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A rapidly growing interest in organic bioelectronic applications has spurred the development of a wide variety of organic mixed ionic‐electronic conductors. While these new mixed conductors have enabled the community to interface organic electronics with biological systems and efficiently transduce biological signals (ions) into electronic signals, the current materials selection does not offer sufficient selectivity towards specific ions of biological relevance without the use of auxiliary components such as ion‐selective membranes. Here, we present the molecular design of an n‐type (electron‐transporting) perylene diimide semiconductor material decorated with pendant oligoether groups to facilitate interactions with cations such as Na+ and K+. Using the cyclic 15‐crown‐5 oligoether motif, we find that the resulting mixed conductor PDI‐crown displays a strong dependence on the size of the electrolyte cation when tested in an organic electrochemical transistor configuration. In stark contrast to the low current response on the order of 1 μA observed with aqueous sodium chloride, a nearly 200‐fold increase in current is observed with aqueous potassium chloride. We ascribe the high selectivity to extended molecular aggregation and therefore efficient charge transport in the presence of K+ due to a favourable sandwich‐like structure between two adjacent 15‐crown‐5 motifs and the potassium ion. [ABSTRACT FROM AUTHOR]

Solid‐state molecular arrangement has been recognized as the most important role in the charge transport properties of organic semiconductors. Although highly ordered molecular stacking is achieved in single crystals, maintaining single‐crystal molecular packing in solution‐processed thin films remains a significant challenge. Herein, a new type of n‐type organic semiconductors based on an asymmetric fluoranthene imide unit is reported, whose intermolecular packing and aggregation behavior in the thin film state can be effectively controlled by regulating the cyano substitution sites and alkyl chain types in the imide group. F10 with cyano groups at 4,9‐sites and branched 2‐ethylhexyl chain encouragingly shows a highly ordered single‐crystal‐like molecular packing in solution‐processed thin film after thermal annealing, and thus the resulting organic field‐effect transistors exhibit impressive charge transport performance, with the electron mobility as high as 0.116 cm2 V−1 s−1. This work opens a new avenue for developing high‐performance solution‐processed n‐type semiconductors. [ABSTRACT FROM AUTHOR]

Developing novel n‐type organic semiconductors is an on‐going research endeavour, given their pivotal roles in organic electronics and their relative scarcity compared to p‐type counterparts. In this study, a new strategy was employed to synthesize n‐type organic semiconductors featuring a fully fused conjugated backbone. By attaching two sets of adjacent amino and formyl groups to the indacenodithiophene‐based central cores and triggering a tandem reaction sequence of a Knoevenagel condensation‐intramolecular cyclization, DFA1 and DFA2 were realized. The solution‐processed organic field effect transistors based on DFA1 exhibited unipolar n‐type transport character with a decent electron mobility of ca. 0.10 cm2 V−1 s−1 (ca. 0.038 cm2 V−1 s−1 for DFA2 based devices). When employing DFA1 as a third component in organic solar cells, a high power conversion efficiency of 19.2 % can be achieved in ternary devices fabricated with PM6 : L8‐BO : DFA1. This work provides a new pathway in the molecular engineering of n‐type organic semiconductors, propelling relevant research forward. [ABSTRACT FROM AUTHOR]

Perylenetetracarboxylic diimide (PTCDI) is an n-type organic semiconductor molecule that has been widely utilized in numerous applications such as photocatalysis and field-effect transistors. Polarizability and dipole moment, which are inherent properties of molecules, are important parameters that determine their responses to external electric and optical fields, physical properties, and reactivity. These parameters are fundamentally important for the design of innovative materials. In this study, the effects of external electric fields on absorption and fluorescence spectra were investigated to obtain the PTCDI parameters. The PTCDI substituted by an octyl group (N,N′-Dioctyl-3,4,9,10-perylenedicarboximide) dispersed in a polymethyl methacrylate (PMMA) matrix was studied in this work. The features of vibronic progression in the absorption spectrum were analogous to those observed in solution. The red shift of the absorption band caused by the Stark effect was mainly observed in the presence of an external electric field. Changes in parameters such as the dipole moment and polarizability between the ground and the Franck–Condon excited states of the PTCDI monomer were determined. The fluorescence spectrum shows a contribution from a broad fluorescence band at wavelengths longer than the monomer fluorescence band. This broad fluorescence is ascribed to the excimer-like fluorescence of PTCDI. The effects of the electric field on the fluorescence spectrum, known as the Stark fluorescence or electrofluorescence spectrum, were measured. Fluorescence quenching is observed in the presence of an external electric field. The change in the polarizability of the monomer fluorescence band is in good agreement with that of the electroabsorption spectrum. A larger change in the polarizability was observed for the excimer-like fluorescence band than that for the monomer band. This result is consistent with exciton delocalization between PTCDI molecules in the excimer-like state. [ABSTRACT FROM AUTHOR]

