Synthesis and Absorption Spectra of n‐Type Conjugated Polymers Based on Perylene Diimide

Two novel n‐type conjugated polymers based on perylene diimide (PDI), poly(PDI‐vinylene) (PDIV), and poly(PDI‐thienylene) (PDITh), have been designed and synthesized by the Stille coupling reaction. In comparison with the PDI monomer (compound M1), PDIV and PDITh films show a significantly broad absorption band from 380 to 720 nm, and a narrower bandgap of ≈1.71 and 1.74 eV, respectively. Cyclic voltammograms of the two polymers display a couple of reversible reduction/re‐oxidation (n‐doping/dedoping) peaks. The onset reduction (n‐doping) potentials of PDIV and PDITh are at −0.62 V and −0.66 V versus Ag/Ag⁺ respectively, which correspond to the electron affinities (EAs) of 4.09 eV for PDIV and 4.05 eV for PDITh. The EA values of the two polymers are the highest among the n‐type conjugated polymers reported to date. The results indicate that PDIV and PDITh could be used as polymer acceptors in all polymer solar cells.

     

A Solution‐Processed Air‐Stable Perylene Diimide Derivative for N‐type Organic Thin Film Transistors

For future all‐soluble organic thin film transistor (OTFT) applications, a new soluble n‐type air‐stable perylene diimide derivative semiconductor material with (trifluoromethyl)benzyl groups (TC–PDI–F) is synthesized. The film is formed by spin‐coating in air and optimized for OTFT fabrications. The transistor characteristics and air‐stability of the TC–PDI–F OTFTs is measured to investigate the feasibility of using solution‐processed TC–PDI–F for future OTFT applications. For all‐solution OTFT process applications, the transistor characteristics are demonstrated by using TC–PDI–F as an n‐type semiconductor material and liquid‐phase‐deposited SiO₂ (LPD–SiO₂) as a gate dielectric material. All processes (except material synthesis and electrode deposition) and electrical measurements are conducted in air.     

Perylene Diimide Hexamer Based on Combination of Direct and Indirect Linkage Manners for Non-fullerene Organic Solar Cells

Perylene diimide (PDI) is one of the most intensively studied building blocks for the construction of non-fullerene acceptors (NFAs). In this contribution, based on combination of the direct and indirect linkage manners of PDI units at the bay position, a propeller-shaped PDI hexamer T-DPDI was designed and synthesized. The singly bonded PDI dimer DPDI and the benzene ring cored PDI trimer TPDI were synthesized for comparison. The photovoltaic performances of these three PDI derivatives were investigated using the commercially available PTB7-Th as electron donor. A best power conversion efficiency (PCE) of 6.58% was obtained for T-DPDI based organic solar cells (OSCs), which is higher than those of DPDI and TPDI based ones. The superior photovoltaic performance of T-DPDI can be ascribed to its stronger absorption and more favorable morphology. This study presents an interesting example of improving the photovoltaic performances of PDI based NFAs by hybridizing the direct and indirect linkage manners.     

Perylene diimide copolymers with dithienothiophene and dithienopyrrole: Use in n‐channel and ambipolar field‐effect transistors

Solution‐processable polymers consisting of perylene diimide (PDI) acceptor moieties alternating with dithienothiophene (DTT), N‐dodecyl‐dithienopyrrole (DTP), or oligomers of these donor groups have been synthesized. We have, in addition to varying the donor, varied the N,N′ substituents of the PDIs. The thermal, optical, electrochemical, and charge‐transport properties of the polymers have been investigated. The polymers show broad absorption extending from 300 to 1000 nm with optical band gaps as low as 1.2 eV; the band gap decreases with increasing the conjugation length of donor block, or by replacement of DTT by DTP. The electron affinities of the polymers, estimated from electrochemical data, range from ?3.87 to ?4.01 eV and are slightly affected by the specific choice of donor moiety, while the estimated ionization potentials (?5.31 to ?5.92 eV) are more sensitive to the choice of donor. Bottom‐gate top‐contact organic field‐effect transistors based on the polymers generally exhibit n‐channel behavior with electron mobilities as high as 1.7 × 10^–2 cm²/V/s and on/off ratios as high as 10⁶; one PDI‐DTP polymer is an ambipolar transport material with electron mobility of 4 × 10^–4 cm²/V/s and hole mobility of 4 × 10^–5 cm²/V/s in air. There is considerable variation in the charge transport properties of the polymers with the chemical structures. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Crystalline Conjugated Polymers for Organic Solar Cells: From Donor,Acceptor to Single‐Component

