Solution‑Processed Transparent Conducting Electrodes for Flexible Organic Solar Cells with 16.61% Efficiency

Nonfullerene organic solar cells(OSCs)have achieved breakthrough with pushing the efficiency exceeding 17%.While this shed light on OSC commercialization,high-performance flexible OSCs should be pursued through solution manufacturing.Herein,we report a solution-processed flexible OSC based on a transparent conducting PEDOT:PSS anode doped with trifluoromethanesulfonic acid(CF3SO3H).Through a low-concentration and low-temperature CF3SO3H doping,the conducting polymer anodes exhibited a main sheet resistance of 35Ωsq−1(minimum value:32Ωsq−1),a raised work function(≈5.0 eV),a superior wettability,and a high electrical stability.The high work function minimized the energy level mismatch among the anodes,hole-transporting layers and electron-donors of the active layers,thereby leading to an enhanced carrier extraction.The solution-processed flexible OSCs yielded a record-high efficiency of 16.41%(maximum value:16.61%).Besides,the flexible OSCs afforded the 1000 cyclic bending tests at the radius of 1.5 mm and the long-time thermal treatments at 85°C,demonstrating a high flexibility and a good thermal stability.

Biomimic Vein-Like Transparent Conducting Electrodes with Low Sheet Resistance and Metal Consumption

In this contribution,inspired by the excellent resource management and material transport function of leaf veins,the electrical transport function of metallized leaf veins is mimicked from the material transport function of the vein networks.By electroless copper plating on real leaf vein networks with copper thickness of only several hundred nanometre up to several micrometre,certain leaf veins can be converted to transparent conductive electrodes with an ultralow sheet resistance 100 times lower than that of state-of-the-art indium tin oxide thin films,combined with a broadband optical transmission of above 80%in the UV–VIS–IR range.Additionally,the resource efficiency of the vein-like electrode is characterized by the small amount of material needed to build up the networks and the low copper consumption during metallization.In particular,the high current density transport capability of the electrode of>6000 A cm^−2 was demonstrated.These superior properties of the vein-like structures inspire the design of high-performance transparent conductive electrodes without using critical materials and may significantly reduce the Ag consumption down to<10%of the current level for mass production of solar cells and will contribute greatly to the electrode for high power density concentrator solar cells,high power density Li-ion batteries,and supercapacitors.

A Mini Review: Can Graphene Be a Novel Material for Perovskite Solar Cell Applications?

Perovskite solar cells(PSCs) have raised research interest in scientific community because their power conversion efficiency is comparable to that of traditional commercial solar cells(i.e., amorphous Si, GaAs,and CdTe). Apart from that, PSCs are lightweight, are flexible, and have low production costs. Recently, graphene has been used as a novel material for PSC applications due to its excellent optical, electrical, and mechanical properties. The hydrophobic nature of graphene surface can provide protection against air moisture from the surrounding medium, which can improve the lifetime of devices. Herein, we review recent developments in the use of graphene for PSC applications as a conductive electrode,carrier transporting material, and stabilizer material. By exploring the application of graphene in PSCs, a new class of strategies can be developed to improve the device performance and stability before it can be commercialized in the photovoltaic market in the near future.

Transparent Supercapacitors: From Optical Theories to Optoelectronics Applications

The ever-increasing demand for smart optoelectronics spurs the relentless pursuit of transparent wireless devices as a game-changing technology that can provide unseen visual information behind the electronics.To enable successful operation of the transparent wireless devices,their power sources should be highly transparent in addition to acquiring reliable electrochemical performance.Among various transparent power sources,supercapacitors(SCs)have been extensively investigated as a promising candidate due to their exceptional cyclability,power capability,material diversity,and scalable/low-cost processability.Herein,we describe current status and challenges of transparent SCs,with a focus on their core materials,performance advancements,and integration with application devices.A special attention is devoted to transparent conductive electrodes(TCEs)which act as a keyenabling component in the transparent SCs.Based on fundamental understanding of optical theories and operating principles of transparent materials,we comprehensively discuss materials chemistry,structural design,and fabrication techniques of TCEs.In addition,noteworthy progresses of transparent SCs are briefly overviewed in terms of their architectural design,opto-electrochemical performance,flexibility,form factors,and integration compatibility with transparent flexible/wearable devices of interest.Finally,development direction and outlook of transparent SCs are explored along with their viable roles in future application fields.

