Achieving Strong Circularly Polarized Luminescence through Cascade Cationic Insertion in Lead-free Hybrid Metal Halides.

Generating circularly polarized luminescence (CPL) with simultaneous high photoluminescence quantum yield (PLQY) and dissymmetry factor (glum) is difficult due to usually unmatched electric transition dipole moment (µ) and magnetic transition dipole moment (m) of materials. Herein we tackle this issue by playing a "cascade cationic insertion" trick to achieve strong CPL (with PLQY of ~100 %) in lead-free metal halides with high glum values reaching -2.3×10-2 without using any chiral inducers. Achiral solvents of hydrochloric acid (HCl) and N, N-dimethylformamide (DMF) infiltrate the crystal lattice via asymmetric hydrogen bonding, distorting the perovskite structure to induce the "intrinsic" chirality. Surprisingly, additional insertion of Cs+ cation to substitute partial (CH3)2NH2 + transforms the chiral space group to achiral but the crystal maintains chiroptical activity. Further doping of Sb3+ stimulates strong photoluminescence as a result of self-trapped excitons (STEs) formation without disturbing the crystal framework. The chiral perovskites of indium-antimony chlorides embedded on LEDs chips demonstrate promising potential as CPL emitters. Our work presents rare cases of chiroptical activity of highly luminescent perovskites from only achiral building blocks via spontaneous resolution as a result of symmetry breaking.

Pre-Endcapping of Hyperbranched Polymers toward Intrinsically Stretchable Semiconductors with Good Ductility and Carrier Mobility.

The advancement of semiconducting polymers stands as a pivotal milestone in the quest to realize wearable electronics. Nonetheless, endowing semiconductor polymers with stretchability without compromising their carrier mobility remains a formidable challenge. This study proposes a "pre-endcapping" strategy for synthesizing hyperbranched semiconducting polymers (HBSPs), aiming to achieve the balance between carrier mobility and stretchability for organic electronics. The findings unveil that the aggregates formed by the endcapped hyperbranched network structure not only ensure efficient charge transport but also demonstrate superior tensile resistance. In comparison to linear conjugated polymers, HBSPs exhibit substantially larger crack onset strains and notably diminished tensile moduli. It is evident that the HBSPs surpass their linear counterparts in terms of both their semiconducting and mechanical properties. Among HBSPs, HBSP-72h-2.5 stands out as the preeminent candidate within the field of inherently stretchable semiconducting polymers, maintaining 93% of its initial mobility even when subjected to 100% strain (1.41 ± 0.206 cm2 V-1 s-1). Furthermore, thin film devices of HBSP-72h-2.5 remain stable after undergoing repeated stretching and releasing cycles. Notably, the mobilities are independent of the stretching directions, showing isotropic charge transport behavior. The preliminary study makes this "pre-endcapping" strategy a potential candidate for the future design of organic materials for flexible electronic devices.

Radical Cation Salts of Hetera-Buckybowls: Polar Crystals, Negative Thermal Expansion and Phase Transition.

Radical cation salts of π-conjugated polycycles are rich in physical properties. Herein, two kinds of hetera-buckybowls, ethoxy-substituted trithiasumanene (3SEt) and triselenasumanene (3SeEt), are synthesized as electron donors. Galvanostatic oxidation of them affords radical cation salts (3SEt)5 (TTFMPB)3 , (3SeEt)5 (TTFMPB)3 , (3SEt)4 PMA, and (3SeEt)4 PMA, where PMA is Keggin-type phosphomolybdate and TTFMPB is tetrakis[3,5-bis(trifluoromethyl)-phenyl]borate. In these salts, 3SEt/3SeEt are partially charged and show distinct conformation change with the site charge and counter anions. In TTFMPB salts, (TTFMPB)- forms hexagonal channels that accommodate the packing columns of 3SEt/3SeEt. In particular, (3SEt)5 (TTFMPB)3 adopts the R3c space group and is a polar crystal with the columns of 3SEt all in the up-bowl direction. The PMA salts of 3SEt/3SeEt are polar crystals (C2 space group) with 3SEt/3SeEt being planar and forming columnar stacks. (3SeEt)4 PMA shows a structural modulation below 200 K, namely, negative thermal expansion (NTE) of the unit cell volume and enlargement of the intermolecular distances between neighboring 3SeEt molecules. The four salts are semiconductors with an activation energy of 0.18-0.38 eV. The conductivity of (3SeEt)4 PMA shows a reversible transition upon cooling and heating, in accordance to the NTE structural modulation. This work paves the way toward conducting materials based on hetera-buckybowls.