Organic solar cells have made rapid progress in the last two decades due to the innovation of conjugated materials and photovoltaic devices. Microphase separation that connects with materials and devices plays a crucial role in the charge generation process. In this account, we summary our recent works of developing new crystalline conjugated polymers to control the microphase separation in thin films in order to realize high performance in solar cells, including crystalline diketopyrrolopyrrole‐based donor polymers, perylene bisimide‐based electron acceptors, and “double‐cable” conjugated polymers that contain covalently‐linked crystalline donor and acceptor in one material for single‐component organic solar cells.     

A Red‐Emissive Sextuple Hydrogen‐Bonding Self‐Assembly Molecular Duplex Bearing Perylene Diimide Fluorophores for Warm‐White Organic Light‐Emitting Diode Application

A novel sextuple hydrogen‐bonding (HB) self‐assembly molecular duplex bearing red‐emitting perylene diimide (PDI) fluorophores, namely PDIHB , was synthesized, and its molecular structure was confirmed by ¹H NMR, ¹³C NMR, TOF‐MS and 2D NMR. Compared with the small molecular reference compound PDI , PDIHB shows one time enhanced fluorescence efficiency in solid state (4.1% vs. 2.1%). More importantly, the presence of bulky HB oligoamide strands in PDIHB could trigger effective spatial separation between guest and host fluorophores in thin solid film state, hence inefficient energy transfer occurs between the blue‐emitting host 2TPhNIHB and red guest PDIHB in the 2 wt% guest/host blending film. As a result, a solution‐processed organic light‐emitting diode (OLED) with quite simple device structure of ITO/PEDOT:PSS (40 nm)/PVK (40 nm)/ PDIHB (2 wt%): 2TPhNIHB (50 nm)/LiF (0.8 nm)/Al (100 nm) could emit bias‐independent warm‐white electroluminescence with stable Commission Internationale de L'Eclairage coordinates of (0.42, 0.33), and the maximum brightness and current efficiency of this device are 260 cd·m^?2 and 0.49 cd·A^?1, respectively. All these results indicated that HB self‐assembly supramolecular fluorophores could act as prospective materials for white OLED application.     

Impact of Fluorine Atoms on Perylene Diimide Derivative for Fullerene‐Free Organic Photovoltaics

The incorporation of fluorine atoms in organic semiconducting materials has attracted much attention recently due to its unique function to manipulate the molecular packing, film morphology and molecular energy levels. In this work, two perylenediimide (PDI) derivatives FPDI‐CDTph and FPDI‐CDTph2F were designed and synthesized to investigate the impact of fluorination on non‐fullerene acceptors. Both FPDI‐CDTph and FPDI‐CDTph2F exhibited strong and broad absorption profiles, suitable lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) energy levels, and good electron transport ability. Compared with FPDI‐CDTph, the fluorinated acceptor (FPDI‐CDTph2F) afforded an optimal bulk heterojunction morphology with an interconnected and nanoscale phase separated structure that allowed more efficient exciton dissociation and balanced charge transport. Consequently, organic solar cells based on FPDI‐CDTph2F showed a much higher power conversion efficiency (PCE) of 6.03 % than that of FPDI‐CDTph based devices (4.10 %) without any post‐fabrication treatment.     

9H‐Quinolino[3,2,1‐k]phenothiazine: A New Electron‐Rich Fragment for Organic Electronics

A new electron‐rich fragment, namely the quinolinophenothiazine (QPTZ) is reported. The QPTZ fragment incorporated in spiroconfigured materials leads to higher performance in blue Phosphorescent OLEDs than structurally related phenylacridine and indoloacridine based materials (increasing the HOMO energy level, modulating the spin‐orbit coupling, etc.) and leads to highly efficient blue phosphorescent organic light emitting diodes, indicating the strong potential of this new molecular fragment in organic electronics.     

