In article number 2002678, Feng He and co‐worker summarize the relationship between structure design, packing arrangement and molecular properties of organic photovoltaic acceptors. The concept of a “3D network acceptor” is proposed, with an aim to deepening the understanding of the electronic processes in the active layer and providing guidance for developing new generation organic photovoltaic materials.
The first survey of the emerging photovoltaic reports initiative summarizes the best achievements published in academic journals in the research of emerging photovoltaic materials, e.g., organic, perovskite, and dye sensitized solar cells. The reports are presented as a function of the bandgap energy for different categories such as transparency, flexibility, and stability, and compared to the Shockley–Queisser limit.
Emerging photovoltaics (PVs) focus on a variety of applications complementing large scale electricity generation. Organic, dye‐sensitized, and some perovskite solar cells are considered in building integration, greenhouses, wearable, and indoor applications, thereby motivating research on flexible, transparent, semitransparent, and multi‐junction PVs. Nevertheless, it can be very time consuming to find or develop an up‐to‐date overview of the state‐of‐the‐art performance for these systems and applications. Two important resources for recording research cells efficiencies are the National Renewable Energy Laboratory chart and the efficiency tables compiled biannually by Martin Green and colleagues. Both publications provide an effective coverage over the established technologies, bridging research and industry. An alternative approach is proposed here summarizing the best reports in the diverse research subjects for emerging PVs. Best performance parameters are provided as a function of the photovoltaic bandgap energy for each technology and application, and are put into perspective using, e.g., the Shockley–Queisser limit. In all cases, the reported data correspond to published and/or properly described certified results, with enough details provided for prospective data reproduction. Additionally, the stability test energy yield is included as an analysis parameter among state‐of‐the‐art emerging PVs.
A narrow bandgap polymer acceptor PYF‐T with fluorinated end groups on monomer sub‐units is synthesized, showing stronger and red‐shifted absorption, lower‐lying frontier molecular orbitals, higher electron mobility, enhanced intermolecular packing, and without sacrificing photovoltage compared to its non‐fluorinated counterpart (PY‐T). When employed in all‐polymer solar cells, PYF‐T yields an outstanding efficiency of 14.10%.
Fluorination of end groups has been a great success in developing efficient small molecule acceptors. However, this strategy has not been applied to the development of polymer acceptors. Here, a dihalogenated end group modified by fluorine and bromine atoms simultaneously, namely IC‐FBr, is first developed, then employed to construct a new polymer acceptor (named PYF‐T) for all‐polymer solar cells (all‐PSCs). In comparison with its non‐fluorinated counterpart (PY‐T), PYF‐T exhibits stronger and red‐shifted absorption spectra, stronger molecular packing and higher electron mobility. Meanwhile, the fluorination on the end groups down‐shifts the energy levels of PYF‐T, which matches better with the donor polymer PM6, leading to efficient charge transfer and small voltage loss. As a result, an all‐PSC based on PM6:PYF‐T yields a higher power conversion efficiency (PCE) of 14.1% than that of PM6:PY‐T (11.1%), which is among the highest values for all‐PSCs reported to date. This work demonstrates the effectiveness of fluorination of end‐groups in designing high‐performance polymer acceptors, which paves the way toward developing more efficient and stable all‐PSCs.
This work is the first to integrate the multimechanism recombination parameters with the density of states (DOS) distribution and effective bandgap in the framework of a semiempirical analytical model of temperature and light intensity dependent V oc. The proposed approach is expected to be a useful tool for quantifying the full spectrum of recombination‐ and DOS‐related parameters of nonfullerene organic solar cells.
The relationship of the temperature–light intensity dependence of open‐circuit voltage V oc in nonfullerene‐based organic solar cells with their material characteristics and multimechanism recombination parameters is described. The systematic variation of the effective bandgap E g,eff and the electrode layers allows the observation of different relative contributions of bimolecular, bulk, and surface trap‐assisted recombination mechanisms. The complementary advantages of the analytical model and the established voltage‐impedance spectroscopy technique provide a useful tool to quantify multimechanism recombination parameters, effective density of states N c, and energetic disorder σ in organic solar cells under operating conditions. The validity of the proposed model to understand the temperature and light intensity dependent of V oc is shown by applying it to four different donor:nonfullerene acceptor blend systems with conventional or inverted device architectures.
A concentrated H2SO4 oxidation technique is developed for etching holes on Ti3C2T x MXene, which simultaneously removes side products such as TiO2. Freestanding film electrodes assembled with H2SO4‐etched small flake Ti3C2T x nanosheets show an optimized ion pathway with reduced flake size, increased interlayer spacing, and in‐plane pores. Ultrahigh rate performance is obtained even at high mass loadings exceeding 12 mg cm−2.
