以昇陳

The Spiro-BD-2OEG with composition-conditioning agent functionality is designed to improve the composition stability in the doped-Spiro-OMeTAD hole transport layer (HTL). By employing this strategy, the HTL shows a pinhole-free and smooth morphology with an enhanced Spiro-OMeTAD ordering. Finally, the resultant perovskite solar cells show an excellent power conversion efficiency of 24.19% and improved thermal, moisture, and operational stabilities.

Abstract

The doped Spiro-OMeTAD hole transport layer (HTL) formed using the lithium bis(trifluoromethane) sulfonimide salt and 4-tert-butylpyridine with phenethylammonium iodide surface treatment on a perovskite film has continuously dominated the record power conversion efficiencies (PCEs) of perovskite solar cells (pero-SCs). However, unstable HTL compositions and iodide salts can cause severe device degradation. In this study, an HTL composition-conditioning agent (CCA), Spiro-BD-2OEG, is designed, which contains a Spiro-OMeTAD-like backbone, functional pyridine units, and oligo (ethylene glycol) chains. This finely designed CCA presents good miscibility with Spiro-OMeTAD and its dopants and acts as a conditioning agent through weak bond interactions. As a result, the CCA-regulated HTL shows a pinhole-free and smooth morphology with enhanced Spiro-OMeTAD ordering and improves dopant stability. In addition, the gradient-distributed CCA in the HTL can narrow the energy level offset with the valence band of the perovskite. The resultant pero-SCs exhibit an excellent PCE of 24.19% without any interface treatment and weak size dependence. A remarkable PCE of 22.63% is obtained even for a 1.004-cm² device. Importantly, the strategy shows good universality and significantly promotes the long-term stability of the pero-SCs based on the classical doped Spiro-OMeTAD.

This review presents a comprehensive overview of the gaps between the materials-level coin cells and device-level pouch cells, mechanistic understanding and quantitative discussion for failure mechanisms of pouch-type Li metal anodes, and the recently proposed strategies to suppress dendrite growth in pouch cells.

Abstract

Lithium metal battery has been considered as one of the potential candidates for next-generation energy storage systems. However, the dendrite growth issue in Li anodes results in low practical energy density, short lifespan, and poor safety performance. The strategies in suppressing Li dendrite growth are mostly conducted in materials-level coin cells, while their validity in device-level pouch cells is still under debate. It is imperative to address dendrite issues in pouch cells to realize the practical application of Li metal batteries. This review presents a comprehensive overview of the failure mechanism and regulation strategies of Li metal anodes in practical pouch cells. First, the gaps between the scientific findings in materials-level coin cells and device-level pouch cells are underscored. Specific attention is paid to the mechanistic understanding and quantitative discussion on the failure mechanisms of pouch-type Li metal batteries. Subsequently, recently proposed strategies are reviewed to suppress dendrite growth in pouch cells. The state-of-the-art electrochemical performance of pouch cells, especially the cell-level energy density and lifespan, is critically concerned. The review concludes with an attempt to summarize the scientific and engineering understandings of pouch-type Li metal anodes and propose some novel insights for the practical applications of Li metal batteries.

The uniform Li₃PO₄ layer in place of Li₂CO₃ contaminant is in situ built on garnet surface by making use of the molten NH₄H₂PO₄ salt driven conversion reaction. The Li₃PO₄-modified layer enables the highly air-stable garnet electrolyte without Li₂CO₃ formation for even 20 days as well as the lithiophilic interface with dendrite-free Li deposition.

Abstract

Garnet-type electrolytes show great potential in application of solid-state lithium batteries due to their high ionic conductivity and wide electrochemical window. However, the formation of surface Li₂CO₃ derived from air exposure triggers uneven contact with Li-metal, leading to undesirable dendrite growth and performance deterioration. Herein, the Li₃PO₄ layer replacing Li₂CO₃ contaminant is built on garnet surface by taking molten NH₄H₂PO₄ salt driven conversion reaction. The high-flowability molten salt contributes to conformal formation of Li₃PO₄, realizing the air-stable garnet by preventing the re-attack of H₂O/CO₂ in air. Besides, the high work of adhesion for Li₃PO₄ on Li-metal along with the transformation from Li₃PO₄ to Li₃P/Li₂O when contacting with molten Li-metal enables a lithiophilic interlayer, leading to a seamless Li/garnet contact with ultralow interfacial resistance of 13 Ω cm². Such ion-conducting but electron-insulating layer regulates the uniform distribution of Li-flux, enabling a large critical current density of 1.2 mA cm⁻². Furthermore, the solid LiCoO₂/Li cell with the modified garnet delivers a discharge capacity of 130 mAh g⁻¹ at 30 °C, accompanied by a capacity retention of 81% after 150 cycles. This study proposes a promising solution for improvement of air stability and interfacial compatibility of garnet using facile molten salt treatment.