An acceptor‐acceptor conjugated copolymer based on perylene diimide for high mobility n‐channel transistor in air

A new solution‐processable acceptor‐acceptor conjugated copolymer ( P1 ) based on perylene diimide (PDI) incorporating planar electron‐deficient fluorenone was synthesized by palladium(0)‐catalyzed Suzuki coupling reaction. Relative to the donor‐acceptor conjugated copolymer ( P2 ) of PDI and dithienothiophene, polymer P1 exhibits 0.1 eV down shift of lowest unoccupied molecular orbital (LUMO) level, 70 nm blue shift of low‐energy absorption band, and 0.36 eV increase of optical band gap. Polymer P1 in top‐contact bottom‐gate organic field‐effect transistors exhibits a saturation electron mobility of 0.01 cm²/(V s) in air, while P2 does not function in the same device in air. The better air stability of P1 is attributed to a more dense packing of the polymer chains excluding oxygen or water and lower LUMO level of P1 . © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Pyromellitic diimide‐based copolymers for ambipolar field‐effect transistors: Synthesis,characterization, and device applications

A pyromellitic diimide building block, 2,6‐bis(2‐decyltetradecyl)?4,8‐di(thiophen‐2‐yl)pyrrolo[3,4‐f]isoindole‐1,3,5,7(2H,6H)‐tetraone ( 4 ), is synthesized. Based on this building block and other electron‐rich units such as 2,2′‐bithiophene, thieno[3,2‐b]thiophene and 4,8‐bis(dodecyloxy)benzo[1,2‐b:4,5‐b′]dithiophene, three conjugated polymers P1 , P2 , and P3 are prepared in good yield via Stille coupling polymerization. These new copolymers have good solubility in common organic solvents and exhibit good thermal stability. The optical, electrochemical, and thermal properties of these polymers P1–P3 are carefully investigated, and their applications in solution‐processed organic field‐effect transistors are also studied. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2454–2464     

Thiophene‐S,S‐dioxidized Indophenine: A Quinoid‐Type Building Block with High Electron Affinity for Constructing n‐Type Polymer Semiconductors with Narrow Band Gaps

Three thiophene‐S,S‐dioxidized indophenine (IDTO) isomers, 3 a (E,E,E), 3 b (Z,E,E), and 3 c (Z,E,Z), were synthesized by oxidation of an indophenine compound. 3 b and 3 c could be converted into the most‐stable 3 a by heating at 110 °C. An IDTO‐containing conjugated polymer, PIDTOTT, was prepared using 3 a as a comonomer through a Stille coupling reaction, and it possesses a narrow band gap and low energy levels. In organic field effect transistors (OFETs), PIDTOTT exhibited unipolar n‐type semiconductor characteristics with unexpectedly high electron mobility (up to 0.14 cm² V^?1 s^?1), despite its rather disordered chain packing.     

Tetrachlorinated Tetraazaperopyrenes (TAPPs): Highly Fluorescent Dyes and Semiconductors for Air‐Stable Organic n‐Channel Transistors and Complementary Circuits

