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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.

By molecular engineering of 1,4-dihydropyridine derivatives, a photoactivatable probe (TPA-DHPy-Py) with high photoactivatable and photodynamic efficiency is developed. Upon photoactivation, TPA-DHPy-Py can monitor lipid droplets and endoplasmic reticulum alteration under light irradiation, and achieve fluorescent visualization of tumor in vivo. Furthermore, TPA-DHPy-Py can effectively kill cancer cells and significantly inhibit tumor growth.

Abstract

Photoactivatable agent is a powerful tool in biomedicine studies due to high-precision spatiotemporal control of light. However, those previously reported agents generally suffer from short wavelength, fluorescence self-quenching effect, and the lack of photosensitizing property, which severely restrict their practical applications. To address these issues, molecular engineering of 1,4-dihydropyridine derivatives is conducted to obtain an optimized agent, namely TPA-DHPy-Py, which exhibits low oxidation potential, high photoactivation efficiency, and excellent type I/II combined photodynamic activity. Concurrently, its photoactivated counterpart is featured by aggregation-induced near-infrared emission and remarkable reactive oxygen species (ROS) production efficiency. Upon photoactivation, TPA-DHPy-Py is capable of precisely identifying cancer cells from co-culturing cancer cells and normal cells without the assistance of any extra targeting units, and in situ monitoring lipid droplets and endoplasmic reticulum alteration under ROS stress, as well as achieving fluorescent visualization of tumor in vivo with supremely high imaging contrast. Furthermore, the unprecedented performance on photodynamic cancer therapy is demonstrated by the significant inhibition of tumor growth. Therefore, the photoactivatable TPA-DHPy-Py with dual-organelle-targeted and excellent photodynamic activity associated with self-monitoring ability is highly promising for cancer theranostics in clinical trials.

Nature Communications, Published online: 03 January 2023; doi:10.1038/s41467-022-35745-w

Nanoscale circularly polarized light sources are an important building block for future integrated photonics. Here the authors demonstrate circularly polarized light emission from a thin organic single crystal light-emitting diode.

A triarylamine-based macrocyclic donor is adopted to design new blue thermally activated delayed fluorescence (TADF) emitter. The restricted conformation of macrocyclic donor twisting against the dimethyl substituted phenylene bridge leads to the reduced singlet–triplet energy difference (ΔE _ST) as well as the enhanced horizontal ratio of emission dipole. These beneficial effects contribute to a highly efficient blue TADF organic light-emitting diode.

Abstract

This work reports the incorporation of a triphenylamine-based macrocyclic donor to design new donor-π-acceptor-configured blue thermally activated delayed fluorescence (TADF) emitters. The X-ray structure analyses manifest the degree of twisted conformations that can be modulated by methyl substituents of the π-bridge and macrocyclic donor, leading to well-separated highest occupied natural transition orbital and lowest unoccupied natural transition orbital frontier orbitals, thus sufficiently small singlet–triplet energy difference (ΔE _ST) for TADF. The theoretical analyses elucidate the structure–property relationship and reveal the beneficial effect of macrocyclic donor on increasing reverse intersystem crossing (RISC) process that can contribute to improved triplet-upconversion efficiency. The blue device employing c-NN-TRZ as emitter gave a maximum external quantum efficiecny (EQE_max) of 26.3% as compared to that (19.1%) of the device using the model compound DPA-MeTRZ without the macrocyclic donor, suggesting the contribution of macrocyclic donor to enhance device performance. Benefiting from the combined advantages of macrocyclic donor and methyl substituents, the device incorporating c-NN-MeTRZ as emitter achieves an outstanding EQE_max of 32.2%, which is attributed to the more horizontally oriented emission dipoles as well as the significantly accelerated RISC rate constant (k _RISC) resulting from reduced ΔE _ST. This work represents a new strategy of designing twisted TADF emitter incorporating macrocyclic donor to achieve highly efficient blue device.

The hygroscopicity of lithium-rich antiperovskites (LiRAPs) is successfully suppressed by weakening the intermolecular hydrogen bond between LiRAPs and H₂O with fluorine doping. Based on the high moisture resistivity and the low melting point of LiRAPs, two prototypes of all ceramic lithium batteries (ACLBs) are assembled in ambient air by means of co-coating sintering and melt-infiltration, respectively.

