Charge Retention Research Articles

Charge transport characteristic and charge stability enhancement mechanism of polyimide aerogel as an ultralight weight electret

In this study, polyimide aerogel (PIA) is applied as an ultralight-weight and thermally stable electret material, meanwhile its charge transport characteristic and charge stability enhancement mechanism are investigated. It is found that PIA can exhibit excellent electret properties at 120 °C after corona charging at room temperature, and its charge stability acquires further promotion after charging at elevated temperatures or heat treatment, which far exceeds conventional polyimide-based electrets. Further research indicates that the outstanding charge retention characteristics of PIA originate from the enhanced local defect density, fast retrapping effect, weakened internal electric field by dipole polarization, and prolonged conduction path, which are inextricably linked to its porous structure. In addition, the high gas breakdown strength in the pores of PIA effectively limits the breakdown induced conductivity, thereby ensuring high space charge density and large piezoelectric response of PIA electrets. Considering the extremely low density and inherently excellent properties of polyimide substances, PIA may have promising prospects as an electret in the lightweight sensing and energy conversion devices at elevated temperatures.

ASSESSMENT OF THE POSSIBILITY OF MODERNIZING A SPACE CHARGE LENS FOR FOCUSING BEAMS OF NEGATIVE HYDROGEN IONS DUE TO CONFINEMENT OF POSITIVE BACKGROUND IONS BY AN ALTERNATING ELECTRIC FIELD

The work is devoted to considering the possibility of improving the focusing properties of a space charge lens due to charge retention of positive ions by an electric field that varies both in time and along the axis of the system. Numerical calculations of motion trajectories of positive argon ion during interaction with an alternating electric field with oscillation frequencies in the range of 1...8 MHz and amplitude in the range of 1.5...6 kV were carried out. A significant increase in the residence time of positive argon ion in the overcompensated beam of negative hydrogen ions is shown, which indicates the possibility of significant influencing focusing charge in the lens for focusing beams of negative hydrogen ions.

Boosted Output Voltage of BiSbTe‐Based Thermoelectric Generators via Coupled Effect between Thermoelectric Carriers and Triboelectric Charges

AbstractThe present work demonstrates the very first approach to enhancing the output voltage of a thermoelectric generator by introducing highly charged polyimide‐based dielectrics. High charge density over 320 µC m−2 in C60‐containing block polyimide (PI‐b‐C60) having excellent charge retention characteristics is obtained through an ion injection process, attached at the cooling part of a thermoelectric generator consisting of Cu/p‐type BiSbTe/Au/Cr/SiO2/Si. This significantly increases the electric potential difference across the thermoelectric generator (TEG) from 4.2 to 8.2 mV at the temperature difference of 20 K, and this increase can be maintained over 1 day. Density functional theory studies support that the enhancement depends on the dielectric constant and the insulating properties of the dielectric. Finally, a TEG consisting of 81 p‐type BiSbTe legs with PI‐b‐C60 generates an output voltage of 0.632 V, and the charged energy of the 10 mF‐capacitor is boosted by 30 s. These results demonstrate the possibility of large‐area TEG fabrication without the need for modification of the TE materials by introducing a new mechanism which is based on the coupling effect between thermoelectric carriers and triboelectric charges.

Study on the triboelectric performance of porphyrin- and phthalocyanine-crosslinked enhanced fluorinated polyimide films for lateral sliding-mode triboelectric nanogenerator