Engineering of donor–acceptor–donor functional enamine hole transporting materials is presented leading to the low-cost hole transporting materia V1359 to reach power conversion efficiency over 22% in perovskite solar cells with excellent stability surpassing the reference spiro-OMeTAD due to the incorporation of the malononitrile acceptor units that passivate the surficial perovskite defects via Pb–N interactions.

Abstract

In this study, a series of donor–acceptor–donor (D-A-D) type small molecules based on the fluorene and diphenylethenyl enamine units, which are distinguished by different acceptors, as holetransporting materials (HTMs) for perovskite solar cells is presented. The incorporation of the malononitrile acceptor units is found to be beneficial for not only carrier transportation but also defects passivation via Pb–N interactions. The highest power conversion efficiency of over 22% is achieved on cells based on V1359, which is higher than that of spiro-OMeTAD under identical conditions. This st shows that HTMs prepared via simplified synthetic routes are not only a low-cost alternative to spiro-OMeTAD but also outperform in efficiency and stability state-of-art materials obtained via expensive cross-coupling methods.

The exciton diffusion and charge transport of PM6:Y6-based organic solar cells are simultaneously enhanced by trans-bis(dimesitylboron)stilbene (BBS), and the PM6:Y6:BBS devices achieve a higher efficiency of 17.6% relative to that without BBS (16.2%).

Abstract

Efficient exciton diffusion and charge transport play a vital role in advancing the power conversion efficiency (PCE) of organic solar cells (OSCs). Here, a facile strategy is presented to simultaneously enhance exciton/charge transport of the widely studied PM6:Y6-based OSCs by employing highly emissive trans-bis(dimesitylboron)stilbene (BBS) as a solid additive. BBS transforms the emissive sites from a more H-type aggregate into a more J-type aggregate, which benefits the resonance energy transfer for PM6 exciton diffusion and energy transfer from PM6 to Y6. Transient gated photoluminescence spectroscopy measurements indicate that addition of BBS improves the exciton diffusion coefficient of PM6 and the dissociation of PM6 excitons in the PM6:Y6:BBS film. Transient absorption spectroscopy measurements confirm faster charge generation in PM6:Y6:BBS. Moreover, BBS helps improve Y6 crystallization, and current-sensing atomic force microscopy characterization reveals an improved charge-carrier diffusion length in PM6:Y6:BBS. Owing to the enhanced exciton diffusion, exciton dissociation, charge generation, and charge transport, as well as reduced charge recombination and energy loss, a higher PCE of 17.6% with simultaneously improved open-circuit voltage, short-circuit current density, and fill factor is achieved for the PM6:Y6:BBS devices compared to the devices without BBS (16.2%).

Vacancy-ordered double perovskite Cs₂ZrCl₆ is employed to fabricate large-area flexible X-ray scintillator screens. Joint experiment–theory characterizations indicate the broadband emission of Cs₂ZrCl₆ originates from the triplet emission of self-trapped excitons. The thermally activated delayed fluorescence feature of Cs₂ZrCl₆ provides a large Stokes shift and supports luminescence collection. The flexible scintillator screen achieves high-quality imaging of non-flat and dynamic objects.

Abstract

Flexible scintillator screens with environmental stability, high sensitivity, and low cost have emerged as candidates for X-ray imaging applications. Here, a large-scale and cost-efficient solution synthesis of the vacancy-ordered double perovskite Cs₂ZrCl₆, which is characterized by thermal activation delayed fluorescence (TADF) dominated by triplet emission under X-ray irradiation, is demonstrated. The large Stokes shift and efficient luminescence collection of TADF effectively ensure the light outcoupling efficiency. Further, flexible X-ray scintillator screens with an area of 400 cm² are prepared using poly(dimethylsiloxane) (PDMS) as the carrier, exhibiting excellent scintillation properties with light yields as high as 49 400 photons MeV⁻¹, spatial resolutions up to 18 lp mm⁻¹ and detection limits as low as 65 nGy s⁻¹. Finally, the high-quality imaging results of non-planar and dynamic objects by such screens are demonstrated. It is believed that the explored Cs₂ZrCl₆@PDMS flexible scintillator screens would offer a big step toward expanding the application range of scintillators in different environments.

