Advanced Functional Materials

Plastic solar cells have been fabricated using a low‐bandgap alternating copolymer of fluorene and a donor–acceptor–donor moiety (APFO‐Green1), blended with 3′‐(3,5‐bis‐trifluoromethylphenyl)‐1′‐(4‐nitrophenyl)pyrazolino[70]fullerene (BTPF70) as electron acceptor. The polymer shows optical absorption in two wavelength ranges, λ < 500 nm and 600 < λ < 1000 nm. The BTPF70 absorbs light at λ < 700 nm. A broad photocurrent spectral response in the wavelength range 300 < λ < 1000 nm is obtained in solar cells. A photocurrent density of 3.4 mA cm^–2, open‐circuit voltage of 0.58 V, and power‐conversion efficiency of 0.7 % are achieved under illumination of AM1.5 (1000 W m^–2) from a solar simulator. Synthesis of BTPF70 is presented. Photoluminescence quenching and electrochemical studies are used to discuss photoinduced charge transfer.

By applying the specific fabrication conditions summarized in the Experimental section and post‐production annealing at 150 °C, polymer solar cells with power‐conversion efficiency approaching 5 % are demonstrated. These devices exhibit remarkable thermal stability. We attribute the improved performance to changes in the bulk heterojunction material induced by thermal annealing. The improved nanoscale morphology, the increased crystallinity of the semiconducting polymer, and the improved contact to the electron‐collecting electrode facilitate charge generation, charge transport to, and charge collection at the electrodes, thereby enhancing the device efficiency by lowering the series resistance of the polymer solar cells.

Nitrogen doping has been proven to be a facile modification strategy to improve the electrochemical performance of 2D MXenes, a group of promising candidates for energy storage applications. However, the underlying mechanisms, especially the positions of nitrogen dopants, and its effect on the electrical properties of MXenes, are still largely unexplored. Herein, a comprehensive study is carried out to disclose the nitrogen doping mechanism in Ti₃C₂ MXene, by employing theoretical simulation and experimental characterization. Three possible sites are found in Ti₃C₂T_x (T = F, OH, and O) to accommodate the nitrogen dopants: lattice substitution (for carbon), function substitution (for –OH), and surface absorption (on –O). Moreover, electrochemical test results confirm that all the three kinds of nitrogen dopants are favorable for improving the specific capacitance of the Ti₃C₂ electrode, and the underlying factors are successfully distinguished. By revealing the nitrogen doping mechanisms in Ti₃C₂ MXene, this work provides theoretical guidelines for modulating the electrochemical properties of MXene materials for energy storage applications.

Triboelectric phenomena can be observed everywhere; however, they are consistently omitted from applications. Although almost all substances exhibit a triboelectrification effect in daily life, chemists as well as materials scientists have performed extensive investigations in both the aspects of basic science and practical applications to promote the development of triboelectric nanogenerators (TENGs). Here, a detailed survey of materials engineering for high triboelectric performance and multifunctional materials toward specific applications is summarized, including constructing micro/nanostructures, chemically modifying the frication surface, modulating bulk friction materials, the mechanism for improved performance, and preparing materials for implantable medical devices, bionic skin, and wearable electronic devices. Moreover, an in depth discussion of the current challenges and future efforts for strengthening the performance of TENGs is elaborated in detail, which will better guide new researchers toward a deeper understanding of and explorations about TENGs.

Making use of water wave energy at large is one of the most attractive, low‐carbon, and renewable ways to generate electric power. The emergence of triboelectric nanogenerator (TENG) provides a new approach for effectively harvesting such low‐frequency, irregular, and “random” energy. In this work, a TENG array consisting of spherical TENG units based on spring‐assisted multilayered structure is devised to scavenge water wave energy. The introduction of spring structure enhances the output performance of the spherical TENG by transforming low‐frequency water wave motions into high‐frequency vibrations, while the multilayered structure increases the space utilization, leading to a higher output of a spherical unit. Owing to its unique structure, the output current of one spherical TENG unit could reach 120 µA, which is two orders of magnitude larger than that of previous rolling spherical TENG, and a maximum output power up to 7.96 mW is realized as triggered by the water waves. The TENG array fabricated by integrating four units is demonstrated to successfully drive dozens of light‐emitting diodes and power an electronic thermometer. This study provides a new type of TENG device with improved performance toward large‐scale blue energy harvesting from the water waves.

