以昇陳

A hybrid acceptor-modulation strategy is demonstrated based on DPP-containing fluorinated triple-acceptor architecture (DFB). Therefore, the DFB-based polymers feature low-lying FMO levels, shape-persistent backbones, and high crystallinity. The above features lead to an electron mobility of 5.04 cm² V⁻¹ s⁻¹ in unipolar n-type transistors, which is the highest electron mobility for DPP-based unipolar n-type semiconducting polymers reported to date.

Abstract

The development of unipolar n-type semiconducting polymers with electron mobility (µ _e) over 5 cm² V⁻¹ s⁻¹ remains a massive challenge in organic semiconductors. Diketopyrrolopyrrole (DPP) has proven to be a successful unit for high-performance p-type and ambipolar polymers. However, DPP's moderate electron-accepting capability leads to the shallow frontier molecular orbital (FMO) levels of the resultant polymers and hence limit the µ _e in unipolar n-type organic transistors. Herein, this issue has been addressed by using a hybrid acceptor-modulation strategy based on DPP-containing “fluorinated triple-acceptor architecture”, namely DPP-difluorobenzothiadiazole-DPP (DFB). Compared with DFB's non-fluorinated counterpart, DFB features deeper FMO levels and a shape-persistent framework. Therefore, a series of DFB-based polymers demonstrate planar backbones and lowered FMO levels by ≈0.10 to 0.25 eV versus that of the control polymer. Intriguingly, all DFB-polymers exhibit excellent unipolar n-type transistor performances. Notably, a full-locked backbone conformation and high crystallinity with crystalline coherence length of 524 Å are observed for pDFB-TF, accounting for its high µ _e of 5.04 cm² V⁻¹ s⁻¹, which is the highest µ _e value for DPP-based unipolar n-type polymers reported to date. This work demonstrates that the strategy of “fluorinated triple-acceptor architecture” opens a new path towards high-performance unipolar n-type semiconducting polymers.

Nature Photonics, Published online: 05 December 2022; doi:10.1038/s41566-022-01113-9

Circularly polarized light emitted from OLEDs exhibits opposite handedness depending on the propagation direction of the light. Switching the current flow in the OLED also switches the light handedness.

Nature Energy, Published online: 15 December 2022; doi:10.1038/s41560-022-01167-7

There is a growing need for sustainable and green solvent processing of organic optoelectronics. Now Corzo et al. show that terpene solvents in a binary formulation enable device performance on par with that of more toxic solvents.

An ultralong charge-carrier lifetime of more than one month in a disordered film of an organic semiconductor stored at room temperature is demonstrated. The charge carriers stored in the film are stabilized by spontaneous orientation polarization. It is also revealed that the charge carriers retain spatial information due to their slow diffusion in the plane of the organic layer.

Abstract

Understanding intrinsic carrier lifetime in disordered organic solid-state semiconductors is essential for improving device performance in not only molecule-based optoelectronic devices such as organic solar cells (OSC) but also photocatalysts used for producing solar fuel cells. Carriers in disordered films are generally thought to have short lifetimes on a scale ranging from nanoseconds to milliseconds. These short carrier lifetimes cause loss of charges in OSCs and low quantum yields in photocatalysts and impede the future application of organic semiconductors to, for example, charge-storage-based memory devices. This study reports an ultralong intrinsic carrier lifetime of more than one month in a disordered film of an organic semiconductor stored at room temperature without external power. This extraordinary lifetime, which is several orders of magnitude longer than that generally believed possible in conventional organic semiconductors, arises from carrier stabilization by spontaneous orientation polarization, excited spin-triplet recycling, and blocking of recombination processes in disordered films.

Lithiophilic Li₂Te is synthesized by exposing the collector to tellurium vapor, followed by in situ Li activation. The Li₂Te significantly reduces the electrodeposition/electrodissolution overpotentials and improves Coulombic efficiency. An anode-free all-solid-state battery employing a sulfide-based solid-electrolyte (argyrodite Li₆PS₅Cl) with NMC811 cathode delivers an initial CE of 83% at 0.2C, with a cycling CE above 99%.