Nature Energy, Published online: 19 September 2022; doi:10.1038/s41560-022-01096-5

A high-performance and self-powered blue perovskite photodetector (PPD) is developed by designing and optimizing A-site of APb(Br_0.65Cl_0.35)₃ (A = formamidinium (FA⁺), methylammonium (MA⁺), Cs⁺) perovskites (PVSKs). The incorporation of Cs⁺ into FA/MA-PVSKs reduces the lattice strain and defect density. Consequently, a best-performing Cs-incorporating device shows an external quantum efficiency (EQE) of 84.9% which is the highest EQE reported in blue PDs.

Abstract

A self-powered, color-filter-free blue photodetector (PD) based on halide perovskites is reported. A high external quantum efficiency (EQE) of 84.9%, which is the highest reported EQE in blue PDs, is achieved by engineering the A-site monovalent cations of wide-bandgap perovskites. The optimized composition of formamidinium (FA)/methylammonium (MA) increases the heat of formation, yielding a uniform and smooth film. The incorporation of Cs⁺ ions into the FA/MA composition suppresses the trap density and increases charge-carrier mobility, yielding the highest average EQE of 77.4%, responsivity of 0.280 A W⁻¹, and detectivity of 5.08 × 10¹² Jones under blue light. Furthermore, Cs⁺ improves durability under repetitive operations and ambient atmosphere. The proposed device exhibits peak responsivity of 0.307 A W⁻¹, which is higher than that of the commercial InGaN-based blue PD (0.289 A W⁻¹). This study will promote the development of next-generation image sensors with vertically stacked perovskite PDs.

Nature Photonics, Published online: 10 October 2022; doi:10.1038/s41566-022-01079-8

This novel, mechanically flexible and bifunctional separator integrates the merits of serving as a highly aligned ion-redistributor to self-regulate/orientate the flux of Na-ions from a chemical molecular level and physically suppresses Na dendrite puncture at a mechanical structural level. Remarkably, Na symmetric cells achieve unprecedented long-term cycling performances at high current densities in additive-free carbonate-based electrolytes.

Abstract

Sodium (Na) is the most appealing alternative to lithium as an anode material for cost-effective, high-energy-density energy-storage systems by virtue of its high theoretical capacity and abundance as a resource. However, the uncontrolled growth of Na dendrites and the limited cell cycle life impede the large-scale practical implementation of Na-metal batteries (SMBs) in commonly used and low-cost carbonate electrolytes. Herein, the employment of a novel bifunctional electrospun nanofibrous separator comprising well-ordered, uniaxially aligned arrays, and abundant sodiophilic functional groups is presented for SMBs. By tailoring the alignment degree, this unique separator integrates with the merits of serving as highly aligned ion-redistributors to self-orientate/homogenize the flux of Na-ions from a chemical molecule level and physically suppressing Na dendrite puncture at a mechanical structure level. Remarkably, unprecedented long-term cycling performances at high current densities (≥1000 h at 1 and 3 mA cm⁻², ≥700 h at 5 mA cm⁻²) of symmetric cells are achieved in additive-free carbonate electrolytes. Moreover, the corresponding sodium–organic battery demonstrates a high energy density and prolonged cyclability over 1000 cycles. This work opens up a new and facile avenue for the development of stable, low-cost, and safe-credible SMBs, which could be readily extended to other alkali-metal batteries.

Nature Communications, Published online: 23 August 2022; doi:10.1038/s41467-022-32478-8

Nature Photonics, Published online: 08 August 2022; doi:10.1038/s41566-022-01046-3

Nature Photonics, Published online: 08 August 2022; doi:10.1038/s41566-022-01051-6

A new acceptor of FTCCBr and frequently-used ITCC is studied, due to their similar optical and electrochemistry properties. Under a light intensity of 1000 lux, the PB2:ITCC-based device with a small electrostatic potential (ESP) offset gives a power conversion efficiency (PCE) of 25.4%, while the PB2:FTCCBr-based device with a large ESP offset achieves a record PCE of 30.2%.

