to a bending radius of less than 1 cm without reaching its fracture limit (≈1% strain). [ 10,11 ] Electronics fabricated on soft polymeric substrate can conform over curvilinear surfaces and form the building blocks for wearable electronics. Powering these devices while maintaining the fl exibility and form-factor of the device is a challenge. Towards this goal there have been numerous attempt to develop thin, fl exible and stretchable supercapacitors, [12][13][14][15][16][17] energy harvesters, [18][19][20][21][22] and batteries. [ 14, Due to their high energy and power density, fl exible rechargeable batteries are an essential part of a power module. [ 53 ] Commercially available batteries are typically rigid due to their packaging and thick electrode stack. Flexible batteries require that all of the key components (current collector, active layer, separator, packaging) be bendable. Such devices are currently fabricated by using a thin conductive layer supported on a non-conductive substrate as a current collector, on which a thin active layer (20-60 µm) is printed. The areal capacities of fl exible lithium-ion batteries have been comparatively low (0.05-0.20 mAh cm −2 vs 1-2 mAh cm −2 for traditional systems) as the active layers are printed thin to reduce the electrode degradation during fl exing and the inactive layers associated with supporting the current collectors increase the thickness of the battery. [ 26,35,41,44,54 ] Here we demonstrate a fl exible rechargeable lithium-ion battery with an areal capacity of ≈1 mAh cm -2 . We use lithium cobalt oxide (LCO) and lithium titanate oxide (LTO) as the positive (cathode) and negative (anode) electrodes, to form a battery with a nominal potential of ≈2.5 V. [55][56][57] The fl exible battery with CNT as the current collector had neglible drop in capacity after electrochemically cycling the battery for 450 cycles at C/2 rate. The areal capacity (mAh cm −2 ) of the battery was increased by printing active layers as thick as 150 µm while improving their mechanical property by embedding the active layers inside a fi brous support. The fi brous membrane binds the active layers while carrying the stress associated with fl exing. The reinforced electrodes have a tensile strength of ≈5.5-7.0 MPa, an order of magnitude higher than conventional non-fl exible electrodes, making the electrode resistant to cracking and mechanical fatigue. The battery maintained capacity during electrochemical cycles under fl ex conditions and after undergoing repeated fl exing cycles. ElS was used to analyze the structural changes Early demonstrations of wearable devices have driven interest in fl exible lithium-ion batteries. Previous demonstrations of fl exible lithium-ion batteries trade off between low areal capacity, poor mechanical fl exibility and/or high thickness of inactive components. Here, a reinforced electrode design is used to support the active layers of the battery and a freestanding carbon nanotube (CNT) layer is used as the current collector. The supported architecture h...
Discovery of structure−property interrelations in organic electrochemical transistors (OECTs) is limited by the small number of high-performing semiconducting polymer families that are electrochemically active in aqueous media. Currently, state-of-the-art polymers often come with processability drawbacks; aqueous-processable polymers, such as poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PE-DOT:PSS) require insulating cross-linkers to protect against dissolution in aqueous electrolyte, while glycolated polymers frequently exhibit marginal solubility in both organic and aqueous solvents. Herein, we show that the carboxylic acidfunctionalized conjugated polymer poly [3-(4-carboxypropyl)thiophene] (P3CPT) can be processed from a water-soluble precursor, yet requires no additives to yield solvent-resistant OECTs which exhibit electroactivity in aqueous and organic electrolytes. Devices fabricated with P3CPT exhibit unipolar p-channel operation in accumulation mode, with maximum transconductance of 26 ± 2 mS on interdigitated electrodes and competitive volumetric capacitance (C*) of 150 ± 18 F-cm −3 , which rank amongst the highest for conjugated polymers with ionic side chain moieties. This work paves the way for future use of carboxylic acid functionalization to modify existing p-and n-channel backbones to yield highly competitive and processable OECT active materials.
Organic electrochemical transistors (OECTs) have been revived as potentially versatile platforms for bioelectronic applications due to their high transconductance, direct ionic-electronic coupling, and unique form factors. This perceived applicability to...
Inducing the self-assembly of π-conjugated polymers into semicrystalline aggregates has been a topic of substantial interest in the field of organic electronics and is typically achieved using energy-intensive solution processing or postfilm deposition methods. Here, we demonstrate the ability of bioderived cellulose nanocrystals (CNCs) to act as structure-directing agents for the conjugated semiconducting polymer, poly(3-hexylthiophene) (P3HT). CNCs were grafted with polystyrene, P3HT or poly(N-isopropylacrylamide), and subsequently blended with P3HT in solution to study the effect on conjugated polymer self-assembly. The presence of polymer-grafted CNCs resulted in an increase in P3HT semicrystalline aggregate formation, the degree of which depended on the surface free energy of the grafted polymer. The time-dependent P3HT aggregation was characterized by UV–vis spectroscopy, and the resulting data was fit to the Avrami crystallization model. The surface energies of each additive were calculated via contact angle measurements and were used to elucidate the mechanism of P3HT aggregation in these blended systems. P3HT aggregation was enhanced by unfavorable polymer–polymer interactions at the CNC surface, and spatial confinement effects that were imposed by phase separation. Finally, films were cast from the P3HT/CNC solutions and their electronic performance was characterized by organic field-effect transistor device measurements. Films containing polymer-grafted CNCs exhibited higher charge-carrier mobilities, in some cases, up to a 6-fold increase. These bioderived particles constituted a significant volume fraction of the deposited P3HT thin films with an increase in performance, showing promise as a method for reducing costs and improving the sustainability of organic electronics.
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