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.     

Efficient and Stable Solid‐State Dye‐Sensitized Solar Cells Based on a High‐Molar‐Extinction‐Coefficient Sensitizer

The high‐molar‐extinction‐coefficient heteroleptic ruthenium dye, cis‐Ru (4,4′‐bis(5‐octylthieno[3,2‐b] thiophen‐2‐yl)‐2,2′‐bipyridine) (4,4′‐dicarboxyl‐2,2′‐bipyridine) (NCS)₂, exhibits an AM 1.5 solar (100 mW cm^?2)‐to‐electric power‐conversion efficiency of 4.6% in a solid‐state dye‐sensitized solar cell (SSDSC) with 2,2′, 7,7′‐tetrakis‐(N,N‐di‐p‐methoxyphenylamine)9,9′‐spirobifluorene (spiro‐MeOTAD) as the organic hole‐transporting material. These SSDSC devices exhibit good durability during accelerated tests under visible‐light soaking for 1000 h at 60 °C. This demonstration elucidates a class of photovoltaic devices with potential for stable and low‐cost power generation. The electron recombination dynamics and charge collection that take place at the dye‐sensitized heterojunction are studied by means of impedance and transient photovoltage decay techniques.     

Perovskite Bifunctional Device with Improved Electroluminescent and Photovoltaic Performance through Interfacial Energy‐Band Engineering

Currently, photovoltaic/electroluminescent (PV/EL) perovskite bifunctional devices (PBDs) exhibit poor performance due to defects and interfacial misalignment of the energy band. Interfacial energy‐band engineering between the perovskite and hole‐transport layer (HTL) is introduced to reduce energy loss, through adding corrosion‐free 3,3′‐(2,7‐dibromo‐9H‐fluorene‐9,9‐diyl) bis(n,n‐dimethylpropan‐1‐amine) (FN‐Br) into a HTL free of lithium salt. This strategy can turn the n‐type surface of perovskite into p‐type and thus correct the misalignment to form a well‐defined N–I–P heterojunction. The tailored PBD achieves a high PV efficiency of up to 21.54% (certified 20.24%) and 4.3% EL external quantum efficiency. Free of destructive additives, the unencapsulated devices maintain >92% of their initial PV performance for 500 h at maximum power point under standard air mass 1.5G illumination. This strategy can serve as a general guideline to enhance PV and EL performance of perovskite devices while ensuring excellent stability.     

Excited-state absorption and anisotropy properties of two-photon absorbing fluorene derivatives

The electronic structure of fluorene derivatives N-(7-benzothiazol-2-yl-9,9-bis-decyl-9H-fluoren-2-yl)-acetamide (1); 9,9-didecyl-2,7-bis-(N,N-benzothiazoyl)fluorene (2); 4,4'-{[9,9-bis(ethyl)-9H-fluorene-2,7-diyl]di-2,1-ethenediyl}bis(N,N-diphenyl)benzeneamine (3); and 4,4',4"{[9,9-bis(ethyl)-9H-fluorene-2,4,7-triyl]tri-2,1-ethenediyl}tris(N,N-diphenyl)benzeneamine (4) were investigated by a steady-state spectral technique, quantum-chemical calculations, and a picosecond pump-probe method. These derivatives are of interest for their relatively high two-photon absorption. The steady-state excitation anisotropy spectra reveal the nature of the ground-state absorption bands. Semiempirical quantum-chemical calculations of the fluorene derivatives (AM1, ZINDO/S) show good agreement with experimental data. The spectral positions and alignment of various electronic transitions of derivatives 1-4 were estimated from their excited-state absorption and anisotropy spectra.     

Multifunctional Conjugated Polymer Nanoparticles for Image‐Guided Photodynamic and Photothermal Therapy

