Chen Weijie

Thin-film, cover, and hybrid encapsulation technologies, that function as a moisture and oxygen permeation barrier and mechanical protection to prevent leakage of toxic by-product, and limit decomposition of reactants in a confined space, can be applied in organic light emitting diodes, organic and perovskite solar cells, leading to robust stability and long lifetime in three types of devices.

Abstract

Organic light emitting diodes (OLEDs) employing organic thin-film based emitters have attracted tremendous attention due to their widespread applications in lighting and as displays in mobile devices and televisions. The novel thin-film photovoltaic techniques using organic or organic–inorganic hybrid materials such as organic photovoltaics (OPVs) and perovskite solar cells (PSCs) have become emerging competitive candidates with regard to the traditional photovoltaic techniques on account of high-efficiency, low-cost, and simple manufacturing processing properties. However, OLEDs, OPVs, and PSCs are vulnerable to the undesired degradation induced by moisture and oxygen. To afford long-term stability, a robust encapsulation technique by employing materials and structures that possess high barrier performance against oxygen and moisture must be explored and employed to protect these devices. Herein, the recent progress on specific encapsulation materials and techniques for three types of devices on the basis of fundamental understanding of device stability is reviewed. First, their degradation mechanisms, as well as, influencing factors are discussed. Then, the encapsulation technologies and materials are classified and discussed. Moreover, the advantages and disadvantages of various encapsulation technologies and materials coupled with their encapsulation applications in different devices are compared. Finally, the ongoing challenges and future perspectives of encapsulation frontier are provided.

An organic–inorganic hybrid electrolyte with aligned energy levels, self‐doping behavior, and improved electron mobility and conductivity was developed. It facilitates electron transport and boosts the power conversion efficiency of organic solar cells to 17.19 %.

Abstract

An organic–inorganic hybrid electrolyte based on a cyclic Ti‐oxo cluster as the inorganic core and naphthalene‐based organic ammonium bromide salts as the electrolyte was developed with easy synthesis and low cost. The new hybrid electrolyte exhibits excellent solubility in methanol, aligned work function, good conductivity, and amorphous state in thin film, enabling its successful application as a cathode interlayer in organic solar cells with a high power conversion efficiency of 17.19 %. This work demonstrates that the hybrid electrolytes are a new kind of semiconductor, exhibiting promising applications in organic electronics.

MAPbI₃ crystal growth in the films made by drop‐casting is regulated by changing the temperature. At low temperature (60 °C), the crystals are (110) oriented, needle‐like. At high temperature (>120 °C), the crystals are (200) oriented, presenting round grains. The different crystal growth mode leads to quite different film morphology and photovoltaic performance.

Abstract

Drop‐casting was used to make MAPbI₃ films for solar cells. The crystal growth in drop‐cast MAPbI₃ films was regulated by adjusting temperature. A mechanism for the formation of different morphology was proposed by combining in situ crystal‐growth study with XRD measurements. The crystals in the films made at low temperature (60 °C) and high temperature (≥120 °C) are (110) and (200) oriented, respectively. The different crystal growth mode leads to quite different film morphology. Compared with spin‐coating, drop‐casting shows much better tolerance to humidity. MAPbI₃ solar cells made under 88 % humidity delivered a PCE of 18.17 %, which is the highest PCE for perovskite solar cells made under >70 % humidity without antisolvent assistance.

The potential of wide bandgap perovskite solar cells is often limited by low open‐circuit voltages. By tuning the lowest‐unoccupied molecular‐orbital of electron transport layers via the use of different fullerenes and fullerene blends, open‐circuit voltages exceeding 1.35 V in CH₃NH₃Pb(I_0.8Br_0.2)₃ device without loss in fill factor leading to a high V _oc FF product of 1.10 V are demonstrated.

