Publication date: December 2021
Source: Materials Today Energy, Volume 22
Author(s): Yuriy N. Luponosov, Alexander N. Solodukhin, Artur L. Mannanov, Petr S. Savchenko, Benedito A.L. Raul, Svetlana M. Peregudova, Nikolay M. Surin, Artem V. Bakirov, Maxim A. Shcherbina, Sergei N. Chvalun, Maxim S. Pshenichnikov, Dmitry Yu Paraschuk, Sergey A. Ponomarenko
Nature Communications, Published online: 21 September 2021; doi:10.1038/s41467-021-25797-9
Though broadband achromatic metalens are attractive for biological applications, existing metalenses show limited performance in the biological imaging window. Here, the authors report high-efficiency broadband achromatic metalens featuring record-high aspect ratio titanium dioxide metasurfaces.
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  This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.
A pair of thermally activated delayed fluorescence enantiomers with aggregation-induced emission properties are developed by introducing the chiral donor based on a triptycene scaffold. Highly efficient solution-processed nondoped circularly polarized organic light-emitting diodes (CP-OLEDs) with external quantum efficiency up to 25.5% is realized based on the emitter. In addition, the CP-OLEDs exhibit intense circularly polarized electroluminescence activities with opposing g EL signals.
Recently, circularly polarized organic light-emitting diodes (CP-OLEDs) fabricated with thermally activated delayed fluorescence (TADF) emitters are developed rapidly. However, most devices are fabricated by vacuum deposition technology, and developing efficient solution-processed CP-OLEDs, especially nondoped devices, is still a challenge. Herein, a pair of triptycene-based enantiomers, (S,S)-/(R,R)-TpAc-TRZ, are synthesized. The novel chiral triptycene scaffold of enantiomers avoids their intermolecular π–π stacking, which is conducive to their aggregation-induced emission characteristics and high photoluminescence quantum yield of 85% in the solid state. Moreover, the triptycene-based enantiomers exhibit efficient TADF activities with a small singlet-triplet energy gap (ΔE ST) of 0.03 eV and delayed fluorescence lifetime of 1.1 µs, as well as intense circularly polarized luminescence with dissymmetry factors (|g PL|) of about 1.9 × 10−3. The solution-processed nondoped CP-OLEDs based on (S,S)-/(R,R)-TpAc-TRZ not only display obvious circularly polarized electroluminescence signals with g EL values of +1.5 × 10−3 and −2.0 × 10−3, respectively, but also achieve high efficiencies with external quantum, current, and power efficiency up to 25.5%, 88.6 cd A−1, and 95.9 lm W−1, respectively.
A new thermally activated delayed fluorescence molecule, BTZ-DMAC-4Br, is used to sensitize triplet-triplet-annihilation upconversion. By increasing the utilization of excitation light through total internal reflection in whispering gallery mode microcavities, a high upconversion quantum yield of 24.6% is observed, suggesting potential prospects of optical cavities in constructing highly efficient and low-threshold upconversion systems.
Triplet-triplet-annihilation (TTA) upconversion sensitized by a new thermally activated delayed fluorescence (TADF) molecule, BTZ-DMAC-4Br, is investigated in whispering gallery mode (WGM) microcavities made of toluene solutions filled into quartz capillaries. Since the utilization of the excitation light is improved in WGM microcavities through total internal reflection, the upconversion efficiency is enhanced greatly and an upconversion quantum yield of 24.6% is observed, which is a dozen times higher than that measured in conventional cuvettes. To the best of knowledge, this is the highest upconversion efficiency achieved in TADF sensitized TTA systems. Not only is a new material designed, but also the results provide a novel way to improve the TTA upconversion performance by utilizing the optical cavity effect, and the TTA microcavities may be used to construct highly efficient and low-threshold photonic devices in many applications.
Composites of a redox-active covalent organic framework intimately grown around carbon nanotubes that were used as the positive electrode in Li-ion cells are reported. The optimized composite material has a tube-type core-shell structure and retains 58% of its capacity at 50 A g−1. This rate translates to charging times of ≈11 s (320 C).
Covalent organic frameworks (COFs) are promising electrode materials for Li-ion batteries. However, the utilization of redox-active sites embedded within COFs is often limited by the low intrinsic conductivities of bulk-grown material, resulting in poor electrochemical performance. Here, a general strategy is developed to improve the energy storage capability of COF-based electrodes by integrating COFs with carbon nanotubes (CNT). These COF composites feature an abundance of redox-active 2,7-diamino-9,10-phenanthrenequinone (DAPQ) based motifs, robust β‑ketoenamine linkages, and well-defined mesopores. The composite materials (DAPQ-COFX—where X = wt% of CNT) are prepared by in situ polycondensation and have tube-type core-shell structures with intimately grown COF layers on the CNT surface. This synergistic structural design enables superior electrochemical performance: DAPQ-COF50 shows 95% utilization of redox-active sites, long cycling stability (76% retention after 3000 cycles at 2000 mA g−1), and ultra-high rate capability, with 58% capacity retention at 50 A g−1. This rate translates to charging times of ≈11 s (320 C), implying that DAPQ-COF50 holds excellent promise for high-power cells. Furthermore, the rate capability outperformed all previous reports for carbonyl-containing organic electrodes by an order of magnitude; indeed, this power density and the rapid (dis)charge time are competitive with electrochemical capacitors.