A multifunctional theranostic platform based on conjugated polymer nanoparticles (CPNs) with tumor targeting, fluorescence detection, photodynamic therapy (PDT), and photothermal therapy (PTT) is developed for effective cancer imaging and therapy. Two conjugated polymers, poly[9,9‐bis(2‐(2‐(2‐methoxyethoxy)ethoxy)‐ethyl)fluorenyldivinylene]‐alt‐4,7‐(2,1,3‐benzothiadiazole) with bright red emission and photosensitizing ability and poly[(4,4,9,9‐tetrakis(4‐(octyloxy)phenyl)‐4,9‐dihydro‐s‐indacenol‐dithiophene‐2,7‐diyl)‐alt‐co‐4,9‐bis(thiophen‐2‐yl)‐6,7‐bis(4‐(hexyloxy)phenyl)‐thiadiazolo‐quinoxaline] with strong near‐infrared absorption and excellent photothermal conversion ability are co‐loaded into one single CPN via encapsulation approach using lipid‐polyethylene glycol as the matrix. The obtained co‐loaded CPNs show sizes of around 30 nm with a high singlet oxygen quantum yield of 60.4% and an effective photothermal conversion efficiency of 47.6%. The CPN surface is further decorated with anti‐HER2 affibody, which bestows the resultant anti‐HER2‐CPNs superior selectivity toward tumor cells with HER2 overexpression both in vitro and in vivo. Under light irradiation, the PDT and PTT show synergistic therapeutic efficacy, which provides new opportunities for the development of multifunctional biocompatible organic materials in cancer therapy.     

New host materials based on fluorene and benzimidazole units for efficient solution-processed green phosphorescent OLEDs

New green host materials 1-(9,9-diphenyl-9H-fluorene-2-yl)-2-phenyl-1H-benzimidazole and 1-(9,9′-spirobifluorene-2-yl)-2-phenyl-1H-benzimidazole for solution-processed green phosphorescent organic light-emitting devices have been designed and synthesized by attaching the electron transporting benzimidazole units to the rigid fluorene units. Owing to the non-planar structures, which decrease the π conjugation length of fluorene and benzimidazole rings, these fluorene derived derivatives show high triplet energy. The high triplet energy of newly host materials ensures efficient energy transfer from the host to the triplet emitter tris(2-phenylpyridine)iridium. Furthermore, the thermal, photophysical, electrochemical properties and crystal structures of 1-(9,9-diphenyl-9H-fluorene-2-yl)-2-phenyl-1H-benzimidazole and 1-(9,9′-spirobifluorene-2-yl)-2-phenyl-1H-benzimidazole were investigated. The solution-processed single-layer green device using 1-(9,9-diphenyl-9H-fluorene-2-yl)-2-phenyl-1H-benzimidazole as the host for the phosphorescence emitter tris(2-phenylpyridine)iridium showed the maximum luminance efficiencies of 10.1 cd/A. This result demonstrated that the newly synthesized, fluorene-based rigid host materials are advantageous for fabrication of highly efficient green phosphorescent organic light-emitting diodes.     

Biocompatible Conjugated Polymer Nanoparticles for Efficient Photothermal Tumor Therapy

Conjugated polymers (CPs) with strong near‐infrared (NIR) absorption and high heat conversion efficiency have emerged as a new generation of photothermal therapy (PTT) agents for cancer therapy. An efficient strategy to design NIR absorbing CPs with good water dispersibility is essential to achieve excellent therapeutic effect. In this work, poly[9,9‐bis(4‐(2‐ethylhexyl)phenyl)fluorene‐alt‐co‐6,7‐bis(4‐(hexyloxy)phenyl)‐4,9‐di(thiophen‐2‐yl)‐thiadiazoloquinoxaline] (PFTTQ) is synthesized through the combination of donor–acceptor moieties by Suzuki polymerization. PFTTQ nanoparticles (NPs) are fabricated through a precipitation approach using 1,2‐distearoyl‐ sn ‐glycero‐3‐phosphoethanolamine‐N‐[methoxy(polyethylene glycol)‐2000] (DSPE‐PEG₂₀₀₀) as the encapsulation matrix. Due to the large NIR absorption coefficient (3.6 L g^‐1 cm^‐1), the temperature of PFTTQ NP suspension (0.5 mg/mL) could be rapidly increased to more than 50 °C upon continuous 808 nm laser irradiation (0.75 W/cm²) for 5 min. The PFTTQ NPs show good biocompatibility to both MDA‐MB‐231 cells and Hela cells at 400 μg/mL of NPs, while upon laser irradiation, effective cancer cell killing is observed at a NP concentration of 50 μg/mL. Moreover, PFTTQ NPs could efficiently ablate tumor in in vivo study using a Hela tumor mouse model. Considering the large amount of NIR absorbing CPs available, the general encapsulation strategy will enable the development of more efficient PTT agents for cancer or tumor therapy.     