Abstract

Nonradiative recombination processes are the biggest hindrance to approaching the radiative limit of the open‐circuit voltage for wide bandgap perovskite solar cells. In addition to high bulk quality, good interfaces and good energy level alignment for majority carriers at charge transport layer‐absorber interfaces are crucial to minimize nonradiative recombination pathways. By tuning the lowest‐unoccupied molecular‐orbital of electron transport layers via the use of different fullerenes and fullerene blends, open‐circuit voltages exceeding 1.35 V in CH₃NH₃Pb(I_0.8Br_0.2)₃ device are demonstrated. Further optimization of mobility in binary fullerenes electron transport layers can boost the power conversion efficiency as high as 18.9%. It is noted in particular that the V _oc fill factor product is >1.096 V, which is the highest value reported for halide perovskites with this bandgap.

A novel IDTT‐based small molecule (SM) additive (IDTT‐ThCz) is developed and introduced into perovskite solar cells (PSCs) through an anti‐solvent engineering method. This IDTT‐ThCz passivates defect states of perovskite layers, providing efficient charge extraction as well as preventing the decomposition of perovskite crystals. Therefore, IDTT‐ThCz treated PSCs achieve a highest efficiency of 22.5% and remarkable thermal stability.

Abstract

Although perovskite solar cells (PSCs) have attracted enormous attention owing to their fascinating optoelectronic properties and solution processability, defects in PSCs, which adversely affect efficiency and stability, are still not completely resolved. Herein, a novel indacenodithieno[3,2‐b]thiophene‐based small molecule (SM) additive (IDTT‐ThCz), capable of interacting with perovskite layers, is developed. In particular, the IDTT‐ThCz, which can perform a surface passivation, is introduced into the perovskite layer to significantly suppress perovskite defects via antisolvent treatment. Furthermore, this facile surface passivation not only significantly improves the charge extraction capability, but also prevents perovskite degradation. The IDTT‐ThCz‐treated PSCs exhibits a power conversion efficiency (PCE) of 22.5% and retains 95% of its initial PCE after 500 h storage under thermal condition (85 °C), representing the most remarkable efficiency as well as stability among the SM additives reported to date.

Bottom-surface defect passivation of perovskite film is enabled by covalently attaching –OH to a hole-transporting polymer. A solvent evaporation-induced self-assembly of the resultant amphiphilic hole-transporting polymer enriches –OH on the film surface, passivating defects of the upper perovskite layer. Inverted perovskite solar cells based on this polymer afford an efficiency of 20.12% with improved device stability compared to its poly(bis(4-phenyl)(2,5,6-trimethylphenyl)amine) counterpart.

Abstract

Bottom-surface defect passivation of perovskite film, lagging far behind easily conducted bulk and top-surface passivations in perovskite solar cells (PSCs), remains rather challenging because most passivation molecules/groups can be eroded by polar solvents used for the subsequent perovskite deposition. In this work, an effective bottom-surface passivation is enabled for enhanced performance of inverted PSCs by covalently attaching a passivation group (hydroxyl) to a hole transporting polymer. A short linker (methylene) between the hydroxyl and the conjugated backbone bearing hydrophobic long alkyl chains is adopted to improve the resistance of the resultant amphiphilic polymer to polar solvents. A solvent evaporation-induced self-assembly of the amphiphilic hole transporting polymer is developed to enrich hydroxyl groups on the film surface, passivating defects of the upper perovskite layer via interactions with undercoordinated Pb²⁺ and I^– sites. Inverted PSCs based on this hole transporting film are superior in efficiency (20.12%), reproducibility, large-area fabrication, and stability to its classical poly(bis(4-phenyl)(2,5,6-trimethylphenyl)amine) counterpart. This work demonstrates that rational introduction of passivation groups into the hole transporting layer combined with self-assembly-modulated component distributions is useful to realize bottom-surface passivation of the perovskite layer for improved photovoltaic performance.

A multi‐cation halide composition of perovskite solar cells is engineered via a two‐step sequential deposition method by adding mixtures of 1D polymorphs of orthorhombic δ‐RbPbI₃ and δ‐CsPbI₃ to the PbI₂. This approach greatly facilitates heterogeneous nucleation which leads to perovskite with high crystallinity and superior optoelectronic properties. Solar cells fabricated with these perovskites exhibit an efficiency of over 22%.

