Kan Li

Wearable energy-dense and power-dense supercapacitor yarns enabled by scalable graphene-metallic textile composite electrodes

One-dimensional flexible supercapacitor yarns are of considerable interest for future wearable electronics. The bottleneck in this field is how to develop devices of high energy and power density, by using economically viable materials and scalable fabrication technologies. Here we report a hierarchical graphene–metallic textile composite electrode concept to address this challenge. The hierarchical composite electrodes consist of low-cost graphene sheets immobilized on the surface of Ni-coated cotton yarns, which are fabricated by highly scalable electroless deposition of Ni and electrochemical deposition of graphene on commercial cotton yarns. Remarkably, the volumetric energy density and power density of the all solid-state supercapacitor yarn made of one pair of these composite electrodes are 6.1 mWh cm−3 and 1,400 mW cm−3, respectively. In addition, this SC yarn is lightweight, highly flexible, strong, durable in life cycle and bending fatigue tests, and integratable into various wearable electronic devices.

Salt-assisted high-throughput synthesis of single- and few-layer transition metal dichalcogenides and their application in organic solar cells

Transition metal dichalcogenides (TMDs) such as MoS 2 , MoSe 2 , WS 2 and WSe 2 have the common chemical formula of MX 2 , where the transition metal M is sandwiched between two layers of chalcogen X. Although atoms in-plane are strongly linked by covalent bonds, the adjacent layers outof-plane are weakly held together by van der Waals force, which allows the exfoliation of bulk TMDs into atomically thin, singleand few-layer two dimensional (2D) materials. Compared with zero-bandgap graphene, these TMD 2D materials possess obvious semiconductor bandgaps, [ 1 ] which show remarkable advantages for a wide range of applications including fi eld effect transistors, [ 2–4 ] sensors, [ 2 ] energy storage devices, [ 5–8 ] and optoelectronics. [ 9–11 ]

Full‐Solution Processed Flexible Organic Solar Cells Using Low‐Cost Printable Copper Electrodes

Full-solution-processed flexible organic solar cells (OSCs) are fabricated using low-cost and high-quality printable Cu electrodes, which achieve a power conversion efficiency as high as 2.77% and show remarkable stability upon 1000 bending cycles. This device performance is thought to be the best among all full-solution-processed OSCs reported in the literature using the same active materials. This printed Cu electrode is promising for application in roll-to-roll fabrication of flexible OSCs.

Bio-inspired chemical fabrication of stretchable transparent electrodes

Stretchable and transparent electrodes are fabricated by chemical deposition of metal thin films on natural veins of leaves at ambient conditions. These vein-based transparent electrodes show excellent electro-optical property (0.9 Ω sq(-1) at 83% T) even at 50% tensile strains, ideal for flexible and stretchable optoelectronic devices.

Photoreactive and Metal‐Platable Copolymer Inks for High‐Throughput, Room‐Temperature Printing of Flexible Metal Electrodes for Thin‐Film Electronics

Photoreactive and metal-platable copolymer inks are reported for the first time to allow high-throughput printing of high-performance flexible electrodes at room temperature. This new copolymer ink accommodates various types of printing technologies, such as soft lithography molding, screen printing, and inkjet printing. Electronic devices including resistors, sensors, solar cells, and thin-film transistors fabricated with these printed electrodes show excellent electrical performance and mechanical flexibility.

Versatile biomimetic haze films for efficiency enhancement of photovoltaic devices

A low-cost biomimetic haze film (BHF) is fabricated by one-step replica molding of the petal texture of yellow roses with polydimethylsiloxane (PDMS). The BHF possesses very high haze transmission (75%) and ultrahigh diffusion transmittance (97%), superior anti-reflection ability, remarkable enhancement of light absorption at small incidence angles, and superb resistance to strong acids. When attached on top of the glass side of photovoltaic cells, the BHF significantly elongates the photon pathway in the active layer and enhances the light harvesting of the solar devices. As a result, the power conversion efficiency of Si solar cells, organic solar cells (OSCs) and perovskite solar cells (PSCs) is respectively improved remarkably by 6.8%, 10% and 15%. In addition, >65% of the photocurrent is maintained even at an extremely small light incidence angle (10°), which equals more than 2.7 times the efficiency enhancement of the solar cell without the BHF.