• Two fluorinated polyimide films crosslinked by TAPP or TAPc were prepared. • The PI/TAPP and PI/TAPc films showed higher dielectric constant than neat PI. • The PI/TAPP and PI/TAPc exhibited smaller charge decay than neat PI in LS-TENGs. • The PI/TAPP and PI/TAPc showed higher friction coefficient stability than neat PI. In order to improve the charge retention, anti-decay ability and durability of traditional triboelectric materials in lateral sliding-mode triboelectric nanogenerators (LS-TENGs), two fluorinated polyimide films crosslinked by porphyrin tetra-amino phenyl porphyrin (TAPP) and tetra-amine phthalocyanine (TAPc) were synthesized, and their contact angles, dielectric properties, output performances and tribological properties were studied in detail. The results showed that the polyimide films crosslinked by TAPP (PI/TAPP) and TAPc (PI/TAPc) with lower surface energies had higher dielectric constants compared with neat PI and Kapton. In addition, TAPP and TAPc not only improved the electrical output with a small decay of charge density, but also reduced the wear of PI films during the whole triboelectrification process, which is attributed to the high permittivity and the crosslinked effect of PI with TAPP or TAPc. Thus, PI films with TAPP and TAPc hold great promise for dielectric research and LS-TENG applications.

Identification of complementary McLafferty rearrangement ions at m/z 222 and 224 of methylstearate using high-resolution electron ionization time-of-flight mass spectrometer

All fragment ions observed in high-resolution electron ionization (EI) mass spectra of methyl stearate have been completely classified into three different series, such as methyl ester (CnHmO2), aliphatic hydrocarbon (CnHm) and acylium (CnHmO) ions. From the EI mass spectra classified into aliphatic hydrocarbon series, complementary McLafferty rearrangement (compMcLR) ion at m/z 224 and complementary McLafferty rearrangement+1 (compMcLR+1) ion at m/z 222 were identified from the standpoints of notable intensity and rearrangement reactions. The fragmentation of the keto- and enol-form molecular ions M.+ was discussed on the basis of the sites of unpaired electron (radical) and positive charge, which were determined by the spin density evaluated by density functional theory (DFT). The structure of M.+ determined by DFT rationally indicated that the compMcLR and compMcLR+1 ions at m/z 224 and 222 are produced by charge migration, while the McLR and McLR+1 ions at m/z 74 and 75 are produced by charge retention. The difference in the peak abundance of m/z 74 and 224 ions were evaluated from the difference in the ionization energy of the corresponding neutral fragments, based on Stevenson's rule.

Multi-output AC/DC triboelectric generator with dual rectification

Triboelectric generators (TEGs) are state-of-the-art powering solutions for low-power Internet of Things (IoT) devices. TEGs convert periodic mechanical vibrations into cyclic charge flow between electrodes, establishing an alternating current (AC). AC output requires rectification prior to charging any load, creating additional circuitry and power requirements. In recent years, the focus has shifted towards developing direct current (DC) generators as potential direct powering solutions. In this work, a DC–TEG is realized using a novel topology involving mechanical switching between a pair of metal contacts. This switching is implemented in vertical contact-separation mode and therefore does not involve any significant friction between the electrodes and metal contacts, overcoming the major limitation of wear and tear in conventional mechanical switching DC–TEGs. The proposed device can obtain each half-cycle rectified output across distinct electrode pairs, which is crucial for conditioning the asymmetric output of the TEGs. An AC output can be simultaneously harvested between the pair of bottom electrodes. The complementary AC–DC outputs of this device can supply power to multiple loads at a time, or coupled together to produce an enhanced output. Placing two complementary TEG pairs adjacent to each other in this topology has the advantage of reducing the ambient electric field, which is critical in improving the charge retention capability of the TEG layers. The proposed device achieves peak instantaneous power of 1.05 μW for the DC output and 1.12 μW for the AC output across a 7 MΩ resistance. The applications of the device in driving commercial electronics, harvesting biomechanical energy, and as progressive alarming system are demonstrated. Due to its simple, flexible topology and AC-DC dual output, this device has the potential for powering multiple loads and applications in diverse scenarios.