Abstract

The performance of perovskite solar cells is highly dependent on the fabrication method; thus, controlling the growth mechanism of perovskite crystals is a promising way towards increasing their efficiency and stability. Herein, a multi‐cation halide composition of perovskite solar cells is engineered via the two‐step sequential deposition method. Strikingly, it is found that adding mixtures of 1D polymorphs of orthorhombic δ‐RbPbI₃ and δ‐CsPbI₃ to the PbI₂ precursor solution induces the formation of porous mesostructured hexagonal films. This porosity greatly facilitates the heterogeneous nucleation and the penetration of FA (formamidinium)/MA (methylammonium) cations within the PbI₂ film. Thus, the subsequent conversion of PbI₂ into the desired multication cubic α‐structure by exposing it to a solution of formamidinium methylammonium halides is greatly enhanced. During the conversion step, the δ‐CsPbI₃ also is fully integrated into the 3D mixed cation perovskite lattice, which exhibits high crystallinity and superior optoelectronic properties. The champion device shows a power conversion efficiency (PCE) over 22%. Furthermore, these devices exhibit enhanced operational stability, with the best device retaining more than 90% of its initial value of PCE under 1 Sun illumination with maximum power point tracking for 400 h.

Despite the defect-tolerance of lead-halide perovskites, defects at the surface of colloidal nanocrystals and grain boundaries in thin films play a critical role in charge-carrier transport and nonradiative recombination, which lowers the photoluminescence quantum yields, device efficiency, and stability. This Review summarizes the defects, their influence on the optical and charge-carrier transport properties, and passivation strategies to mitigate the effects of defects.

Abstract

Lead-halide perovskites (LHPs), in the form of both colloidal nanocrystals (NCs) and thin films, have emerged over the past decade as leading candidates for next-generation, efficient light-emitting diodes (LEDs) and solar cells. Owing to their high photoluminescence quantum yields (PLQYs), LHPs efficiently convert injected charge carriers into light and vice versa. However, despite the defect-tolerance of LHPs, defects at the surface of colloidal NCs and grain boundaries in thin films play a critical role in charge-carrier transport and nonradiative recombination, which lowers the PLQYs, device efficiency, and stability. Therefore, understanding the defects that play a key role in limiting performance, and developing effective passivation routes are critical for achieving advances in performance. This Review presents the current understanding of defects in halide perovskites and their influence on the optical and charge-carrier transport properties. Passivation strategies toward improving the efficiencies of perovskite-based LEDs and solar cells are also discussed.

Nature Materials, Published online: 15 March 2021; doi:10.1038/s41563-021-00947-y

Publication date: 21 April 2021

Source: Joule, Volume 5, Issue 4

Author(s): Di Wang, Haoran Liu, Yuhao Li, Guanqing Zhou, Lingling Zhan, Haiming Zhu, Xinhui Lu, Hongzheng Chen, Chang-Zhi Li

Publication date: 17 March 2021

Source: Joule, Volume 5, Issue 3

Author(s): Minjin Kim, In-woo Choi, Seung Ju Choi, Ji Won Song, Sung-In Mo, Jeong-Ho An, Yimhyun Jo, SeJin Ahn, Seoung Kyu Ahn, Gi-Hwan Kim, Dong Suk Kim

Nature Energy, Published online: 17 March 2021; doi:10.1038/s41560-021-00800-1

A moisture‐triggered self‐healing flexible perovskite photodetector is presented. The lateral photodetector shows a high responsivity of 11.3 A W⁻¹ and a good stability to both moisture and mechanical damage. Meanwhile, damaged perovskite film can repair cracks with the assistance of a poly(vinyl alcohol) microscaffold under a humid environment and recover to 90% of its initial performance for several cycles.

Abstract

Flexible devices are urgently required to meet the demands of next‐generation optoelectronic devices and metal halide perovskites are proven to be suitable materials for realizing flexible photovoltaic devices. However, the tolerance to moisture corrosion and repeated mechanical bending remains a critical challenge for flexible perovskite devices. Herein, a self‐healing formamidinium lead iodide (FAPbI₃) film is fabricated to cure mechanical damage by absorbing moisture from the surrounding environment. A poly(vinyl alcohol) microscaffold is designed not only to stabilize the black phase of the FAPbI₃ film but also to endow it with self‐healing ability in a humid environment. The photodetector based on a self‐healing film exhibits a high responsivity of 11.3 A W⁻¹ and recovers to over 90% of the initial responsivity after the self‐healing process. This work provides an effective self‐healing strategy to stabilize the operation of flexible perovskite devices under normal high‐humidity environmental conditions.

