High Conductivity and Electron‐Transfer Validation in an n‐Type Fluoride‐Anion‐Doped Polymer for Thermoelectrics in Air

Air‐stable and soluble tetrabutylammonium fluoride (TBAF) is demonstrated as an efficient n‐type dopant for the conjugated polymer ClBDPPV. Electron transfer from F^? anions to the π‐electron‐deficient ClBDPPV through anion–π electronic interactions is strongly corroborated by the combined results of electron spin resonance, UV–vis–NIR, and ultraviolet photoelectron spectroscopy. Doping of ClBDPPV with 25 mol% TBAF boosts electrical conductivity to up to 0.62 S cm^?1, among the highest conductivities that have been reported for solution‐processed n‐type conjugated polymers, with a thermoelectric power factor of 0.63 µW m^?1 K^?2 in air. Importantly, the Seebeck coefficient agrees with recently published correlations to conductivity. Moreover, the F^?‐doped ClBDPPV shows significant air stability, maintaining the conductivity of over 0.1 S cm^?1 in a thick film after exposure to air for one week, to the best of our knowledge the first report of an air‐stable solution‐processable n‐doped conductive polymer with this level of conductivity. The result shows that using solution‐processable small‐anion salts such as TBAF as an n‐dopant of organic conjugated polymers possessing lower LUMO (lowest unoccupied molecular orbital), less than ?4.2 eV) can open new opportunities toward high‐performance air‐stable solution‐processable n‐type thermoelectric (TE) conjugated polymers.     

Enhancing Molecular n‐Type Doping of Donor–Acceptor Copolymers by Tailoring Side Chains

In this contribution, for the first time, the molecular n‐doping of a donor–acceptor (D–A) copolymer achieving 200‐fold enhancement of electrical conductivity by rationally tailoring the side chains without changing its D–A backbone is successfully improved. Instead of the traditional alkyl side chains for poly{[N,N′‐bis(2‐octyldodecyl)‐naphthalene‐1,4,5,8‐bis(dicarboximide)‐2,6‐diyl](NDI)‐alt‐5,5′‐(2,2′‐bithiophene)} (N2200), polar triethylene glycol type side chains is utilized and a high electrical conductivity of 0.17 S cm^?1 after doping with (4‐(1,3‐dimethyl‐2,3‐dihydro‐1H‐benzoimidazol‐2‐yl)phenyl)dimethylamine is achieved, which is the highest reported value for n‐type D–A copolymers. Coarse‐grained molecular dynamics simulations indicate that the polar side chains can significantly reduce the clustering of dopant molecules and favor the dispersion of the dopant in the host matrix as compared to the traditional alkyl side chains. Accordingly, intimate contact between the host and dopant molecules in the NDI‐based copolymer with polar side chains facilitates molecular doping with increased doping efficiency and electrical conductivity. For the first time, a heterogeneous thermoelectric transport model for such a material is proposed, that is the percolation of charge carriers from conducting ordered regions through poorly conductive disordered regions, which provides pointers for further increase in the themoelectric properties of n‐type D–A copolymers.     

Thiazole Imide‐Based All‐Acceptor Homopolymer: Achieving High‐Performance Unipolar Electron Transport in Organic Thin‐Film Transistors

High‐performance unipolar n‐type polymer semiconductors are critical for advancing the field of organic electronics, which relies on the design and synthesis of new electron‐deficient building blocks with good solubilizing capability, favorable geometry, and optimized electrical properties. Herein, two novel imide‐functionalized thiazoles, 5,5′‐bithiazole‐4,4′‐dicarboxyimide (BTzI) and 2,2′‐bithiazolothienyl‐4,4′,10,10′‐tetracarboxydiimide (DTzTI), are successfully synthesized. Single crystal analysis and physicochemical study reveal that DTzTI is an excellent building block for constructing all‐acceptor homopolymers, and the resulting polymer poly(2,2′‐bithiazolothienyl‐4,4′,10,10′‐tetracarboxydiimide) (PDTzTI) exhibits unipolar n‐type transport with a remarkable electron mobility (μ_e) of 1.61 cm² V^?1 s^?1, low off‐currents (I_off) of 10^?10?10^?11 A, and substantial current on/off ratios (I_on/I_off) of 10⁷?10⁸ in organic thin‐film transistors. The all‐acceptor homopolymer shows distinctive advantages over prevailing n‐type donor?acceptor copolymers, which suffer from ambipolar transport with high I_offs > 10^?8 A and small I_on/I_offs < 10⁵. The results demonstrate that the all‐acceptor approach is superior to the donor?acceptor one, which results in unipolar electron transport with more ideal transistor performance characteristics.     