Effects of Carboxyl Functionalized CNT on Electrochemical Behaviour of Polyluminol-CNT Composites

The effect of carboxyl groups on the redox activity of polyluminol-carbon nanotube composites was studied. Carboxyl groups were selected due to their known contributions toward surface wettability and pseudocapacitance while often present on naturally derived low-cost porous carbons. Density functional theory (DFT) predicted energetically favoured bonding and a significantly reduced band gap between the luminol and carboxylated graphene relative to that of bare graphene, suggesting improved charge storage for carboxylated carbon substrates. The prediction was validated using bare carbon nanotubes (CNTs) and carboxylated CNTs (COOH-CNTs) as the substrates for in situ chemical polymerized luminol (CpLum). Surface morphological studies showed a ca. 1.1 nm thick coating of CpLum on CNT (CpLum/CNT) and a ca. 1.3 nm on COOH-CNT (CpLum/COOH-CNT), while surface chemical analysis revealed ca. 10% nitrogen from CpLum on both CpLum/CNT and CpLum/COOH-CNT. However, with merely 4.4% of COOH functionalization, CpLum/COOH-CNT was able to store more charge (137.1 ± 17.1 C cm−3) relative to CpLum/CNT (86.1 ± 14.1 C cm−3) and had increased charge retention over 5000 cycles. The insights from these studies can be used to engineer the surface of carbons such as CNTs and ACs to improve the interfacial properties for redox active materials and composites.

Piezoelectric composites from sandwiched polydimethylsiloxane sponges

A novel elastomer-based composite material with enhanced piezoelectric performances is proposed in this paper, which is composed of the top and bottom polytetrafluoroethylene (PTFE) solid films with the middle PTFE nanoparticle–polydimethylsiloxane (PDMS) sponge layer. To enhance the charge retention capability of elastomers, PTFE nanoparticles are introduced to form PTFE–PDMS interfaces, which can trap charges with longevity. Besides, PTFE solid films take on the role of the charge blocking layers to further improve the piezoelectric performances. As a result, the PTFE–PDMS sandwich structure shows the advantages of remarkable sensitivity (1053 pC/N), high stability, and flexibility. After a 6 h of annealing treatment at the temperature of 100 °C, no significant deterioration of the piezoelectric properties can be observed, which reveals the great thermal stability of the sandwich structure. In addition, the sandwich structure can be immersed in water for 24 h without any loss of piezoelectric activity. Finally, the experiment of lighting one LED by hand pressing successfully demonstrates that the sandwich structure has good applicability in the field of energy harvesting. Considering the excellent electrical and mechanical features, the PTFE–PDMS sandwich structure has promising applications in sensing, energy harvesting, and actuation.

N-doped porous carbon from direct KOH activation of Victorian brown coal for high-rate energy storage performance

N-doped highly porous carbons (NHPCs) derived from Victorian brown coal (VBC) were prepared through direct KOH activation in the presence of urea as the N source. Different weight ratios of KOH (VBC-urea mixture: KOH=1:0, 1:1, 1:2, and 1:3) have been used to optimize the porosity of NHPCs. Benefiting from the synergistic effect of the high porosity and N doping, the synthesized material with a high specific surface area of 687 m2/g and the N content at ∼11 at% exhibited a high specific discharge capacity of 604.6 mAh/g at a current density of 0.1 A/g after 100 cycles and a high-rate performance of 245 mAh/g at 3 A/g. The developed material delivered a reversible capacity of 707.7 mAh/g at 0.05 A/g at the end of rate performance. The long-term cycling test performed at 1 A/g illustrates a stable and reversible capacity of 268 mAh/g after 1000 cycles with a coulombic efficiency of 100% and charge retention of 88%. The hierarchically porous carbon matrix with N doping can increase the Li+ diffusion efficiency and accelerate the charge transfer, thus leading to enhanced high-rate performance, superior reversibility, and high cyclic stability.

