Revealing Size‐Dependency of Ionic Liquid to Assist Perovskite Film Formation Mechanism for Efficient and Durable Perovskite Solar Cells
Ionic liquids (ILs) are extensively utilized for the manipulation of crystallization kinetics of perovskite, morphology optimization, and defect passivation for the fabrication of highly efficient and stable devices. However, comparing ILs with different chemical structures and selecting the appropriate ILs from the many types available to enhance perovskite device performance remains a challenge. In this study, a range of ILs containing different sizes of anions are introduced as additives for assisting in film formation in perovskite photovoltaics. Specifically, ILs with various sizes significantly affects the strength of chemical interaction between ILs and perovskite composition, inducing varying degrees of conversion of lead iodide to perovskite as well as the formation of perovskite films with markedly disparate grain sizes and morphology. Theoretical calculations in conjunction with experimental measurements revealed that small-sized anion can more effectively reduce defect density by filling halide vacancies within perovskite bulk materials, resulting in suppression of charge-carrier recombination, an extended photoluminescence lifetime, and significantly improved device performance. Boosted by ILs with appropriate size, the champion power conversion efficiency of 24.09% for the ILs-treated device is obtained, and the unencapsulated devices retain 89.3% of its original efficiency under ambient conditions for 2000 h.
Autonomous and directional flow of water and transport of particles across a subliming dynamic crystal surface
Chemical and morphological traits of natural substrates that can propel and transport fluids over their surfaces have long provided inspiration for the engineering of artificial materials that can harvest and collect water from aerial humidity. Here we report that the gradual widening of parallel microchannels on a surface of a slowly subliming hexachlorobenzene crystal can promote the autonomous and bidirectional transduction of condensed aerial water. Driven by topology changes on the surface of the crystal and water exchange with the gas phase, droplets of condensed water migrate over the crystal. These droplets are also able to transport silver particles and other particulate matter, such as dust. The velocity of the particles was shown to be dependent on both the sublimation rate of the crystal and the relative humidity of its environment. This example of a sublimation-powered water flow demonstrates that topological surface changes accompanying crystal phase transitions can be harnessed to transport liquid and solid matter over surfaces.
Elastic Organic Crystals as Bioinspired Hair‐Like Sensors
One of the typical haptic elements are natural hairy structures that animals and plants rely on for feedback. Although these hair sensors are an admirable inspiration, the development of active flow sensing components having low elastic moduli and high aspect ratios remains a challenge. Here, we report a new sensing approach based on a flexible, thin and optically transmissive organic crystal of high aspect ratio, which is stamped with fluorescent dye for tracking. When subjected to gas flow and exposed to laser, the crystal bends due to exerted pressure and acts as an optical flow (hair) sensor with low detection limit (≈1.578 m s−1) and fast response time (≈2.70 s). The air-flow-induced crystal deformation and flow dynamics response are modelled by finite element analysis. Due to having a simple design and being lightweight and mechanically robust this prototypical crystal hair-like sensor opens prospects for a new class of sensing devices ranging from wearable electronics to aeronautics.
Ionic Liquid Engineering in Perovskite Photovoltaics
Over the past decade, perovskite photovoltaics have approached other currently available technologies and proven to be the most prospective type of solar cells. Although the many-sided research in this very active field has generated consistent results with regards to their undisputed consistently increasing power conversion efficiency, it also produced several rather contradictory opinions. Among other important details, debate surrounding their proneness to surface degradation and poor mechanical robustness, as well as the environmental footprint of this materials class remains a moot point. The application of ionic liquids appears as one of the potential remedies to some of these challenges due to their high conductivity, the opportunities for chemical ‘tuning’ of the structure, and relatively lower environmental footprint. This article provides an overview, classification, and applications of ionic liquids in perovskite solar cells. We summarize the use and role of ionic liquids as versatile additives, solvents, and modifiers in perovskite precursor solution, charge transport layer, as well as for interfacial and stability engineering. Finally, challenges and the future prospects for the design and/or selection of ionic liquids with a specific profile that meets the requirements for next generation highly efficient and stable perovskite solar cells are proposed.
The Role of Ionic Liquids in Performance Enhancement of Two‐Step Perovskite Photovoltaics
Much of the research efforts of late that are directed toward enhancement of the efficiency of perovskite-based photovoltaics are focused on the application of ionic liquids (ILs) in a one-step approach. On the contrary, the details of the alternative two-step approach, such as the role of the ILs in the perovskite film solidification and its optoelectronic properties, remain poorly understood despite the increasing evidence that this latter method might offer considerable advantages, including better reproducibility and control over crystallization. Herein, the effect of IL methylammonium acetate (MAAc) introduced into the PbI2 layer by a sequential deposition process on the optoelectronic properties of the perovskite film and the performance of the ensuing photovoltaic devices are studied. The addition of MAAc lowers the MAAc–perovskite formation enthalpy, leading to an accelerated solidification process. Moreover, MAAc suppresses the formation of Pb0, thereby facilitating the perovskite formation while lowering the deep defect states caused by Pb0. In addition to grain boundary passivation, the acetate ions can diffuse into the bulk of the perovskite material, filling up the halide vacancies with reduced trap state density. As a result, a decent power conversion efficiency of 23.36% is achieved, with noticeably improved durability.