Transforming Hetera-Buckybowls into Chiral Conjugated Polycycles Incorporating Epoxycyclooctadiene: a Two-Step Approach.

Chiral π-conjugated polycycles have garnered increasing attention due to versatile applications in optoelectronic materials and biological sciences. In this study, we report the synthesis of chiral π-conjugated polycycles incorporating a chiral epoxycyclooctadiene moiety. Our synthetic strategy capitalizes on the novel reactions of hetera-buckybowl triselenasumanene (TSS) and is achieved in two-step manner. Firstly, the TSS is regio-selectively transformed into its ortho-quinone form. Subsequently, the nucleophilic addition reactions of TSS ortho-quinone by phenylethynides are metal ion-dependent. When utilizing (phenylethynyl)magnesium bromide as the nucleophile, two phenylethynyls are furnished onto the edged benzene ring of TSS. When the nucleophile is (phenylethynyl)lithium, a cascade of nucleophilic addition, intermolecular electron-transfer, ring-opening, and tetradehydro-Diels-Alder (TDDA) reactions occur sequentially in one-pot, ultimately affording chiral π-conjugated polycycles featuring the epoxycyclooctadiene moiety as an integral part of their backbones. This work represents a step forward in the synthesis of chiral π-conjugated polycycles using TSS as synthon.

Utilizing Topological Insulator Two-Dimensional Bismuth for Ultrasensitive Acoustic Detection.

Topological insulators (TIs) are characterized by a full insulating gap in the bulk and gapless edge or surface states, which have attracted tremendous attention. 2D Bi (110), as a typical TI, is of particular interest due to its low symmetry structure and topologically protected and spin-momentum-locked Dirac surface states. However, the material's potential applications are hindered by difficulties in fabrication, due to its strong semi-metallic bonding and poor stability. In this study, a novel electrochemical intercalation method for the fabrication of ultrathin Bi (110) nanosheets with the highest yield ever reported is presented. These nanosheets are stabilized through cathodic exfoliation in a reductive environment and further modification with polymer ionic liquids. The versatility of these nanosheets is demonstrated by fabricating flexible acoustic sensors with ultrahigh sensitivity. These sensors can even detect sounds as quiet as 45 dB. Furthermore, these sensors are utilized for acoustic-to-electric energy conversion and information transfer. This work offers a promising approach for scalable fabrication and preservation of ultrathin 2D TI Bi (110) nanosheets and paves the way for their integration into smart devices.

Intrinsic Ferromagnetic Semiconductors with High Saturation Magnetization from Hybrid Perovskites.

Ferromagnetic semiconductors (FMS) enable simultaneous control of both charge and spin transport of charge carriers, and they have emerged as a class of highly desirable but rare materials for applications in spin field-effect transistors and quantum computing. Organic-inorganic hybrid perovskites with high compositional adjustability and structural versatility can offer unique benefits in the design of FMS but has not been fully explored. Here, a series of molecular FMSs based on the 2D organic-inorganic hybrid perovskite structure, namely (2ampy)CuCl4 , (3ampy)CuCl4 , and (4ampy)CuCl4 , is demonstrated, which exhibits high saturation magnetization, dramatic temperature-dependent conductivity change, and tunable ferromagnetic resonance. Magnetic measurements reveal a high saturation magnetization up to 18.56 emu g-1 for (4ampy)CuCl4 , which is one of the highest value among reported hybrid FMSs to date. Conductivity studies of the three FMSs demonstrate that the smaller adjacent octahedron distance in the 2D layer results in higher conductivity. Systematic ferromagnetic resonance investigation shows that the gyromagnetic ratio and Landau factor values are strongly dependent on the types of organic cations used. This work demonstrates that 2D hybrid perovskite materials can simultaneously possess both tunable long-range ferromagnetic ordering and semiconductivity, providing a straightforward strategy for designing and synthesizing high-performance intrinsic FMSs.