The lengthened ion pathway in restacked 2D materials greatly limits the electrochemical performance of practically dense film electrodes (mass loading >10 mg cm−2). Typical strategies such as the insertion of nanomaterials and 3D‐structure design is expected to reduce the volumetric capacitance of Ti3C2T x electrodes, diminishing the dominating advantage of Ti3C2T x over other electrode materials. Here, a novel, facile, and controllable H2SO4 oxidation method is developed for alleviating the restacking issue of Ti3C2T x film with few electrochemically inactive side‐products such as TiO2. A hierarchical ion path “highway” in Ti3C2T x film is fabricated with porous structure, atomic‐level increased interlayer spacing, and reduced flake size (through probe‐sonication). As a result, ultra‐high rate performance is obtained with high volumetric capacitance. For a ≈1.1 µm thick Ti3C2T x film, capacitance retention of 64% is obtained (208 F g−1/756 F cm−3) when the scan rate is increased from 5 to 10,000 mV s−1. Even at higher mass loadings exceeding 12 mg cm−2 (48 µm thickness), the rate capability is still comparable to unoptimized Ti3C2T x electrodes with low mass loading (1 mg cm−2). Consequently, a high areal capacitance of ≈3.2 F cm−2 is achieved for pathway‐optimized thick Ti3C2T x film, which is of great significance for practical applications.
The relationship between structure design, packing arrangement, and molecular property of organic photovoltaic (OPV) acceptors is explored, in which the 3D network packing originating from non‐covalent intermolecular interactions and aggregation states, is found to promote OPV device performance. This review sheds light on charge transport processes in acceptors and provides a guideline for developing new generation OPV materials.
The power conversion efficiency of organic solar cell (OSC) devices has surpassed 18% rapidly. In order to further promote OSC development, it is necessary to understand the packing information at the atomic level to help develop acceptor systems with superior performance. The packing arrangements and intermolecular interactions of these acceptors in the solid state, observed by single crystal X‐ray crystallography, are often used to design materials with expected physicochemical properties. In this review, the chemical structures of acceptors revealed by single crystal X‐ray crystallography are summarized, and the relationship between structural design, packing arrangement, and device properties is discussed. In addition, the concept of “3D network packing” in acceptor systems is proposed, which offers better charge transfer properties in reported chlorinated, fluorinated, brominated, and trifluoromethylated systems, an understanding of 3D network transport also provides guidance in high‐performance materials design. Finally, some current issues related to single crystal studies in OSCs are discussed, with an emphasis on the significance of developing acceptors by understanding and adjusting the aggregation states and intermolecular interactions of materials by single crystal analysis.
A comparative study is reported on the Brønsted acid and Lewis acid doping of poly(3‐hexylthiophene) with a largely soluble molecular dopant, tris(pentafluorophenyl)borane. The Brønsted acid doping enables the formation of unconventional type II polymorph of the polymer, thereby leading to drastic increases in electrical and thermoelectric properties and excellent air stabilities via simple one‐step solution mixing.
Molecular doping is essential for improving the thermoelectric properties of conjugated polymers, but dopants of low solubility either restrict the formation of high quality films or complicate fabrication steps. Although a highly soluble molecular dopant, tris(pentafluorophenyl)borane (BCF), has been sporadically studied, its potential has not yet been fully explored. Herein, particularly intriguing effects of Brønsted acid doping with BCF‐water complexes for poly(3‐hexylthiophene) (P3HT) are reported, which can facilitate substantial increases in electrical and thermoelectric properties with remarkable doping stabilities. Interestingly, a unique polymorph of P3HT with interdigitated alkyl chains (called type II) is observed in the Brønsted acid doping with BCF‐water complexes. Moreover, the doped P3HT shows conformational change to the quinoid structure, enabling increased backbone planarity. As a result, the Brønsted acid‐doped P3HT films exhibit outstanding electrical conductivities, thermoelectric power factors, and figure‐of‐merit of up to 33.0 S cm−1, 28.3 µW m−1 K−2, and 0.034, respectively. These values are at least an order of magnitude higher than those of P3HT films doped with a conventional molecular dopant, 7,7,8,8‐tetracyano‐2,3,5,6‐tetrafluoroquinodimethane. The Brønsted acid doping with BCF‐water complexes also affords excellent air stabilities of P3HT films, which potentially provides a strong comparative advantage over existing highly reactive salt‐type dopants, such as FeCl3.