9,9′-联芴烯衍生物在有机光伏电池中的应用

由于具有独特的14π电子芳香结构和扭曲的非平面构型,9,9′-联芴烯衍生物成为近年来被广泛研究的一类新型有机光伏材料。9,9′-联芴烯衍生物含有两个刚性平面内的联苯单元,因此具有良好的热稳定性和化学稳定性;且其具有优良的光电特性,很容易接受电子,从而提升自身的最低未占分子轨道(LUMO)能级,使得其有机光伏器件的开路电压增大。此外,9,9′-联芴烯有12个不同的取代位,与富勒烯衍生物相比,其结构更具灵活性。但是,该类化合物的电子迁移率较低,使得其光伏电池的光电转化效率过低。如何通过提高该类材料的电子迁移率、拓展其光谱吸收范围和吸收强度来提高光伏器件的光电转换效率,受到越来越多的关注和研究。阐述了近年来联芴烯衍生物在有机光伏电池中的研究进展,并对其结构、性能进行了简要的分析。最后,对联芴烯类材料的发展前景进行了展望。     

Enhanced Charge Injection Properties of Organic Field‐Effect Transistor by Molecular Implantation Doping

Organic semiconductors (OSCs) have been widely studied due to their merits such as mechanical flexibility, solution processability, and large‐area fabrication. However, OSC devices still have to overcome contact resistance issues for better performances. Because of the Schottky contact at the metal–OSC interfaces, a non‐ideal transfer curve feature often appears in the low‐drain voltage region. To improve the contact properties of OSCs, there have been several methods reported, including interface treatment by self‐assembled monolayers and introducing charge injection layers. Here, a selective contact doping of 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F₄‐TCNQ) by solid‐state diffusion in poly(2,5‐bis(3‐hexadecylthiophen‐2‐yl)thieno[3,2‐b]thiophene) (PBTTT) to enhance carrier injection in bottom‐gate PBTTT organic field‐effect transistors (OFETs) is demonstrated. Furthermore, the effect of post‐doping treatment on diffusion of F₄‐TCNQ molecules in order to improve the device stability is investigated. In addition, the application of the doping technique to the low‐voltage operation of PBTTT OFETs with high‐k gate dielectrics demonstrated a potential for designing scalable and low‐power organic devices by utilizing doping of conjugated polymers.     

A Nonconventional Approach to Patterned Nanoarrays of DNA Strands for Template‐Assisted Assembly of Polyfluorene Nanowires

DNA molecules have been widely recognized as promising building blocks for constructing functional nanostructures with two main features, that is, self‐assembly and rich chemical functionality. The intrinsic feature size of DNA makes it attractive for creating versatile nanostructures. Moreover, the ease of access to tune the surface of DNA by chemical functionalization offers numerous opportunities for many applications. Herein, a simple yet robust strategy is developed to yield the self‐assembly of DNA by exploiting controlled evaporative assembly of DNA solution in a unique confined geometry. Intriguingly, depending on the concentration of DNA solution, highly aligned nanostructured fibrillar‐like arrays and well‐positioned concentric ring‐like superstructures composed of DNAs are formed. Subsequently, the ring‐like negatively charged DNA superstructures are employed as template to produce conductive organic nanowires on a silicon substrate by complexing with a positively charged conjugated polyelectrolyte poly[9,9‐bis(6′‐N,N,N‐trimethylammoniumhexyl)fluorene dibromide] (PF2) through the strong electrostatic interaction. Finally, a monolithic integration of aligned arrays of DNA‐templated PF2 nanowires to yield two DNA/PF2‐based devices is demonstrated. It is envisioned that this strategy can be readily extended to pattern other biomolecules and may render a broad range of potential applications from the nucleotide sequence and hybridization as recognition events to transducing elements in chemical sensors.     

SMART Design of a Bulk‐Capped Supramolecular Segment for the Assembly into Organic Interdigital Lipid Bilayer‐Like (ILB) Nanosheets

Rational molecular design for the organic nanocrystal morphology still remains a challenge due to the structural diversity and complicated weak intermolecular interactions. In this work, a typical attractor–repulsor molecule N,N‐diphenyl‐4‐(9‐phenyl‐fluoren‐9‐yl) phenylamine (TPA‐PF) is designed to explore a general assembly strategy for 2D nanocrystals. Via an interdigital lipid bilayer‐like (ILB) molecular packing mode, large‐sized lamellar 2D nanosheets are obtained with a length:width:thickness ratio as ≈2500:1000:1. The d‐spacing of the largest (001) plane is 1.32 nm, which equals to the thickness of a single interdigital stacking layer. The synergetic effect of the attractive supramolecular segment (TPA) and the repulsive bulky group (PF) is supposed to be the critical factor for the ILB packing that leads to the 2D structures. The attractor–repulsor molecule design is expected to be an effective strategy for the growth of 2D nanocrystals based on small organic molecules.     

