以昇陳

Combining the layer‐by‐layer processing method and a ternary strategy, 18.16% efficiency, which is among the highest values reported to date, is achieved in single‐junction organic photovoltaics (OPVs) based on the PM6:BO‐4Cl:BTP‐S2 blend, superior to that (18.03%) of bulk‐heterojunction OPVs, proving that layer‐by‐layer processed ternary OPVs could be a promising approach to high efficiencies.

Abstract

Obtaining a finely tuned morphology of the active layer to facilitate both charge generation and charge extraction has long been the goal in the field of organic photovoltaics (OPVs). Here, a solution to resolve the above challenge via synergistically combining the layer‐by‐layer (LbL) procedure and the ternary strategy is proposed and demonstrated. By adding an asymmetric electron acceptor, BTP‐S2, with lower miscibility to the binary donor:acceptor host of PM6:BO‐4Cl, vertical phase distribution can be formed with donor‐enrichment at the anode and acceptor‐enrichment at the cathode in OPV devices during the LbL processing. In contrast, LbL‐type binary OPVs based on PM6:BO‐4Cl still show bulk‐heterojunction like morphology. The formation of the vertical phase distribution can not only reduce charge recombination but also promote charge collection, thus enhancing the photocurrent and fill factor in LbL‐type ternary OPVs. Consequently, LbL‐type ternary OPVs exhibit the best efficiency of 18.16% (certified: 17.8%), which is among the highest values reported to date for OPVs. The work provides a facile and effective approach for achieving high‐efficiency OPVs with expected morphologies, and demonstrates the LbL‐type ternary strategy as being a promising procedure in fabricating OPV devices from the present laboratory study to future industrial production.

A thermally stable perovskite solar cell is developed by capturing mobile lithium ions using a new molecular hole transporter, 1,3‐bis(5‐(4‐(bis(4‐methoxyphenyl)amino)phenyl)thieno[3,2‐b]thiophen‐2‐yl)‐5‐octyl‐4H‐thieno[3,4‐c]pyrrole‐4,6(5H)‐dione (coded HL38), where a strong interaction of the lithium ions in lithium bis(trifluoromethanesulfonyl)imide with the 5‐octylthieno[3,4‐c]pyrrole‐4,6‐dione (octyl‐TPD) moiety in HL38 is responsible for maintaining ≈86% of the initial power conversion efficiency for over 1000 h at 85 °C.

Abstract

A thermally stable perovskite solar cell (PSC) based on a new molecular hole transporter (MHT) of 1,3‐bis(5‐(4‐(bis(4‐methoxyphenyl) amino)phenyl)thieno[3,2‐b]thiophen‐2‐yl)‐5‐octyl‐4H‐thieno[3,4‐c]pyrrole‐4,6(5H)‐dione (coded HL38) is reported. Hole mobility of 1.36 × 10⁻³ cm² V⁻¹ s⁻¹ and glass transition temperature of 92.2 °C are determined for the HL38 doped with lithium bis(trifluoromethanesulfonyl)imide and 4‐tert‐butylpyridine as additives. Interface engineering with 2‐(2‐aminoethyl)thiophene hydroiodide (2‐TEAI) between the perovskite and the HL38 improves the power conversion efficiency (PCE) from 19.60% (untreated) to 21.98%, and this champion PCE is even higher than that of the additive‐containing 2,2′,7,7′‐tetrakis(N,N‐di‐p‐methoxyphenylamine)‐9,9′‐spirobifluorene (spiro‐MeOTAD)‐based device (21.15%). Thermal stability testing at 85 °C for over 1000 h shows that the HL38‐based PSC retains 85.9% of the initial PCE, while the spiro‐MeOTAD‐based PSC degrades unrecoverably from 21.1% to 5.8%. Time‐of‐flight secondary‐ion mass spectrometry studies combined with Fourier transform infrared spectroscopy reveal that HL38 shows lower lithium ion diffusivity than spiro‐MeOTAD due to a strong complexation of the Li⁺ with HL38, which is responsible for the higher degree of thermal stability. This work delivers an important message that capturing mobile Li⁺ in a hole‐transporting layer is critical in designing novel MHTs for improving the thermal stability of PSCs. In addition, it also highlights the impact of interface design on non‐conventional MHTs.

A semiconducting polymer nanoengager (SPNE) with both tumor‐associated antigens and T cell stimulating factors is designed to elicit potent multicellular engagement among tumor cells and immunocytes, enabling dual vaccination effects on both dendritic cells and T cells. Thus, the SPNE mediates synergistic second‐near‐infrared‐window (NIR‐II) photothermal immunotherapy that efficiently inhibits tumor growth and metastasis.