Halide perovskite memristive barristors (diodes with variable Schottky barriers) portraying tunable diffusive dynamics and ionic drift as nociceptive and synaptic emulators for neuromorphic sensory signal computing are experimentally demonstrated. Poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate interfaces promote diffusive kinetics while NiO _x interfaces support drift kinetics with CH₃NH₃PbBr₃ as the switching matrix, resulting in modulatable diffusive and drift memristors respectively.

Abstract

With the current research impetus on neuromorphic computing hardware, realizing efficient drift and diffusive memristors are considered critical milestones for the implementation of readout layers, selectors, and frameworks in deep learning and reservoir computing networks. Current demonstrations are predominantly limited to oxide insulators with a soft breakdown behavior. While organic ionotronic electrochemical materials offer an attractive alternative, their implementations thus far have been limited to features exploiting ionic drift a.k.a. drift memristor technology. Development of diffusive memristors with organic electrochemical materials is still at an early stage, and modulation of their switching dynamics remains unexplored. Here, halide perovskite (HP) memristive barristors (diodes with variable Schottky barriers) portraying tunable diffusive dynamics and ionic drift are proposed and experimentally demonstrated. An ion permissive poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate interface that promotes diffusive kinetics and an ion source nickel oxide (NiO _x ) interface that supports drift kinetics are identified to design diffusive and drift memristors, respectively, with methylammonuim lead bromide (CH₃NH₃PbBr₃) as the switching matrix. In line with the recent interest on developing artificial afferent nerves as information channels bridging sensors and artificial neural networks, these HP memristive barristors are fashioned as nociceptive and synaptic emulators for neuromorphic sensory signal computing.

Publication date: July 2021

Source: Nano Energy, Volume 85

Author(s): Difei Zhang, Wenkai Zhong, Lei Ying, Baobing Fan, Meijing Li, Ziqi Gan, Zhaomiyi Zeng, Dongcheng Chen, Ning Li, Fei Huang, Yong Cao

Publication date: 17 March 2021

Source: Joule, Volume 5, Issue 3

Author(s): Qian Kang, Zhong Zheng, Yunfei Zu, Qing Liao, Pengqing Bi, Shaoqing Zhang, Yi Yang, Bowei Xu, Jianhui Hou

Publication date: 21 April 2021

Source: Joule, Volume 5, Issue 4

Author(s): Gongya Zhang, Haijun Ning, Hui Chen, Qiuju Jiang, Jiaquan Jiang, Pengwei Han, Li Dang, Meichen Xu, Ming Shao, Feng He, Qinghe Wu

Thermodynamically stable β‐CsPbI₃ nanocrystals are prepared, and they are demonstrated to function as a stable, efficient red‐emitting layer. With incorporation of poly(maleic anhydride‐alt‐1‐octadecene), the β‐CsPbI₃ further exhibits reduced deep defects of Pb_Cs, increased exciton binding energy, and reduced longitudinal‐optical phonon energy. Red‐emitting perovskite light‐emitting diodes (PeLEDs) based on β‐CsPbI₃ achieve both high external quantum efficiency and superior operational stability.

Abstract

The long‐term operational stability of perovskite light‐emitting diodes (PeLEDs), especially red PeLEDs with only several hours typically, has always faced great challenges. Stable β‐CsPbI₃ nanocrystals (NCs) are demonstrated for highly efficient and stable red‐emitting PeLEDs through incorporation of poly(maleic anhydride‐alt‐1‐octadecene) (PMA) in synthesizing the NCs. The PMA can chemically interact with PbI₂ in the precursors via the coupling effect between O groups in PMA and Pb²⁺ to favor crystallization of stable β‐CsPbI₃ NCs. Meanwhile, the cross‐linked PMA significantly reduces the Pb_Cs anti‐site defect on the surface of the β‐CsPbI₃ NCs. Benefiting from the improved crystal phase quality, the photoluminescence quantum yield for β‐CsPbI₃ NCs films remarkably increases from 34% to 89%. The corresponding red‐emitting PeLEDs achieves a high external quantum efficiency of 17.8% and superior operational stability with the lifetime, the time to half the initial electroluminescence intensity (T ₅₀) reaching 317 h at a constant current density of 30 mA cm⁻².