Abstract

Lithium-rich antiperovskites (LiRAPs) solid electrolytes have attracted extensive interest due to their advantages of structural tunability, mechanical flexibility, and low cost. However, LiRAPs are instinctively hygroscopic and suffer from decomposition in air, which not only diversifies their electrochemical performances in present reports but also hinders their application in all-solid-state lithium batteries (ASSLBs). Herein, the origin of the hygroscopicity, and also the effect of the hygroscopicity on the electrochemical performances of Li_3−x (OH _x )Cl are systematically investigated. Li_3−x (OH _x )Cl is demonstrated to be unstable in the air and prone to decompose into LiOH and LiCl. Nevertheless, with fluorine doping on chlorine sites, the hygroscopicity of LiRAPs is suppressed by weakening the intermolecular hydrogen bond between LiRAPs and H₂O, forming a moisture-resistive Li_3−x (OH _x )Cl_0.9F_0.1. Taking advantage of its low melting point (274 °C), two prototypes of ASSLBs are assembled in the ambient air by means of co-coating sintering and melt-infiltration. With LiRAPs as the solder, low-temperature sintering of the ASSLBs with low interfacial resistance is demonstrated as feasible. The understanding of the hygroscopic behavior of LiRAPs and the integration of the moisture-resistive LiRAPs with ASSLBs provide an effective way toward the fabrication of the ASSLBs.

By synthesizing a high weight-average molecular weight polymer donor PBDB-TF and combining a ternary blending strategy, favorable phase separation morphology featuring more compact π–π stacking distance can be attained. A maximum power conversion efficiency of 18.2% (certified value of 17.7%) with excellent mechanical properties in all-polymer organic photovoltaic cells is demonstrated.

Abstract

All-polymer organic photovoltaic (OPV) cells possessing high photovoltaic performance and mechanical robustness are promising candidates for flexible wearable devices. However, developing photoactive materials with good mechanical properties and photovoltaic performance so far remains challenging. In this work, a polymer donor PBDB-TF with a high weight-average molecular weight (M _w) is introduced to enable highly efficient all-polymer OPV cells featuring excellent mechanical reliability. By incorporating the high-M _w PBDB-TF as a third component into the PBQx-TF:PY-IT blend, the bulk heterojunction morphology is finely tuned with a more compact π–π stacking distance, affording efficient pathways for charge transport as well as mechanical stress dissipation. Hence, all-polymer OPV cells based on the ternary blend film demonstrate a maximum power conversion efficiency (PCE) of 18.2% with an outstanding fill factor of 0.796. The flexible OPV cell delivers a decent PCE of 16.5% with high mechanical stability. These results present a promising strategy to address the mechanical properties and boost the photovoltaic performance of all-polymer OPV cells.

A high-mobility fullerene liquid crystal is introduced into the active layer of organic solar cells (OSCs) to provide a fast channel for charge-carrier transport, reduce energetic disorder and trap density via enhancing crystallization, and then realize micrometer-scale charge-carrier diffusion, leading to the impressive power conversion efficiencies of 15.23% for OSCs with the thickness approaching 500 nm.

Abstract

The short charge-carrier diffusion length (L _D) (100–300 nm) in organic bulk heterojunction (BHJ) impedes the further improvement in power conversion efficiency (PCE) of organic solar cells (OSCs), especially for thick-film (>400 nm) devices matching with industrial solution processing. Here a facile method is developed to efficiently increase L _D and then improve PCEs of OSCs via introducing a fullerene liquid crystal, F1, into the active layer. F1 combines the inherent high electron mobility of fullerene and strong self-assembly capacity of liquid crystal, providing a fast channel for charge-carrier transport and reducing energetic disorder and trap density in BHJ film via enhancing crystallization. Typically, in PM6:Y6:F1 BHJ, the enhanced charge-carrier mobility (>10⁻² cm⁻² V⁻¹ s⁻¹) and prolonged charge-carrier lifetime (55.3 µs) are acquired to realize the record L _D of 1.6 or 2.4 µm for electron or hole, respectively, which are much higher than those of the PM6:Y6 binary sample and comparable to or even better than those values reported for some inorganic/hybrid materials, such as CuIn _x Ga_{(1− x )}Se₂ (CIGS) and perovskite thin films. Benefitting from the micrometer-scale L _D, the PM6:Y6:F1 ternary OSCs sustain a remarkable PCE of 15.23% with the active layer thickness approaching 500 nm.

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.

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.