By comparison of three different boron dipyrromethene compounds, the heavy-atom-free 10-(anthracen-9-yl)-3,7-bis((E)-4-(diphenylamino)styryl)-5,5-difluoro-1,9-dimethyl-5H-dipyrrolo[1,2-c:2“,1” f][1,3,2] diazaborinin-4-ium-5-uide is used for near-infrared-II fluorescence-imaging-guided phototherapy, in which the anthracene module is able to capture singlet oxygen with laser irradiation and release it in dark conditions for “afterglow” photodynamic therapy, leading to the complete suppression of tumors.
Improving singlet oxygen (1O2) lifespan by fractionated delivery in dark and hypoxic conditions is a better way to achieve enhanced phototherapeutic efficacy. Herein, three boron dipyrromethene (BODIPY) dyes are synthesized to demonstrate that anthracence-functionalized BODIPY, namely ABDPTPA is an efficient heavy-atom-free photosensitizer for the reversible capture and release of 1O2. The spin–orbit charge-transfer intersystem crossing of ABDPTPA promises a high 1O2 quantum yield of 60% in dichloromethane. Under light irradiation, the anthracene group reacts with 1O2 to produce endoperoxide. Interestingly, after termination of irradiation, the endoperoxide undergoes thermal cycloreversion to produce 1O2, and regenerates the anthracene module to achieve 1O2 “afterglow,” which results in a prolonged half lifetime of 1O2 for 9.2 min. In vitro cytotoxicity assays indicate that ABDPTPA nanoparticles have a low half-maximal inhibitory concentration (IC50) of 3.6 µg mL−1 on U87MG cells. Further, the results of near-infrared-II fluorescence-imaging-guided phototherapy indicate that ABDPTPA nanoparticles can inhibit tumor proliferation even at a low dose (200 µg mL−1, 100 µL) without any side effects. Therefore, the study provides a generalized 1O2 “afterglow” strategy to enhance phototheranostics for complete tumor regression.
A green thermally activated delayed fluorescence (TADF) emitter with an extended π-system of linear donor (D)–acceptor (A)–donor (D) structure is established to simultaneously obtain a horizontal emitting dipole orientation ratio of 92%, a reverse intersystem crossing rate of 1.16 × 106 s–1 and a photoluminescence quantum yield of 95%, together affording a champion maximum external quantum efficiency of 39.1%.
Thermally activated delayed fluorescence (TADF) emitters featuring preferential horizontal emitting dipole orientation (EDO) are in urgent demand for enhanced optical outcoupling efficiency in organic light-emitting diodes (OLEDs). However, simultaneously manipulating EDO and optoelectronic properties remains a formidable challenge. Here, an extended linear D–A–D structure with both enlarged donor (D) and acceptor (A) π-systems is established, not only elaborately manipulating parallel horizontal molecular orientation and EDO along its long axis by multi-driving-forces for a high horizontal dipole ratio (Θ //), but also delocalizing distribution of frontier energy levels for optimized electronic properties. The proof-of-the-concept emitter simultaneously affords a high Θ // of 92%, a high photoluminescence quantum yield of 95%, and a fast reverse intersystem crossing rate of 1.16 × 106 s-1. The corresponding OLED achieves a champion maximum external quantum efficiency of 39.1% among all green TADF devices without any external light-extraction techniques, together with a maximum power efficiency of 112.0 lm W-1 and alleviated efficiency roll-off. These findings may inspire even better full-color TADF emitters that push the device efficiency toward the theoretical limits.
Chlorination is an important strategy to explore the structure–property relationship of nonfullerene acceptors. BTIC-4Cl-TCl-γ with chlorine at the γ-position of the conjugated thiophene shows a 3D network structure while BTIC-4Cl-TCl-β is found to be reformed to a quasi-3D network, which promotes a champion open-circuit voltage of 0.86 V and has the highest efficiency (15.65%).