The organic electrochemical transistor (OECT) is one of the most versatile building blocks within the bioelectronics device toolbox. While p‐type organic semiconductors have progressed as OECT channel materials, only a few n‐type semiconductors have been reported, precluding the development of advanced sensor‐integrated OECT‐based complementary circuits. Herein, green aldol polymerization is uses to synthesize lactone‐based n‐type conjugated polymers. Fluorination of the lactone‐based acceptor endows a fully locked backbone with a low‐lying lowest unoccupied molecular orbital, facilitating efficient ionic‐to‐electronic charge coupling. The resulting polymer has a record‐high n‐type OECT performance with a high product of mobility and capacitance (µC* = 108 F cm−1 V−1 s−1), excellent mobility (0.912 cm2 V−1 s−1), low threshold voltage (0.02 V), and fast switching speed (τON, τOFF = 336 µs,108 µs). This work demonstrates two types of device architectures and applications enabled by the high performance of this n‐type OECT, i.e., an artificial synapse and a complementary amplifier for detecting α‐synuclein, a potential biomarker of Parkinson's disease. This study shows that materials that enable high gain and fast speed n‐type OECTs can be developed via a green polymerization route, and the diverse form factors that these devices take promise for exploration of other application areas. [ABSTRACT FROM AUTHOR]

The development of n-type organic semiconductors has evolved significantly slower in comparison to that of p-type organic semiconductors mainly due to the lack of electron-deficient building blocks with stability and processability. However, to realize a variety of organic optoelectronic devices, high-performance n-type polymer semiconductors are essential. Herein, conjugated microporous polymers (CMPs) comprising isoindigo acceptor units linked to benzene or pyrene donor units (BI and PI) showing n-type semiconducting behavior are reported. In addition, considering the challenges of deposition of a continuous and homogeneous thin film of CMPs for accurate Hall measurements, a plasma-assisted fabrication technique is developed to yield uniform thin films. The fully conjugated 2D networks in PI- and BI-CMP films display high electron mobility of 6.6 and 3.5 cm² V-1 s-1, respectively. The higher carrier concentration in PI results in high conductivity (5.3 mS cm-1. Both experimental and computational studies are adequately combined to investigate structure-property relations for this intriguing class of materials in the context of organic electronics. [ABSTRACT FROM AUTHOR]

Perylenetetracarboxylic diimide (PTCDI) is an n-type organic semiconductor molecule that has been widely utilized in numerous applications such as photocatalysis and field-effect transistors. Polarizability and dipole moment, which are inherent properties of molecules, are important parameters that determine their responses to external electric and optical fields, physical properties, and reactivity. These parameters are fundamentally important for the design of innovative materials. In this study, the effects of external electric fields on absorption and fluorescence spectra were investigated to obtain the PTCDI parameters. The PTCDI substituted by an octyl group (N,N′-Dioctyl-3,4,9,10-perylenedicarboximide) dispersed in a polymethyl methacrylate (PMMA) matrix was studied in this work. The features of vibronic progression in the absorption spectrum were analogous to those observed in solution. The red shift of the absorption band caused by the Stark effect was mainly observed in the presence of an external electric field. Changes in parameters such as the dipole moment and polarizability between the ground and the Franck–Condon excited states of the PTCDI monomer were determined. The fluorescence spectrum shows a contribution from a broad fluorescence band at wavelengths longer than the monomer fluorescence band. This broad fluorescence is ascribed to the excimer-like fluorescence of PTCDI. The effects of the electric field on the fluorescence spectrum, known as the Stark fluorescence or electrofluorescence spectrum, were measured. Fluorescence quenching is observed in the presence of an external electric field. The change in the polarizability of the monomer fluorescence band is in good agreement with that of the electroabsorption spectrum. A larger change in the polarizability was observed for the excimer-like fluorescence band than that for the monomer band. This result is consistent with exciton delocalization between PTCDI molecules in the excimer-like state.

