cm⁻¹), and transparent in the visible (T_Vis > 90%). Furthermore, the amorphous IZO thin films demonstrate remarkable functional and structural stability with respect to heating up to 600 °C in either air or argon. Hence, though not completely understood at present, these amorphous materials constitute a new class of fundamentally interesting and technologically important high performance transparent conductors.     

Hole Transport Bilayer Structure for Quasi‐2D Perovskite Based Blue Light‐Emitting Diodes with High Brightness and Good Spectral Stability

Substantial achievements have been made in green and red perovskite light emitting diodes (PeLEDs) recently. However, blue PeLEDs still lag behind with much lower performances. One of the main reasons is the mass undesirable nonradiative recombination at interfaces and within the perovskite films. In this work, an efficient hole transport bi‐layer structure composed of PSSNa and NiO_x is demonstrated to simultaneously inhibit the nonradiative decays between NiO_x and perovskite films by reducing NiO_x surface defects and improving quasi‐2D perovskite thin film quality by minimizing its pin‐holes and reducing the film roughness. The results show that the dipole feature of PSSNa improves the hole transportation and thus PeLED performances. Moreover, by introducing KBr into the perovskite, its film quality improves and trap states reduce. Eventually, the blue PeLEDs is achieved with a very low turn‐on voltage of 3.31 V accompanied with an external quantum efficiency of 1.45% and a remarkable luminance of 4359 cd m^‐2. With further optimization of the perovskite precursor concentration, the highest luminance reaches 5737 cd m^‐2, which represents the brightest blue PeLEDs reported to date as far as it is known. Furthermore, the devices also show better spectral stability and operation lifetime as compared to other blue PeLEDs.     

Substrate‐Dependent Spin–Orbit Coupling in Hybrid Perovskite Thin Films

Solution‐processing hybrid metal halide perovskites are promising materials for developing flexible thin‐film devices. This work reports the substrate effects on the spin–orbit coupling (SOC) in perovskite films through thermal expansion under thermal annealing. X‐ray diffraction (XRD) measurements show that using a flexible polyethylene naphthalate (PEN) substrate introduces a smaller mechanical strain in perovskite MAPbI_3?xCl_x films, as compared to conventional glass substrates. Interestingly, the linear/circular photoexcitation‐modulated photocurrent studies find that decreasing mechanical strain gives rise to a weaker orbit–orbit interaction toward decreasing the SOC in the MAPbI_3?xCl_x films prepared on flexible PEN substrates relative to rigid glass substrates. Simultaneously, decreasing the mechanical strain causes a reduction in the internal magnetic parameter inside the MAPbI_3?xCl_x films, providing further evidence to show that introducing mechanical strain can affect the SOC in hybrid perovskite films upon using flexible substrates toward developing flexible perovskite thin‐film devices. Furthermore, thermal admittance spectroscopy indicates that the trap states are increased in the perovskite films prepared on flexible PEN substrates as compared to glass substrates. Consequently, PEN and rigid glass substrates lead to shorter and longer photoluminescence lifetimes, respectively. Clearly, these findings provide an insightful understanding on substrate effects on optoelectronic properties in flexible perovskite thin‐film devices.     

LED用石墨烯复合透明电极厚度组合的仿真与优化

为降低石墨烯(Gr)透明电极与p-GaN之间的肖特基势垒与接触电阻,进行了将银、金、镍和铂四种金属或氧化镍作为中间层引入它们两者之间的尝试。使用有限元方法模拟研究了Gr与金属或氧化镍的不同厚度组合对LED的光、热和电特性的影响。发现:透明导电层的透光率和LED芯片的表面温度均随石墨烯和金属或氧化镍厚度的增加而降低;1.5nm的Ag、Ni、Pt,1nm Au或1nm的NiO_x分别与3层(3L)Gr复合时为优化厚度组合,其中,1.5nm Ni/3L Gr为最佳Gr/金属复合透明电极。     

High‐Performance Quantum‐Dot Light‐Emitting Diodes Using NiOx Hole‐Injection Layers with a High and Stable Work Function

Solution‐processed oxide thin films are actively pursued as hole‐injection layers (HILs) in quantum‐dot light‐emitting diodes (QLEDs), aiming to improve operational stability. However, device performance is largely limited by inefficient hole injection at the interfaces of the oxide HILs and high‐ionization‐potential organic hole‐transporting layers. Solution‐processed NiO_x films with a high and stable work function of ≈5.7 eV achieved by a simple and facile surface‐modification strategy are presented. QLEDs based on the surface‐modified NiO_x HILs show driving voltages of 2.1 and 3.3 V to reach 1000 and 10 000 cd m^?2, respectively, both of which are the lowest among all solution‐processed LEDs and vacuum‐deposited OLEDs. The device exhibits a T₉₅ operational lifetime of ≈2500 h at an initial brightness of 1000 cd m^?2, meeting the commercialization requirements for display applications. The results highlight the potential of solution‐processed oxide HILs for achieving efficient‐driven and long‐lifetime QLEDs.     