Highly ordered graphene architectures by duplicating melamine sponges as a three-dimensional deformation- tolerant electrode

In this study, macroscopic graphene-wrapped melamine foams （MF-G） were fabricated by an MF-templated layer-by-layer （LBL） assembly using graphene oxide as building blocks, followed by solution-processed reduction. By concisely duplicating sponge-like, highly ordered three-dimensional architectures from MF, the resulting MF-G with an interconnected graphene-based scaffold and tunable nanostructure was explored as compressible, robust electrodes for efficient energy storage. A thin layer of pseudocapacitive polypyrrole （PPy） was then attached and uniformly coated on MF-G, resulting in a well-defined core- double-shell configuration of the MF-G-PPy ternary composite sponges. The as-assembled devices exhibited enhancement of supercapacitor performance, with a high specific capacitance of 427 F·g-1 under a compressive strain of 75% and an excellent cycling stability with only 18% degradation after 5,000 charge- discharge cycles. Besides, the MF-G-PPy electrode maintained stable capacitance up to 100 compression-release cycles, with a compressive strain of 75%. These encouraging results thus provide a new route towards the low-cost, easily scalable fabrication of lightweight and deformation-tolerant electrodes.

Printable inorganic nanomaterials for flexible transparent electrodes:from synthesis to application

Printed and flexible electronics are definitely promising cutting-edge electronic technologies of the future. They offer a wide-variety of applications such as flexible circuits, flexible displays, flexible solar cells, skinlike pressure sensors, and radio frequency identification tags in our daily life. As the most-fundamental component of electronics, electrodes are made of conductive materials that play a key role in flexible and printed electronic devices. In this review, various inorganic conductive materials and strategies for obtaining highly conductive and uniform electrodes are demonstrated. Applications of printed electrodes fabricated via these strategies are also described. Nevertheless, there are a number of challenges yet to overcome to optimize the processing and performance of printed electrodes.

Graphene-based flexible and wearable electronics

Graphene with an exceptional combination of electronic, optical and outstanding mechanical features has been proved to lead a completely different kind of 2-D electronics. The most exciting feature of graphene is its ultra-thin thickness, that can be conformally contacted to any kind of rough surface without losing much of its transparency and conductivity. Graphene has been explored demonstrating various prototype flexible electronic applications, however, its potentiality has been proven wherever transparent conductive electrodes（TCEs） are needed in a flexible, stretchable format. Graphene-based TCEs in flexible electronic applications showed greatly superior performance over their conventionally available competitor indium tin oxide（ITO）. Moreover, enormous applications have been emerging, especially in wearable devices that can be potentially used in our daily life as well as in biomedical areas. However, the production of high-quality, defect-free large area graphene is still a challenge and the main hurdle in the commercialization of flexible and wearable products. The objective of the present review paper is to summarize the progress made so far in graphene-based flexible and wearable applications. The current developments including challenges and future perspectives arc also highlighted.

Applications of transition-metal sulfides in the cathodes of lithium-sulfur batteries

Lithium-sulfur(Li-S)batteries are considered as one of the most promising candidates for next-generation energy storage systems with high energy density and reliable performance.However,the commercial applications of lithium-sulfur batteries is hindered by several shortcomings like the poor conductivity of sulfur and its reaction products,and the loss of active materials owing to the diffusion of lithium polysulfides(LiPSs)into the electrolyte.Hence,the effective restraining of the LiPSs and the promotion of the sluggish conversion are highly demanded to fulfill the potential of lithium-sulfur batteries.Here,we summarize the applications of transition-metal sulfides(TMSs)in the cathodes over recent years and demonstrate the unique advantages they possess to realize reliable long-life lithium-sulfur batteries.

Resistive switching characteristics of Ni/HfO_2/Pt ReRAM

This study investigated the resistive switching characteristics of the Ni/HfCVPt structure for nonvolatile memory application.The Ni/HfO_2/Pt device showed bipolar resistive switching（RS） without a forming process, and the formation and rupture of conducting filaments are responsible for the resistive switching phenomenon.In addition,the device showed some excellent memory performances,including a large on/off ratio（〉 3×10~5）,very good data retention（〉 10~3 s @ 200℃） and uniformity of switching parameters.Considering these results,the Ni/HfO_2/Pt device has the potential for nonvolatile memory applications.

Regulating silver nanowire size enables efficient photoelectric conversion

The increasing demand for the state-of-the-art transparent conductive electrodes has received great interest in synthesizing silver nanowires(AgNWs)with a uniform diameter that exhibit excellent conductance,transparency,flexibility and mechanical ductility.Herein,we report the controllable synthesis of ultrathin AgNWs with high aspect ratio via a polyol-assisted process.The diameter of AgNWs can be continuously modulated from 20 to 80 nm by simply adjusting the aging time.The selfassembled films fabricated by using AgNWs with a diameter of 20 nm as building blocks enable an excellent performance and show a sheet resistance of^30Ω/sq and an optical transmittance of 94%.In addition,such nanowire-based conductive films can keep the excellent flexibility and resistance after bending 10,000 cycles.Similarly,the intelligent dimming films prepared by this AgNW films also have excellent flexibility and stability.