Hyperbranched Polymers for Organic Semiconductors.

Hyperbranched polymers (HBPs) have attracted increasing attention owing to their distinct highly branched topological structures, resulting in unique properties and wide applications in organic semiconductors (OSCs). In this Review, recent progress in functional HBPs is outlined in the field of OSCs, including organic light-emitting diodes (OLEDs), organic photovoltaics (OPVs), dye-sensitized solar cells (DSSCs), and organic field effect transistors (OFETs), among others. Prospects of HBPs-based materials in OSCs are examined. The results revealed that multi-dimensional topologies not only regulate the electron (hole) transport but also adjust the film morphology, thereby affecting the efficiency and long life of organic electronic devices. Many studies showed the usefulness of HBPs as hole transport materials but reports dealing with n-type and ambipolar materials are still lacking. In addition, the interchain covalent bond in hyperbranched polymers could mitigate the damage caused by stretching, conducive to building stable flexible stretchable devices with long-term durability and good safety under harsh environmental conditions. Overall, the flexible stretchable design may enrich the applications of HBPs in organic semiconductors and provide new ideas for guiding the future design of functional organic semiconductor materials.

Flexible optical limiters based on Cu3VSe4 nanocrystals.

Optical limiters are greatly needed to protect eyes and sensitive optoelectronic devices such as photodetectors and sensors from laser damage, but they are currently plagued by low efficiency. In this work, we utilized Cu3VSe4 nanocrystals (NCs) to enhance laser protection performance, and they exhibit higher saturation intensity and broader nonlinear spectral response extending into the near IR region than the C60 benchmark. A flexible optical limiter goggle prototype based on the NCs significantly attenuated the incident laser beam, with Z scan and I scan measurements demonstrating a giant nonlinear absorption coefficient ß value of 1.0 × 10-7 m W-1, a large optical damage threshold of 3.5 J cm-2, and a small starting threshold of 0.22 J cm-2. Transient absorption spectroscopy disclosed that the origin of the excellent nonlinearity was associated with quasi-static dielectric resonance behavior and a large TPA cross-section of 3.3 × 106 GM was measured for Cu3VSe4 NCs, suggesting the potential of intermediate bandgap (IB) semiconductors as alternatives to plasmonic noble metals for ultrafast photonics. Hence, optical limiters based on such semiconductors offer new avenues for laser protection in optoelectronic and defense fields.

Optical Fibers Embedded with As-Grown Carbon Nanotubes for Ultrahigh Nonlinear Optical Responses.

Photonic crystal fiber (PCF) embedded with functional materials has demonstrated diverse applications ranging from ultrafast lasers, optical communication to chemical sensors. Many efforts have been made to fabricating carbon nanotube (CNT) based optical fibers by ex situ transfer method; however, often suffer poor uniformity and coverage. Here, the direct growth of CNTs on the inner walls of PCFs by the chemical vapor deposition (CVD) method is reported. A two-step growth method is developed to control the narrow diameter distribution of CNTs to ensure desirable nanotube optical transitions. In the as-fabricated CNT- embedded fiber, third-harmonic generation (THG) has been enhanced by ≈15 times compared with flat CNT film on fused silica. A dual-wavelength all-fiber mode-locked ultrafast laser (≈1561 and ≈1064 nm) is further demonstrated by integrating the 1.36±0.15 nm-diameter CNTs into two kinds of photonic bandgap hollow core PCF (named HC-1550 and HC-1060) as saturable absorbers, using their S11 (≈0.7 eV) and S22 (≈1.2 eV) interband transition respectively. The fiber laser shows stable output of ≈10 mW, ≈800 fs pulse width, and ≈71 MHz repetition rate at 1561 nm wavelength. These results can enable the large-scale applications of CNTs in PCF-based optical devices.