Bifunctional Nickel Phosphide Nanocatalysts Supported on Carbon Fiber Paper for Highly Efficient and Stable Overall Water Splitting

Self‐supported electrodes comprising carbon fiber paper (CP) integrated with bifunctional nickel phosphide (Ni‐P) electrocatalysts are fabricated by electrodeposition of Ni on functionalized CP, followed by a convenient one‐step phosphorization treatment in phosphorus vapor at 500 °C. The as‐fabricated CP@Ni‐P electrode exhibits excellent electrocatalytic performance toward hydrogen evolution in both acidic and alkaline solutions, with only small overpotentials of 162 and 250 mV, respectively, attaining a cathodic current density of 100 mA cm^?2. Furthermore, the CP@Ni‐P electrode also exhibits superior catalytic performance toward oxygen evolution reaction (OER). An exceptionally high OER current of 50.4 mA cm^?2 is achieved at an overpotential of 0.3 V in 1.0 m KOH. The electrode can sustain 10 mA cm^?2 for 180 h with only negligible degradation, showing outstanding durability. Detailed microstructural and compositional studies reveal that upon OER in alkaline solution the surface Ni‐P is transformed to NiO covered with a thin Ni(OH)_x layer, forming a Ni‐P/NiO/Ni(OH)_x heterojunction, which presumably enhances the electrocatalytic performance for OER. Given the well‐defined bifunctionality, a full alkaline electrolyzer is constructed using two identical CP@Ni‐P electrodes as cathode and anode, respectively, which can realize overall water splitting with efficiency as high as 91.0% at 10 mA cm^?2 for 100 h.     

20.7% efficient ion‐implanted large area n‐type front junction silicon solar cells with rear point contacts formed by laser opening and physical vapor deposition

In this work, we report on ion‐implanted, high‐efficiency n‐type silicon solar cells fabricated on large area pseudosquare Czochralski wafers. The sputtering of aluminum (Al) via physical vapor deposition (PVD) in combination with a laser‐patterned dielectric stack was used on the rear side to produce front junction cells with an implanted boron emitter and a phosphorus back surface field. Front and back surface passivation was achieved by thin thermally grown oxide during the implant anneal. Both front and back oxides were capped with SiN_x, followed by screen‐printed metal grid formation on the front side. An ultraviolet laser was used to selectively ablate the SiO₂/SiN_x passivation stack on the back to form the pattern for metal–Si contact. The laser pulse energy had to be optimized to fully open the SiO₂/SiN_x passivation layers, without inducing appreciable damage or defects on the surface of the n⁺ back surface field layer. It was also found that a low temperature annealing for less than 3 min after PVD Al provided an excellent charge collecting contact on the back. In order to obtain high fill factor of ~80%, an in situ plasma etching in an inert ambient prior to PVD was found to be essential for etching the native oxide formed in the rear vias during the front contact firing. Finally, through optimization of the size and pitch of the rear point contacts, an efficiency of 20.7% was achieved for the large area n‐type passivated emitter, rear totally diffused cell. Copyright © 2014 John Wiley & Sons, Ltd.     

Printable,Transparent, and Flexible Touch Panels Working in Sunlight and Moist Environments

The ongoing revolution of touch‐based user interfaces sets new requirements for touch panel technologies, including the need to operate in a wide range of environments. Such touch panels need to endure moisture and sunlight. Moreover, they often need to be curved or flexible. Thus, there is a need for new technologies suitable, for example, for home appliances used in the kitchen or the bathroom, automotive applications, and e‐paper. In this work, the development of transparent and flexible touch panels for moist environments is reported. A piezoelectric polymer, poly(vinylidene difluoride) (PVDF), is used as a functional substrate material. Transparent electrodes are fabricated on both sides of a PVDF film using a graphene‐based ink and spray coating. The excellent performance of the touch panels is demonstrated in moist and underwater conditions. Also, the transparent device shows very small pyroelectric response to radiative heating in comparison to a non‐transparent device. Solution processable electrode materials in combination with functional substrates allow the low‐cost and high‐throughput manufacturing of touch panels using printing technologies.     

NiOX/MoO3 Bi‐Layers as Efficient Hole Extraction Contacts in Organic Solar Cells

The electronic structure of a bi‐layer hole extraction contact consisting of nickel oxide (NiO_x) and molybdenum trioxide (MoO₃) is determined via ultraviolet and X‐ray photoemission spectroscopy. The bi‐layer presents ideal energetics for the extraction of holes and suppression of carrier recombination at the interface. The application of the NiO_x/MoO₃ bi‐layer as the anode of organic bulk heterojunction solar cells based on PCDTBT/PC₇₁BM leads to improved device performance, which is explained by an intricate charge transfer process across the interface.     