Abstract

A stable anode-free all-solid-state battery (AF-ASSB) with sulfide-based solid-electrolyte (SE) (argyrodite Li₆PS₅Cl) is achieved by tuning wetting of lithium metal on “empty” copper current-collector. Lithiophilic 1 µm Li₂Te is synthesized by exposing the collector to tellurium vapor, followed by in situ Li activation during the first charge. The Li₂Te significantly reduces the electrodeposition/electrodissolution overpotentials and improves Coulombic efficiency (CE). During continuous electrodeposition experiments using half-cells (1 mA cm⁻²), the accumulated thickness of electrodeposited Li on Li₂Te–Cu is more than 70 µm, which is the thickness of the Li foil counter-electrode. Full AF-ASSB with NMC811 cathode delivers an initial CE of 83% at 0.2C, with a cycling CE above 99%. Cryogenic focused ion beam (Cryo-FIB) sectioning demonstrates uniform electrodeposited metal microstructure, with no signs of voids or dendrites at the collector-SE interface. Electrodissolution is uniform and complete, with Li₂Te remaining structurally stable and adherent. By contrast, an unmodified Cu current-collector promotes inhomogeneous Li electrodeposition/electrodissolution, electrochemically inactive “dead metal,” dendrites that extend into SE, and thick non-uniform solid electrolyte interphase (SEI) interspersed with pores. Density functional theory (DFT) and mesoscale calculations provide complementary insight regarding nucleation-growth behavior. Unlike conventional liquid-electrolyte metal batteries, the role of current collector/support lithiophilicity has not been explored for emerging AF-ASSBs.

Intrinsic defects in quenched lithium titanate anodes enable reversible extraction of Li ions that are unextractable in pristine state, thus facilitating these native Li ions to participate in electrochemical cycling, which leads to a sustained capacity of 202 mAh g⁻¹ in the 1.0–2.5 V range with excellent rate capability and cycling stability.

Abstract

Interest in defect engineering for lithium-ion battery (LIB) materials is sparked by its ability to tailor electrical conductivity and introduce extra active sites for electrochemical reactions. However, harvesting excessive intrinsic defects in the bulk of the electrodes rather than near their surface remains a long-standing challenge. Here, a versatile strategy of quenching is demonstrated, which is exercised in lithium titanate (Li₄Ti₅O₁₂, LTO), a renowned anode for LIBs, to achieve off-stoichiometry in the interior region. In situ synchrotron analysis and atomic-resolution microscopy reveal the enriched oxygen vacancies and cation redistribution after ice-water quenching, which can facilitate the native unextractable Li ions to participate in reversible cycling. The fabricated LTO anode delivers a sustained capacity of 202 mAh g⁻¹ in the 1.0–2.5 V range with excellent rate capability and overcomes the poor cycling stability seen in conventional defective electrodes. The feasibility of tuning the degree of structural defectiveness via quenching agents is also proven, which can open up an intriguing avenue of research to harness the intrinsic defects for improving the energy density of rechargeable batteries.

Lithium-rich layered oxide (LLO) cathode theoretically enables all-solid-state batteries with high energy density owing to its high capacity. However, the low electronic conductivity and highly reactive lattice oxygen impede its application. By introducing conductive additives in electrodes and modifying the surface chemistry of LLO, high-efficiency electronic networks and stable LLO/electrolyte interfaces can be obtained, thus boosting the charge-transfer kinetics.

Abstract

Employing lithium-rich layered oxide (LLO) as the cathode of all-solid-state batteries (ASSBs) is highly desired for realizing high energy density. However, the poor kinetics of LLO, caused by its low electronic conductivity and significant oxygen-redox-induced structural degradation, has impeded its application in ASSBs. Here, the charge transfer kinetics of LLO is enhanced by constructing high-efficiency electron transport networks within solid-state electrodes, which considerably minimizes electron transfer resistance. In addition, an infusion-plus-coating strategy is introduced to stabilize the lattice oxygen of LLO, successfully suppressing the interfacial oxidation of solid electrolyte (Li₃InCl₆) and structural degradation of LLO. As a result, LLO-based ASSBs exhibit a high discharge capacity of 230.7 mAh g⁻¹ at 0.1 C and ultra-long cycle stability over 400 cycles. This work provides an in-depth understanding of the kinetics of LLO in solid-state electrodes, and affords a practically feasible strategy to obtain high-energy-density ASSBs.

