Yingzhi Jin

Precise molecular design of optical materials requires in‐depth understanding of structure–property relationships. The principles and guidelines that endow aggregation‐induced emission fluorogens (AIEgens) with long‐wavelength absorption/emission, high quantum yields, large molar absorptivity, improved two‐photon absorption cross sections, fine‐tuned singlet–triplet energy gap, and high contrast in mechanochromism and triboluminescence are discussed.

Abstract

Precise design of fluorescent molecules with desired properties has enabled the rapid development of many research fields. Among the different types of optically active materials, luminogens with aggregation‐induced emission (AIEgens) have attracted significant interest over the past two decades. The negligible luminescence of AIEgens as a molecular species and high brightness in aggregate states distinguish them from conventional fluorescent dyes, which has galvanized efforts to bring AIEgens to a wide array of multidisciplinary applications. Herein, the useful principles and emerging structure–property relationships for precise molecular design toward AIEgens with desirable properties using concrete examples are revealed. The cutting‐edge applications of AIEgens and their excellent performance in enabling new research directions in biomedical theranostics, optoelectronic devices, stimuli‐responsive smart materials, and visualization of physical processes are also highlighted.

Nonfullerene acceptors‐based terpolymer, SMD2, is designed and synthesized to continuously fabricate high‐performance organic solar cell (OSC) modules, and multifunctional hole transport layers are developed, and applied to flexible modules via an all‐solution process. the flexible OSC modules fabricated in an industrial production line have a PCE of 5.25% (P _max = 419.6 mW) on an area of 80 cm².

Abstract

To ensure laboratory‐to‐industry transfer of next‐generation energy harvesting organic solar cells (OSCs), it is necessary to develop flexible OSC modules that can be produced on a continuous roll‐to‐roll basis and to apply an all‐solution process. In this study, nonfullerene acceptors (NFAs)‐based donor polymer, SMD2, is newly designed and synthesized to continuously fabricate high‐performance flexible OSC modules. Also, multifunctional hole transport layers (HTLs), WO₃/HTL solar bilayer HTLs, are developed and applied via an all‐solution process called “ProcessOne” into inverted structure. SMD2, the donor terpolymer, has a deep highest occupied molecular orbital (HOMO) level and can achieve a power conversion efficiency (PCE) of 11.3% with NFAs without any pre‐/post‐treatment because of its optimal balance between crystallinity and miscibility. Furthermore, the integration of multifunctional HTLs enables the recovery of the drop in open circuit voltage (V _OC) caused by a mismatch in energy levels between the deep HOMO level of the NFAs‐based bulk‐heterojunction layer and the solution‐processed HTLs. Also, the photostability under ultraviolet‐exposure necessary for “ProcessOne” is greatly improved because of the integration of multifunctional HTLs. Consequently, because of the synergistic effects of these approaches, the flexible OSC modules fabricated in an industrial production line have a PCE of 5.25% (P _max = 419.6 mW) on an active area of 80 cm².

In article number https://doi.org/10.1002/aenm.2019018051901805, Doojin Vak, Seok‐In Na and co‐workers report a highly efficient single‐junction ternary polymer solar cell (PSC) based on PTB7‐Th, PC₇₁BM, and COi8DFIC using slot‐die coating. This approach is readily translated into large‐area module and roll‐to‐roll processed PSCs, which produce the highest power conversion efficiency among the printing‐based PSCs.

The first entirely, intrinsically, and autonomously self‐healable, highly transparent, and superstretchable triboelectric nanogenerator is developed for not only energy sources but also self‐powered electronic skins. This unprecedented triboelectric nanogenerator with energy‐extracting and activity‐sensing abilities is timely and able to usher vast emerging fields including flexible/self‐powered electronics, smart interfaces, and prosthetic and robotic skins.