Synthesis and Superior Optical‐Limiting Properties of Fluorene‐Thiophene‐Benzothiadazole Polymer‐Functionalized Graphene Sheets

A polymer based on fluorene, thiophene, and benzothiadazole as the donor–spacer–acceptor triad is covalently coupled to reduced graphene oxide (rGO) sheets via diazonium coupling with phenyl bromide, followed by Suzuki coupling. These polymer–graphene hybrids show good solubility in organic solvents, such as chloroform, tetrahydrofuran (THF), toluene, dichlorobenzene, and N,N‐dimethylformamide (DMF), and exhibit an excellent optical‐limiting effect with a 532‐nm laser beam. The optical‐limiting threshold energy values (0.93 J cm^?2 for G–polymer 1 and 1.12 J cm^?2 for G–polymer 2) of these G–polymer hybrids are better than that of carbon nanotubes (3.6 J cm^?2).     

An Alkylated Indacenodithieno[3,2‐b]thiophene‐Based Nonfullerene Acceptor with High Crystallinity Exhibiting Single Junction Solar Cell Efficiencies Greater than 13% with Low Voltage Losses

A new synthetic route, to prepare an alkylated indacenodithieno[3,2‐b]thiophene‐based nonfullerene acceptor (C8‐ITIC), is reported. Compared to the reported ITIC with phenylalkyl side chains, the new acceptor C8‐ITIC exhibits a reduction in the optical band gap, higher absorptivity, and an increased propensity to crystallize. Accordingly, blends with the donor polymer PBDB‐T exhibit a power conversion efficiency (PCE) up to 12.4%. Further improvements in efficiency are found upon backbone fluorination of the donor polymer to afford the novel material PFBDB‐T. The resulting blend with C8‐ITIC shows an impressive PCE up to 13.2% as a result of the higher open‐circuit voltage. Electroluminescence studies demonstrate that backbone fluorination reduces the energy loss of the blends, with PFBDB‐T/C8‐ITIC‐based cells exhibiting a small energy loss of 0.6 eV combined with a high J_SC of 19.6 mA cm^?2.     

Simultaneous Boost of Power Factor and Figure‐of‐Merit in In–Cu Codoped SnTe

Significantly enhanced thermoelectric performance is achieved for eco‐friendly SnTe by a coorperative effect between a dopant resonant energy level and interstitial defects. By manipulating the band structure through indium doping, the Seebeck coefficient is remarkably improved, leading to an enhanced power factor, with a high level of ≈29 µW cm^?1 K^?2 at 873 K. Lattice thermal conductivity is sharply reduced, approaching the amorphous limit, through the strong phonon scattering induced by multiple scales of Cu₂Te nanoprecipitates, as well as Cu interstitials, leading to a high ZT value of ≈1.55 at 873 K.     