Nature Communications, Published online: 04 March 2021; doi:10.1038/s41467-021-21683-6

A moiré interference structure augments light‐diffraction channels, leading to elongated optical paths, and “folds” sunlight into the perovskite layer. Besides, the sets of moiré diffracted light achieve “1 + 1 = 3” comparing to the single diffraction grating. Therefore, moiré perovskite solar cells are constructed by way of a commercial DVD disc, resulting in a champion efficiency up to 20.17% (MAPbI₃) and 21.76% ((FAPbI₃)_{1‐ x} (MAPbBr₃) _x ).

Abstract

Light harvesting is crucial for thin‐film solar cells. To substantially reduce optical loss in perovskite solar cells (PSCs), hierarchical light‐trapping nano‐architectures enable absorption enhancement to exceed the conventional upper limit and have great potential for achieving state‐of‐the art optoelectronic performances. However, it remains a great challenge to design and fabricate a superior hierarchical light‐trapping nano‐architecture, which exhibits extraordinary light‐harvesting ability and simultaneously avoids deteriorating the electrical performance of PSCs. Herein, colorful efficient moiré‐PSCs are designed and fabricated incorporating moiré interference structures by the imprinting method with the aid of a commercial DVD disc. It is experimentally and theoretically demonstrated that the light harvesting ability of the moiré interference structure can be well manipulated through changing the rotation angle (0°–90°). The boosted short‐circuit current is credited to augment light diffraction channels, leading to elongated optical paths, and fold sunlight into the perovskite layer. Moreover, the imprinting process suppresses the trap sites and voids at the active‐layer interfaces with eliminated hysteresis. The moiré‐PSC with an optimized 30° rotation angle achieves the best enhancement of light harvesting (28.5% higher than the pristine), resulting in efficiencies over 20.17% (MAPbI₃) and 21.76% ((FAPbI₃)_{1‐ x} (MAPbBr₃) _x ).

A facile strategy of employing an acceptor‐analogue is developed to efficiently reduce trap density to a magnitude of 10¹⁵ cm⁻³ for organic photovoltaic materials, which is comparable to and even lower than those of some inorganic counterparts, and boosts the power conversion efficiency of organic solar cells up to 17.8%.

Abstract

Typical organic semiconductor materials exhibit a high trap density of states, ranging from 10¹⁶ to 10¹⁸ cm⁻³, which is one of the important factors in limiting the improvement of power conversion efficiencies (PCEs) of organic solar cells (OSCs). In order to reduce the trap density within OSCs, a new strategy to design and synthesize an electron acceptor analogue, BTPR, is developed, which is introduced into OSCs as a third component to enhance the molecular packing order of electron acceptor with and without blending a polymer donor. Finally, the as‐cast ternary OSC devices employing BTPR show a notable PCE of 17.8%, with a low trap density (10¹⁵ cm⁻³) and a low energy loss (0.217 eV) caused by non‐radiative recombination. This PCE is among the highest values for single‐junction OSCs. The trap density of OSCs with the BTPR additives, as low as 10¹⁵ cm⁻³, is comparable to and even lower than those of several typical high‐performance inorganic/hybrid counterparts, like 10¹⁶ cm⁻³ for amorphous silicon, 10¹⁶ cm⁻³ for metal oxides, and 10¹⁴ to 10¹⁵ cm⁻³ for halide perovskite thin film, and makes it promising for OSCs to obtain a PCE of up to 20%.

Room‐temperature high‐efficiency light‐emitting diodes based on metal halide perovskite FAPbI₃ can work perfectly at low temperatures. A peak external quantum efficiency of 32.8%, corresponding to an internal quantum efficiency of 100%, is achieved at 45 K. Importantly, the device shows almost no degradation after working at a constant current density of 200 mA m⁻² for 330 h.