Abstract The development of n‐type organic semiconductors has evolved significantly slower in comparison to that of p‐type organic semiconductors mainly due to the lack of electron‐deficient building blocks with stability and processability. However, to realize a variety of organic optoelectronic devices, high‐performance n‐type polymer semiconductors are essential. Herein, conjugated microporous polymers (CMPs) comprising isoindigo acceptor units linked to benzene or pyrene donor units (BI and PI) showing n‐type semiconducting behavior are reported. In addition, considering the challenges of deposition of a continuous and homogeneous thin film of CMPs for accurate Hall measurements, a plasma‐assisted fabrication technique is developed to yield uniform thin films. The fully conjugated 2D networks in PI‐ and BI‐CMP films display high electron mobility of 6.6 and 3.5 cm2 V−1 s−1, respectively. The higher carrier concentration in PI results in high conductivity (5.3 mS cm−1). Both experimental and computational studies are adequately combined to investigate structure–property relations for this intriguing class of materials in the context of organic electronics.

The active layer of organic solar cells (OSCs) is composed of a p-type conjugated polymer as the donor and an n-type organic semiconductor as the acceptor. Since the report of bulk-heterojunction OSCs with soluble C60 derivative PCBM as the acceptor in 1995, fullerene derivatives, including PCBM and the C70 derivative PC71BM, have been the dominant acceptors in OSCs for 20 years. In 2015, the A–D–A structured small molecule acceptor (SMA) was developed, which possesses the advantages of a narrow bandgap, strong absorption in the long wavelength region, and suitable electronic energy levels, in contrast to the fullerene derivative acceptors. A–D–A SMAs boost the power conversion efficiency (PCE) of OSCs to the 10–14% level. Recently, benefiting from the innovation of A–DA′D–A structured SMAs, the PCE of OSCs has rapidly increased from 15% to 19%. In this review, the development history of n-type organic semiconductor acceptor materials is briefly introduced. The molecular structures and the physicochemical and photovoltaic properties of acceptors, including fullerene derivatives and narrow bandgap SMAs, are described. In particular, the effect of regulating the molecular packing and miscibility of SMAs on their photovoltaic performance is discussed. Finally, current challenges and prospects for n-type organic semiconductor acceptors are analyzed and discussed.

A family of novel highly π‐extended tetracyano‐substituted acene diimides, named as tetracyanodiacenaphthoanthracene diimides (TCDADIs), have been synthesized using a facile four‐fold Knoevenagel condensation strategy. Unlike conventional cyano substitution reactions, our approach enables access to a large π‐conjugated backbone with the in‐situ formation of four cyano substitutents at room temperature while avoiding extra cyano‐functionalization reactions. TCDADIs decorated with different N‐alkyl substituents present good solubility, near‐coplanar backbones, good crystallinity, and low‐lying lowest unoccupied molecular orbital energies of −4.33 eV, all of which contribute to desirable electron‐transport performance when applied in organic field‐effect transistors (OFET). The highest electron mobility of an OFET based on a 2‐hexyldecyl‐substituted TCDADI single crystal reaches 12.6 cm2 V−1 s−1, which is not only among the highest values for the reported n‐type organic semiconductor materials (OSMs) but also exceeds that of most n‐type OSMs decorated with imide units. [ABSTRACT FROM AUTHOR]

A family of novel highly π‐extended tetracyano‐substituted acene diimides, named as tetracyanodiacenaphthoanthracene diimides (TCDADIs), have been synthesized using a facile four‐fold Knoevenagel condensation strategy. Unlike conventional cyano substitution reactions, our approach enables access to a large π‐conjugated backbone with the in‐situ formation of four cyano substitutents at room temperature while avoiding extra cyano‐functionalization reactions. TCDADIs decorated with different N‐alkyl substituents present good solubility, near‐coplanar backbones, good crystallinity, and low‐lying lowest unoccupied molecular orbital energies of −4.33 eV, all of which contribute to desirable electron‐transport performance when applied in organic field‐effect transistors (OFET). The highest electron mobility of an OFET based on a 2‐hexyldecyl‐substituted TCDADI single crystal reaches 12.6 cm2 V−1 s−1, which is not only among the highest values for the reported n‐type organic semiconductor materials (OSMs) but also exceeds that of most n‐type OSMs decorated with imide units. [ABSTRACT FROM AUTHOR]