Abstract

The correlation between molecular structure and photovoltaic performance is lagging for constructing high-performance indoor organic photovoltaic (OPV) cells. Herein, this relationship is investigated in depth by employing two medium-bandgap nonfullerene acceptors (NFAs). The newly synthesized NFA of FTCCBr exhibits a similar bandgap and molecular energy level, but a much stronger dipole moment and larger average electrostatic potential (ESP) compared with ITCC. After blending with the polymer donor PB2, the PB2:ITCC and PB2:FTCCBr blends exhibit favorable bulk-heterojunction morphologies and the same driving force, but the PB2:FTCCBr blend exhibits a large ESP difference. In OPV cells, the PB2:ITCC-based device produces a power conversion efficiency (PCE) of 11.0%, whereas the PB2:FTCCBr-based device gives an excellent PCE of 14.8% with an open-circuit voltage (V _OC) of 1.05 V, which is the highest value among OPV cells with V _OC values above 1.0 V. When both acceptor-based devices work under a 1000 lux of 3000 K light-emitting diode, the PB2:ITCC-based 1 cm² device yields a good PCE of 25.4%; in contrast, the PB2:FTCCBr-based 1 cm² device outputs a record PCE of 30.2%. These results suggest that a large ESP offset in photovoltaic materials is important for achieving high-performance OPV cells.

Zn-battery issues in aqueous media are fundamentally studied, revealing that besides the well-known H₂ evolution and dendrite growth, Zn electrodes also face an O₂-involving corrosion reaction. Thus, a one-off electrolyte regulation is proposed by introducing the triple-function C₃H₇Na₂O₆P additive, which can take effects to suppress the O₂-involving corrosion reaction, water decomposition, and dendritic deposition during the shelf time.

Abstract

The poor Zn reversibility has been criticized for limiting applications of aqueous Zn-ion batteries (ZIBs); however, its behavior in aqueous media is not fully uncovered yet. Here, this knowledge gap is addressed, indicating that Zn electrodes face a O₂-involving corrosion, besides H₂ evolution and dendrite growth. Differing from aqueous Li/Na batteries, removing O₂ cannot enhance ZIB performance because of the aggravated competing H₂ evolution. To address Zn issues, a one-off electrolyte strategy is reported by introducing the triple-function C₃H₇Na₂O₆P, which can take effects during the shelf time of battery. It regulates H⁺ concentration and reduces free-water activity, inhibiting H₂ evolution. A self-healing solid/electrolyte interphase (SEI) can be triggered before battery operation, which suppresses O₂ adsorption corrosion and dendritic deposition. Consequently, a high Zn reversibility of 99.6% is achieved under a high discharge depth of 85%. The pouch full-cell with a lean electrolyte displays a record lifespan with capacity retention of 95.5% after 500 cycles. This study not only looks deeply into Zn behavior in aqueous media but also underscores rules for the design of active metal anodes, including Zn and Li metals, during shelf time toward real applications.

A room-temperature molten salt dimethylamine acetate is developed as the solvent for precursor solutions, which also regulates the phase conversion process of the CsPbI₃ film. Consequently, 1.25 V of the open-circuit voltage and >21% power conversion efficiency are achieved, which is the record highest for CsPbI₃ perovskite solar cells reported so far.

Abstract

All-inorganic CsPbI₃ perovskite has emerged as an important photovoltaic material due to its high thermal stability and suitable bandgap for tandem devices. Currently, the cell performance of CsPbI₃ solar cells is mainly subject to a large open-circuit voltage (V _OC) deficit. Herein, a multifunctional room-temperature molten salt, dimethylamine acetate (DMAAc) is demonstrated, which not only directly acts as a solvent for precursor solutions, but also regulates the phase conversion process of the CsPbI₃ film for high-efficiency photovoltaics. DMAAc can stabilize the DMAPbI₃ structure and eliminate the Cs₄PbI₆ intermediate phase, which is easily spatially segregated. Meanwhile, a new homogeneous intermediate phase DMAPb(I,Ac)₃ is formed, which finally affords high-quality CsPbI₃ films. With this approach, the charge capture activity of defects in the CsPbI₃ film is significantly suppressed. Consequently, a V _OC of 1.25 V and >21% power conversion efficiency are achieved, which is the record highest reported thus far. This intermediate phase-regulation strategy is believed to be applicable to other perovskite material systems.

Phenethylammonium bromine-modified CsPbBr₃ nanocrystals are successfully introduced into perovskite film to passivate the intrinsic defects and accelerate the energy-transfer process. Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate/poly[9,9-dioctylfluoreneco-N-[4-(3-methylpropyl)]diphenylamine]:black phosphorus is also constructed to enhance carrier injection and charge-transport ability. Consequently, a champion external quantum efficiency of 25.32% and a maximal brightness of 128 842 cd m⁻² are successfully achieved.