Water-borne foldable polymer solar cells: one-step transferring free-standing polymer films onto woven fabric electrodes

In this paper, foldable polymer solar cells (PSCs) were fabricated on woven fabrics by a free-standing, wet transfer method. A new concept of ‘water-borne PSCs’ was proposed to show the ultra-stability of organic photoactive materials under extremely humid conditions and even in water. There were a series of particular designs in the fabrication process: (1) flexible conductive woven fabrics were fabricated by polymer-assisted metal deposition; (2) a free-standing, wet transfer method was applied to laminate an active layer and a top electrode onto the as-prepared fabric electrodes simultaneously; (3) an interface modification layer was formed by diffusing a dilute polymer solution through fibers. The best device performances were achieved for the PSC on fabric A with a power conversion efficiency almost equal to those of the conventional devices using the same active materials, which would enrich wearable electronics by utilizing more comfortable and flexible un-modified woven fabrics.

Large-area patterning of metal nanostructures by dip-pen nanodisplacement lithography for optical applications

Au nanostructures are remarkably important in a wide variety of fields for decades. The fabrication of Au nanostructures typically requires time-consuming and expensive electron-beam lithography (EBL) that operates in vacuum. To address this challenge, this paper reports the development of massive dip-pen nanodisplacement lithography (DNL) as a desktop fabrication tool, which allows high-throughput and rational design of arbitrary Au nanopatterns in ambient condition. Large-area (1 cm2 ) and uniform (<10% variation) Au nanostructures as small as 70 nm are readily fabricated, with a throughput 100-fold higher than that of conventional EBL. As a proof-of-concept of the applications in the opitcal field, we fabricate discrete Au nanorod arrays that show significant plasmonic resonance in the visible range, and interconnected Au nanomeshes that are used for transparent conductive electrode of solar cells.

Printed light-trapping nanorelief Cu electrodes for full-solution-processed flexible organic solar cells

Light-trapping nanorelief metal electrodes have been proven to be an effective approach to improve the absorption performance of flexible organic solar cells (FOSCs). These nanorelief electrodes have been made by conventional vacuum deposition techniques, which are difficult to integrate with roll-to-roll fabrication processes. To address this challenge, this paper reports, for the first time, the fabrication of highly conductive nanorelief Cu electrodes on the flexible substrates through solution printing and polymer-assisted metal deposition at room temperature in the air. FOSCs made with these printed nanorelief Cu electrodes possess not only much improved power conversion efficiency, by 13.5%, but also significant enhancement in flexibility when compared with those made with flat Cu electrodes. Because of the low material and fabrication cost, these printed nanorelief Cu electrodes show great promise in roll-to-roll fabrication of FOSCs in the future.

Interfacial engineering of printable bottom back metal electrodes for full-solution processed flexible organic solar cells

Printing of metal bottom back electrodes of flexible organic solar cells (FOSCs) at low temperature is of great significance to realize the full-solution fabrication technology. However, this has been difficult to achieve because often the interfacial properties of those printed electrodes, including conductivity, roughness, work function, optical and mechanical flexibility, cannot meet the device requirement at the same time. In this work, we fabricate printed Ag and Cu bottom back cathodes by a low-temperature solution technique named polymer-assisted metal deposition (PAMD) on flexible PET substrates. Branched polyethylenimine (PEI) and ZnO thin films are used as the interface modification layers (IMLs) of these cathodes. Detailed experimental studies on the electrical, mechanical, and morphological properties, and simulation study on the optical properties of these IMLs are carried out to understand and optimize the interface of printed cathodes. We demonstrate that the highest power conversion efficiency over 3.0% can be achieved from a full-solution processed OFSC with the device structure being PAMD-Ag/PEI/P3HT:PC61BM/PH1000. This device also acquires remarkable stability upon repeating bending tests.