ABSTRACT
High-performance foldable metal-coated ionic polymer-metal nanocomposites (IPMNCs) with crack minimized electrode are desired for wearable electronics, energy harvesting devices, tactile sensors, structural health monitors, humidity sensors, and supercapacitor devices. However, the IPMNC shows the cracked structure that seriously decreases the performance of IPMNCs for sensors and actuators applications. To overcome the issue of the cracked metal electrode, here we propose a metal-coated hierarchical porous structured IPMNC via minimizing the cracks in the Platinum (Pt) electrode using attachment of poly(2-acrylamide-2-methyl-1-propane-sulfonic acid) (PAMPS) in poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE))/polyvinylpyrrolidone (PVP) blend. The crack-minimized Pt electrode deposition on PAMPS attached P(VDF-TrFE)/PVP-based IPMNCs showed enhanced electrical and sensing signals compared to the Nafion, ionic liquid, and polystyrene sulphonic acid-based IPMNCs. The developed IPMNCs with an optimized composition depict stable sensing signals up to 10,000 cycles. The hierarchical porous structure and the crack-minimized metal electrode on the P(VDF-TrFE)/PVP/PAMPS IPMNC can be utilized in various attractive applications such as energy harvesting, wearable electronics, humidity sensor, pulse, braille recognition, catalyst supports, bio-interfacing, and sensors.
Subject(s)
Nanocomposites , Wearable Electronic Devices , Electrodes , Polymers , PorosityABSTRACT
The low-temperature processability of molecular ferroelectric (FE) crystals makes them a potential alternative for perovskite oxide-based ferroelectric thin films. Quinuclidinium perrhenate (HQReO4) is one such molecular FE crystal that exhibits ferroelectricity when crystallized in an intermediate temperature phase (ITP). However, bulk HQReO4 crystals exhibit ferroelectricity only for a narrow temperature window (22 K), above and below which the polar phase transforms to a non-FE phase. The FE phase or ITP of HQReO4 should be stabilized in a much wider temperature range for practical applications. Here, to stabilize the FE phase (ITP) in a wider temperature range, highly oriented thin films of HQReO4 were prepared using a simple solution process. A slow evaporation method was adapted for drying the HQReO4 thin films to control the morphology and the temperature window. The temperature window of the intermediate temperature FE phase was successfully widened up to 35 K by merely varying the film drying temperature between 333 and 353 K. The strategy of stabilizing the FE phase in a wider temperature range can be adapted to other molecular FE materials to realize flexible electronic devices.
ABSTRACT
Understanding the mechanism of thermal energy transport in a single nanotube (NT) is essential for successfully engineering nanostructured conducting polymers to apply to thermoelectrics or flexible electronic devices. We report the characterization of the in-plane thermal energy transport in a single poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) NT via direct measurement of the in-plane thermal conductivity (κ). We also demonstrate that the in-plane κ of PEDOT:PSS NT can be tuned within the range of 0.19 to 1.92 W·m-1·K-1 merely by changing the solvent used to treat the NTs in the post-fabrication stage. The in-plane thermal energy transport in a pristine NT, with its low in-plane κ, is primarily due to phonons; in a sulfuric acid-treated NT however, significant electronic contributions lead to a high in-plane κ. The present study will contribute to understanding the mechanism of thermal energy transport in highly disordered structures, such as conducting polymers, and to designing highly efficient polymer-based devices in which in-plane κ plays a pivotal role in determining the energy conversion efficiency.
ABSTRACT
Phosphor-converted white light-emitting diodes (pc-WLEDs) are excellent energy-efficient light sources for artificial lighting applications. One goal of artificial lighting is to make objects/images look natural - as they look under the sunlight. The ability of a light source to accurately render the natural color of an object is gauged by the parameter - color rendering index (CRI). A conventional pc-WLED has an average CRI ~ 80, which is very low for accurate color reproduction. To utilize the pc-WLEDs for artificial lighting applications, all the CRI points (R1 - R15) should be above 95. However, there is a trade-off between CRI and luminous efficacy (LER), and it is challenging to increase both CRI and LER. Herein we propose a novel LED package (PKG) design to achieve CRI points ≥95 and efficiency ~100 lm/W by introducing two blue LEDs and a UV LED in combination with green and red phosphors. The silicone encapsulant, the current through the LEDs, and the green/red phosphor ratio were optimized for achieving high CRI and LER. Our re-designed LED PKG will find applications in stadium lighting as well as for ultra-high-definition television production where high CRI points are required for the artificial light source.