Semiconducting polymer nanoparticles (SPNs) in the second near-infrared (NIR-II) window have attracted a great deal of interest for their superior optical properties and versatile functionalities. This review describes recent advances made on SPNs for NIR-II imaging and therapy, including the design strategies and specific applications in fluorescence imaging, photoacoustic imaging, photothermal therapy, photodynamic therapy, and drug delivery.

Abstract

Semiconducting polymers are attractive optical materials in optoelectronic devices and biomedical applications because of their superior optical properties and remarkable versatility. Optical imaging in the second near-infrared window (NIR-II) has become increasingly popular owing to the merits of large penetration depth and high signal to noise ratio, leading to a great deal of interest in the exploration and development of optical probes in the NIR-II region. In this review, recent advances in the development of semiconducting polymer nanoparticles (SPNs) in the NIR-II region for biomedical imaging and therapeutics are summarized. This review focuses on the design strategies in semiconducting polymers toward enhancing their NIR-II emission for deep tissue imaging, improving their performance in photoacoustic imaging, utilizing their large absorptivity for photothermal and photodynamic therapy, and a number of comprehensive applications for multifunctional imaging and optical therapeutics. Finally, the current challenges of semiconducting polymer probes are discussed and the perspectives on the future development in the field are shared.

Fibrillization of non-fullerene acceptor L8-BO is realized by employing a conjugated fused-ring solvent additive 1-fluoronaphtalene that acts as the molecular bridge, which contributes to realize a power conversion efficiency of 19% in the pseudo-bulk heterojunction D18/L8-BO binary organic solar cell, featuring a high fill factor of 80% with improved charge transport.

Abstract

The structural order and aggregation of non-fullerene acceptors (NFA) are critical toward light absorption, phase separation, and charge transport properties of their photovoltaic blends with electron donors, and determine the power conversion efficiency (PCE) of the corresponding organic solar cells (OSCs). In this work, the fibrillization of small molecular NFA L8-BO with the assistance of fused-ring solvent additive 1-fluoronaphthalene (FN) to substantially improve device PCE is demonstrated. Molecular dynamics simulations show that FN attaches to the backbone of L8-BO as the molecular bridge to enhance the intermolecular packing , inducing 1D self-assembly of L8-BO into fine fibrils with a compact polycrystal structure. The L8-BO fibrils are incorporated into a pseudo-bulk heterojunction (P-BHJ) active layer with D18 as a donor, and show enhanced light absorption, charge transport, and collection properties, leading to enhanced PCE from 16.0% to an unprecedented 19.0% in the D18/L8-BO binary P-BHJ OSC, featuring a high fill factor of 80%. This work demonstrates a strategy for fibrillating NFAs toward the enhanced performance of OSCs.

The atomic layer deposition (ALD) growth mode on the commonly used electron transportation layer (ETL) PCBM is activated from island growth to layer-by-layer growth mode by introducing reaction sites. As a result, the excellent stability, efficient semi-transparent device, and perovskite/silicon tandem device with reaction sites are available.

Abstract

Atomic layer deposition (ALD) turns out to be particularly attractive technology for the sputtering buffer layer when preparing the semi-transparent (ST) perovskite solar cells (PSCs) and the tandem solar cells. ALD process turns to be island growth when the substrate is unreactive with the ALD reactants, resulting in the pin-hole layer, which causes an adverse effect on anti-sputtering. Here, p–i–n structured PSCs with ALD SnO _x as sputtering buffer layer are conducted. The commonly used electron transportation layer (ETL) PCBM in the p–i–n structured PVK solar cell is an unreactive substrate that prevents the layer-by-layer growth for the ALD SnO _x . PCBM layer is activated by introducing reaction sites to form impermeable ALD layers. By introducing reaction sites/ALD SnO _x as sputtering buffer layer, the authors succeed to fabricate ST-PSCs and perovskite/silicon (double-side polished) tandem solar cells with power conversion efficiency (PCE) of 20.25% and 23.31%, respectively. Besides, the unencapsulated device with reaction sites maintains more than 99% of the initial PCE after aging over 5100 h. This work opens a promising avenue to prepare impermeable layer for stable PSCs, ST-PSCs, tandem solar cells, and the related scale-up solar cells.