Non-symmetric Half-Fused B←N Coordinated Diketopyrrolopyrrole Building Block for n-type Semiconducting Polymers.

The development of conjugated polymers with high semiconducting performance and high reliability is of great significance for flexible electronics. Herein, we developed a new type of electron-accepting building block; i.e., non-symmetric half-fused B←N coordinated diketopyrrolopyrrole (DPP) (HBNDPP), for amorphous conjugated polymers toward flexible electronics. The rigid B←N fusion part of HBNDPP endows the resulting polymers with decent electron transport, while its non-symmetric structure causes the polymer to exhibit multiple conformation isomers with flat torsional potential energies. Thus, it gets packed in an amorphous manner in solid state, ensuring good resistance to bending strain. Combined with hardness and softness, the flexible organic field-effect transistor devices exhibit n-type charge properties with decent mobility, good bending resistance, and good ambient stability. The preliminary study makes this building block a potential candidate for future design of conjugated materials for flexible electronic devices.

Self-Doping Naphthalene Diimide Conjugated Polymers for Flexible Unipolar n-Type OTFTs.

The development of high-performance organic thin-film transistor (OTFT) materials is vital for flexible electronics. Numerous OTFTs are so far reported but obtaining high-performance and reliable OTFTs simultaneously for flexible electronics is still challenging. Herein, it is reported that self-doping in conjugated polymer enables high unipolar n-type charge mobility in flexible OTFTs, as well as good operational/ambient stability and bending resistance. New naphthalene diimide (NDI)-conjugated polymers PNDI2T-NM17 and PNDI2T-NM50 with different contents of self-doping groups on their side chains are designed and synthesized. The effects of self-doping on the electronic properties of resulting flexible OTFTs are investigated. The results reveal that the flexible OTFTs based on self-doped PNDI2T-NM17 exhibit unipolar n-type charge-carrier properties and good operational/ambient stability thanks to the appropriate doping level and intermolecular interactions. The charge mobility and on/off ratio are fourfold and four orders of magnitude higher than those of undoped model polymer, respectively. Overall, the proposed self-doping strategy is useful for rationally designing OTFT materials with high semiconducting performance and reliability.

Hyperbranched Diketopyrrolopyrrole-based Polymers Constructed via Linear Side-Chains towards Organic Field-Effect Transistors.

Conjugated polymers with high charge mobilities have drawn increasing attention in organic field-effect transistors (OFETs) in recent years. However, OFETs of conjugated polymers with high mobility and good device stability remain a challenge. In this article, we report a hyperbranched polymer approach to improve the charge mobility and device stability. Three hyperbranched diketopyrrolopyrrole-based polymers were designed and synthesized via linear alkyl side-chain linkers. The results show that 2D topological hyperbranched polymers form stable thin film microstructures, and thus improve the device stability, since the conjugated moiety is interconnected by linear alkyl chain. Besides, the incorporation of linear alkyl chain instead of branching alkyl one reduce steric hindrance, and improve the microstructure ordering as well as the charge mobility. Bar-coated OFETs result demonstrates that the devices mobilities and operational stabilities (bias stability and bending resistance) are both improved. All these indicate that hyperbranched polymer is a potential candidate for future application.

Photo-controllable Luminescence from Radicals Leading to Ratiometric Emission Switching via Dynamic Intermolecular Coupling.