A power conversion efficiency of 16.17% is achieved in the doctor‐bladed PM6:Y6‐2Cl device with CF:CB co‐solvent, which is much higher than those of CF‐ and CB‐processed devices. Of note is that the use of this co‐solvent approach in the other two high‐performance photovoltaic systems is also confirmed, demonstrating its good generality of employing in the printing organic solar cells.
Studies of the relationship between blend microstructure and photovoltaic performance are becoming more common, which is a prerequisite for rationally improving device performance. Non‐fullerene acceptors usually have planar backbone conformation and strong intermolecular packing, normally resulting in excessive phase separation. Herein, an effective co‐solvent blending strategy to turn the molecular organization of a chlorinated small molecule acceptor Y6‐2Cl and phase separation of the corresponding active layer with PM6 as donor is demonstrated. The in situ photoluminescence measurements and relevant morphological characterizations illustrate that the film‐forming process is fine‐turned when using the mixtures of chloroform (CF) and chlorobenzene (CB) solvents, and the blend showed high domain purity with suitable phase‐separated networks. Thus, better exciton dissociation and charge generation, more balanced charge transport, and less recombination loss are obtained in the co‐solvent blade‐coated devices. As a result, a maximum power conversion efficiency (PCE) of 16.17% is achieved, which is much higher than those of CF‐ and CB‐bladed devices (14.08% and 11.44%, respectively). Of note is that the use of this co‐solvent approach in the other two high‐performance photovoltaic systems is also confirmed, demonstrating its good generality of employing in the printing organic solar cells.
Three new dithieno[2,3‐d;2ʹ,3ʹ‐dʹ]benzo[1,2‐b;4,5‐bʹ]dithiophene based small‐molecule donors with different branching points for alkyl side chains are designed and synthesized for all small molecular organic solar cells. Modifying the branching points tunes the properties in the aggregation state, and an optimal nanofiber‐based hierarchical morphology for efficient charge separation and transport is successfully demonstrated.
The optimization of bulk heterojunction morphology is one of the most challenging topics in all‐small‐molecule organic solar cells. Herein, three small molecular donors based on dithieno[2,3‐d;2′,3′‐d′]benzo[1,2‐b;4,5‐b′]dithiophene (DTBDT) unit by systematically moving the branching point of the alkyl chain have been designed, synthesized, and applied in organic solar cells. Modifying the branching points enables the properties of the aggregation state to be tuned, and an efficient nanofiber‐based hierarchical morphology is successfully demonstrated by combining with different nonfullerene acceptors. The molecules with far branching points can form nanofibers in active layers, and theses nanofibers help the charge separation and charge transport in a large donor‐rich or acceptor‐rich domain of approximately 100 nm. Using nonfullerrene Y6 as an acceptor, the highest power conversion efficiency of 14.78% is obtained, which is one of the highest efficiencies in all‐small‐molecule organic solar cells. The strategy of modification of alkyl side chain branching points can be a practical way to actualize crystallinity control and active layer morphology for improving the performance of all‐small‐molecule organic solar cells.
Three benzo[1,2‐b:4,5‐b']dithiophene‐thienothiophene π‐bridged N‐octylthieno[3,4‐c]pyrrole‐4,6‐dione‐based polymer donors named as PBDT‐X (X=H, F, Cl) are developed. While a planar accepting unit helps improve the crystallinity, all three photovoltaic parameters are simultaneously increased with the introduction of halogen atoms. PBDT‐Cl:Y6‐based devices yield an efficiency of 15.63%, attributed to the enhanced crystallinity, hole mobility, and domain purity.
In this work, a new series of polymer donors consisting of thienothiophene π‐bridged N‐octylthieno[3,4‐c]pyrrole‐4,6‐dione (8ttTPD) and benzo[1,2‐b:4,5‐b']dithiophene (BDT) units for producing highly efficient organic solar cells (OSCs) paired with a Y6 acceptor is developed. The incorporation of the highly planar 8ttTPD unit enhances crystalline properties as well as hole mobilities of the BDT‐based polymers that typically have amorphous features. Further, the 2D side chains with halogen atoms (fluorine and chlorine) are designed as another handle to control the crystallinity and energy levels of the BDT‐based polymer donors: PBDT‐X (X = H, F, or Cl). Synergistic effects of incorporated 8ttTPD unit and the halogenated 2D side chain generate significantly enhanced charge transport and recombination properties of the OSCs, which is mainly attributed to optimized crystallinity and hole mobility of the polymer donors. Therefore, the PBDT‐Cl:Y6‐based OSCs exhibit the highest power conversion efficiency (PCE) of 15.63% with simultaneous improvements of open‐circuit voltage, short‐circuit current density, and fill factor, which outperforms the PCEs of PBDT‐H:Y6 (11.84%) and PBDT‐F:Y6 (14.86%).