Abstract

Cell‐membrane‐coated nanoparticles (CCNPs) that integrate the biophysiological advantages of cell membranes with the multifunctionalities of synthetic materials hold great promise in cancer immunotherapy. However, strategies have yet to be revealed to further improve their immunotherapeutic efficacy. Herein, a polymer multicellular nanoengager (SPNE) for synergistic second‐near‐infrared‐window (NIR‐II) photothermal immunotherapy is reported. The nanoengager consists of an NIR‐II absorbing polymer as the photothermal core, which is camouflaged with fused membranes derived from immunologically engineered tumor cells and dendritic cells (DCs) as the cancer vaccine shell. In association with the high accumulation in lymph nodes and tumors, the multicellular engagement ability of the SPNE enables effective cross‐interactions among tumor cells, DCs, and T cells, leading to augmented T cell activation relative to bare or tumor‐cell‐coated nanoparticles. Upon deep‐tissue penetrating NIR‐II photoirradiation, SPNE eradicates the tumor and induces immunogenic cell death, further eliciting anti‐tumor T cell immunity. Such a synergistic photothermal immunotherapeutic effect eventually inhibits tumor growth, prevents metastasis and procures immunological memory. Thus, this study presents a general cell‐membrane‐coating approach to develop photo‐immunotherapeutic agents for cancer therapy.

The history of emitter development and industry's interest in organic light‐emitting diode (OLED) technology are reviewed. OLED device technology has equally inspired and driven innovation in academia and industry. Three generations of emitters based on different emission mechanisms have been designed. Recently, research in both academia and industry points toward a fourth generation of light‐emitting materials for OLEDs.

Abstract

Organic light‐emitting diodes (OLEDs) have come a long way ever since their first introduction in 1987 at Eastman Kodak. Today, OLEDs are especially valued in the display and lighting industry for their promising features. As one of the research fields that equally inspires and drives development in academia and industry, OLED device technology has continuously evolved over more than 30 years. OLED devices have come forward based on three generations of emitter materials relying on fluorescence (first generation), phosphorescence (second generation), and thermally activated delayed fluorescence (third generation). Furthermore, research in academia and industry toward the fourth generation of OLEDs is in progress. Excerpts from the history of green, orange‐red, and blue OLED emitter development on the side of academia and milestones achieved by key players in the industry are included in this report.

Three nonfullerene acceptors (M5, M6, and M7) are developed by using different ending groups, among which M6 with chlorinated ending groups exhibits a reduced ππ interaction distance with enhanced molecular ordering compared to M7 (or M5) with brominated (or unsubstituted) ending groups. With a wide‐bandgap copolymer, the best‐performance device based on M6 exhibits an outstanding power conversion efficiency of 15.45%.

Abstract

Ending group halogenation is an effective strategy for modulating the energy levels, bandgaps, and intermolecular interactions of nonfullerene acceptors. Understanding the influence of different halogen atoms on the acceptor properties is of great importance for designing high‐performance nonfullerene acceptors. Here, three acceptor–donor–acceptor (A‐D‐A) type nonfullerene acceptors (M5, M6, and M7), which are constructed by using a ladder‐type heteroheptacene core without the traditional sp³ carbon‐bonded side chains as the electron‐rich core, and 2‐(3‐oxo‐2,3‐dihydro‐1H‐inden‐1‐ylidene)malononitrile without or with halogen atoms as the ending groups. The nonfullerene acceptors with chlorinated (M6) and brominated (M7) ending groups exhibit broadened absorption spectra, down‐shifted energy levels, and enhanced molecular ordering compared to the counterpart without any halogenated ending groups (M5). Among the nonfullerene acceptors, M6 has the strongest intermolecular ππ interaction with its shortest ππ interaction distance and the longest coherent length which are beneficial for enhancing the charge transport and therefore boosting the photovoltaic performance. An excellent power conversion efficiency of 15.45% is achieved for the best‐performing polymer solar cell based on M6. These results suggest that the halogenated ending groups are essential for high‐performance heteroheptacene‐based nonfullerene acceptors considering their simultaneous enhancements in both the light‐harvesting and the charge transport.

Nature Chemistry, Published online: 15 February 2021; doi:10.1038/s41557-020-00629-3

Solvent plays a critical role in electron-transfer reactions, but short-range solvation dynamics are challenging to observe. Now, femtosecond X-ray solution scattering has been used to directly monitor the reorganization of water upon ultrafast intramolecular electron transfer in a bimetallic complex. Coherent motions of the first-shell water molecules are observed, arising from changes in solute–solvent hydrogen bonding.