Abstract

Quasi-2D perovskites have emerged as a promising luminescent material for perovskite light-emitting diodes (Pe-LEDs). However, efficiency and stability are still obstacles to practical application due to numerous defects and inefficient energy transfer of perovskite films. Herein, functional phenethylammonium bromine-modified CsPbBr₃ nanocrystals (PEA-CsPbBr₃ NCs) are first introduced as multifunctional additive to simultaneously improve abovementioned problems. PEA-CsPbBr₃ NCs not only serve as heteronuclear seeds and trigger growth, thus greatly reducing leakage current, but also deliver Cs⁺ and Br⁻ to passivate the intrinsic defects inside film. More importantly, the PEA-CsPbBr₃ construct a new carrier-transfer pathway from the small-n phase of the quasi-2D perovskite to the PEA-CsPbBr₃, which not only accelerates the energy-transfer process but also promotes radiation recombination of carriers due to stronger quantum confinement effect. Afterward, the poly(3,4-ethylenedioxythiophene):polystyrene sulfonate/poly[9,9-dioctylfluoreneco-N-[4-(3-methylpropyl)]diphenylamine]:black phosphorus quantum dot double hole-transport layer is successfully constructed to enhance its carrier-injection and charge-transport abilities. Consequently, a champion external quantum efficiency of 25.32% and maximal brightness of 128 842 cd m⁻² are achieved, which is the record efficiency of the quasi-2D Pe-LED with pure green emission at 530 nm. Moreover, an impressive 174 min lifetime is obtained at T ₅₀, which is about five times longer than the control device.

Efficient In(Zn)As–In(Zn)P–GaP–ZnS colloidal quantum dot (CQD) light-emitting diodes (LEDs) that operate with an external quantum efficiency (EQE) of 13.3% at 1006 nm are reported. The implementation of a thin hole-transporting poly(vinylcarbazole) (PVK) layer at the electron-injecting side of the device gives rise to improved charge balance and luminescence efficiencies.

Abstract

Short-wave infrared (SWIR) light emission is important for a diverse range of modern applications, such as eye-safe depth sensing, light detection and ranging (LiDAR), facial recognition, eye tracking, optical communication, and health-monitoring technologies. However, there are a very limited number of known semiconductors that can emit efficiently in the SWIR spectral range. Presently, SWIR light-emitting diodes (LEDs) based on colloidal quantum dots (CQD) are dominated by lead chalcogenide systems, despite the presence of heavy metal and modest efficiencies. Here, a highly efficient SWIR LED based on heavy-metal-free indium arsenide (InAs) core–shell CQDs is presented. In the LED design, the implementation of an otherwise hole-transporting poly(vinylcarbazole) (PVK) layer on the electron-injecting side of the device stack leads to a surprising enhancement in device performance, giving remarkably high external quantum efficiencies (EQEs) of 13.3% at 1006 nm. Single-carrier device and optical investigations reveal the origins of enhancement to be the electronic decoupling of the CQD layer with the electron-injecting zinc oxide (ZnO) layer, which mitigates luminescence quenching and improves charge balance. This work marks one of the highest efficiencies reported for heavy-metal-free solution-processed LEDs in the SWIR spectral region, and can find significant applications in emerging consumer electronic technologies.

Organic Light-Emitting Diodes

Intrinsically stretchable light-emitting diodes (ISOLEDs) are becoming increasingly important for wearable electronics. In article number 2203040, Han-Young Woo, Tae-Woo Lee, and co-workers report the design of highly efficient ISOLEDs that use a graphene-based 2D-contact stretchable electrode. As a benefit of a newly designed conjugated polyelectrolyte with efficient electron injection capability, the ISOLED yields an unprecedently high current efficiency of 20.3 cd A⁻¹.

Photoactive Materials

Next-generation photovoltaics will be lightweight, flexible, and (semi)transparent. Highly transparent organic photoactive materials are reported by Thuc-Quyen Nguyen, Viktor Brus, and co-workers in article number 2203796. The changes in the fundamental processes in solar cells comprising a near-IR-absorbing acceptor and a visible-light-absorbing donor are revealed upon dilution of the donor material, paving the way for integrated energy-harvesting solutions based on semitransparent organic photovoltaics.