In this work, well-designed polymer acceptor materials for layer-by-layer (LbL) processing are combined with a ternary strategy to improve the active layer morphology. The optimized LbL-type ternary system not only shows the best efficiency of 18.14% among the all-polymer solar cells but also exhibits insensitivity to the active layer thickness ranging from 82–180 nm.

Abstract

Achieving a finely tuned active layer morphology with a suitable vertical phase to facilitate both charge generation and charge transport has long been the main goal for pursuing the highly efficient bulk heterojunction all-polymer solar cells (all-PSCs). Herein, a solution to address the above challenge via synergistically combining the ternary blend strategy and the layer-by-layer (LbL) procedure is proposed. By introducing a synthesized polymer acceptor (P _A), PY-Cl, with higher crystallinity into the designed host acceptor PY-SSe-V, vertical phase distribution and molecular ordering of the LbL-type ternary all-PSCs can be improved in comparison to the LbL-type PM6/PY-SSe-V binary all-PSCs. The formation of the superior bulk microstructure can not only promote charge transport and extraction properties but also reduce energetic disorder and non-radiative recombination loss, thus improving all three photovoltaic parameters simultaneously. Consequently, the PM6/(PY-SSe-V:PY-Cl) ternary all-PSCs show the best efficiency of 18.14%, which is among the highest values reported to date for all-PSCs. This work provides a facile and effective LbL-type ternary strategy for obtaining high-efficiency all-PSCs.

The current understanding of cathode performance and aging issues under fast charging conditions is summarized, mitigation strategies are discussed, and remaining challenges identified.

Abstract

Charging lithium-ion batteries (LiBs) in 10 to 15 min via extreme fast-charging (XFC) is important for the widespread adoption of electric vehicles (EVs). Lately, the battery research community has focused on identifying XFC bottlenecks and determining novel design solutions. Like other LiB components, cathodes can present XFC bottlenecks, especially when considering long-term battery life. Therefore, it is necessary to develop a comprehensive understanding of how XFC conditions degrade LiB cathodes. The present article reviews relevant cathode-focused studies and summarizes the current understanding regarding cathode performance and aging issues under XFC conditions. Dominant aging modes and mechanisms are identified at different length-scales with electrochemical correlations for LiNi _x Mn _y Co _z O₂ (NMC)-based cathodes. A range of electrochemical techniques and models provide key insights into cathode performance and life issues. A suite of multimodal and multiscale microscopy and X-ray techniques is surveyed to quantify chemical, structural, and crystallographic NMC-cathode degradation. Cathode cycle-life is scaled to equivalent EV miles to illustrate how cathode degradation translates to real-world scenarios and quantifies cathode-related bottlenecks that hinder XFC adoption. Finally, the article discusses several cathode cycle-life aging mitigation strategies with example case studies and identifies remaining challenges.

Nature Energy, Published online: 14 November 2022; doi:10.1038/s41560-022-01138-y

Organic solar cells with a bulk-heterojunction architecture suffer from photocurrent loss driven by triplet states. Now, Jiang et al. show that sequentially deposited donor–acceptor planar–mixed heterojunctions suppress triplet formation, enabling efficiencies over 19%.

Nature Energy, Published online: 15 November 2022; doi:10.1038/s41560-022-01158-8

A phase heterojunction (PHJ) solar cell is formed by interfacing two phases of the perovskite CsPbI3 — each of which exhibits different opto-electronic properties. Devices based on PHJs reach a maximum power conversion efficiency of 20.17%, surpassing the 15% achieved by devices based on either of the single phases alone.

Since an initial report in 2016, the thermopowers of ionic organics-based thermoelectrics have been enhanced by ≈4 times for p-type and >10 times for n-type electrolytes, whereas ionic conductivities of the ionic liquids (ILs)/polymers binary system are increased yet remain relatively lower than that of neat conducting polymers used in the early years.