Highly Luminescent 2D‐Type Slab Crystals Based on a Molecular Charge‐Transfer Complex as Promising Organic Light‐Emitting Transistor Materials

A new 2:1 donor (D):acceptor (A) mixed‐stacked charge‐transfer (CT) cocrystal comprising isometrically structured dicyanodistyrylbenzene‐based D and A molecules is designed and synthesized. Uniform 2D‐type morphology is manifested by the exquisite interplay of intermolecular interactions. In addition to its appealing structural features, unique optoelectronic properties are unveiled. Exceptionally high photoluminescence quantum yield (Φ _F ≈ 60%) is realized by non‐negligible oscillator strength of the S₁ transition, and rigidified 2D‐type structure. Moreover, this luminescent 2D‐type CT crystal exhibits balanced ambipolar transport (µ _h and µ _e of ≈10^?4 cm² V^?1 s^?1). As a consequence of such unique optoelectronic characteristics, the first CT electroluminescence is demonstrated in a single active‐layered organic light‐emitting transistor (OLET) device. The external quantum efficiency of this OLET is as high as 1.5% to suggest a promising potential of luminescent mixed‐stacked CT cocrystals in OLET applications.     

Thiophene‐Bridged Donor–Acceptor sp2‐Carbon‐Linked 2D Conjugated Polymers as Photocathodes for Water Reduction

Photoelectrochemical (PEC) water reduction, converting solar energy into environmentally friendly hydrogen fuel, requires delicate design and synthesis of semiconductors with appropriate bandgaps, suitable energy levels of the frontier orbitals, and high intrinsic charge mobility. In this work, the synthesis of a novel bithiophene‐bridged donor–acceptor‐based 2D sp²‐carbon‐linked conjugated polymer (2D CCP) is demonstrated. The Knoevenagel polymerization between the electron‐accepting building block 2,3,8,9,14,15‐hexa(4‐formylphenyl) diquinoxalino[2,3‐a:2′,3′‐c]phenazine (HATN‐6CHO) and the first electron‐donating linker 2,2′‐([2,2′‐bithiophene]‐5,5′‐diyl)diacetonitrile (ThDAN) provides the 2D CCP‐HATNThDAN (2D CCP‐Th). Compared with the corresponding biphenyl‐bridged 2D CCP‐HATN‐BDAN (2D CCP‐BD), the bithiophene‐based 2D CCP‐Th exhibits a wide light‐harvesting range (up to 674 nm), a optical energy gap (2.04 eV), and highest energy occupied molecular orbital–lowest unoccupied molecular orbital distributions for facilitated charge transfer, which make 2D CCP‐Th a promising candidate for PEC water reduction. As a result, 2D CCP‐Th presents a superb H₂‐evolution photocurrent density up to ≈7.9 µA cm^?2 at 0 V versus reversible hydrogen electrode, which is superior to the reported 2D covalent organic frameworks and most carbon nitride materials (0.09–6.0 µA cm^?2). Density functional theory calculations identify the thiophene units and cyano substituents at the vinylene linkage as active sites for the evolution of H₂.     

Revealing the Enhanced Thermoelectric Properties of Controllably Doped Donor-Acceptor Copolymer: The Impact of Regioregularity

Albeit considerable attention to the fast-developing organic thermoelectric (OTE) materials due to their flexibility and non-toxic features, it is still challenging to design an OTE polymer with superior thermoelectric properties. In this work, two “isomorphic” donor–acceptor (D–A) conjugated polymers are studied as the semiconductor in OTE devices, revealing for the first time the internal mechanism of regioregularity on thermoelectric performances in D–A type polymers. A higher molecular structure regularity can lead to higher crystalline order and mobility, higher doping efficiency, order of energy state, and thermoelectric (TE) performance. As a result, the regioregular P2F exhibits a maximum power factor (PF) of up to 113.27 µW m⁻¹ K⁻², more than three times that of the regiorandom PRF (35.35 µW m⁻¹ K⁻²). However, the regular backbone also implies lower miscibility with a dopant, negatively affecting TE performance. Therefore, the trade-off between doping efficiency and miscibility plays a vital role in OTE materials, and this work sheds light on the molecular design strategy of OTE polymers with state-of-the-art performances.     

