Performance Of Flexible Devices Research Articles

Rubrene/CuInP2S6 organic/inorganic heterojunctions for ferroelectric organic transistor memory devices

Ferroelectric organic field-effect transistor (Fe-OFET) memory devices exhibit low power consumption, low cost and good flexibility, which are indispensable to next generation flexible and wearable memory devices. However, up until the present, the ferroelectric materials used in Fe-OFETs have been limited to ferroelectric polymers, i.e. poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)], and suffer from large surface roughness and high-risk of depolarization. This work integrates a new two-dimensional CuInP2S6 crystal into Fe-OFET, which can introduce excellent ferroelectric property due to its single crystalline smoothness and noncentrosymmetric crystal structure. Meanwhile, the high-mobility rubrene crystal is selected as the channel material to construct rubrene/CuInP2S6 organic/inorganic van der Waals heterojunctions. Associated with synergetic effect of single-crystalline nature of the heterojunction and atomically flat/defect-free interface, the memory devices possess a high programming speed of 0.5 s and long retention time of 104 s with a current ratio larger than 103. Furthermore, the performance of flexible devices is also demonstrated, including a programming/erase cycle of 1000 with a current on/off ratio approaching 103, data retention time of 104 s with a current on/off ratio of 103 and a current on/off ratio maintained at 102 even after 100 bending cycles under a bending radius of 25 mm, which are qualified for memory buffer usage or short-term data storage especially when they are integrated with other flexible electronics. The proposed configuration of memory transistors using organic/inorganic heterojunctions provides a rational design of device structure toward flexible Fe-OFET non-volatile memory applications.

Mixed-Dimensional MXene-Based Composite Electrodes Enable Mechanically Stable and Efficient Flexible Perovskite Light-Emitting Diodes.

Significant advancements in perovskite light-emitting diodes (PeLEDs) based on ITO glass substrates have been realized in recent years, yet the overall performance of flexible devices still lags far behind, mainly being ascribed to the high surface roughness and poor optoelectronic properties of flexible electrodes. Here, we report efficient and robust flexible PeLEDs based on a mixed-dimensional (0D-1D-2D-3D) composite electrode consisting of 0D Ag nanoparticles (AgNPs)/1D Ag nanowires (AgNWs)/2D MXene/3D poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). Our designed MXene-based electrodes combine the advantages of facile formation of a film of low-dimensional materials and excellent optical and electrical properties of metal, inorganic, and organic semiconductors, which endow the electrodes with high electrical/thermal conductivity, flexibility, a smooth surface, and good transmittance. Consequently, the resulting flexible PeLEDs (without a light-coupling structure) demonstrate a record external quantum efficiency of 16.5%, a high luminance of close to 50000 cd/m2, a large emitting area of 8 cm2, and significantly enhanced mechanical stability.

Study of indium tin oxide films deposited on colorless polyimide film by magnetron sputtering

Polyimide attracted most interest for its high performance as a flexible substrate of touch panels. Experimental models were built to evaluate production feasibility. The solution with monomer was coated on a glass substrate, cured at 250 °C to form a solid colorless polyimide (CPI) film. Then, a supporting layer with silicon oxide and a conducting layer with indium tin oxide (ITO) were deposited on the CPI film by magnetron sputtering. Composite with a CPI substrate and ITO patterns were prepared via a series of procedures. Test results indicated ITO film thickness and sheet resistance could be controlled by adjusting sputtering power, and the film showed smooth curves on the contour line chart. The transmittance of CPI/ITO film composite was up to 80%. The bending durability of the film was evaluated by two-point bending method, and it could be significantly improved by shielding the ITO pattern with ultraviolet cured resin as an external buffer layer. Samples with buffer layers passed 64,000 cycles bend test, and the minimum fracture radius reached 4 mm. The increase of ITO film thickness had no significant negative impact on the performance of flexible devices.

Molybdenum Disulfide Nanosheets Aligned Vertically on Carbonized Silk Fabric as Smart Textile for Wearable Pressure-Sensing and Energy Devices.

Flexible electronics have gained considerable research concern due to their wide prospect for health monitoring, soft robotics, and artificial intelligence, wherein flexible pressure sensors are necessary components of wearable devices. It is well known that the synergistic functions and multiscale structures of hybrid materials exert tremendous effects on the performance of flexible devices. Herein, inspired by the unique structure of the faceplate of sunflowers, we construct a hierarchical structure by in situ grown vertically aligned molybdenum disulfide (MoS2) nanosheets on carbonized silk fabric (MoS2/CSilk), which is applied as the sensing material in flexible pressure sensors. The MoS2/CSilk sensor displayed high sensitivity and good stability. We demonstrated its applications in monitoring subtle physiology signals, such as pulse wave and voice vibrations. In addition, it served as electrodes in lithium-ion batteries. The MoS2/CSilk electrode delivered ultrahigh first-cycle discharge and charge capacities of 2895 and 1594 mA h g-1, respectively. The MoS2/CSilk electrode exhibited a high capacity of 810 mA h g-1 with a CE close to 100% even after 300 cycles, suggesting good stability. The excellent overall performances are ascribed to the unique structure of the MoS2/CSilk and the synergistic effect of CSilk and MoS2. The concept and strategy of this work can be extended to the design and fabrication of other multifunctional devices.

Assembly Strategy and Performance Evaluation of Flexible Thermoelectric Devices.

Although organic and composite thermoelectric (TE) materials have witnessed explosive developments in the past five years, the research of flexible TE devices is rather limited. In particular, their assembly strategies and device performance reported in the literature cannot be directly compared, due to a variety of deviances including p‐ and n‐type component materials, shape and dimensions of p‐n flexible films, and applied temperature gradient (ΔT). Here, three types of assembly strategies for flexible TE devices, that is, serial, folding, and stacking, are compared by fixing the corresponding experimental parameters. Furthermore, a convenient and general method to evaluate the flexible device performance (FDP) is put forward, that is, FDP = PmaxmΔTN, where the maximum output power (P max) is divided by product mass (m), ΔT, and pair number of p‐n couples (N). The FDPs for the present serial, folding, and stacking devices are 11.13, 8.87, and 0.05 nW g−1 K−1, respectively, confirming that the serial configuration is the best among the three strategies for flexible device fabrication. The preliminary evaluation method proposed herein will pave the way for a design strategy of flexible TE devices and speed up their applications in waste‐heat harvesting, e‐skin, wearable electronics, etc.

High-Resolution Resistless Nanopatterning on Polymer and Flexible Substrates for Plasmonic Biosensing Using Stencil Masks

The development of nanoscale lithographic methods on polymer materials is a key requirement to improve the spatial resolution and performance of flexible devices. Here, we report the fabrication of metallic nanostructures down to 20 and 50 nm in size on polymer materials such as polyimide, parylene, SU-8, and PDMS substrates without any resist processing using stencil lithography. Metallic nanodot array analysis of their localized surface plasmon spectra is included. We demonstrate plasmon resonance detection of biotin and streptavidin using a PDMS flexible film with gold nanodots. We also demonstrate the fabrication of metallic nanowires on polyimide substrates with their electrical characteristics showing an ohmic behavior. These results demonstrate high-resolution nanopatterning and device nanofabrication capability of stencil lithography on polymer and flexible substrates.