Automated,Ultra‐Fast Laser‐Drilling of Nanometer Scale Pores and Nanopore Arrays in Aqueous Solutions

The ability to quickly and reliably fabricate nanoscale pore arrays in ultra‐thin membranes such as silicon nitride (Si_xN) is extremely important for the growing field of nanopore biosensing. Laser‐based etching of thin Si_xN membranes immersed in aqueous solutions has recently been demonstrated as a method to produce stable functional pores. Herein, the principal mechanism governing material etching and pore formation using light is investigated. It is found that the process is extremely sensitive to the relative content of Si over N atoms in the amorphous membrane, produced by chemical vapor deposition. Commonly, Si_xN membranes are made to be Si‐rich to increase their mechanical stability, which substantially reduces the material's bandgap and increases the density of Si‐dangling bonds. Hence, even minimal batch‐to‐batch variation may lead to remarkably different etch rates. It is shown that higher Si content results in orders of magnitude faster etching rates. This rate is further accelerated in an alkaline environment allowing on‐demand controlled nanopore formation in about 10 s time even at low laser radiation intensities. These results highlight that photoactivation of the Si_xN by the incident beam is critical to the chemical etching process and can be used to readily produce nanopore arrays at any specific location.     

Wide‐Range‐Tunable p‐Type Conductivity of Transparent CuI1−xBrx Alloy

Transparent p‐type semiconductors with wide‐range tunability of the hole density are rare. Developing such materials is a challenge in the field of transparent electronics that utilize invisible electric circuits. In this paper, a CuI–CuBr alloy (CuI_1?xBr_x) is proposed as a hole‐density‐tunable p‐type transparent semiconductor that can be fabricated at room temperature. First‐principles calculations predict that the acceptor state originating from copper vacancies in CuBr is deeper than that in CuI, leading to the hypothesis that the hole density in CuI_1?xBr_x can be tuned over a wide range by varying x between 0 and 1. The experimental results support this hypothesis. The hole density in CuI_1?xBr_x polycrystalline alloy layers can be tuned by over three orders of magnitude (10¹⁷–10²⁰ cm^?3) by varying x. In other words, the p‐type conductivity of the CuI_1?xBr_x alloy shows metallic and semiconducting properties. Such alloy layers can be prepared at room temperature without sacrificing transparency. Furthermore, CuI_1?xBr_x forms transparent p–n diodes with n‐type amorphous In–Ga–Zn–O layers, and these diodes have satisfactory rectification performance. Therefore, CuI_1?xBr_x alloy is an excellent p‐type transparent semiconductor for which the p‐type conductivity can be tailored in a wide range.     

3D Micromolding of Arrayed Waveguide Gratings on Upconversion Luminescent Layers for Flexible Transparent Displays without Mirrors,Electrodes, and Electric Circuits

A new technique for the fabrication of arrayed waveguide gratings on upconversion luminescent layers for flexible transparent displays is reported. Ho³⁺‐ and Yb³⁺‐codoped NaYF₄ nanoparticles are synthesized by hydrothermal techniques. Transparent films consisting of two transparent polymers on the NaYF₄ nanoparticle films exhibit mechanical flexibility and high transparence in visible region. Patterned NaYF₄ nanoparticle films are fabricated by calcination‐free micromolding in capillaries. Arrayed waveguide gratings consisting of the two transparent polymers are formed on the patterned NaYF₄ nanoparticle films by micromolding in capillaries. Green and red luminescence is observed from the upconversion luminescent layers of the NaYF₄ nanoparticle films in the arrayed waveguide gratings under excitation at 980 nm laser light. Arrayed waveguide gratings on the upconversion luminescent layers are fabricated with Er³⁺‐doped NaYF₄ nanoparticles which can convert two photons at 850 and 1500 nm into single photon at 550 nm. These results demonstrate that flexible transparent displays can be fabricated by constructing arrayed waveguide gratings on upconversion luminescent layers, which can operate in nonprojection mode without mirrors, transparent electrodes, and electric circuits.     

Chemical Control of Correlated Metals as Transparent Conductors

Correlated metallic transition metal oxides offer a route to thin film transparent conductors that is distinct from the degenerate doping of broadband wide gap semiconductors. In a correlated metal transparent conductor, interelectron repulsion shifts the plasma frequency out of the visible region to enhance optical transmission, while the high carrier density of a metal retains sufficient conductivity. By exploiting control of the filling, position, and width of the bands derived from the B site transition metal in ABO₃ perovskite oxide films, it is shown that pulsed laser deposition‐grown films of cubic SrMoO₃ and orthorhombic CaMoO₃ based on the second transition series cation 4d² Mo⁴⁺ have superior transparent conductor properties to those of the first transition series 3d¹ V⁴⁺‐based SrVO₃. The increased carrier concentration offered by the greater bandfilling in the molybdates gives higher conductivity while retaining sufficient correlation to keep the plasma edge below the visible region. The reduced binding energy of the n=4 frontier orbitals in the second transition series materials shifts the energies of oxide 2p to metal nd transitions into the near‐ultraviolet to enhance visible transparency. The A site size‐driven rotation of MoO₆ octahedra in CaMoO₃ optimizes the balance between plasma frequency and conductivity for transparent conductor performance.