High‐Performance n‐Channel Organic Transistors Using High‐Molecular‐Weight Electron‐Deficient Copolymers and Amine‐Tailed Self‐Assembled Monolayers

While high‐performance p‐type semiconducting polymers are widely reported, their n‐type counterparts are still rare in terms of quantity and quality. Here, an improved Stille polymerization protocol using chlorobenzene as the solvent and palladium(0)/copper(I) as the catalyst is developed to synthesize high‐quality n‐type polymers with number‐average molecular weight up to 10⁵ g mol^?1. Furthermore, by sp²‐nitrogen atoms (sp²‐N) substitution, three new n‐type polymers, namely, pBTTz, pPPT, and pSNT, are synthesized, and the effect of different sp²‐N substitution positions on the device performances is studied for the first time. It is found that the incorporation of sp²‐N into the acceptor units rather than the donor units results in superior crystalline microstructures and higher electron mobilities. Furthermore, an amine‐tailed self‐assembled monolayer (SAM) is smoothly formed on a Si/SiO₂ substrate by a simple spin‐coating technique, which can facilitate the accumulation of electrons and lead to more perfect unipolar n‐type transistor performances. Therefore, a remarkably high unipolar electron mobility up to 5.35 cm² V^?1 s^?1 with a low threshold voltage (≈1 V) and high on/off current ratio of ≈10⁷ is demonstrated for the pSNT‐based devices, which are among the highest values for unipolar n‐type semiconducting polymers.     

Fused Hexacyclic Nonfullerene Acceptor with Strong Near‐Infrared Absorption for Semitransparent Organic Solar Cells with 9.77% Efficiency

A fused hexacyclic electron acceptor, IHIC, based on strong electron‐donating group dithienocyclopentathieno[3,2‐b ]thiophene flanked by strong electron‐withdrawing group 1,1‐dicyanomethylene‐3‐indanone, is designed, synthesized, and applied in semitransparent organic solar cells (ST‐OSCs). IHIC exhibits strong near‐infrared absorption with extinction coefficients of up to 1.6 × 10⁵m ^?1 cm^?1, a narrow optical bandgap of 1.38 eV, and a high electron mobility of 2.4 × 10^?3 cm² V^?1 s^?1. The ST‐OSCs based on blends of a narrow‐bandgap polymer donor PTB7‐Th and narrow‐bandgap IHIC acceptor exhibit a champion power conversion efficiency of 9.77% with an average visible transmittance of 36% and excellent device stability; this efficiency is much higher than any single‐junction and tandem ST‐OSCs reported in the literature.     

Improved Performance of All‐Polymer Solar Cells Enabled by Naphthodiperylenetetraimide‐Based Polymer Acceptor

A new polymer acceptor, naphthodiperylenetetraimide‐vinylene (NDP‐V), featuring a backbone of altenating naphthodiperylenetetraimide and vinylene units is designed and applied in all‐polymer solar cells (all‐PSCs). With this polymer acceptor, a new record power‐conversion efficiencies (PCE) of 8.59% has been achieved for all‐PSCs. The design principle of NDP‐V is to reduce the conformational disorder in the backbone of a previously developed high‐performance acceptor, PDI‐V, a perylenediimide‐vinylene polymer. The chemical modifications result in favorable changes to the molecular packing behaviors of the acceptor and improved morphology of the donor–acceptor (PTB7‐Th:NDP‐V) blend, which is evidenced by the enhanced hole and electron transport abilities of the active layer. Moreover, the stronger absorption of NDP‐V in the shorter‐wavelength range offers a better complement to the donor. All these factors contribute to a short‐circuit current density (J _sc) of 17.07 mA cm^?2. With a fill factor (FF) of 0.67, an average PCE of 8.48% is obtained, representing the highest value thus far reported for all‐PSCs.     

High Performance Photoswitches Based on Flexible and Amorphous D–A Polymer Nanowires

A fluorene‐based donor–acceptor conjugated polymer is synthesized and the polymer nanowires are successfully prepared with high quality and large scale using a simple and practical template dipping method. These amorphous polymer nanowires are flexible and show excellent photoconductive properties with reliable reproducibility. The individual nanowire photoswitches exhibit a responsivity as high as 1700 mA W^?1 and an on/off ratio as high as 2000 under a light intensity of 5.76 mW cm^?2 and a driving voltage of 40 V.     