Abstract

Power and electronic components that are self‐healable, deformable, transparent, and self‐powered are highly desirable for next‐generation energy/electronic/robotic applications. Here, an energy‐harvesting triboelectric nanogenerator (TENG) that combines the above features is demonstrated, which can serve not only as a power source but also as self‐powered electronic skin. This is the first time that both of the triboelectric‐charged layer and electrode of the TENG are intrinsically and autonomously self‐healable at ambient conditions. Additionally, comparing with previous partially healable TENGs, its fast healing time (30 min, 100% efficiency at 900% strain), high transparency (88.6%), and inherent superstretchability (>900%) are much more favorable. It consists of a metal‐coordinated polymer as the triboelectrically charged layer and hydrogen‐bonded ionic gel as the electrode. Even after 500 cutting‐and‐healing cycles or under extreme 900%‐strain, the TENG retains its functionality. The generated electricity can be used directly or stored to power commercial electronics. The TENG is further used as self‐powered tactile‐sensing skin in diverse human–machine interfaces including smart glass, an epidermal controller, and phone panel. This TENG with merits including fast ambient‐condition self‐healing, high transparency, intrinsic stretchability, and energy‐extraction and actively‐sensing abilities, can meet wide application needs ranging from deformable/portable/transparent electronics, smart interfaces, to artificial skins.

A photo‐/thermal‐responsive field‐effect transistor is successfully fabricated by blending conjugated semiconducting polymer with a photochromic and thermally responsive hexaarylbiimidazole derivative and using octadecyltrichlorosilane‐modified SiO₂ as the gate dielectric. Such transistors can be utilized to fabricate photonically programmable and thermally erasable FET‐based nonvoltaile memory devices with outstanding memory performance.

Abstract

It is shown that the semiconducting performance of field‐effect transistors (FETs) with PDPP4T (poly(diketopyrrolopyrrole‐quaterthiophene)) can be reversibly tuned by UV light irradiation and thermal heating after blending with the photochromic hexaarylbiimidazole compound (p‐NO₂‐HABI). A photo‐/thermal‐responsive FET with a blend thin film of PDPP4T and p‐NO₂‐HABI is successfully fabricated. The transfer characteristics are altered significantly with current enhanced up to 10⁶‐fold at V _G = 0 V after UV light irradiation. However, further heating results in the recovery of the transfer curve. This approach can be extended to other semiconducting polymers such as P3HT (poly(3‐hexyl thiophene)), PBTTT (poly(2,5‐bis(3‐tetradecylthiophen‐2‐yl)thieno[3,2‐b] thiophene)) and PDPPDTT (poly(diketopyrrolopyrrole‐dithienothiophene)). It is hypothesized that TPIRs (2,4,5‐triphenylimidazolyl radicals) formed from p‐NO₂‐HABI after UV light irradiation can interact with charge defects at the gate dielectric–semiconductor interface and those in the semiconducting layer to induce more hole carriers in the semiconducting channel. The application of the blend thin film of PDPP4T and p‐NO₂‐HABI is further demonstrated to fabricate the photonically programmable and thermally erasable FET‐based nonvolatile memory devices that are advantageous in terms of i) high ON/OFF current ratio, ii) nondestructive reading at low electrical bias, and iii) reasonably highly stable ON‐state and OFF‐state.

The use of biobased carbons to fabricate conductive, highly stretchable, and biocompatible silk‐based composite biomaterials is demonstrated. Biomass is converted into a carbonaceous material via hydrothermal processing, and subsequently applied upon activation as a conductive filler in silk thin films. These conductive composite biomaterials, made entirely from renewable sources, have promising applications in fields like biomedicine, energy, and electronics.

Abstract

There is great interest in developing conductive biomaterials for the manufacturing of sensors or flexible electronics with applications in healthcare, tracking human motion, or in situ strain measurements. These biomaterials aim to overcome the mismatch in mechanical properties at the interface between typical rigid semiconductor sensors and soft, often uneven biological surfaces or tissues for in vivo and ex vivo applications. Here, the use of biobased carbons to fabricate conductive, highly stretchable, flexible, and biocompatible silk‐based composite biomaterials is demonstrated. Biobased carbons are synthesized via hydrothermal processing, an aqueous thermochemical method that converts biomass into a carbonaceous material that can be applied upon activation as conductive filler in composite biomaterials. Experimental synthesis and full‐atomistic molecular dynamics modeling are combined to synthesize and characterize these conductive composite biomaterials, made entirely from renewable sources and with promising applications in fields like biomedicine, energy, and electronics.