Repair and Splicing of Centimeter‐Size Organic Crystalline Optical Waveguides
Organic single crystals that are capable of transmitting light and charge are quickly shaping into a new forefront of research in photoelectronic materials that is thought to hold a tremendous potential for the broader field of organic electronics. However, one of the main disadvantages that currently stands against the direct application of organic single crystals in that capacity is their pronounced proneness to mechanical damage due to brittleness, abrasion, and wear. To account for this drawback, here a simple and universal strategy is proposed for the recovery of macroscopic integrity of cracked or completely fractured crystals based on the layer-by-layer charged polymer assembly approach that can be used to effectively recover the damaged crystals. It is shown that in addition to being an effective means for reasonable restoration of their optical waveguiding ability, this approach can also be used to combine different crystals into hybrid organic photonic integrated circuits (OPICs) and even to construct dynamic hybrid OPICs as active and/or passive optical waveguides. The resulting integrated crystalline OPIC bundles act as optical waveguides for transmission of light with different colors and can also be used for light mixing to generate white light.
Construction of Microporous Zincophilic Interface for Stable Zn Anode
Aqueous zinc ion batteries (AZIBs) are promising electrochemical energy storage devices due to their high theoretical specific capacity, low cost, and environmental friendliness. However, uncontrolled dendrite growth poses a serious threat to the reversibility of Zn plating/stripping, which impacts the stability of batteries. Therefore, controlling the disordered dendrite growth remains a considerable challenge in the development of AZIBs. Herein, a ZIF-8-derived ZnO/C/N composite (ZOCC) interface layer was constructed on the surface of the Zn anode. The homogeneous distribution of zincophilic ZnO and the N element in the ZOCC facilitates directional Zn deposition on the (002) crystal plane. Moreover, the conductive skeleton with a microporous structure accelerates Zn2+ transport kinetics, resulting in a reduction in polarization. As a result, the stability and electrochemical properties of AZIBs are improved. Specifically, the ZOCC@Zn symmetric cell sustains over 1150 h at 0.5 mA cm−2 with 0.25 mA h cm−2, while the ZOCC@Zn half-cell achieves an outstanding Coulombic efficiency of 99.79% over 2000 cycles. This work provides a simple and effective strategy for improving the lifespan of AZIBs.
Collective photothermal bending of flexible organic crystals modified with MXene-polymer multilayers as optical waveguide arrays
The performance of any engineering material is naturally limited by its structure, and while each material suffers from one or multiple shortcomings when considered for a particular application, these can be potentially circumvented by hybridization with other materials. By combining organic crystals with MXenes as thermal absorbers and charged polymers as adhesive counter-ionic components, we propose a simple access to flexible hybrid organic crystal materials that have the ability to mechanically respond to infrared light. The ensuing hybrid organic crystals are durable, respond fast, and can be cycled between straight and deformed state repeatedly without fatigue. The point of flexure and the curvature of the crystals can be precisely controlled by modulating the position, duration, and power of thermal excitation, and this control can be extended from individual hybrid crystals to motion of ordered two-dimensional arrays of such crystals. We also demonstrate that excitation can be achieved over very long distances (>3 m). The ability to control the shape with infrared light adds to the versatility in the anticipated applications of organic crystals, most immediately in their application as thermally controllable flexible optical waveguides for signal transmission in flexible organic electronics.
A catalytic enantioselective stereodivergent aldol reaction
The aldol reaction is among the most powerful and strategically important carbon–carbon bond–forming transformations in organic chemistry. The importance of the aldol reaction in constructing chiral building blocks for complex small-molecule synthesis has spurred continuous efforts toward the development of direct catalytic variants. The realization of a general catalytic aldol reaction with control over both the relative and absolute configurations of the newly formed stereogenic centers has been a longstanding goal in the field. Here, we report a decarboxylative aldol reaction that provides access to all four possible stereoisomers of the aldol product in one step from identical reactants. The mild reaction can be carried out on a large scale in an open flask, and generates CO2 as the only by-product. The method tolerates a broad substrate scope and generates chiral β-hydroxy thioester products with substantial downstream utility.
Bioinspired soft robots based on organic polymer-crystal hybrid materials with response to temperature and humidity
The capability of stimulated response by mechanical deformation to induce motion or actuation is the foundation of lightweight organic, dynamic materials for designing light and soft robots. Various biomimetic soft robots are constructed to demonstrate the vast versatility of responses and flexibility in shape-shifting. We now report that the integration of organic molecular crystals and polymers brings about synergistic improvement in the performance of both materials as a hybrid materials class, with the polymers adding hygroresponsive and thermally responsive functionalities to the crystals. The resulting hybrid dynamic elements respond within milliseconds, which represents several orders of magnitude of improvement in the time response relative to some other type of common actuators. Combining molecular crystals with polymers brings crystals as largely overlooked materials much closer to specific applications in soft (micro)robotics and related fields.