Diketopyrrolopyrrole (DPP)‐Based Donor–Acceptor Polymers for Selective Dispersion of Large‐Diameter Semiconducting Carbon Nanotubes

Low‐bandgap diketopyrrolopyrrole (DPP)‐based polymers are used for the selective dispersion of semiconducting single‐walled carbon nanotubes (s‐SWCNTs). Through rational molecular design to tune the polymer–SWCNT interactions, highly selective dispersions of s‐SWCNTs with diameters mainly around 1.5 nm are achieved. The influences of the polymer alkyl side‐chain substitution (i.e., branched vs linear side chains) on the dispersing yield and selectivity of s‐SWCNTs are investigated. Introducing linear alkyl side chains allows increased polymer–SWCNT interactions through close π–π stacking and improved C–H–π interactions. This work demonstrates that polymer side‐chain engineering is an effective method to modulate the polymer–SWCNT interactions and thereby affecting both critical parameters in dispersing yield and selectivity. Using these sorted s‐SWCNTs, high‐performance SWCNT network thin‐film transistors are fabricated. The solution‐deposited s‐SWCNT transistors yield simultaneously high mobilities of 41.2 cm² V^?1 s^?1 and high on/off ratios of greater than 10⁴. In summary, low‐bandgap DPP donor–acceptor polymers are a promising class of polymers for selective dispersion of large‐diameter s‐SWCNTs.     

A Narrow‐Bandgap n‐Type Polymer Semiconductor Enabling Efficient All‐Polymer Solar Cells

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.     

Unprecedented Enhancement of Thermoelectric Power Factor Induced by Pressure in Small‐Molecule Organic Semiconductors

Establishing the relationship between pressure and heat–electricity interconversion in van der Waals bonded small‐molecule organic semiconductors is critical not only in designing flexible thermoelectric materials, but also in developing organic electronics. Here, based on first‐principles calculations and using naphthalene as a case study, an unprecedented elevation of p‐type thermoelectric power factor induced by pressure is demonstrated; and the power factor increases by 267% from 159.5 µW m^?1 K^?2 under ambient conditions to 585.8 µW m^?1 K^?2 at 2.1 GPa. The underlying mechanism is attributed to the dramatic inhibition of lattice‐vibration‐caused electronic scattering. Furthermore, it is revealed that both restraining low‐frequency intermolecular vibrational modes and increasing intermolecular electronic coupling are two essential factors that effectively suppress the electron–phonon scattering. From the standpoint of molecular design, these two conditions can be achieved by extending the π‐conjugated backbones, introducing long alkyl sidechains to the π‐cores, and substituting heteroatoms in the π‐cores.     

Fused Benzothiadiazole: A Building Block for n‐Type Organic Acceptor to Achieve High‐Performance Organic Solar Cells

Narrow bandgap n‐type organic semiconductors (n‐OS) have attracted great attention in recent years as acceptors in organic solar cells (OSCs), due to their easily tuned absorption and electronic energy levels in comparison with fullerene acceptors. Herein, a new n‐OS acceptor, Y5, with an electron‐deficient‐core‐based fused structure is designed and synthesized, which exhibits a strong absorption in the 600–900 nm region with an extinction coefficient of 1.24 × 10⁵ cm^?1, and an electron mobility of 2.11 × 10^?4 cm² V^?1 s^?1. By blending Y5 with three types of common medium‐bandgap polymers (J61, PBDB‐T, and TTFQx‐T1) as donors, all devices exhibit high short‐circuit current densities over 20 mA cm^?2. As a result, the power conversion efficiency of the Y5‐based OSCs with J61, TTFQx‐T1, and PBDB‐T reaches 11.0%, 13.1%, and 14.1%, respectively. This indicates that Y5 is a universal and highly efficient n‐OS acceptor for applications in organic solar cells.     