Abstract

As the worldwide energy crisis is worsened, thermoelectric materials that can harvest low-grade waste heat and directly convert it into electricity provide promising alternative energy sources. Emerging ionic thermoelectrics (iTEs) have recently attracted widespread attention thanks to their impressively high thermopower that can reach hundreds of times more than conventional electronic thermoelectrics (eTEs). Based on the Soret effect, the performances of iTEs depend on the thermo-diffusion of mobile ions in electrolytes, resulting in electrical characteristics distinct from eTE materials and opening up additional potential applications of thermoelectrics. Among these materials, organics-based iTEs (i-OTEs) provide unique advantages such as low-cost, light-weight, and eco-friendliness, thereby offering more promising application scenarios that can utilize dissipated heat, for example, from human bodies or mobile devices. This concise review begins with the comparison of iTE and eTE, and then discusses their different mechanisms and applied devices in detail. Next, the recent advances of i-OTEs will be in-depth highlighted, including the merits and weaknesses of representative types of materials, effects of additives, and effective strategies for performance optimization. Finally, the state-of-the-art achievements of i-OTEs are summarized, and an overview is provided of the existing challenges and an outlook of prospective development and applications in future efforts.

The structure–property–electrochemical performance relationship of the elastomeric electrolyte system is established to demonstrate the importance of balancing Li-ion transport and mechanical properties for achieving high energy Li metal batteries.

Abstract

Solid-state lithium (Li)-metal batteries (LMBs) are garnering attention as a next-generation battery technology that can surpass conventional Li-ion batteries in terms of energy density and operational safety under the condition that the issue of uncontrolled Li dendrite is resolved. In this study, various plastic crystal-embedded elastomer electrolytes (PCEEs) are investigated with different phase-separated structures, prepared by systematically adjusting the volume ratio of the phases, to elucidate the structure-property-electrochemical performance relationship of the PCEE in the LMBs. At an optimal volume ratio of elastomer phase to plastic-crystal phase (i.e., 1:1), bicontinuous-structured PCEE, consisting of efficient ion-conducting, plastic-crystal pathways with long-range connectivity within a crosslinked elastomer matrix, exhibits exceptionally high ionic conductivity (≈10⁻³ S cm⁻¹) at 20 °C and excellent mechanical resilience (elongation at break ≈ 300%). A full cell featuring this optimized PCEE, a 35 µm thick Li anode, and a high loading LiNi_0.83Mn_0.06Co_0.11O₂ (NMC-83) cathode delivers a high energy density of 437 Wh kg_{anode+cathode+electrolyte} ⁻¹. The established structure–property–electrochemical performance relationship of the PCEE for solid-state LMBs is expected to inform the development of the elastomeric electrolytes for various electrochemical energy systems.

Nature Energy, Published online: 10 November 2022; doi:10.1038/s41560-022-01155-x

Achieving both high efficiency and stability in organic solar cells is challenging. Now, Liang et al. show that oligomer acceptors improve the molecular packing and morphology of the active layer, affording a 15% efficiency and enhanced stability.

A deep-blue multiple-resonance-type thermally activated delayed fluorescence (MR-TADF) compound (3tPAB) is selected as sensitizer for both blue traditional fluorescence and MR-TADF organic light-emitting diodes. TADF-sensitized fluorescent (TSF) and TADF-sensitized TADF (TST) device using 3tPAB as sensitizer presents maximum external quantum efficiency (EQE_max) of 14.4% and 33.9%, respectively. Compared with the device without sensitizer, the efficiency is increased ≈2.4 and 1.25 times, respectively.

Abstract

Due to the limitation of donor and acceptor group selection, the efficient thermally activated delayed fluorescence (TADF) type sensitizer used for blue organic light-emitting diodes (OLEDs) is rare. Multiple resonance (MR) type TADF emitters can easily achieve efficient blue emission. And the compounds exhibit small Stokes shift and lower absorption energy under the same emission color compared with traditional TADF, mitigating the damage of high-energy absorption of sensitizer on material stability. However, their characteristics as sensitizers have not been explored. In this work, a deep-blue MR-TADF compound (3tPAB) is selected as a sensitizer for both blue traditional fluorescence and MR-TADF OLED. Given the improved photoluminescence quantum yield and the utilization of triplet excitons, the TADF-sensitized fluorescent device using 3tPAB as sensitizer presents a maximum external quantum efficiency (EQE_max) of 14.4%, showing ≈2.4 times increase compared with the device without sensitizer. More impressively, TADF-sensitized TADF (TST) device using 3tPAB as sensitizer and MR-TADF compound PhDMAC-BN as emitter exhibits EQE_max of 33.9%. And in TST device, efficient Förster energy transfer is demonstrated, thus, the device can maintain high color purity. The work first demonstrates the feasibility of MR-TADF as a sensitizer and provides a new strategy for developing high-performance blue OLED with high color purity.