Design and development of novel ferrocene-containing carbon nanotube-butacene/graphene oxide nanocomposite for high-performance supercapacitor

Supercapacitors are critical for storing alternative energy and powering electrical systems or portable electronics. By combining carbon-based nanomaterials with redox-active materials such as ferrocene (Fc), it should be possible to improve energy and power densities. Here, carbon nanotube (CNT) was first incorporated into an Fc-containing polymer matrix under simple and mild conditions (room temperature). Then, the Fc-modified CNT was intercalated into graphene oxide layers (GO). The advantages of these novel electrode materials are the fast redox response of the as-prepared nanocomposites due to the presence of Fc and the durable stability of the nanocomposites due to the presence of carbon-based nanomaterials such as GO and CNT. The CNT-But/GO1:1 electrode exhibits a high specific capacity of 456 mAh g−1 at a current density of 2.5 A g−1 with excellent charge retention (96 % after 5000 GCD cycles). The symmetric cell was then successfully fabricated based on the CNT-But/GO1:1 nanocomposite. The fabricated cell exhibits high specific capacity (104 mAh g−1), excellent charge storage retention (91 %), and high energy and power densities of 94.5 Wh Kg−1, and 8370 W Kg−1, respectively.

Supercapacitive behavior of polyaniline-waste derived carbon-copper cobaltite based ternary composite

Polyaniline based ternary composites have demonstrated their transcendence in the recent past. This study reports on the synthesis of polyaniline/waste coconut shell derived activated carbon/copper cobaltite based ternary composite for supercapacitor applications. The XPS results confirmed the presence of C, N, O along with Cu and Co peaks. The electrochemical characterizations revealed an excellent specific capacitance of 613.52 Fg−1 and a specific energy density of 44.16 Wh kg−1. The prepared ternary composite offered an astonishingly low charge transfer resistance of 5.6 Ω. An outstanding charge retention capacity of 90.76 % was observed over 4000 cycles. An extended investigation of frequency response analysis was also performed to study the total admittance, capacitance, impedance, and phase of Z with frequency. The promising results were obtained due to the synergy between participating species.

All‐Printed Wearable Triboelectric Nanogenerator with Ultra‐Charged Electron Accumulation Polymers Based on MXene Nanoflakes

AbstractThe multilayer triboelectric nanogenerators (TENGs) are widely developed to enhance the output performance of device. However, these TENGs consisting of electron transfer, transport, trap layers toward a large volumetric charge density should be wearable and mass‐produced for commercialization. Thus, appropriate material selection in respective layers and fabrication method are crucial for the commercialization of multilayer TENG. This study presents all‐printed, sustainable wearable TENGs based on electron accumulation polymers (EAPs) with superior charge retention capability. The EAPs consisting of polytetrafluoroethylene (PTFE), carboxyl functionalized single‐walled carbon nanotubes (SWCNTs:COOH), and Ti3C2Tx (MXene) in a fluorinated polymer matrix, are used. Compared to the reference, the EAPs not only lead to approximately six times higher output performance (300 V and 40 µA) but also four times more sustainable charge retention capability (92%) for an hour. These are attributed to the three‐step electron‐trapping mechanism with electron transfer/transport from PTFE/SWCNT and electron trapping in MXene. In addition, TENGs with EAPs exhibit excellent mechanical stability and reliability with fascinating single‐electrode demonstrations. Finally, the TENG with EAPs can efficiently operate various portable electronics and pH monitoring systems with a pH sensor and a seven‐segment display in realistic scenarios.

(Digital Presentation) The Influence of Alkali Metal Cations on the Redox Processes of Copper Hexacyanoferrate in Rechargeable Aqueous Zinc-Ion Batteries