Systematic investigation of three nonfullerene acceptors, BTIC-4Cl-T, BTIC-4Cl-TCl-γ, and BTIC-4Cl-TCl-b, with or without a chlorine substituent at the γ/b-position of the side chain thiophene ring, reveals that molecular planarity, stacking structure, and photovoltaic performance of the compounds are dependent on the position of the chlorine substituent. Of the materials using thiophenes in conjugated side chains, BTIC-4Cl-T shows a relatively lower open-circuit voltage of 0.81 V, decreased current density, leading to an efficiency of only 10.86%. BTIC-4Cl-TCl-γ with chlorine at the γ-position of the conjugated thiophene shows a 3D network structure, a greatly increased current density, and an efficiency of 14.35%. BTIC-4Cl-TCl-b, with a chlorine atom in b-position, is found to have been reformed to a quasi-3D network, in which electron hopping can be efficiently realized in adjacently positioned, linearly arranged molecules due to S···S interactions. With this quasi-3D network, BTIC-4Cl-TCl-b promotes the open-circuit voltage up to 0.86 V and has the highest efficiency (15.65%) among the three acceptors. These results prove that chlorination is an effective strategy to improve photovoltaic performance and highlights the decisive relationship between structural regulation and molecular arrangement. It also provides a good starting point for the exploration and design of next generation high-performance materials.
The translation of photoresponsive biomaterials to clinical applications hinges on effective light delivery in the body. This review highlights the challenges of in vivo light delivery and the materials-based light management technologies that can facilitate the photoactivation of biomaterials in the human body, particularly upconversion nanoparticles and optical waveguides.
Photoresponsive biomaterials are experiencing a transition from in vitro models to in vivo demonstrations that point toward clinical translation. Dynamic hydrogels for cell encapsulation, light-responsive carriers for controlled drug delivery, and nanomaterials containing photosensitizers for photodynamic therapy are relevant examples. Nonetheless, the step to the clinic largely depends on their combination with technologies to bring light into the body. This review highlights the challenge of photoactivation in vivo, and presents strategies for light management that can be adopted for this purpose. The authors’ focus is on technologies that are materials-driven, particularly upconversion nanoparticles that assist in “direct path” light delivery through tissue, and optical waveguides that “clear the path” between external light source and in vivo target. The authors’ intention is to assist the photoresponsive biomaterials community transition toward medical technologies by presenting light delivery concepts that can be integrated with the photoresponsive targets. The authors also aim to stimulate further innovation in materials-based light delivery platforms by highlighting needs and opportunities for in vivo photoactivation of biomaterials.
Fundamental limits to the refractive index for any material are established, depending only on electron density, dispersion, and frequency of interest. Natural materials nearly reach the upper bounds for low to moderate dispersion across a wide range of optical frequencies. Composite theory suggests that plasmonic metamaterials can achieve low-loss refractive indices significantly higher than those of current best materials.
Increasing the refractive index available for optical and nanophotonic systems opens new vistas for design, for applications ranging from broadband metalenses to ultrathin photovoltaics to high-quality-factor resonators. In this work, fundamental limits to the refractive index of any material are derived, given only the underlying electron density and either the maximum allowable dispersion or the minimum bandwidth of interest. In the realm of small to modest dispersion, the bounds are closely approached and not surpassed by a wide range of natural materials, showing that nature has already nearly reached a Pareto frontier for refractive index and dispersion. Conversely, for narrow-bandwidth applications, nature does not provide the highly dispersive, high-index materials that the bounds suggest should be possible. The theory of composites to identify metal-based metamaterials that can exhibit small losses and sizeable increases in refractive index over the current best materials is used. Moreover, if the “elusive lossless metal” can be synthesized, it is shown that it would enable arbitrarily high refractive index in the high-dispersion regime, nearly achieving the bounds even at refractive indices of 100 and beyond at optical frequencies.
A hybrid planar/bulk heterojunction is constructed by introducing a p-type polymer (PTO3) and an n-type naphthalene imide (NDI-i8) on both sides of a mixed donor:acceptor active layer. The tailored hybrid heterojunction presents a decreased energy loss and improved efficiency. As a result, an outstanding PCE of 18.5% is achieved, which is among the top values in the field of organic solar cells.
The donor:acceptor heterojunction has proved as the most successful approach to split strongly bound excitons in organic solar cells (OSCs). Establishing an ideal architecture with selective carrier transport and suppressed recombination is of great importance to improve the photovoltaic efficiency while remains a challenge. Herein, via tailoring a hybrid planar/bulk structure, highly efficient OSCs with reduced energy losses (E losss) are fabricated. A p-type benzodithiophene-thiophene alternating polymer and an n-type naphthalene imide are inserted on both sides of a mixed donor:acceptor active layer to construct the hybrid heterojunction, respectively. The tailored structure with the donor near the anode and the acceptor near the cathode is beneficial for obtaining enhanced charge transport, extraction, and suppressed charge recombination. As a result, the photovoltaic characterizations suggest a reduced nonradiative E loss by 25 meV, and the best OSC records a high efficiency of 18.5% (certified as 18.2%). This study highlights that precisely regulating the structure of donor:acceptor heterojunction has the potential to further improve the efficiencies of OSCs.