The absorption band edge of benchmark double perovskite Cs2AgBiBr6 is significantly broadened to the near‐infrared range through Cu‐doping. It is demonstrated that the absorption extension is due to subbandgap states induced by Cu‐doping; interestingly, these subbandgap states can generate considerable band carriers upon excitation. The results demonstrate the great potential of Cs2(Ag:Cu)BiBr6 perovskites for near‐infrared light detection and optoelectronic applications.
Lead‐free halide double perovskites (A2BIBIIIX6) with attractive optical and electronic features are considered to be a promising candidate to overcome the toxicity and stability issues of lead halide perovskites (APbX3). However, their poor absorption profiles limit device performance. Here the absorption band edge of Cs2AgBiBr6 double perovskite to the near‐infrared range is significantly broadened by developing doped double perovskites, Cs2(Ag:Cu)BiBr6. The partial replacement of Ag ions by Cu ions in the crystal lattice is confirmed by the X‐ray photoelectron spectroscopy (XPS) and solid‐state nuclear magnetic resonance (ssNMR) measurements. Cu doping barely affects the bandgap of Cs2AgBiBr6; instead it introduces subbandgap states with strong absorption to the near‐infrared range. More interestingly, the near‐infrared absorption can generate band carriers upon excitation, as indicated by the photoconductivity measurement. This work sheds new light on the absorption modulation of halide double perovskites for future efficient optoelectronic devices.
Liquid crystal (LC)‐based metamaterial devices, which can sense targeted stimuli such as electric‐field, temperature and pressure, and report them optically by displaying corresponding holograms, are demonstrated. The demonstrated systems enable a variety of applications like hologram labels that indicate freshness of temperature‐sensitive products during storage or transport and interactive holographic displays with touch sensing or motion recognition.
Flat optics, realized by the artificially created 2D material platform called optical metasurfaces, is currently undergoing a science‐to‐technology transition. However, “real‐time” active operations of such flat optical devices remain yet unresolved. Here, liquid crystals (LCs)‐integrated metaholograms for ultracompact dynamic holographic displays are proposed. The anisotropic nature of the LCs allows facile and repeatable manipulation of the polarization of light. Specifically designed (“designer”) LCs and efficient helicity‐encoded metaholograms are combined to realize stimuli‐responsive dynamic displays. The designer LC modulators are used as switches that enable a variety of external stimuli (e.g., electric field, heat, surface pressure) to operate holographic images in real‐time. Such a dynamic metaholographic platform will provide a path to external stimuli‐driven “smart” sensing and display applications such as hologram labels for temperature/pressure/touch monitoring and interactive holographic displays with haptic motion recognition.
Energy resolved–electrochemical impedance spectroscopy is a relatively simple electrochemical impedance technique that allows determining the density of states (DOS) of neat and blend films with high resolution. It is shown that the DOS of a MeLPPP donor with non‐fullerene or fullerene acceptors are Gaussians with increased width in the blend film due to increased structural disorder.
Although the density of states (DOS) distribution of charge transporting states in an organic semiconductor is vital for device operation, its experimental assessment is not at all straightforward. In this work, the technique of energy resolved–electrochemical impedance spectroscopy (ER‐EIS) is employed to determine the DOS distributions of valence (highest occupied molecular orbital (HOMO)) as well as electron (lowest unoccupied molecular orbital (LUMO)) states in several organic semiconductors in the form of neat and blended films. In all cases, the core of the inferred DOS distributions are Gaussians that sometimes carry low energy tails. A comparison of the HOMO and LUMO DOS of P3HT inferred from ER‐EIS and photoemission (PE) or inverse PE (IPE) spectroscopy indicates that the PE/IPE spectra are by a factor of 2–3 broader than the ER‐EIS spectra, implying that they overestimate the width of the distributions. A comparison of neat films of MeLPPP and SF‐PDI2 or PC(61)BM with corresponding blends reveals an increased width of the DOS in the blends. The results demonstrate that this technique does not only allow mapping the DOS distributions over five orders of magnitude and over a wide energy window of 7 eV, but can also delineate changes that occur upon blending.