Side Chain Engineering on Medium Bandgap Copolymers to Suppress Triplet Formation for High‐Efficiency Polymer Solar Cells

Suppression of carrier recombination is critically important in realizing high‐efficiency polymer solar cells. Herein, it is demonstrated difluoro‐substitution of thiophene conjugated side chain on donor polymer can suppress triplet formation for reducing carrier recombination. A new medium bandgap 2D‐conjugated D–A copolymer J91 is designed and synthesized with bi(alkyl‐difluorothienyl)‐benzodithiophene as donor unit and fluorobenzotriazole as acceptor unit, for taking the advantages of the synergistic fluorination on the backbone and thiophene side chain. J91 demonstrates enhanced absorption, low‐lying highest occupied molecular orbital energy level, and higher hole mobility, in comparison with its control polymer J52 without fluorination on the thiophene side chains. The transient absorption spectra indicate that J91 can suppress the triplet formation in its blend film with n‐type organic semiconductor acceptor m ‐ITIC (3,9‐bis(2‐methylene‐(3‐(1,1‐dicyanomethylene)‐indanone)‐5,5,11,11‐tetrakis(3‐hexylphenyl)‐dithieno[2,3‐d:2,3′‐d′]‐s‐indaceno[1,2‐b:5,6‐b′]‐dithiophene). With these favorable properties, a higher power conversion efficiency of 11.63% with high V _OC of 0.984 V and high J _SC of 18.03 mA cm^?2 is obtained for the polymer solar cells based on J91 /m ‐ITIC with thermal annealing. The improved photovoltaic performance by thermal annealing is explained from the morphology change upon thermal annealing as revealed by photoinduced force microscopy. The results indicate that side chain engineering can provide a new solution to suppress carrier recombination toward high efficiency, thus deserves further attention.     

Inkjet‐Printed High‐Efficiency Multilayer QLEDs Based on a Novel Crosslinkable Small‐Molecule Hole Transport Material

Quantum dots light‐emitting diodes (QLEDs) have attracted much interest owing to their compatibility with low‐cost inkjet printing technology and potential for use in large‐area full‐color pixelated display. However, it is challenging to fabricate high efficiency inkjet‐printed QLEDs because of the coffee ring effects and inferior resistance to solvents from the underlying polymer film during the inkjet printing process. In this study, a novel crosslinkable hole transport material, 4,4′‐bis(3‐vinyl‐9H‐carbazol‐9‐yl)‐1,1′‐biphenyl (CBP‐V) which is small‐molecule based, is synthesized and investigated for inkjet printing of QLEDs. The resulting CBP‐V film after thermal curing exhibits excellent solvent resistance properties without any initiators. An added advantage is that the crosslinked CBP‐V film has a sufficiently low highest occupied molecular orbital energy level (≈?6.2 eV), high film compactness, and high hole mobility, which can thus promote the hole injection into quantum dots (QDs) and improve the charge carrier balance within the QD emitting layers. A red QLED is successfully fabricated by inkjet printing a CBP‐V and QDs bilayer. Maximum external quantum efficiency of 11.6% is achieved, which is 92% of a reference spin‐coated QLED (12.6%). This is the first report of such high‐efficiency inkjet‐printed multilayer QLEDs and demonstrates a unique and effective approach to inkjet printing fabrication of high‐performance QLEDs.     

Correlation of Morphology with Photocurrent Generation in a Polymer Blend Photovoltaic Device

Morphological effects on photovoltaic (PV) properties are studied through scanning photocurrent (PC) and photoluminescence (PL) microscopy of a solution processed, polymer blend PV device composed of PFB [poly(9,9′‐dioctylfluorene‐co‐bis‐N,N‐(4‐butylphenyl)‐bis‐N,N‐phenyl‐1,4‐phenylenediamine] and F8BT [poly(9,9′‐dioctylfluorene‐co‐benzothiadiazole]. As PFB and F8BT have unique absorbance bands, it is possible to selectively excite only F8BT (488 nm) or both PFB and F8BT (408 nm). Local voltage‐dependent photocurrent (LVPC) measurements from particular regions of interest in the PV show that the diode characteristics between different morphologies are essentially the same, except in regard to the magnitude of PC generated. A local PL spectrum is measured simultaneously with PC generation at each pixel in the image maps. Through integration of the local PL spectrum over particular wavelength ranges, PL image maps are created of PFB‐PL (435 to 475 nm), F8BT‐PL (530 to 570 nm), exciplex‐PL (620 to 685 nm) and total‐PL (entire spectrum). These data allow direct correlation of PC generation with local chemical composition variations within the PV device. PL image maps show morphological variations on the order of 0.5 to 1 µm of alternating PFB‐rich and F8BT‐rich phases. While illuminating only F8BT (488 nm light), the PFB‐rich phases produce the most PC, however, while illuminating both polymers but mostly PFB (408 nm light), the F8BT‐rich phases produce the most PC. These results show that in the morphology where the light absorbing material is less concentrated, the PC generation is increased. Additionally, the exciplex‐PL is found to not be a significant radiative loss mechanism of charge carriers for PC generation.     