Incorporating dicyanobenzothiadiazole into polymer yields an n‐type semiconductor DCNBT‐IDT, which exhibits a narrow bandgap of 1.43 eV and a high absorption coefficient of 6.15 × 10⁴ cm⁻¹. The DCNBT‐IDT‐based all‐polymer solar cells achieve a remarkable power conversion efficiency of 8.32% with a small energy loss of 0.53 eV and a photoresponse of up to 870 nm.

Abstract

Currently, n‐type acceptors in high‐performance all‐polymer solar cells (all‐PSCs) are dominated by imide‐functionalized polymers, which typically show medium bandgap. Herein, a novel narrow‐bandgap polymer, poly(5,6‐dicyano‐2,1,3‐benzothiadiazole‐alt‐indacenodithiophene) (DCNBT‐IDT), based on dicyanobenzothiadiazole without an imide group is reported. The strong electron‐withdrawing cyano functionality enables DCNBT‐IDT with n‐type character and, more importantly, alleviates the steric hindrance associated with typical imide groups. Compared to the benchmark poly(naphthalene diimide‐alt‐bithiophene) (N2200), DCNBT‐IDT shows a narrower bandgap (1.43 eV) with a much higher absorption coefficient (6.15 × 10⁴ cm⁻¹). Such properties are elusive for polymer acceptors to date, eradicating the drawbacks inherited in N2200 and other high‐performance polymer acceptors. When blended with a wide‐bandgap polymer donor, the DCNBT‐IDT‐based all‐PSCs achieve a remarkable power conversion efficiency of 8.32% with a small energy loss of 0.53 eV and a photoresponse of up to 870 nm. Such efficiency greatly outperforms those of N2200 (6.13%) and the naphthalene diimide (NDI)‐based analog NDI‐IDT (2.19%). This work breaks the long‐standing bottlenecks limiting materials innovation of n‐type polymers, which paves a new avenue for developing polymer acceptors with improved optoelectronic properties and heralds a brighter future of all‐PSCs.

The use of liquid exfoliated 2D WS₂ and MoS₂ as hole‐transporting layers (HTLs) in ultrahigh efficiency organic solar cells is reported. WS₂ yields cells with higher power conversion efficiency (PCE), fill‐factor, and short‐circuit current than MoS₂ and poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate). When WS₂ is introduced as HTL in PBDB‐T‐2F:Y6:PC₇₁BM organic solar cells, a maximum PCE value of 17% is achieved.

Abstract

The application of liquid‐exfoliated 2D transition metal disulfides (TMDs) as the hole transport layers (HTLs) in nonfullerene‐based organic solar cells is reported. It is shown that solution processing of few‐layer WS₂ or MoS₂ suspensions directly onto transparent indium tin oxide (ITO) electrodes changes their work function without the need for any further treatment. HTLs comprising WS₂ are found to exhibit higher uniformity on ITO than those of MoS₂ and consistently yield solar cells with superior power conversion efficiency (PCE), improved fill factor (FF), enhanced short‐circuit current (J _SC), and lower series resistance than devices based on poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) and MoS₂. Cells based on the ternary bulk‐heterojunction PBDB‐T‐2F:Y6:PC₇₁BM with WS₂ as the HTL exhibit the highest PCE of 17%, with an FF of 78%, open‐circuit voltage of 0.84 V, and a J _SC of 26 mA cm⁻². Analysis of the cells' optical and carrier recombination characteristics indicates that the enhanced performance is most likely attributed to a combination of favorable photonic structure and reduced bimolecular recombination losses in WS₂‐based cells. The achieved PCE is the highest reported to date for organic solar cells comprised of 2D charge transport interlayers and highlights the potential of TMDs as inexpensive HTLs for high‐efficiency organic photovoltaics.

In article number https://doi.org/10.1002/aenm.2019018051901805, Doojin Vak, Seok‐In Na and co‐workers report a highly efficient single‐junction ternary polymer solar cell (PSC) based on PTB7‐Th, PC₇₁BM, and COi8DFIC using slot‐die coating. This approach is readily translated into large‐area module and roll‐to‐roll processed PSCs, which produce the highest power conversion efficiency among the printing‐based PSCs.