Abstract

Room‐temperature‐high‐efficiency light‐emitting diodes based on metal halide perovskite FAPbI₃ are shown to be able to work perfectly at low temperatures. A peak external quantum efficiency (EQE) of 32.8%, corresponding to an internal quantum efficiency of 100%, is achieved at 45 K. Importantly, the devices show almost no degradation after working at a constant current density of 200 mA m⁻² for 330 h. The enhanced EQEs at low temperatures result from the increased photoluminescence quantum efficiencies of the perovskite, which is caused by the increased radiative recombination rate. Spectroscopic and calculation results suggest that the phase transitions of the FAPbI₃ play an important role for the enhancement of exciton binding energy, which increases the recombination rate.

Notable developments of SnO₂ as an electron‐selective layer for efficient perovskite solar cells (PSCs) are reviewed, along with an overview of the fabrication methods and interfacial passivation routes. Furthermore, techno‐economic and toxicology analyses of SnO₂ are discussed for possible large‐scale deployment of PSCs. Finally, the role of SnO₂ in scaled module and tandem solar cell production is revealed.

Abstract

Perovskite solar cells (PSCs) have become a promising photovoltaic (PV) technology, where the evolution of the electron‐selective layers (ESLs), an integral part of any PV device, has played a distinctive role to their progress. To date, the mesoporous titanium dioxide (TiO₂)/compact TiO₂ stack has been among the most used ESLs in state‐of‐the‐art PSCs. However, this material requires high‐temperature sintering and may induce hysteresis under operational conditions, raising concerns about its use toward commercialization. Recently, tin oxide (SnO₂) has emerged as an attractive alternative ESL, thanks to its wide bandgap, high optical transmission, high carrier mobility, suitable band alignment with perovskites, and decent chemical stability. Additionally, its low‐temperature processability enables compatibility with temperature‐sensitive substrates, and thus flexible devices and tandem solar cells. Here, the notable developments of SnO₂ as a perovskite‐relevant ESL are reviewed with emphasis placed on the various fabrication methods and interfacial passivation routes toward champion solar cells with high stability. Further, a techno‐economic analysis of SnO₂ materials for large‐scale deployment, together with a processing‐toxicology assessment, is presented. Finally, a perspective on how SnO₂ materials can be instrumental in successful large‐scale module and perovskite‐based tandem solar cell manufacturing is provided.

The solvent engineering of precursor solutions toward efficient perovskite solar cells (PSCs) is reviewed comprehensively. The key role of solvent engineering for solution‐processed perovskite film is highlighted, especially for the large‐area production of PSCs. Light is shed on the significance of solvent engineering in PSCs, and critical guidance for future commercialization development of highly efficient PSCs is provided.

Abstract

Solar cells based on emerging organic–inorganic hybrid perovskite materials have reached certified power conversion efficiency as high as 25.5%, showing great potential in the next generation of photovoltaics toward large‐scale industrialization. The most competitive feature of perovskite solar cells (PSCs) is that the perovskite light absorber can be fabricated by a low‐cost solution method. For the solution method, the characteristics of the solvent play a key role in determining the crystallization kinetics, growth orientation, and optoelectronic properties of the perovskite film. Although significant progress has been made in the field of solvent engineering in PSCs, it is still challenging for the solution method to sustainably produce industrial‐scale PSCs for future commercialization applications. Herein, the advanced progress of solvent engineering of precursor solution in terms of coordination regulation and toxicity reduction is highlighted. The physical and chemical characteristics of different solvents in reducing the toxicity of the solvent system, regulating the coordination property of the precursor solution, controlling the film‐forming process of the perovskite film, and adjusting the photovoltaic performance of the PSC are systematically discussed. Lastly, important perspectives on solvent engineering of the perovskite precursor solution toward future industrial production of high‐performance PSCs are provided.

Small‐molecule organic solar cells based on a new electron donor reach power conversion efficiencies exceeding 13% with and without the use of electrode interlayers, but differ strongly in stability. Surprisingly, the surface composition and morphology of the interlayers deteriorate with time even under inert conditions, reducing device performance. Without interlayers, the cells give stable high performance.

