High-Performance Organic Electrochemical Transistors Achieved by Optimizing Structural and Energetic Ordering of Diketopyrrolopyrrole-Based Polymers.

For optimizing steady-state performance in organic electrochemical transistors (OECTs), both molecular design and structural alignment approaches must work in tandem to minimize energetic and microstructural disorders in polymeric mixed ionic-electronic conductor films. Herein, a series of poly(diketopyrrolopyrrole)s bearing various lengths of aliphatic-glycol hybrid side chains (PDPP-mEG; m = 2-5) is developed to achieve high-performance p-type OECTs. PDPP-4EG polymer with the optimized length of side chains exhibits excellent crystallinity owing to enhanced lamellar and backbone interactions. Furthermore, the improved structural ordering in PDPP-4EG films significantly decreases trap state density and energetic disorder. Consequently, PDPP-4EG-based OECT devices produce a mobility-volumetric capacitance product ([µC*]) of 702 F V-1 cm-1 s-1 and a hole mobility of 6.49 ± 0.60 cm2 V-1 s-1 . Finally, for achieving the optimal structural ordering along the OECT channel direction, a floating film transfer method is employed to reinforce the unidirectional orientation of polymer chains, leading to a substantially increased figure-of-merit [µC*] to over 800 F V-1 cm-1 s-1 . The research demonstrates the importance of side chain engineering of polymeric mixed ionic-electronic conductors in conjunction with their anisotropic microstructural optimization to maximize OECT characteristics.

A Mediator-Free Multi-Ply Biofuel Cell Using an Interfacial Assembly between Hydrophilic Enzymes and Hydrophobic Conductive Oxide Nanoparticles with Pointed Apexes.

Biofuel cells (BFCs) based on enzymatic electrodes hold great promise as power sources for biomedical devices. However, their practical use is hindered by low electron transfer efficiency and poor operational stability of enzymatic electrodes. Here, a novel mediator-free multi-ply BFC that overcomes these limitations and exhibits both substantially high-power output and long-term operational stability is presented. The approach involves the utilization of interfacial interaction-induced assembly between hydrophilic glucose oxidase (GOx) and hydrophobic conductive indium tin oxide nanoparticles (ITO NPs) with distinctive shapes, along with a multi-ply electrode system. For the preparation of the anode, GOx and oleylamine-stabilized ITO NPs with bipod/tripod type are covalently assembled onto the host fiber electrode composed of multi-walled carbon nanotubes and gold (Au) NPs. Remarkably, despite the contrasting hydrophilic and hydrophobic properties, this interfacial assembly approach allows for the formation of nanoblended GOx/ITO NP film, enabling efficient electron transfer within the anode. Additionally, the cathode is prepared by sputtering Pt onto the host electrode. Furthermore, the multi-ply fiber electrode system exhibits unprecedented high-power output (≈10.4 mW cm-2 ) and excellent operational stability (2.1 mW cm-2 , ≈49% after 60 days of continuous operation). The approach can provide a basis for the development of high-performance BFCs.

Fibril-Type Textile Electrodes Enabling Extremely High Areal Capacity through Pseudocapacitive Electroplating onto Chalcogenide Nanoparticle-Encapsulated Fibrils.

Effective incorporation of conductive and energy storage materials into 3D porous textiles plays a pivotal role in developing and designing high-performance energy storage devices. Here, a fibril-type textile pseudocapacitor electrode with outstanding capacity, good rate capability, and excellent mechanical stability through controlled interfacial interaction-induced electroplating is reported. First, tetraoctylammonium bromide-stabilized copper sulfide nanoparticles (TOABr-CuS NPs) are uniformly assembled onto cotton textiles. This approach converts insulating textiles to conductive textiles preserving their intrinsically porous structure with an extremely large surface area. For the preparation of textile current collector with bulk metal-like electrical conductivity, Ni is additionally electroplated onto the CuS NP-assembled textiles (i.e., Ni-EPT). Furthermore, a pseudocapacitive NiCo-layered double hydroxide (LDH) layer is subsequently electroplated onto Ni-EPT for the cathode. The formed NiCo-LDH electroplated textiles (i.e., NiCo-EPT) exhibit a high areal capacitance of 12.2 F cm-2 (at 10 mA cm-2 ), good rate performance, and excellent cycling stability. Particularly, the areal capacity of NiCo-EPT can be further increased through their subsequent stacking. The 3-stack NiCo-EPT delivers an unprecedentedly high areal capacitance of 28.8 F cm-2 (at 30 mA cm-2 ), which outperforms those of textile-based pseudocapacitor electrodes reported to date.