A flexible color‐tunable electroluminescent device based on double‐stacked emissive layers of ZnS phosphors/dielectric polymer composite is fabricated using an all‐solution‐processed method. The dielectric difference between the two emissive layers, resulting in the color combination between two independent emissions from different ZnS phosphors at varied electric fields, contributes to the dynamic color tunability.
Intrinsically flexible alternating current electroluminescent devices have sparked widespread research interest due to their tremendous potential in bioinspired electronics, smart wearables, and human–machine interfaces. In these applications, it is highly desirable to possess real‐time color tunability but this has not been reported yet. Herein, a flexible color‐tunable electroluminescent device composed of simple double‐stacked emissive layers of ZnS phosphors/dielectric polymer composite is developed by an all‐solution processable method. The color tuning capability can be attributed to the dielectric difference between the two emissive layers, leading to the color combination between two independent emissions originating from different ZnS phosphors at varied electric fields. With the rational selection of the dielectric polymer matrices, a wide‐range color tuning from orange to white and to blue can be realized in a single device just by varying the electric field. It also exhibits high mechanical robustness with well‐maintained performance even after 1000 cycles of bending. Similar natural functionalities like camouflage and visual communication can be further reproduced in the artificial color‐tunable system, thereby opening a general and effective avenue for developing smart wearables and soft electronics.
A spray‐lyophilization strategy is proposed to transform 2D nanosheets such as Ti3C2T x , Ti2CT x , and graphene oxide into 3D architectures. The obtained 3D Ti3C2T x presents an aggregation‐resistant, large specific surface, and a short ion transport path, leading to enhanced K ion storage ability. A 3D Ti3C2T x ‖hierarchical porous activated carbon (HPAC) K‐ion hybrid capacitor is assembled and displays remarkable energy and power densities with ultrastable cycling performance.
Potassium‐ion hybrid capacitors have attracted increasing attention due to good energy density, high power density, and low cost. Ti3C2T x ‐MXene is considered as a promising anode material for K ion storage. However, undesirable stacking issues decrease its exposed area and breeds sluggish K ion transport. Herein, a facile spray‐lyophilization strategy is proposed to construct stacking‐resistant Ti3C2T x with 3D structures. As‐prepared Ti3C2T x hollow spheres/tubes present stack resistance, a large specific surface area, and a short ion diffusion pathway. When serving as an anode material, it shows enhanced capacity and thickness‐independent rate performance compared to 2D Ti3C2T x . After 10 000 cycles, a specific capacity of 122 mAh g−1 is obtained at 1 A g−1. Systematic kinetics analyses demonstrate the significance of concentration polarization on the electrode's rate ability. Furthermore, a 3D Ti3C2T x ‖hierarchical porous activated carbon (HPAC) K‐ion hybrid capacitor is assembled and displays remarkable energy and power densities with energy retention of 100% after 10 000 cycles at 1 A g−1 . Following this strategy, other 3D structures from nanosheets can also be obtained, such as 3D Ti3C2T x microtubes and graphene oxide nanoscrolls. This study provides a viable approach to solve the stacking issues of 2D nanosheets to promote the application of 2D materials.
A new class of black gold hierarchical nanoturf on membranes with micro‐through holes exhibiting high solar thermal energy efficiency is presented. Owing to its omnidirectional and broad range light absorption, high thermal/light stability (four weeks), and large area fabrication (15 × 15 cm2), continuous solar steam generation capability is achieved.
Solar‐thermal materials have been intensively studied in the context of production and localization of thermal energy, targeting an industry level application. Although photonic and optical strategies for enhancing light absorption have increased the efficiency of photo excitation/conversion into thermal energy, most of them have several limitations such as large area fabrication, thermal stability and broadband/omnidirectional light absorption. In this study, a gold‐coated hierarchical nanoturf membrane (Au/h‐Nanoturf membrane) incorporated with randomly distributed high aspect ratio (AR) nanostructures and micro‐through holes is proposed. The Au/h‐Nanoturf has peculiar black structures that provide advantages in forming a membrane with a large area and in absorbing broadband solar light spectrum. Furthermore, the membrane is combined with micro‐cone array which makes it exhibit exceptionally omnidirectional light absorption properties. Using computational analysis, it is confirmed that the micro‐cone array substantially contributes to the omnidirectional solar absorption irrespective of the wavelength. The optimized structural parameters for the maximum efficiency of the solar‐thermal materials are also found. The prepared solar‐vapor generator with the optimized structural features exhibits 91% average conversion efficiency under one sun condition. The efficiency is sustainable for up to four weeks. The highly efficient and omnidirectional broadband‐absorbing solar‐thermal membrane can be readily employed, targeting an industry level application.