ABSTRACT
Among the conducting polymers, poly(3,4-ethylene dioxythiophene):polystyrene sulfonate (PEDOT:PSS) has been extensively investigated for organic thermoelectric device applications owing to its high electrical conductivity (σ), flexibility and easy processability. The thermoelectric (TE) power factor - a factor that determines the efficiency of a thermoelectric material, is very critical in developing high-efficiency thermoelectric devices. The TE power factor of PEDOT:PSS requires further enhancement in realizing efficient organic TE devices. Recently, we have reported a layer-by-layer deposition technique to deposit PEDOT:PSS and poly aniline-camphor sulfonic acid (PANI-CSA) forming a PEDOT:PSS/PANI-CSA multilayer (ML) thin film structure with an enhanced thermoelectric power factor up to 49 µW m-1 K-1. However, there exist several ambiguities regarding the parameters that control the TE power factor in (ML) thin films. In order to identify the parameters that control the TE power factor of ML thin films, PEDOT:PSS/PANI-CSA ML thin films have been deposited by varying the deposition conditions such as spin speed, the number of layers, solvent treatment, and thickness of each layer. A thermoelectric power factor up to 325 µW m-1 K-1 is achieved by properly optimizing the spin speed, number of layers, and the thickness of each layer in ML thin films. The enhanced thermoelectric power factor is the result of multiple factors such as stretching of PEDOT chains, structural conformation change from benzoid to quinoid, and excess PSS removal from the top of the PEDOT:PSS layer through solvent treatment and at the PEDOT:PSS/PANI-CSA interface. Our study provides the basis for realizing an enhanced thermoelectric power factor of organic thermoelectric multilayer structures consisting of ultra-thin polymer thin films similar to inorganic superlattices having 2D confinement.
ABSTRACT
In ferroelectric (FE) polymer-semiconducting polymer blend based organic resistive random access memory devices (ReRAM), the carriers are injected into the semiconductor region of the blend because of the polarization originated internal electric field in the FE polymer. A higher concentration of semiconducting polymer in the FE polymer-semiconducting polymer blends usually generate a high leakage current and degrades the FE characteristics of the FE polymer resulting in a high OFF current and consequently a low ON/OFF ratio. In order to achieve a high ON/OFF ratio in the FE polymer/semiconducting polymer blends, the FE properties of the FE polymer should be preserved. In this study, organic ReRAMs based on ferroelectric poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) and ZnO nanoparticle (NPs) blends exhibiting bipolar resistive switching and a high ON/OFF ratio were realized using a low-cost solution process. Unlike conventional ferroelectric polymer-semiconducting polymer blend systems where FE characteristics are suppressed in ReRAMs, our Au/P(VDF-TrFE)_ZnO NPs/n++Si devices retain the FE characteristics of the P(VDF-TrFE) polymers. Our devices switch between bi-stable resistance states via the ferroelectric-assisted filamentary conduction mechanism. Based on ex situ transmission electron microscopy and elemental mapping analyses, we found that the resistive switching occurs through the formation of conduction paths consisting of Zn-rich/F-deficient regions. The device fabricated at a blend ratio of 20 wt% ZnO NPs in P(VDF-TrFE) matrix exhibited optimal stable resistive switching behavior with an ON/OFF ratio of up to 2 × 107 and a retention time of 104 s.
ABSTRACT
The long-term instability of the presently available best commercial phosphor-converted light-emitting diodes (pcLEDs) is the most serious obstacle for the realization of low-cost and energy-saving lighting applications. Emission from pcLEDs starts to degrade after approximately 200 h of operation because of thermal degradation of the phosphors. We propose a new strategy to overcome this thermal degradation problem of phosphors by wrapping the phosphor particles with reduced graphene oxide (rGO). Through the rGO wrapping, we have succeeded in controlling the thermal degradation of phosphors and improving the stability of fabricated pcLEDs. We have fabricated pcLEDs with long-term stability that maintain nearly 98% of their initial luminescence emission intensity even after 800 h of continuous operation at 85 °C and 85% relative humidity. The pcLEDs fabricated using SrBaSi2O2N2:Eu2+ phosphor particles wrapped with reduced graphene oxide are thermally stable because of enhanced heat dissipation that prevents the ionization of Eu2+ to Eu3+. We believe that this technique can be applied to other rare-earth doped phosphors for the realization of highly efficient and stable white LEDs.