The development of photoinduced luminescent radicals with dynamic emission color is still challenging. Herein we report a novel molecular radical system (TBIQ) that shows photo-controllable luminescence, leading to a wide range of ratiometric color changes via light excitation. The conjugated skeleton of TBIQ is decorated with steric-demanding tertiary butyl groups that enable appropriate intermolecular interaction to make dynamic intermolecular coupling possible for controllable behaviors. We reveal that the helicenic pseudo-planar conformation of TBIQ experiences a planarization process after light excitation, leading to more compactly stacked supermolecules and thus generating radicals via intermolecular charge transfer. The photo-controllable luminescent radical system is employed for a high-level information encryption application. This study may offer unique insight into molecular dynamic motion for optical manufacturing and broaden the scope of smart-responsive materials for advanced applications.

Enhanced Photodynamic of Carriers and Suppressed Charge Recombination Enable Approaching 18% Efficiency in Nonfullerene Organic Solar Cells.

Regulation of the exciton generation, diffusion, and carrier transport, as well as optimization of the non-radiative energy loss could further overcome the power conversion efficiency limitation of organic solar cells. However, the relationship between exciton properties and non-radiative energy loss has seldom been investigated. Herein, taking D18-series devices as the research model, the exciton diffusion length (LD) and hole transfer dynamics can be remarkably improved by the variation of electron-withdrawing halogen and the non-radiative energy loss simultaneously can be suppressed. By combining the analysis results of hole transfer, exciton diffusion, charge separation, and recombination, this work demonstrates that the photo-induced exciton in the chlorinated polymer donor can diffuse to a longer distance within the effective exciton lifetime, suppress the exciton recombination, and enhance device performance. The results define the relationship between the exciton behaviors and non-radiative energy loss and further reveal the significance of controlling the bulk heterojunction with superior photo-physical properties.

Ultra-sensitive H2S sensor based on sunflower-like In-doped ZnO with enriched oxygen vacancies.

Metal oxide sensors face the challenge of high response and fast recovery at low operating temperatures for the detection of toxic and flammable hydrogen sulfide (H2S) gases. Herein, novel In-doped ZnO with a sunflower-like structure and tunable surface properties was rationally synthesized. The substitutional In atom in the ZnO crystal can dramatically enhance the concentration of oxygen vacancies (Ov), the In-ZnO sites are responsible for fast recovery, and the formation of sub-stable sulfide intermediates gives rise to the high response towards H2S. As a result, the response of the optimized 4In-ZnO sensor is 3538.36 to 50 ppm H2S at a low operating temperature of 110 °C, which is 106 times higher than that of pristine ZnO. Moreover, the response time and recovery time to 50 ppm H2S are 100 s and 27 s, respectively, with high selectivity and stability. First-principles calculations revealed that 4In-ZnO with rich Ov exhibited higher adsorption energy for the H2S molecule than pristine ZnO, resulting in effortless H2S detection. Our work lays the foundation for the rational design of highly sensitive gas sensors through precise doping of atoms in oxygen-rich vacancies in semiconductor materials.

Bottom-Up Preparation of Twisted Graphene Nanoribbons by Cu-Catalyzed Deoxygenative Coupling.

Graphene nanoribbons (GNRs) are promising in organic optoelectronic materials, and their properties largely depend on the size, edge, and conformation. Herein, the fully armchair-edged GNRs (AGNRs) with lengths up to 2.65 nm by using a Cu-catalyzed deoxygenative coupling as a key step. The resulting AGNRs (2HBT, 3HBT, and 4HBT) possess highly twisted π-scaffolds, and the torsion angles between the adjacent triphenylene moieties are larger than 32°, as proved by crystallographic analyses. Theoretical and spectroscopic studies show that the butoxy groups endow AGNRs with electron-rich features, the extension of the π-system from 2HBT to 4HBT reinforces S0 →S1 excitation, and the distortion of the π-scaffold enhances the fluorescence quantum yield (ΦF ). In particular, 4HBT has the lowest oxidation potential (Eox 1 =0.55 V vs. SCE) and displays red fluorescence with a ΦF value of 81 %.