The most‐up‐to date progress and cutting‐edge advances in the rational microstructure design of MXenes‐based materials for energy storage and conversion are comprehensively summarized with a focus on the interlayer structure design, interfacial functionalization, and the construction of heterojunctions. Existing challenges and perspectives for the future development of 2D MXene‐based nanostructures are highlighted.
MXenes have attracted increasing attention due to their unique advantages, excellent electronic conductivity, tunable layer structure, and controllable interfacial chemistry. However, the practical applications of MXenes in energy storage devices are severely limited by the issues of torpid reaction kinetics, limited active sites, and poor material utilization efficiency. Herein, the most‐up‐to date advances in the rational microstructure design to enhance electrochemical reaction kinetics and energy storage performance of MXene‐based materials are comprehensively summarized. This review begins with the preparation and properties of MXenes, classified into fluorine‐containing acid etching and fluoride‐free etching approaches. Afterwards, the interlayer structure design and interfacial functionalization of MXenes with respect to interlayer spacing and porous structure, terminal groups, and surface defects are summarized. Then the focus turns to the construction of advanced MXene‐based heterojunctions based on in situ derivation and surface self‐assembly. Based on these microstructure modulating strategies, the state‐of‐the‐art progress of MXene‐based applications with respect to supercapacitors, alkali metal‐ion batteries, metal–sulfur batteries, and photo/electrocatalysis are highlighted. Finally, the critical challenges and perspectives for the future research of 2D MXene‐based nanostructures are highlighted, aiming to present a comprehensive reference for the design of MXene‐based electrodes for electrochemical energy storage.
A stretchable and shape‐adaptive triboelectric nanogenerator (TENG) based on a MXene liquid electrode is proposed. The TENG possesses outstanding output performance under various deformations, such as stretching, folding, and twisting. Furthermore, the flexible MXene‐based TENG, which can be used for biomechanical energy harvesting and self‐powered motion monitoring, has potential applications in soft robotics, green energy sources, human‐machine interactions, and wearable electronics.
Growing demand in intelligent wearable electronics raises an urgent requirement to develop deformable and durable power sources with high electrical performance. Here, a stretchable and shape‐adaptive triboelectric nanogenerator (TENG) based on a MXene liquid electrode is proposed. The open‐circuit voltage of an MXene‐based TENG reaches up to 300 V. The excellent fluidity and highly electronegativity of the MXene liquid electrode, gives the TENG long‐term reliability and stable electrical output regardless of diverse extreme deformations. With harvesting mechanical energy from hand tapping motion, the TENG in a self‐charging system can charge up capacitors to drive wearable electronics. Moreover, the TENG can be attached to both human skin and clothes as a human motion monitoring sensor, which can inspect the frequency and amplitude of various physiological movements. This work provides a new methodology for the construction of stretchable power sources and self‐powered sensors, which have potential applications in diverse fields such as robotics, kinesiology, and biomechanics.
This work proposes an efficient method to produce tri‐iodide ions, which has been known as an efficient additive that improves the crystallinity, grain size, and morphology of perovskite films in a precursor solution using a photoassited process within short time, resulting in achieving the device performance up to 22%.
One of the most effective methods to achieve high‐performance perovskite solar cells (PSCs) is to employ additives as crystallization agents or to passivate defects. Tri‐iodide ion has been known as an efficient additive to improve the crystallinity, grain size, and morphology of perovskite films. However, the generation and control of this tri‐iodide ion are challenging. Herein, an efficient method to produce tri‐iodide ion in a precursor solution using a photoassisted process for application in PSCs is developed. Results suggest that the tri‐iodide ion can be synthesized rapidly when formamidinium iodide (FAI) dissolved isopropyl alcohol (IPA) solution is exposed to LED light. Specifically, the photoassisted FAI–IPA solution facilitates the formation of fine perovskite films with high crystallinity, large grain size, and low trap density, thereby improving the device performance up to 22%. This study demonstrates that the photoassisted process in FAI dissolved IPA solution can be an alternative strategy to fabricate highly efficient PSCs with significantly reduced processing times.
This paper describes a novel ionic bioartificial muscle based on ionically crosslinked polypyrrole‐coated functional carboxylated bacterial cellulose. The ionic actuator demonstrates enhanced electromechanical performance, including a large bending strain under ultralow voltages, fast response time, broad frequency bandwidth, excellent actuation durability, high energy density, high power density, as well as excellent biocompatibility, and as shows promising applications in soft robots.