Water wave energy is a vital renewable‐energy resource, but it is less developed due to the characteristics of water wave with low and varying frequency. Herein, a bifilar‐pendulum coupled hybrid nanogenerator (BCHNG) module, which includes an electromagnetic generator (EMG), two piezoelectric nanogenerators (PENGs), and two multilayer‐structured triboelectric nanogenerators (TENGs), is incorporated into a vessel‐like platform for wave energy harvesting. The combination of the lightweight TENG and the heavy PENG and EMG can not only increase the ability of power take‐off to capture water wave energy, but also improve the space utilization rate of BCHNG module and facilitate the design of the floating wave energy collecting device. Furthermore, the BCHNG module can harvest the kinetic energy and gravitational potential energy of the water wave at the same time, which benefits from the two degrees of swing freedom of the bifilar‐pendulum. Importantly, thanks to the accurate geometric design and the reasonable utilization of space, the BCHNG module achieves a high peak power density of 358.5 W m⁻³. The findings not only provide a novel method for the large‐scale development of blue energy, but also offer an opportunity for the development of self‐powered marine resources.

Excellent triboelectric and mechanical properties are achieved on the same material for the first time by developing an effective, general, straightforward, and area‐scalable approach to surface modification of a polyethylene terephthalate (PET) film via inductive‐coupled plasma etching. The modification enables gigantic enhancement of triboelectric charge density on the PET surface. Based on the modified PET as a contact material, a triboelectric nanogenerator (TENG) exhibits significantly promoted electric output compared to the one without the modification. The obtained electric output is even superior to a TENG made of conventional polytetrafluoroethylene that is known for its strongest ability of being charged by triboelectrification among all engineering plastics. Detailed characterizations reveal that the enhancement of triboelectric charge density on the PET is attributed to both chemical modification of fluorination and physical modification of roughened morphology in nanoscale. Therefore, this work proposes a new route to obtaining high‐performance TENGs by manipulating and modifying surface properties of materials.

Bismuth (Bi³⁺)‐included lead‐free metal halide (LFMH) materials attract much attention in lighting, display, photodetectors, X‐ray detectors, and photovoltaic fields, due to the tunable luminescence and optoelectronic performance in response to crystal and electronic structure, morphology, and particle sizes. This review summarizes Bi³⁺‐included LFMH materials about their preparation approach, crystal and electronic structure properties, luminescence performance, and emerging applications. Notably, Bi³⁺ ions not only can act as framework cation to construct stable LFMH structure, but can also incorporate into LFMH materials as activators or sensitizers to generate remarkable luminescence tuning and band engineering. The Bi³⁺ effect on the luminescence and optoelectronic properties of LFMH materials, including, promotion of exciton localization, enhancement of light absorption in near‐ultraviolet region, action as sensitizer ions to transfer energy to rare earth or transition metal ions and emission of highly‐efficient light is systematically summarized. The proposed structure‐luminescence relationship offers guidance for the optimization of current Bi³⁺‐included LFMH materials and the exploitation of new LFMH derivatives.

Molybdenum disulfide (MoS₂), which is composed of active edge sites and a catalytically inert basal plane, is a promising catalyst to replace the state‐of‐the‐art Pt for electrochemically catalyzing hydrogen evolution reaction (HER). Because the basal plane consists of the majority of the MoS₂bulk materials, activation of basal plane sites is an important challenge to further enhance HER performance. Here, an in situ electrochemical activation process of the MoS₂basal planes by using the atomic layer deposition (ALD) technique to improve the HER performance of commercial bulk MoS₂is first demonstrated. The ALD technique is used to form islands of titanium dioxide (TiO₂) on the surface of the MoS₂basal plane. The coated TiO₂on the MoS₂surface (ALD(TiO₂)‐MoS₂) is then leached out using an in situ electrochemical activation method, producing highly localized surface distortions on the MoS₂basal plane. The MoS₂catalysts with activated basal plane surfaces (ALD(Act.)‐MoS₂) have dramatically enhanced HER kinetics, resulting from more favorable hydrogen‐binding.

Due to the high costs, slow reaction kinetics, and methanol poisoning of platinum‐based cathode catalysts, designing and exploring non‐Pt or low‐Pt cathode electrocatalysts with a low cost, high catalytic performance, and high methanol‐tolerance are crucial for the commercialization of fuel cells. Here, a facile method to fabricate a system of PdAg nanorings supported by graphene nanosheets is demonstrated; the fabrication is based on the galvanic displacement reaction between pre‐synthesized Ag nanoparticles and palladium ions. X‐ray diffraction and high‐resolution transmission electron microscopy show that the synthesized PdAg nanocrystals exhibit a ring‐shaped hollow structure with an average size of 27.49 nm and a wall thickness of 5.5 nm. Compared to the commercial Pd–C catalyst, the PdAg nanorings exhibit superior properties as a cathode electrocatalyst for oxygen reduction. Based on structural and electrochemical studies, these advantageous properties include efficient usage of noble metals and a high surface area because of the effective utilization of both the exterior and interior surfaces, high electrocatalytic performance for oxygen reduction from the synergistic effect of the alloyed PdAg crystalline phase, and most importantly, excellent tolerance of methanol crossover at high concentrations. It is anticipated that this synthesis of graphene‐based PdAg nanorings will open up a new avenue for designing advanced electrocatalysts that are low in cost and that exhibit high catalytic performance for alkaline fuel cells.