Single‐Junction Polymer Solar Cells with 16.35% Efficiency Enabled by a Platinum(II) Complexation Strategy

A new strategy of platinum(II) complexation is developed to regulate the crystallinity and molecular packing of polynitrogen heterocyclic polymers, optimize the morphology of the active blends, and improve the efficiency of the resulting nonfullerene polymer solar cells (NF‐PSCs). The newly designed s‐tetrazine (s‐TZ)‐containing copolymer of PSFTZ (4,8‐bis(5‐((2‐butyloctyl)thio)‐4‐fluorothiophen‐2‐yl)benzo[1,2‐b:4,5‐b′]dithiophene‐alt‐3,6‐bis(4‐octylthiophen‐2‐yl)‐1,2,4,5‐tetrazine) has a strong aggregation property, which results in serious phase separation and large domains when blending with Y6 ((2,2′‐((2Z,2′Z)‐((12,13‐bis(2‐ethylhexyl)‐3,9‐diundecyl‐12,13‐dihydro‐[1,2,5]thiadiazolo[3,4‐e]thieno[2″,3″:4′,5′]thieno[2′,3′:4,5]pyrrolo[3,2‐g]thieno[2′,3′:4,5]thieno[3,2‐b]indole‐2,10‐diyl)bis(methanylylidene))bis(5,6‐difluoro‐3‐oxo‐2,3‐dihydro‐1H‐indene‐2,1‐diylidene))dimalononitrile)), and produces a power‐conversion efficiency (PCE) of 13.03%. By adding small amount of Pt(Ph)₂(DMSO)₂ (Ph, phenyl and DMSO, dimethyl sulfoxide), platinum(II) complexation would occur between Pt(Ph)₂(DMSO)₂ and PSFTZ. The bulky benzene ring on the platinum(II) complex increases the steric hindrance along the polymer main chain, inhibits the polymer aggregation strength, regulates the phase separation, optimizes the morphology, and thus improves the efficiency to 16.35% in the resulting devices. 16.35% is the highest efficiency for single‐junction PSCs reported so far.     

High efficiency simple white phosphorescent organic light-emitting diodes using a phosphine oxide host

Highly efficient simple white organic light-emitting diodes (WOLEDs) were fabricated using a mixed host of 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC) and 2,7-bis(diphenylphosphoryl)-9,9'-spirobi[fluorene] (SPPO13) in the light-emitting layer. A two layer WOLED structure of TAPC hole transport layer and TAPC:SPPO13 emitting layer was developed. Red and blue phosphorescent emitters were doped in the TAPC:SPPO13 mixed host emitting layer and a high quantum efficiency of 16.0% was obtained. In addition, the maximum power efficiency of the WOLEDs was 37.5 Im/W and color coordinate was (0.43, 0.41). The color coordinate could be kept stable irrespective of the luminance of the device.     

N‐Type Organic Thermoelectrics: Improved Power Factor by Tailoring Host–Dopant Miscibility

In this contribution, for the first time, the polarity of fullerene derivatives is tailored to enhance the miscibility between the host and dopant molecules. A fullerene derivative with a hydrophilic triethylene glycol type side chain (PTEG‐1) is used as the host and (4‐(1,3‐dimethyl‐2,3‐dihydro‐1H‐benzoimidazol‐2‐yl)phenyl)dimethylamine n ‐DMBI) as the dopant. Thereby, the doping efficiency can be greatly improved to around 18% (<1% for a nonpolar reference sample) with optimized electrical conductivity of 2.05 S cm^?1, which represents the best result for solution‐processed fullerene derivatives. An in‐depth microstructural study indicates that the PTEG‐1 molecules readily form layered structures parallel to the substrate after solution processing. The fullerene cage plane is alternated by the triethylene glycol side chain plane; the n ‐DMBI dopants are mainly incorporated in the side chain plane without disturbing the π–π packing of PTEG‐1. This new microstructure, which is rarely observed for codeposited thin films from solution, formed by PTEG‐1 and n ‐DMBI molecules explains the increased miscibility of the host/dopant system at a nanoscale level and the high electrical conductivity. Finally, a power factor of 16.7 µW m^?1 K^?2 is achieved at 40% dopant concentration. This work introduces a new strategy for improving the conductivity of solution‐processed n‐type organic thermoelectrics.     