The development of ultralow voltage high‐performance bioartificial muscles with large bending strain, fast response time, and excellent actuation durability is highly desirable for promising applications such as soft robotics, active biomedical devices, flexible haptic displays, and wearable electronics. Herein, a novel high‐performance low‐priced bioartificial muscle based on functional carboxylated bacterial cellulose (FCBC) and polypyrrole (PPy) nanoparticles is reported, exhibiting a large bending strain of 0.93%, long actuated bending durability (96% retention for 5 h) under an ultralow harmonic input of 0.5 V, broad frequency bandwidth up to 10 Hz, fast response time (≈4 s) in DC responses, high energy density (6.81 KJ m−3), and high power density (5.11 KW m−3), all of which mainly stem from its high surface area and porosity, large specific capacitance, tuned mechanical properties, and strong ionic interactions of cations and anions in ionic liquid with FCBC and PPy nanoparticles. More importantly, bioinspired applications such as the grapple robot, bionic medical stent, bionic flower, and wings‐vibrating have been realized. These successful demonstrations offer a viable means for developing high‐performance bioartificial muscles for next‐generation soft bioelectronics including bioinspired robotics, biomedical microdevices, and wearable electronics.
Phase‐change nanocrystals (C18‐UCNCs) are prepared via surface esterification and further thiol–ene reaction on cellulose nanocrystals. These nanocrystals can assemble into flaky structures in the solid‐state, which exhibit excellent thermoinduced imaging property, thermoinduced reversibility, and a self‐healing property. The multifunctional flaky structures can manipulate energy conversion, surface morphology, surface wetting, and optical properties, largely expanding their potential uses in various fields.
Owing to advantageous properties attributed to well‐organized structures, multifunctional materials with reversible hierarchical and highly ordered arrangement in solid‐state assembled structures have drawn tremendous interest. However, such materials rarely exist. Based on the reversible phase transition of phase‐change materials (PCMs), phase‐change nanocrystals (C18‐UCNCs) are presented herein, which are capable of self‐assembling into well‐ordered hierarchical structures. C18‐UCNCs have a core–shell structure consisting of a cellulose crystalline core that retains the basic structure and a soft shell containing octadecyl chains that allow phase transition. The distinct core–shell structure and phase transition of octadecyl chains allow C18‐UCNCs to self‐assemble into flaky nano/microstructures. These self‐assembled C18‐UCNCs exhibit efficient thermal transport and light‐to‐thermal energy conversion, and thus are promising for thermosensitive imaging. Specifically, flaky self‐assembled nano/microstructures with manipulable surface morphology, surface wetting, and optical properties are thermoreversible and show thermally induced self‐healing properties. By using phase‐change nanocrystals as a novel group of PCMs, reversible self‐assembled multifunctional materials can be engineered. This study proposes a promising approach for constructing self‐assembled hierarchical structures by using phase‐change nanocrystals and thereby significantly expands the application of PCMs.
The role of methylammonium chloride (MACl) in sequentially deposited bromine (Br)‐free formamidinium lead iodide (FAPbI3)‐based perovskite is systematically demonstrated to regulate the PbI2/FAI reaction, tune the phase transition at room temperature, and adjust the PbI2 residual through an intermediate‐related perovskite decomposition during thermal annealing. The resulting optimized solar cells achieve a remarkable efficiency of 23.1% with considerably improved photostability.
So far, the combination of methylammonium bromide/methylammonium chloride (MABr/MACl) or methylammonium iodide (MAI)/MACl is the most frequently used additives to stabilize formamidinium lead iodide (FAPbI3) fabricated by the sequential deposition method. However, the enlarged bandgap due to the addition of bromide and the ambiguous functions of these additives in lead iodide (PbI2) transformation are still worth considering. Herein, the roles of MACl in sequentially deposited Br‐free FA‐based perovskites are systematically investigated. It is found that MACl can finely regulate the PbI2/FAI reaction, tune the phase transition at room temperature, and adjust intermediate‐related perovskite crystallization and decomposition during thermal annealing. Compared to FAPbI3, the perovskite with MACl exhibits larger grain, longer carrier lifetime, and reduced trap density. The resultant solar cell therefore achieves a champion power conversion efficiency (PCE) of 23.1% under reverse scan with a stabilized power output of 23.0%. In addition, it shows much improved photostability under 100 mW cm−2 white illumination (xenon lamp) in nitrogen atmosphere without encapsulation.