Flavanthrene derivatives as photostable and efficient singlet exciton fission materials.

Singlet exciton fission (SF) is believed to have the potential to break the Shockley-Queisser limit for third-generation solar cell devices, so it has attracted great attention. Conventional linear acene based SF materials generally suffer from low triplet energy and poor photostability. We report herein two flavanthrene derivatives, EH-Fla and TIPS-Fla, as new photostable singlet exciton fission materials. These N-doped two-dimensional angular fused acenes have three sets of aromatic Clar sextets, making them significantly more stable than linear acenes with only one sextet. Time-resolved spectroscopy characterization reveals that the SF process occurs in the polycrystalline films of EH-Fla and TIPS-Fla, with maximal triplet yields of 32% and 159%, respectively. The SF processes of these two molecules are mediated by excimer states. In EH-Fla, the low-lying excimer prevents the SF process from occurring effectively, resulting in a low triplet yield. In contrast, the excimer state in TIPS-Fla is mixed with strong CT coupling, which prompts efficient SF and results in a high triplet yield. Our results show that flavanthrene is a promising SF chromophore for photoenergy conversion applications, while a fine-tune of the intermolecular interaction is crucial for achieving high SF efficiency.

Visible-Light-Induced α-C(sp3)-H Phosphinylation of Unactivated Ethers under Photocatalyst- and Additive-Free Conditions.

A photocatalyst- and additive-free visible-light-induced α-C(sp3)-H phosphinylation of unactivated ethers involving a C-O bond cleavage with molecular oxygen as the sole oxidant at room temperature has been achieved. This method provides a sustainable access to α-hydroxyphosphine oxides in up to 88% yield with good functional group compatibility under mild and neutral conditions (34 examples). Moreover, the subsequent two-step conversion of the resulting dihydroxy diarylphosphine oxides afforded α-phosphinylated cyclic ethers in good overall yields (10 examples).

A Cathode Interface Layer Based on 4,5,9,10-Pyrene Diimide for Highly Efficient Binary Organic Solar Cells.

Efficient cathode interfacial layers (CILs) are becoming essential elements for organic solar cells (OSCs). However, the absorption of commonly used cathode interfacial materials (CIMs) is either too weak or overlaps too much with that of photoactive materials, hindering their contribution to the light absorption. In this work, we demonstrate the construction of highly efficient CIMs based on 2,7-di-tert-butyl-4,5,9,10-pyrene diimide (t-PyDI) framework. By introducing amino, amino N-oxide and quaternary ammonium bromide as functional groups, three novel self-doped CIMs named t-PyDIN, t-PyDINO and t-PyDINBr are synthesized. These CIMs are capable of boosting the device performances by broadening the absorption, forming ohmic contact at the interface of active layer and electrode, as well as facilitating electron collection. Notably, the device based on t-PyDIN achieved a power conversion efficiency of 18.25 %, which is among the top efficiencies reported to date in binary OSCs.

Singlet Fission Materials for Photovoltaics: From Small Molecules to Macromolecules.

Singlet fission (SF) is a spin-allowed process in which a singlet state splits into two triplet states. Materials that enable SF have attracted great attention in the last decade, mainly stemming from the potential of overcoming the Shockley-Queisser (SQ) limit in photoenergy conversion. In the past decade, a large number of new molecules exhibiting SF are explored and many devices based on SF materials are studied, though the mechanistic understanding is still obscure. This review focuses on the recent developments of SF materials, including small molecules, oligomers, and polymers. The molecular design strategies and related mechanisms of SF are discussed. Then the dynamics of charge transfer and energy transfer between SF materials and other materials are introduced. Further, the progresses of implementing SF in photovoltaics are discussed. It is hoped that a comprehensive understanding to the SF materials, devices, and mechanism may pave a new way for the design of next generation photovoltaics.