A Layer-by-Layer Assembly Route to Electroplated Fibril-Based 3D Porous Current Collectors for Energy Storage Devices.

Electrical conductivity, mechanical flexibility, and large electroactive surface areas are the most important factors in determining the performance of various flexible electrodes in energy storage devices. Herein, a layer-by-layer (LbL) assembly-induced metal electrodeposition approach is introduced to prepare a variety of highly porous 3D-current collectors with high flexibility, metallic conductivity, and large surface area. In this study, a few metal nanoparticle (NP) layers are LbL-assembled onto insulating paper for the preparation of conductive paper. Subsequent Ni electroplating of the metal NP-coated substrates reduces the sheet resistance from ≈103 to <0.1 Ω sq-1 while maintaining the porous structure of the pristine paper. Particularly, this approach is completely compatible with commercial electroplating processes, and thus can be directly extended to electroplating applications using a variety of other metals in addition to Ni. After depositing high-energy MnO NPs onto Ni-electroplated papers, the areal capacitance increases from 68 to 811 mF cm-2 as the mass loading of MnO NPs increases from 0.16 to 4.31 mg cm-2 . When metal NPs are periodically LbL-assembled with the MnO NPs, the areal capacitance increases to 1710 mF cm-2 .

Charge-Transfer-Modulated Transparent Supercapacitor Using Multidentate Molecular Linker and Conductive Transparent Nanoparticle Assembly.

One of the most critical issues in preparing high-performance transparent supercapacitors (TSCs) is to overcome the trade-off between areal capacitance and optical transmittance as well as that between areal capacitance and rate capability. Herein, we introduce a TSC with high areal capacitance, fast rate capability, and good optical transparency by minimizing the charge transfer resistance between pseudocapacitive nanoparticles (NPs) using molecular linker- and conductive NP-mediated layer-by-layer (LbL) assembly. For this study, bulky ligand-stabilized manganese oxide (MnO) and indium tin oxide (ITO) NP multilayers are LbL-assembled through a ligand exchange reaction between native ligands and small multidentate linkers (tricarballylic acid). The introduced molecular linker substantially decreases the separation distance between neighboring NPs, thereby reducing the contact resistance of electrodes. Moreover, the periodic insertion of ITO NPs into the MnO NP-based electrodes can lower the charge transfer resistance without a meaningful loss of transmittance, which can significantly improve the areal capacitance. The areal capacitances of the ITO NP-free electrode and the ITO NP-incorporated electrode are 24.6 mF cm-2 (at 61.6% transmittance) and 40.5 mF cm-2 (at 60.8%), respectively, which outperforms state of the art TSCs. Furthermore, we demonstrate a flexible symmetric solid-state TSC that exhibits scalable areal capacitance and optical transmittance.

Highly Conductive Paper/Textile Electrodes Using Ligand Exchange Reaction-Induced in Situ Metallic Fusion.

Here, we report that metal nanoparticle (NP)-based paper/textile electrodes with bulk metallic conductivity can be prepared via organic linker-modulated ligand exchange reaction and in situ room-temperature metallic fusion without additional chemical or thermal treatments. For this study, amine-functionalized molecule linkers instead of bulky polymer linkers were layer-by-layer (LbL)-assembled with tetraoctylammonium bromide (TOABr)-stabilized Au NPs to form Au NP multilayered films. By conversion of the amine groups of the organic molecule linkers from -NH3+ to the -NH2 groups, as well as by a decrease in the size of the organic linkers, the LbL-assembled Au NPs became highly interconnected and fused during LbL deposition, resulting in Au NP multilayers with adjustable conductivity and transport behavior. These phenomena were also predicted by a density functional theory investigation for the model system. Particularly, LbL-assembled films composed of TOABr-Au NPs and diethylenetriamine ( Mw: ∼104) exhibited a remarkable electrical conductivity of 2.2 × 105 S·cm-1, which was higher than the electrical conductivity of the metal NP-based electrodes as well as the carbon material-based electrodes reported to date. Furthermore, based on our approach, a variety of insulating flexible papers and textiles were successfully converted into real metal-like paper and textile electrodes with high flexibility preserving their highly porous structure. This approach can provide a basis for further improving and controlling the electrical properties of flexible electrodes through the control of organic linkers.