Zn‐Ion Hybrid Micro‐Supercapacitors with Ultrahigh Areal Energy Density and Long‐Term Durability

On‐chip micro‐supercapacitors (MSCs), as promising power candidates for microdevices, typically exhibit high power density, large charge/discharge rates, and long cycling lifetimes. However, as for most reported MSCs, the unsatisfactory areal energy density (<10 µWh cm^?2) still hinders their practical applications. Herein, a new‐type Zn‐ion hybrid MSC with ultrahigh areal energy density and long‐term durability is demonstrated. Benefiting from fast ion adsorption/desorption on the capacitor‐type activated‐carbon cathode and reversible Zn stripping/plating on the battery‐type electrodeposited Zn‐nanosheet anode, the fabricated Zn‐ion hybrid MSCs exhibit remarkable areal capacitance of 1297 mF cm^?2 at 0.16 mA cm^?2 (259.4 F g^?1 at a current density of 0.05 A g^?1), landmark areal energy density (115.4 µWh cm^?2 at 0.16 mW cm^?2), and a superb cycling stability without noticeable decay after 10 000 cycles. This work will inspire the fabrication and development of new high‐performance microenergy devices based on novel device design.     

Conducting‐Polymer Nanotubes Improve Electrical Properties,Mechanical Adhesion,Neural Attachment,and Neurite Outgrowth of Neural Electrodes

An in vitro comparison of conducting‐polymer nanotubes of poly(3,4‐ethylenedioxythiophene) (PEDOT) and poly(pyrrole) (PPy) and to their film counterparts is reported. Impedance, charge‐capacity density (CCD), tendency towards delamination, and neurite outgrowth are compared. For the same deposition charge density, PPy films and nanotubes grow relatively faster vertically, while PEDOT films and nanotubes grow more laterally. For the same deposition charge density (1.44 C cm^?2), PPy nanotubes and PEDOT nanotubes have lower impedance (19.5 ± 2.1 kΩ for PPy nanotubes and 2.5 ± 1.4 kΩ for PEDOT nanotubes at 1 kHz) and higher CCD (184 ± 5.3 mC cm^?2 for PPy nanotubes and 392 ± 6.2 mC cm^?2 for PEDOT nanotubes) compared to their film counterparts. However, PEDOT nanotubes decrease the impedance of neural‐electrode sites by about two orders of magnitude (bare iridium 468.8 ± 13.3 kΩ at 1 kHz) and increase capacity of charge density by about three orders of magnitude (bare iridium 0.1 ± 0.5 mC cm^?2). During cyclic voltammetry measurements, both PPy and PEDOT nanotubes remain adherent on the surface of the silicon dioxide while PPy and PEDOT films delaminate. In experiments of primary neurons with conducting‐polymer nanotubes, cultured dorsal root ganglion explants remain more intact and exhibit longer neurites (1400 ± 95 µm for PPy nanotubes and 2100 ± 150 µm for PEDOT nanotubes) than their film counterparts. These findings suggest that conducting‐polymer nanotubes may improve the long‐term function of neural microelectrodes.     

Zero‐Field Nernst Effect in a Ferromagnetic Kagome‐Lattice Weyl‐Semimetal Co3Sn2S2

The discovery of magnetic topological semimetals has recently attracted significant attention in the field of topology and thermoelectrics. In a thermoelectric device based on the Nernst geometry, an external magnet is required as an integral part. Reported is a zero‐field Nernst effect in a newly discovered hard‐ferromagnetic kagome‐lattice Weyl‐semimetal Co₃Sn₂S₂. A maximum Nernst thermopower of ≈3 µV K^?1 at 80 K in zero field is achieved in this magnetic Weyl‐semimetal. The results demonstrate the possibility of application of topological hard magnetic semimetals for low‐power thermoelectric devices based on the Nernst effect and are thus valuable for the comprehensive understanding of transport properties in this class of materials.