Nature Photonics, Published online: 15 February 2021; doi:10.1038/s41566-021-00763-5

Exciton energy cascade transfer and recycling bring improvements in the efficiency and lifetime of deep-blue organic light-emitting diodes.

High electron mobility copolymer semiconductors are realized through control over conjugated backbone planarity and order using the naphthalene bisamide (NBA) building block. NBA favors highly planar backbone conformations; thus, comonomers that limit torsional displacement and disorder correlate to enhanced copolymer morphological order across multiple length scales and electron mobilities ranging from 0.4 to 4.5 cm² V^–1 s^–1.

Abstract

The synthesis and experimental/theoretical characterization of a new series of electron‐transporting copolymers based on the naphthalene bis(4,8‐diamino‐1,5‐dicarboxyl)amide (NBA) building block are reported. Comonomers are designed to test the emergent effects of manipulating backbone torsional characteristics, and density functional theory (DFT) analysis reveals the key role of backbone conformation in optimizing electronic delocalization and transport. The NBA copolymer conformational and electronic properties are characterized using a broad array of molecular/macromolecular, thermal, optical, electrochemical, and charge transport techniques. All NBA copolymers exhibit strongly aggregated morphologies with significant nanoscale order. Copolymer charge transport properties are investigated in thin‐film transistors and exhibit excellent electron mobilities ranging from 0.4 to 4.5 cm² V⁻¹ s⁻¹. Importantly, the electron transport efficiency correlates with the film mesoscale order, which emerges from comonomer‐dependent backbone planarity and extension. These results illuminate the key NBA building block structure–morphology–bulk property design relationships essential for processable, electronics‐applicable high‐performance polymeric semiconductors.

Using newly developed high‐quality FlexAgNEs, flexible OPV devices are fabricated and studied with the newly emerging star acceptor Y6 and its derivatives. Comparable performance with rigid counterparts is achieved for all the tested materials. The flexible devices display superior and robust mechanical stability under extreme bending or even folding conditions. Furthermore, the mechanism underlying the super mechanical robustness of these flexible devices is thoroughly investigated.

Abstract

Among the various advantages of organic photovoltaics (OPVs), the key one is their ability to be a highly flexible renewable energy source. However, the power conversion efficiencies for flexible OPV devices still lag behind those of their rigid counterparts, and their mechanical stability cannot meet the requirements for practical applications at present. These, in particular, depend on flexible transparent electrodes (FTEs). Here, a high‐quality FTE (called FlexAgNE), with the simultaneously combined excellent characteristics, has been tested with a series of efficient active materials for flexible OPV devices, and high performance comparable with rigid counterparts has been achieved. In addition, due to the synergistic effect of FlexAgNE and the upper ZnO transport layer, including strong binding between the polyethylene terephthalate substrate and a hydrophilic polyelectrolyte (the key component of FlexAgNE), together with the capillary force effect of crossed silver nanowires and tight filling of ZnO, the flexible devices demonstrate robust mechanical stability even under extreme bending or folding conditions.

The efficient spin transition between a high‐lying excited triplet state and the lowest excited singlet state in aggregation‐induced emission materials is demonstrated by magnetic field effects. A highly efficient deep‐blue aggregation‐induced emission (AIE)‐based organic light‐emitting diode (OLED) is achieved by further regulating utilization of excitons, which shows an excellent external quantum efficiency of 10.2%, low efficiency roll‐off, and a high brightness of 16 817 cd m⁻².

Abstract

Aggregation‐induced emission (AIE) materials are attractive for achieving highly efficient nondoped organic light‐emitting diodes (OLEDs) owing to their strong luminescence in the solid state. However, the electroluminescence efficiency of most AIE‐based OLEDs remains low owing to the waste of triplet excitons. Here, using theoretical calculations, photophysical dynamics, and magnetoluminescence measurements, the spin conversion process is demonstrated between the high‐lying triplet state (T _n ) and the lowest excited singlet state (S₁) in AIE materials. Moreover, the relative positions of T _n (n < 4) and S₁ are shown to have a significant impact on the spin‐conversion efficiency, thus influencing the harvesting of triplet excitons and the device efficiency. Finally, by selecting an upconversion material with an appropriate energy level for further utilizing the triplet excitons, a deep‐blue fluorescent OLED with CIE coordinates of (0.15, 0.08), a maximum external quantum efficiency of 10.2%, low efficiency roll‐off, and a high brightness of 16817 cd m⁻² is developed. This is one of the most efficient deep‐blue OLEDs based on AIE materials reported so far. These findings also provide new insights into the design of more efficient AIE molecules and corresponding OLEDs by managing high‐lying triplet excitons.