Light-emitting characteristics of organic light-emitting diodes with the MoOx-doped NPB and C60/LiF layer

The hole ohmic properties of the MoO_x-doped NPB layer have been investigated by analyzing the current density-voltage properties of hole-only devices and by assigning the energy levels of ultraviolet photoemission spectra. The result showed that the performance of organic light-emitting diodes (OLEDs) is markedly improved by optimizing both the thickness and the doping concentration of a hole-injecting layer (HIL) of N, N′-diphenyl-N, N′-bis(1-naphthyl)-1,1′-biphenyl-4,4′-diamine (NPB) doped with molybdenum oxide (MoO_x) which was inserted between indium tin oxide (ITO) and NPB. For the doping concentration of above 25%, the device composed of a glass/ITO/MoO_x-doped NPB (100 nm)/Al structure showed the excellent hole ohmic property. The investigation of the valence band structure revealed that the p-type doping effects in the HTL layer and the hole concentration increased at the anode interfaces cause the hole-injecting barrier lowering. With both MoO_x-doped NPB as a hole ohmic contact and C₆₀/LiF as an electron ohmic contact, the device, which is composed of glass/ITO/MoO_x-doped NPB (25%, 5 nm)/NPB (63 nm)/Alq₃ (37 nm)/C₆₀ (5 nm)/LiF (1 nm)/Al (100 nm), showed the luminance of about 58,300 cd/m² at the low bias voltage of 7.2 V.     

A Twisted Thieno[3,4‐b]thiophene‐Based Electron Acceptor Featuring a 14‐π‐Electron Indenoindene Core for High‐Performance Organic Photovoltaics

With an indenoindene core, a new thieno[3,4‐b ]thiophene‐based small‐molecule electron acceptor, 2,2′‐((2Z,2′Z)‐((6,6′‐(5,5,10,10‐tetrakis(2‐ethylhexyl)‐5,10‐dihydroindeno[2,1‐a]indene‐2,7‐diyl)bis(2‐octylthieno[3,4‐b]thiophene‐6,4‐diyl))bis(methanylylidene))bis(5,6‐difluoro‐3‐oxo‐2,3‐dihydro‐1H‐indene‐2,1‐diylidene))dimalononitrile ( NITI ), is successfully designed and synthesized. Compared with 12‐π‐electron fluorene, a carbon‐bridged biphenylene with an axial symmetry, indenoindene, a carbon‐bridged E ‐stilbene with a centrosymmetry, shows elongated π‐conjugation with 14 π‐electrons and one more sp³ carbon bridge, which may increase the tunability of electronic structure and film morphology. Despite its twisted molecular framework, NITI shows a low optical bandgap of 1.49 eV in thin film and a high molar extinction coefficient of 1.90 × 10⁵m ^?1 cm^?1 in solution. By matching NITI with a large‐bandgap polymer donor, an extraordinary power conversion efficiency of 12.74% is achieved, which is among the best performance so far reported for fullerene‐free organic photovoltaics and is inspiring for the design of new electron acceptors.     

Characterization of an insoluble poly(9,9-diphenyl-2,7-fluorene) by solvent-free sample preparation for MALDI-TOF mass spectrometry

The application of solvent-free sample preparation for matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) allowed the characterization of an insoluble fraction of poly(9,9-diphenylfluorene) that was previously hindered by the lack of suitable characterization methods. The MALDI mass spectrometric analysis gives valuable mechanistic information about the heterogeneous polymerization process of the insoluble high molecular weight fraction of the polymer. The fragmentation appearing even under moderate desorption and ionization conditions of this rigid backbone analyte is identified as a multiple loss of the bulky phenyl side groups and can be avoided by applying the new MALDI matrix 7,7,8,8-tetracyanoquinodimethane. A specialized fragmentation study by postsource decay MALDI-TOF MS reveals a molecular weight dependent change in fragmentation mechanism from an exclusive cleavage of side groups from long polymer chains to an additional cleavage of the polymer backbone of short polymer chains.