A range of 2,9‐perfluoroalkyl‐substituted tetraazaperopyrene (TAPP) derivatives ( 1 – 5 ) was synthesised by reacting 4,9‐diamino‐3,10‐perylenequinone diimine (DPDI) with the corresponding carboxylic acid chloride or anhydride in the presence of a base. The reaction of compounds 1 – 4 with dichloroisocyanuric acid (DIC) in concentrated sulphuric acid resulted in the fourfold substitution of the tetraazaperopyrene core, yielding the 2,9‐bisperfluoroalkyl‐4,7,11,14‐tetrachloro‐1,3,8,10‐tetraazaperopyrenes 6 – 9 , respectively. The optical and electrochemical data demonstrate the drastic influence of the core substitution on the properties. All compounds are highly luminescent (fluorescence quantum yields of up to Φ=0.8). The LUMO energies of the tetrachlorinated TAPP derivatives (determined by cyclic voltammetry and computed by DFT calulations) were found to be below ?4 eV. In the course of this work the performance of TAPP derivatives in organic thin‐film transistors (TFTs) was investigated, and their n‐channel characteristics with field‐effect mobilities of up to 0.14 cm² V^?1 s^?1 and an on/off current ratio of >10⁶ were confirmed. Long‐term stabilities of 3–4 months under ambient conditions of the devices were established. Complementary inverters and ring oscillators with n‐channel TFTs based on compound 8 and p‐channel TFTs based on dinaphtho‐[2,3‐b:2′,3′‐f]thieno[3,2‐b]thiophene (DNTT) were fabricated on a glass substrate.     

Bismuth Interfacial Doping of Organic Small Molecules for High Performance n‐type Thermoelectric Materials

Development of chemically doped high performance n‐type organic thermoelectric (TE) materials is of vital importance for flexible power generating applications. For the first time, bismuth (Bi) n‐type chemical doping of organic semiconductors is described, enabling high performance TE materials. The Bi interfacial doping of thiophene‐diketopyrrolopyrrole‐based quinoidal (TDPPQ) molecules endows the film with a balanced electrical conductivity of 3.3 S cm^?1 and a Seebeck coefficient of 585 μV K^?1. The newly developed TE material possesses a maximum power factor of 113 μW m^?1 K^?2, which is at the forefront for organic small molecule‐based n‐type TE materials. These studies reveal that fine‐tuning of the heavy metal doping of organic semiconductors opens up a new strategy for exploring high performance organic TE materials.     

Self‐Directed Orientation of Molecular Columns Based on n‐Type Hexaazatrinaphthylenes (HATNAs) for Electron Transport

Self‐organizing n‐type hexaazatrinaphthylenes (HATNAs) with various bay‐located side chains have been synthesized. The HATNA derivatives are able to form long‐range molecular columns with self‐directed growth directions. In particular, alkyl‐substituted HATNAs showed in‐plane molecular columns with axes parallel to substrates, whereas the columnar orientation of the HATNAs with alkylethynyl or alkylthio groups strongly depended on the length of the introduced side chains. Interestingly, the derivative with octylthio chains exhibited out‐of‐plane molecular columns, in which electron mobility of up to 10^?3 cm² V^?1 s^?1 was determined through the time‐of‐flight technique, highlighting the fact that such molecular columns based on bay‐substituted HATNAs are promising n‐type semiconductors for device applications.     

Oriented Synthesis of One‐Dimensional Polypyrrole Molecule Chains in a Metal‐Organic Framework

We report for the first time the preparation of single polypyrrole (PPy) molecule chains using a “metal‐organic framework” with 1 nm channels as a template. The obtained one‐dimensional (1‐D) PPy has highly structure order and excellent conductivity, which has improved by as much as five orders of magnitude in comparison with that of 2‐D PPy.

     

The Impact of Interlayer Electronic Coupling on Charge Transport in Organic Semiconductors: A Case Study on Titanylphthalocyanine Single Crystals

Traditionally, it is believed that three‐dimensional transport networks are preferable to those of lower dimensions. We demonstrate that inter‐layer electronic couplings may result in a drastic decrease of charge mobilities by utilizing field‐effect transistors (FET) based on two phases of titanyl phthalocyanine (TiOPc) crystals. The α‐phase crystals with electronic couplings along two dimensions show a maximum mobility up to 26.8 cm² V^?1 s^?1. In sharp contrast, the β‐phase crystals with extra significant inter‐layer electronic couplings show a maximum mobility of only 0.1 cm² V^?1 s^?1. Theoretical calculations on the bulk crystals and model slabs reveal that the inter‐layer electronic couplings for the β‐phase devices will diminish remarkably the device charge transport abilities owing to the coupling direction perpendicular to the current direction. This work provides new insights into the impact of the dimensionality and directionality of the packing arrangements on charge transport in organic semiconductors.