Abstract

Electron transport layers (ETLs) placed between the electrodes and a photoactive layer can enhance the performance of organic solar cells but also impose limitations. Most ETLs are ultrathin films, and their deposition can disturb the morphology of the photoactive layers, complicate device fabrication, raise cost, and also affect device stability. To fully overcome such drawbacks, efficient organic solar cells that operate without an ETL are preferred. In this study, a new small‐molecule electron donor (H31) based on a thiophene‐substituted benzodithiophene core unit with trialkylsilyl side chains is designed and synthesized. Blending H31 with the electron acceptor Y6 gives solar cells with power conversion efficiencies exceeding 13% with and without 2,9‐bis[3‐(dimethyloxidoamino)propyl]anthra[2,1,9‐def:6,5,10‐d′e′f ′]diisoquinoline‐1,3,8,10(2H,9H)‐tetrone (PDINO) as the ETL. The ETL‐free cells deliver a superior shelf life compared to devices with an ETL. Small‐molecule donor–acceptor blends thus provide interesting perspectives for achieving efficient, reproducible, and stable device architectures without electrode interlayers.

Non‐solvent induced phase separation is introduced as a versatile and facile method to synthesize redox flow battery electrodes with hierarchical microstructures unachievable via conventional manufacturing approaches. Flow cell studies reveal that the novel materials can outperform conventional carbon fiber electrodes owing to better mass transfer and higher surface area, demonstrating that this method may enable new classes of porous electrodes tailored for particular electrochemical flow technologies.

Abstract

Porous carbonaceous electrodes are performance‐defining components in redox flow batteries (RFBs), where their properties impact the efficiency, cost, and durability of the system. The overarching challenge is to simultaneously fulfill multiple seemingly contradictory requirements—i.e., high surface area, low pressure drop, and facile mass transport—without sacrificing scalability or manufacturability. Here, non‐solvent induced phase separation (NIPS) is proposed as a versatile method to synthesize tunable porous structures suitable for use as RFB electrodes. The variation of the relative concentration of scaffold‐forming polyacrylonitrile to pore‐forming poly(vinylpyrrolidone) is demonstrated to result in electrodes with distinct microstructure and porosity. Tomographic microscopy, porosimetry, and spectroscopy are used to characterize the 3D structure and surface chemistry. Flow cell studies with two common redox species (i.e., all‐vanadium and Fe^2+/3+) reveal that the novel electrodes can outperform traditional carbon fiber electrodes. It is posited that the bimodal porous structure, with interconnected large (>50 µm) macrovoids in the through‐plane direction and smaller (<5 µm) pores throughout, provides a favorable balance between offsetting traits. Although nascent, the NIPS synthesis approach has the potential to serve as a technology platform for the development of porous electrodes specifically designed to enable electrochemical flow technologies.

Recent advances in the fabrication of 2D metal oxides (2DMOs) via liquid metals are comprehensively reviewed. The introduction of progress in fabricating 2DMOs by virtue of the features of liquid metals improves diversity in the development and applications of 2DMOs. The current challenges concerning the fabrication of 2DMOs are discussed to promote future research.

Abstract

2D metal oxides (2DMOs) have been widely applied in the fields of electronic, magnetic, optical, and catalytic materials, owing to their rich surface chemistry and unique electronic structures. However, their further development faces challenges such as the difficulty in fabricating 2DMOs with unstable surface induced by strong surface polarizability, or the high cost and limited yield of the fabrication process. Recently, liquid metals have shown great potential in the fabrication of 2DMOs. The native oxide skin formed on the surface of liquid metals can be considered as a perfect 2D planar material. Due to the solubility, fluidity, and reactivity of liquid metals, they can act as the solvent, reactant, and interface in the fabrication of 2DMOs. Moreover, liquid metals undergo a liquid–solid phase transition, enabling them to be a symmetric matched substrate for growing high‐quality 2DMOs. An insightful survey of the recent progress in this research direction is presented. The features of liquid metals including good solubility, chemical reactivity, weak interface force, and liquid–solid phase transitions are introduced in detail. Furthermore, strategies for the fabrication of 2DMOs by virtue of these features are summarized comprehensively. Finally, current challenges and prospects regarding the future development in the fabrication of 2DMOs via liquid metals are highlighted.