Selective increase in the Seebeck coefficient and improvement of the power factor by a factor of ≈5 in an n‐doped donor–acceptor copolymer are realized by the use of amphipathic side chains. This strategy can properly control the dopant sites away from the backbone, which minimizes the adverse influence of counterions. Therefore, an excellent power factor of 18 µW m–1 K–2 is achieved.
There is no molecular strategy for selectively increasing the Seebeck coefficient without reducing the electrical conductivity for organic thermoelectrics. Here, it is reported that the use of amphipathic side chains in an n‐type donor–acceptor copolymer can selectively increase the Seebeck coefficient and thus increase the power factor by a factor of ≈5. The amphipathic side chain contains an alkyl chain segment as a spacer between the polymer backbone and an ethylene glycol type chain segment. The use of this alkyl spacer does not only reduce the energetic disorder in the conjugated polymer film but can also properly control the dopant sites away from the backbone, which minimizes the adverse influence of counterions. As confirmed by kinetic Monte Carlo simulations with the host–dopant distance as the only variable, a reduced Coulombic interaction resulting from a larger host–dopant distance contributes to a higher Seebeck coefficient for a given electrical conductivity. Finally, an optimized power factor of 18 µW m–1 K–2 is achieved in the doped polymer film. This work provides a facile molecular strategy for selectively improving the Seebeck coefficient and opens up a new route for optimizing the dopant location toward realizing better n‐type polymeric thermoelectrics.
An extraordinarily long stability, exceeding 1.5 years, for crosslinked perovskite nanoparticles (NPs) under harsh environments, by a novel materials design strategy, is reported. Surprisingly, the photoluminescence of the perovskite NPs is significantly increased under air, moisture, and chemicals, overcoming their instability in oxygen, water, and polar chemicals.
Organic–inorganic hybrid perovskite nanoparticles (NPs) are a very strong candidate emitter that can meet the high luminescence efficiency and high color standard of Rec.2020. However, the instability of perovskite NPs is the most critical unsolved problem that limits their practical application. Here, an extremely stable crosslinked perovskite NP (CPN) is reported that maintains high photoluminescence quantum yield for 1.5 years (>600 d) in air and in harsher liquid environments (e.g., in water, acid, or base solutions, and in various polar solvents), and for more than 100 d under 85 °C and 85% relative humidity without additional encapsulation. Unsaturated hydrocarbons in both the acid and base ligands of NPs are chemically crosslinked with a methacrylate‐functionalized matrix, which prevents decomposition of the perovskite crystals. Counterintuitively, water vapor permeating through the crosslinked matrix chemically passivates surface defects in the NPs and reduces nonradiative recombination. Green‐emitting and white‐emitting flexible large‐area displays are demonstrated, which are stable for >400 d in air and in water. The high stability of the CPN in water enables biocompatible cell proliferation which is usually impossible when toxic Pb elements are present. The stable materials design strategies provide a breakthrough toward commercialization of perovskite NPs in displays and bio‐related applications.
Molecular sequential doping using conjugated polymers is a promising approach to modulate or improve electrical conductivity without sacrificing the morphology of a pristine polymer film. In article number 2005129, Hyungtak Seo, Jong H. Kim, Bong‐Gi Kim, and co‐workers develop a cascade doping strategy that realizes excellent electrical conductivity through a separated doping process using two different dopants. The first dopant provides a kinetically favorable working environment for the second dopant, through regeneration, reengagement, and replacement during the secondary doping step.
The interface property of perovskite is governed by the surface termination. The combination of ultraviolet photoelectron and metastable‐atom electron spectroscopies is demonstrated as a versatile technique to prove the surface termination. This method is applied to a solution‐processed CH3NH3PbI3 perovskite film to show that the surface is terminated with a layer consisting of CH3NH3 and I.
The interfaces of a perovskite solar cell significantly influence the charge processes in the cell, which contributes to the device performance with direct implication for surface potential, electronic structure, and chemical reactivity. The properties of the interface are strongly affected by the surface termination. In this work, the combination of ultraviolet photoelectron spectroscopy (UPS) and metastable‐atom electron spectroscopy is demonstrated, to examine the surface termination of a solution‐processed CH3NH3PbI3 perovskite film. The results show that the surface of the CH3NH3PbI3 perovskite film is terminated with a layer consisting of CH3NH3 and I. The interface energy level alignment for both occupied and unoccupied levels between CH3NH3PbI3 and C60 is also examined using UPS and low‐energy inverse photoelectron spectroscopy. It turns out that an ideal energy level alignment is established for the electron collection and hole block at the perovskite and C60 interface.