In article number https://doi.org/10.1002/adfm.2019031121903112, Liang‐Sheng Liao, Chun‐Sing Lee, and co‐workers report the formation of dimeric single‐component charge‐transfer complexes (SCCTCs) by self‐complexation of a donor‐π‐acceptor molecule (PIPAQ), wherein the strong intermolecular charge transfer leads to unusual deep‐red/near‐infrared thermally activated delayed fluorescence. Notably, PIPAQ can be applied in light‐emitting devices as an emissive layer to realize unprecedented SCCTC‐based electroluminescence.

An electron‐deficient unit containing B←N bonds, namely BNIDT, is developed to construct polymer acceptors for photovoltaic applications. Desirable optoelectronic properties such as broad absorption profiles, low‐lying energy levels, ambipolar charge transport properties, and strong electron‐affinity are found for these polymers. All‐polymer solar cells using these B←N embedded polymers as acceptor materials exhibit an enhanced efficiency of 8.78%.

Abstract

In the field of all‐polymer solar cells (all‐PSCs), all efficient polymer acceptors that exhibit efficiencies beyond 8% are based on either imide or dicyanoethylene. To boost the development of this promising solar cell type, creating novel electron‐deficient units to build high‐performance polymer acceptors is critical. A novel electron‐deficient unit containing B←N bonds, namely, BNIDT, is synthesized. Systematic investigation of BNIDT reveals desirable properties including good coplanarity, favorable single‐crystal structure, narrowed bandgap and downshifted energy levels, and extended absorption profiles. By copolymerizing BNIDT with thiophene and 3,4‐difluorothiophene, two novel conjugated polymers named BN‐T and BN‐2fT are developed, respectively. It is shown that these polymers possess wide absorption spectra covering 350–800 nm, low‐lying energy levels, and ambipolar film‐transistor characteristics. Using PBDB‐T as the donor and BN‐2fT as the acceptor, all‐PSCs afford an encouraging efficiency of 8.78%, which is the highest for all‐PSCs excluding the devices based on imide and dicyanoethylene‐type acceptors. Considering that the structure of BNIDT is totally different from these classical units, this work opens up a new class of electron‐deficient unit for constructing efficient polymer acceptors that can realize efficiencies beyond 8% for the first time.

In bulk heterojunctions with small energetic offsets between donor and acceptor materials, the donor polymer can assist the electron transport by providing “bridges” or a “shortcut” for electron transport across the small‐molecular domains and facilitates the overall electron transport. This finding can be also applied to other fields to tune the charge transport property of organic materials or slush blends.

Abstract

Conventional organic solar cell (OSC) systems have significant energy offsets between the donor and acceptor both at the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels. Because of this, in a bulk heterojunction (BHJ) system, electrons typically transport in acceptors, whereas holes typically transport in donors. It is not favorable for electrons to hop back and forth between the donor and acceptor because the hopping is energetically disfavored. In such conventional OSC systems, the addition of donor polymer to acceptor films should typically reduce the electron mobility. In this study, a surprisingly large increase (up to 30×) in electron mobility is observed in an OSC blend when introducing a polymer donor into small molecular acceptor. By ruling out morphology reasons, it is shown that the donor polymer can assist the electron transport by providing “bridges” or a “shortcut” for electron transport across the domains of small molecular acceptors. This can happen because, for these systems, the LUMO offset is small. The study shows the benefits of donor‐assisted electron transport in BHJ systems with small energetic offsets. This finding could be also applied to other fields to tune the optimized charge transport property of organic materials or slush blends.

Supramolecular‐macrocycle‐based crystalline organic materials (COMs) are reviewed. These crystalline materials are categorized by various types of macrocycles. The main discussion is focused on the structures of these COMs and their structure–function relationships. Perspectives and future challenges in the field of supramolecular‐macrocycle‐based COMs are also presented.