Rechargeable aqueous batteries are of high interest for future stationary grid-scale energy storage applications where high safety is needed (1). Copper hexacyanoferrate (CuHCF), a Prussian Blue Analogue (PBA) material, has recently gained interest as positive electrode for aqueous Zn-ion batteries (ZIBs) (2,3). Reversible Zn2+ ion insertion is facilitated by its open-framework with large channels that can host a variety of monovalent and divalent cations. Recent studies have shown that the charge compensation process takes place via Zn2+ ions swapping position between tunnel sites and vacancy sites (4).Among aqueous ZIBs, the Zn/CuHCF cell has attracted noticeable attention, as it can combine abundant and inexpensive materials with a good trade-off between capacity and performance. Zinc can supply a high capacity (820 mAh g-1), while CuHCF typically provides a moderate capacity of ca. 60-80 mAh g-1.However, it exhibits one of the highest operating voltages among PBA-type cathodes (1.7 V vs. Zn2+/Zn) and exhibits a cubic-type structure with wide channels. In comparison to many other materials, CuHCF undergoes minimal volume and structural changes during ion insertion/de-insertion, exhibits a high Coulombic efficiency of ca. 99%, and can be cycled at high rates without compromising the capacity, which makes it an interesting material for high-power applications.Nevertheless, CuHCF suffers from capacity fade owing to instabilities of Cu, which we have demonstrated in details in a recent investigation (5). In that study, we also highlighted that the characteristic aging effect, observed as a growth of a two-phase plateau in the charge/discharge profiles and associated with capacity loss (6), can be explained by Cu dissolution and thereby a displacement of the two Cu2+/Cu+ and Fe3+/Fe2+ redox-couples (5). Alkali metal cations (Li+, Na+, K+, Rb+, Cs+) have recently been shown to impact the capacity of the Zn/CuHCF cell along with a modulation of the characteristic redox-features in the voltammetric profiles (7). Cycling of large cations (Rb+, Cs+) was linked to a reduced capacity, while moderately sized cations (K+) resulted in optimal capacity and higher charge retention. This has motivated us to investigate the effect of the alkali metal cations on the charge compensation and redox processes in CuHCF in more detail in this study.By employing X-ray photoelectron spectroscopy (XPS), we show that small cations (Li+) have negligible impact on the Cu and Fe redox processes, while moderately sized cations (K+) suppress Cu redox and enhance Fe redox, which optimizes the capacity and improves the cycling stability, accordingly. Large cations (Cs+), on the other hand, prevent reversible redox and lock both metal centers in their most reduced states (Cu+, Fe2+), which impedes the charge compensation process and reduces the capacity. Our study unveils how alkali metal cations influence the performance of ZIBs by affecting the synergy of the Cu2+/Cu+ and Fe3+/Fe2+ redox couples in CuHCF and demonstrates how tailoring the electrolyte formulation can conveniently impact the capacity retention of this compound in PBA-type ZIBs. Figure 1. The aqueous Zn/CuHCF cell. (a) Schematic figures illustrating the structure of the CuHCF cathode and its wide channels that can host ions. (b) Cyclic voltammograms (CV) of the Zn/CuHCF cell in pure 1M ZnSO4 and in presence of 0.2 M alkali metal cation additives (Li+, K+, Cs+). (c) X-ray photoelectron spectroscopy (XPS) showing the Cu 2p3/2 and Fe 2p3/2 spectra of the same electrolytes as shown in (b). References J. Shin, and J. W. Choi, Advanced Energy Materials, 10, 2001386–2001386 (2020).R. Trócoli, and F. La Mantia, ChemSusChem, 8, 481–485 (2015).Z. Jia, B. Wang, and Y. Wang, Materials Chemistry and Physics, 149–150, 601–606 (2015).V. Renman, D. O. Ojwang, M. Valvo, C. P. Gómez, T. Gustafsson, G. Svensson, Journal of Power Sources, 369, 146–153 (2017).M. Görlin, D. O., Ojwang, M.-T. Lee, V. Renman, C.-W. Tai, and M. Valvo, ACS Applied Materials & Interfaces, 13, 59962–59974 (2021)R. Trócoli, G. Kasiri, and F. La Mantia, Journal of Power Sources, 400, 167–171 (2018).D. Phadke, R. Mysyk, and M. Anouti, Journal of Energy Chemistry 40, 31–38 (2020). Figure 1