The recombination and accumulation of polarons are investigated by the numerical model for transient electroluminescence. These are induced by the different recombination coefficients and degradation mechanisms. As a result, it is demonstrated that the longer device lifetime is attributed to the suppression of the exciton–polaron interaction via fast polaron recombination.

Abstract

The device performance of phosphorescent organic light-emitting diodes (PHOLEDs) is improved by using the exciplex-forming cohost with the thermally activated delayed fluorescence (TADF) property. This work comprehensively investigates the excitons and polarons management of exciplex host and dopant to understand the device degradation of PHOLEDs with various host materials. The recombination and accumulation of polarons is newly integrated in the numerical model for understanding transient electroluminescence in order to theoretically characterize a diversity of the polaron dynamics. Based on the unique excitons kinetics, polarons kinetics, and recombination coefficients coming from the exciplex host materials, the device degradation is examined. As a result, it is revealed that the longer device lifetime is attributed to the suppression of the exciton–polaron interaction by minimizing the steady-state polarons via fast polaron recombination. The combination of the exciton–polaron coupled kinetics model and the device degradation model show that the recombination coefficient should be considered a key parameter of the host materials to design long-lived PHOLEDs.

A rational molecular design strategy for developing efficient thermally-activated delayed fluorescence materials is presented through the additional introduction of donor (D) or acceptor (A) units in D-A framework, enabling the corresponding organic light-emitting diodes with external quantum efficiency enhanced from 8.5% to 11.6% and up to 27.5%, respectively, due to improved photophysical and horizontal dipole ratio properties.

Abstract

Thermally-activated delayed fluorescence (TADF) emitters are usually constructed with twisted donor-acceptor (D-A) frameworks, while studies on the relationship between diverse D-A structures are still in high demand to achieve high-performance emitters. Herein, by adopting triphenylamine as electron donor and dibenzo[a,c]phenazine as electron acceptor, three TADF molecules are reported with different frameworks of D-A (TPZ), D-A-D (DPZ) and D-A-A (APZ). Theoretical and experimental results demonstrate that different D-A frameworks play significant effects on photophysical, horizontal dipole ratio, and electroluminescence properties of the TADF molecules. In comparison, the APZ-OLED device achieves the best performance with a maximum external quantum efficiency of 27.5%, resulting from its low energy gap between the singlet and triplet, effective reverse intersystem crossing, high photoluminescence quantum yield, and horizontal dipole ratio. This work provides an insight into the relationship between efficient TADF emitters and rational molecular design engineering.

A red thermally activated delayed fluorescence emitter with cruciform structure is developed by rational molecular isomer engineering, exhibiting a high photoluminescence efficiency of 95%, a small singlet–triplet energy split of 0.24 eV, and a large horizontal emitting dipole ratio of 86% simultaneously. An external quantum efficiency up to 34.3% with a peak wavelength of 610 nm is achieved.

Abstract

The development of red organic emissive materials with high-efficiency and low-cost is of great significance but formidable challenge for organic light-emitting diodes (OLEDs). Herein, through isomer engineering, a pair of red thermally activated delayed fluorescence (TADF) isomers with Y-shape and cruciform structures, namely TPA-APQDCN-Y and TPA-APQDCN-C, are developed by integrating two triphenylamine (TPA) donor moieties into different positions of rigid planar acenaphtho[1,2-b]quinoxaline-9,10-dicarbonitrile (APQDCN) acceptor core. Compared to common Y-shape structure, the unique cruciform structure can result in the formation of intramolecular H-bonding, the limited molecular packing, the balance of the contradiction between the small spatial overlap of frontier molecular orbitals, and high oscillator strength, contributing to a higher photoluminescence quantum yield of 95%, a smaller singlet–triplet energy split of 0.24 eV and a larger horizontal emitting dipole ratio of 86%. An external quantum efficiency of 34.3% with an emission peak at 610 nm is achieved for TPA-APQDCN-C based red electroluminescent device, which is the highest value for red TADF-OLEDs with emission maximum beyond 600 nm ever reported.