Abstract

Supramolecular macrocycles are well known as guest receptors in supramolecular chemistry, especially host−guest chemistry. In addition to their wide applications in host−guest chemistry and related areas, macrocycles have also been employed to construct crystalline organic materials (COMs) owing to their particular structures that combine both rigidity and adaptivity. There are two main types of supramolecular‐macrocycle‐based COMs: those constructed from macrocycles themselves and those prepared from macrocycles with other organic linkers. This review summarizes recent developments in supramolecular‐macrocycle‐based COMs, which are categorized by various types of macrocycles, including cyclodextrins, calixarenes, resorcinarenes, pyrogalloarenes, cucurbiturils, pillararenes, and others. Effort is made to focus on the structures of supramolecular‐macrocycle‐based COMs and their structure–function relationships. In addition, the application of supramolecular‐macrocycle‐based COMs in gas storage or separation, molecular separation, solid‐state electrolytes, proton conduction, iodine capture, water or environmental treatment, etc., are also presented. Finally, perspectives and future challenges in the field of supramolecular‐macrocycle‐based COMs are discussed.

This work demonstrates the single‐step fabrication of solid‐state symmetric batteries with inter‐connected pore honeycomb electrodes and a solid‐state electrolytes using scalable spray‐printing. The active material is based on a low‐cost and nonhazardous textile dye that is suitable for both negative and positive electrode reactions in a symmetric configuration. The half‐cell electrode potentials are amongst the lowest and the highest within the quinone family.

Abstract

A symmetric solid‐state battery based on organic porous electrodes is fabricated using scalable spray‐printing. The active electrode material is based on a textile dye (disperse blue 134 anthraquinone) and is capable of forming divalent cations and anions in oxidation and reduction processes. The resulting molecule can be used in both negative and positive electrode reactions. After spray printing an inter‐connected pore honeycomb electrode, a solid‐state electrolyte (σ_Li: × 10⁻⁴ S cm⁻¹) based on a polymeric ionic liquid is spray‐printed as a second layer and infiltrated through the porous electrodes. A symmetric all‐organic battery is then formed with the addition of another identical set of electrode and electrolyte layers. Both density functional theory calculations and charge‐discharge profiles show that the potentials for the negative and positive electrode reactions are amongst the lowest (≈2.0 V vs Li) and the highest (≈3.5 V vs Li), respectively, for quinone‐type molecules. Over the C‐rate range 0.2 to 5 C, the battery has a discharge cell voltage of more than 1 V even up to 250 charge‐discharge cycles and capacities are in the range 50–80 mA h g⁻¹ at 0.5 C.

In article number https://doi.org/10.1002/aenm.2019018291901829, Jin Young Kim, Taiho Park and co‐workers report that cross‐linkable semiconducting polymers and nonfullerene acceptors can lead to thermal stability in a green‐solvent processed organic photovoltaic. The burn‐in loss due to thermal aging and light soaking is dramatically suppressed due to the frozen morphology from the cross‐linkable polymers and high miscibility from the nonfullerene acceptors.

Charge extraction in bulk‐heterojunction (BHJ) organic photovoltaics is most efficient when the contact area between the semiconductors and electrodes is maximized. We show that ≈99% of this area can in fact be insulating without degrading the efficiency of charge carrier extraction, provided the spacing of the conducting areas is less than or equal to twice the BHJ thickness.

Abstract

It is widely considered that charge carrier extraction in bulk‐heterojunction organic photovoltaics (BHJ OPVs) is most efficient when the area of contact between the semiconductor layers and the electrodes is maximized and the electrodes are electrically homogeneous. Herein, it is shown that ≈99% of the electrode surface can in fact be insulating without degrading the efficiency of charge carrier extraction, provided the spacing of the conducting areas is less than or equal to twice the optimal thickness of the BHJ layer. This striking result is demonstrated for BHJ OPVs with both conventional and inverted device architectures using two different types of BHJ OPVs, namely, PCDTBT:PC₇₀BM and the ternary blend PBDB‐T:ITIC‐m:PC₇₀BM. This finding opens the door to the use of a large pallet of materials for optical spacers and charge transport layers, based on a low density of conducting particles embedded in a wide bandgap insulating matrix.

Herein, a low crystalline indacenodithiophene‐co‐benzothiadiazole (IDTBT) donor–acceptor copolymer is reported to be able to preserve electrical functionality under high strain. The mechanical properties and morphological evolution for IDTBT thin films during stretching is systematically investigated. This kind of near‐amorphous polymer signifies a promising direction regarding molecular design principles toward intrinsically stretchable high‐performance polymer semiconductors.