Smart polydimethylsiloxane sponges with high piezoelectric responses

AbstractIn recent years, soft and stretchable electrets have drawn considerable attention for their wide applications in energy harvesters, sensors, and actuators. However, existing electrets struggle to attain both longevity and stretchability (softness), which means charge retention capability and stretchability (softness) of electrets conflict. In this article, one novel soft and stretchable electret (PPSE) with great electromechanical performance is demonstrated. The PPSE is composed of a polydimethylsiloxane (PDMS) sponge and polytetrafluoroethylene (PTFE) particles. The uniformly distributed pores obtained by the sugar leaching method inside the PPSE can not only accumulate macroscopic dipoles but also provide great stretchability, flexibility, and softness for the material. The resulting PPSE has a large value up to 477 pC/N and great charge stability. Moreover, by the virtue of stretchability and softness, it can output electric signals from twisting, bending, and other mechanical interactions without breaking apart. With these great performances, PPSE will potentially enable applications for actuation, sensing, and energy harvesting.

Interfacial Effect Boosts the Performance of All‐Polymer Ionic Thermoelectric Supercapacitors

AbstractIonic thermoelectric supercapacitors (ITESCs) have recently been developed for converting low‐grade waste heat into electricity. Until now, most reports of ITESCs have been focused on the development of electrolytes, which then have been combined with a specific electrode material. Here, it is demonstrated that the electrode is not only critical for electrical energy storage but also greatly affects the effective thermopower (Seff) of an ITESC. It is shown that the same ion gel can generate a positive thermopower in an ITESC when using gold nanowire (AuNW) electrodes, while generating a negative thermopower when using poly(3,4‐ethylendioxythiophene):polystyrene sulfonate (PEDOT:PSS) electrodes. The achieved negative sign of the Seff could be attributed to the Donnan exclusive effect from the polyanions in the PEDOT:PSS electrodes. After examining the thermovoltage, capacitance and charge retention performance of the two ITESCs, it is concluded that PEDOT:PSS is superior to AuNWs as electrodes. Moreover, a new strategy of constructing an ionic thermopile of multiple p‐ and n‐type legs is achieved by series‐connecting these legs with same electrolyte but different electrodes. Using interfacial effect at ionic gels/PEDOT:PSS electrode interface, an enhanced thermoelectric effect in ITESCs is obtained, which constitutes one more step towards efficient, low‐cost, flexible, and printable ionic thermoelectric modules for energy harvesting.

Memory Properties of Zr-Doped ZrO2 MOS-like Capacitor

The high-k-based MOS-like capacitors are a promising approach for the domain of non-volatile memory devices, which currently is limited by SiO2 technology and cannot face the rapid downsizing of the electronic device trend. In this paper, we prepare MOS-like trilayer memory structures based on high-k ZrO2 by magnetron sputtering, with a 5% and a 10% concentrations of Zr in the Zr–ZrO2 floating gate layer. For crystallization of the memory structure, rapid thermal annealing at different temperatures between 500 °C and 700 °C was performed. Additionally, Al electrodes were deposited in a top-down configuration. High-resolution transmission electron microscopy reveals that ZrO2 has a polycrystalline–columnar crystallization and a tetragonal crystalline structure, which was confirmed by X-ray diffraction measurements. It is shown that the tetragonal phase is stabilized during the crystallization by the fast diffusion of oxygen atoms. The capacitance–voltage characteristics show that the widest memory window (ΔV = 2.23 V) was obtained for samples with 10% Zr annealed at 700 °C for 4 min. The charge retention characteristics show a capacitance decrease of 36% after 10 years.

Recent Advances in Materials for Supercapacitors

The fluctuating availability of energy sources has encouraged the development of energy storage devices such as supercapacitors. Supercapacitors are good electrochemical energy storage materials that have demonstrated promising efficiencies in diverse applications. They are able to release high power at low energy operating conditions. In this article, we introduce basic knowledge on supercapacitors, their different classifications, and their relevance to material development. We outline the progress made on diverse materials adopted in improving the performance, charge retention, and stability of supercapacitive materials. Finally, we discuss the different methods utilised in obtaining highly stable supercapacitors.

Charge Storage and Reliability Characteristics of Nonvolatile Memory Capacitors with HfO2/Al2O3-Based Charge Trapping Layers.