Abstract

For wearable and implantable electronics applications, developing intrinsically stretchable polymer semiconductor is advantageous, especially in the manufacturing of large‐area and high‐density devices. A major challenge is to simultaneously achieve good electrical and mechanical properties for these semiconductor devices. While crystalline domains are generally needed to achieve high mobility, amorphous domains are necessary to impart stretchability. Recent progresses in the design of high‐performance donor–acceptor polymers that exhibit low degrees of energetic disorder, while having a high fraction of amorphous domains, appear promising for polymer semiconductors. Here, a low crystalline, i.e., near‐amorphous, indacenodithiophene‐co‐benzothiadiazole (IDTBT) polymer and a semicrystalline thieno[3,2‐b]thiophene‐diketopyrrolopyrrole (DPPTT) are compared, for mechanical properties and electrical performance under strain. It is observed that IDTBT is able to achieve both a high modulus and high fracture strain, and to preserve electrical functionality under high strain. Next, fully stretchable transistors are fabricated using the IDTBT polymer and observed mobility ≈0.6 cm² V⁻¹ s⁻¹ at 100% strain along stretching direction. In addition, the morphological evolution of the stretched IDTBT films is investigated by polarized UV–vis and grazing‐incidence X‐ray diffraction to elucidate the molecular origins of high ductility. In summary, the near‐amorphous IDTBT polymer signifies a promising direction regarding molecular design principles toward intrinsically stretchable high‐performance polymer semiconductor.

UV‐ozone treatments for different times (0, 10, 30, and 60 min) are examined on the 2D metallic Ti₃C₂T_x films to take advantage of the tunable optoelectronic properties of MXenes as electron transport layers in low‐temperature processed planar‐structured perovskite solar cells, resulting in augmentation of the power conversion efficiency (PCE) from 5.00% to the champion PCE of 17.17%.

Abstract

MXenes are a large and rapidly expanding family of 2D materials that, owing to their unique optoelectronic properties and tunable surface termination, find a wide range of applications including energy storage and energy conversion. In this work, Ti₃C₂T_x MXene nanosheets are applied as a novel type of electron transport layer (ETL) in low‐temperature processed planar‐structured perovskite solar cells (PSCs). Interestingly, simple UV‐ozone treatment of the metallic Ti₃C₂T_x that increases the surface TiO bonds without any change in its bulk properties such as high electron mobility improves its suitability as an ETL. Improved electron transfer and suppressed recombination at the ETL/perovskite interface results in augmentation of the power conversion efficiency (PCE) from 5.00% in the case of Ti₃C₂T_x without UV‐ozone treatment to the champion PCE of 17.17%, achieved using the Ti₃C₂T_x film after 30 min of UV‐ozone treatment. As the first report on the use of pure MXene layer as an ETL in PSCs, this work shows the great potential of MXenes to be used in PSCs and displays their promise for applications in photovoltaic technology in general.

Ti₃C₂‐based MXene contacts—spin‐coated from an aqueous colloidal suspension onto a GaAs substrate—are compared with vacuum‐deposited titanium/gold electrodes for the photodetection of light. Such an MXene‐based device has better detectivity, quantum efficiency, and a higher dynamic range as compared to the conventional Au‐based metal–semiconductor–metal devices.

Abstract

2D transition metal carbides, known as MXenes, are transparent when the samples are thin enough. They are also excellent electrical conductors with metal‐like carrier concentrations. Herein, these characteristics are exploited to replace gold (Au) in GaAs photodetectors. By simply spin‐coating transparent Ti₃C₂‐based MXene electrodes from aqueous suspensions onto GaAs patterned with a photoresist and lifted off with acetone, photodetectors that outperform more standard Au electrodes are fabricated. Both the Au‐ and MXene‐based devices show rectifying contacts with comparable Schottky barrier heights and internal electric fields. The latter, however, exhibit significantly higher responsivities and quantum efficiencies, with similar dark currents, hence showing better dynamic range and detectivity, and similar sub‐nanosecond response speeds compared to the Au‐based devices. The simple fabrication process is readily integratable into microelectronic, photonic‐integrated circuits and silicon photonics processes, with a wide range of applications from optical sensing to light detection and ranging and telecommunications.