Flash memories are the preferred choice for data storage in portable gadgets. The charge trapping nonvolatile flash memories are the main contender to replace standard floating gate technology. In this work, we investigate metal/blocking oxide/high-k charge trapping layer/tunnel oxide/Si (MOHOS) structures from the viewpoint of their application as memory cells in charge trapping flash memories. Two different stacks, HfO2/Al2O3 nanolaminates and Al-doped HfO2, are used as the charge trapping layer, and SiO2 (of different thickness) or Al2O3 is used as the tunneling oxide. The charge trapping and memory windows, and retention and endurance characteristics are studied to assess the charge storage ability of memory cells. The influence of post-deposition oxygen annealing on the memory characteristics is also studied. The results reveal that these characteristics are most strongly affected by post-deposition oxygen annealing and the type and thickness of tunneling oxide. The stacks before annealing and the 3.5 nm SiO2 tunneling oxide have favorable charge trapping and retention properties, but their endurance is compromised because of the high electric field vulnerability. Rapid thermal annealing (RTA) in O2 significantly increases the electron trapping (hence, the memory window) in the stacks; however, it deteriorates their retention properties, most likely due to the interfacial reaction between the tunneling oxide and the charge trapping layer. The O2 annealing also enhances the high electric field susceptibility of the stacks, which results in better endurance. The results strongly imply that the origin of electron and hole traps is different—the hole traps are most likely related to HfO2, while electron traps are related to Al2O3. These findings could serve as a useful guide for further optimization of MOHOS structures as memory cells in NVM.

Tuning Ambipolarity of the Conjugated Polymer Channel Layers of Floating-Gate Free Transistors: From Volatile Memories to Artificial Synapses.

Three-terminal synaptic transistor has drawn significant research interests for neuromorphic computation due to its advantage of facile device integrability. Lately, bulk-heterojunction-based synaptic transistors with bipolar modulation areproposed to exempt the use of an additional floating gate. However, the actual correlation between the channel's ambipolarity, memory characteristic, and synaptic behavior for a floating-gate free transistor has not been investigated yet. Herein, by studying five diketopyrrolopyrrole-benzotriazole dual-acceptor random conjugated polymers, a clear correlation among the hole/electron ratio, the memory retention characteristic, and the synaptic behavior for the polymer channel layer in a floating-gate free transistor is described. It reveals that the polymers with balanced ambipolarity possess better charge trapping capabilities and larger memory windows; however, the high ambipolarity results in higher volatility of the memory characteristics, namely poor memory retention capability. In contrast, the polymer with a reduced ambipolarity possesses an enhanced memory retention capability despite showing a reduced memory window. It isfurther manifested that this enhanced charge retention capability enables the device to present artificial synaptic characteristics. Theresults highlight the importance of the channel's ambipolarity of floating-gate free transistors on the resultant volatile memory characteristics and synaptic behaviors.

High-k Lead-Free Ferroelectric KNN as an Electron Blocking Layer toward Efficient Hybrid Piezoelectric–Triboelectric Nanogenerators

Lead-free ferroelectric one-dimensional nanostructures exhibit great potential in building micro/nanoenergy harvesters owing to their high dielectric constant and piezoelectric properties. Herein, potassium sodium niobate (KNN) nanostructures are embedded into a poly(dimethylsiloxane) (PDMS) film to develop a hybrid piezoelectric–triboelectric nanogenerator (PTENG) that scavenges mechanical energy efficiently. By comparing different structures with and w/o the functional KNN layer, the spontaneous polarized electric field produced by the KNN-Mn film is systematically investigated, and its function as an electron blocking layer to hinder electron transfer is also well illustrated. Furthermore, after embedding KNN-Ca nanorods into PDMS to enhance relative permittivity, we find that the induced polarized electric field initiated by KNN-Ca nanorods binds free electrons and acts as a charge retention transition layer to further boost surface charge density. This work brings ideas to prepare high-performance PTENGs by applying ferroelectric materials with high permittivity.