A family of novel highly π‐extended tetracyano‐substituted acene diimides, named as tetracyanodiacenaphthoanthracene diimides (TCDADIs), have been synthesized using a facile four‐fold Knoevenagel condensation strategy. Unlike conventional cyano substitution reactions, our approach enables access to a large π‐conjugated backbone with the in‐situ formation of four cyano substitutents at room temperature while avoiding extra cyano‐functionalization reactions. TCDADIs decorated with different N‐alkyl substituents present good solubility, near‐coplanar backbones, good crystallinity, and low‐lying lowest unoccupied molecular orbital energies of −4.33 eV, all of which contribute to desirable electron‐transport performance when applied in organic field‐effect transistors (OFET). The highest electron mobility of an OFET based on a 2‐hexyldecyl‐substituted TCDADI single crystal reaches 12.6 cm2 V−1 s−1, which is not only among the highest values for the reported n‐type organic semiconductor materials (OSMs) but also exceeds that of most n‐type OSMs decorated with imide units. [ABSTRACT FROM AUTHOR]

A family of novel highly π‐extended tetracyano‐substituted acene diimides, named as tetracyanodiacenaphthoanthracene diimides (TCDADIs), have been synthesized using a facile four‐fold Knoevenagel condensation strategy. Unlike conventional cyano substitution reactions, our approach enables access to a large π‐conjugated backbone with the in‐situ formation of four cyano substitutents at room temperature while avoiding extra cyano‐functionalization reactions. TCDADIs decorated with different N‐alkyl substituents present good solubility, near‐coplanar backbones, good crystallinity, and low‐lying lowest unoccupied molecular orbital energies of −4.33 eV, all of which contribute to desirable electron‐transport performance when applied in organic field‐effect transistors (OFET). The highest electron mobility of an OFET based on a 2‐hexyldecyl‐substituted TCDADI single crystal reaches 12.6 cm2 V−1 s−1, which is not only among the highest values for the reported n‐type organic semiconductor materials (OSMs) but also exceeds that of most n‐type OSMs decorated with imide units. [ABSTRACT FROM AUTHOR]

In this study, we synthesized and evaluated graft copolymers with polystyrene (PSt) as side chains on poly {[ N,N´ -bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]- alt -5,5′-(2,2′ -bithiophene)} [P(NDI2OD-T2)], which is a typical n-type semiconducting polymer applied to in organic photovoltaics due to its intense optical absorption for the visible light, and high electron affinity. A well-controlled structure was confirmed by 1H-NMR analysis. It was found that enhanced electron mobilities in graft copolymer films were observed compared with the homopolymer. In order to clarify the role of PSt chains and the origins of the enhanced mobility, UV–vis absorption, electrochemical, morphological and thermal characteristics, and crystalline nature were investigated. As the results, it is suggested that the improved mobilities were attributed to the enhanced growth of π – π stacks, and increased crystallinity induced by PSt graft chains. [ABSTRACT FROM AUTHOR]

The fascinating characteristic of organic light‐emitting transistors (OLETs) of being electrical switches with an intrinsic light‐emitting capability makes them attractive candidates for a wide variety of applications, ranging from sensors to displays. To date, the OLET ambipolar trilayer heterostructure is the most developed architecture for maximizing device performance. However, a major challenge of trilayer OLETs remains the inverse correlation between external quantum efficiency and brightness under ambipolar conditions. The complex interconnection between electroluminescent and ambipolar charge transport properties, in conjunction with the limited availability of electron transport semiconducting materials, has indeed hampered the disruptive evolution of the OLET technology. Here, an in‐depth study of the interplay of the key fundamental features that determine the device performance is reported by exploring electron transport semiconductors with different properties in ambipolar trilayer OLETs. Through the selection of compounds with tailored chemical structures, the relation between intrinsic optoelectronic characteristics of the electron transport semiconductor, energy level alignment within the structure, and morphological features is unraveled. Furthermore, the introduction of a suitable electron injector at the emissive/semiconducting layers interface sheds light into the bidimensional nature of OLETs that is a distinguishing factor of this class of devices with respect to prototypical organic light‐emitting diodes. [ABSTRACT FROM AUTHOR]

We report the synthesis and properties of acridino[2,1,9,8‐klmna]acridine bisimide (AABI), a nitrogen‐doped anthanthrene with two imide functionalities. AABI exhibits excellent electron affinity as evident by its low‐lying LUMO level (−4.1 eV vs. vacuum). Single‐electron reduction of one AABI derivative afforded the corresponding radical anion, which was stable under ambient conditions. Photoconductivity measurements suggest that the intrinsic electron mobility of an N‐phenethyl AABI derivative obeys a band‐transport model. Accordingly, an electron mobility of 0.90 cm2 V−1 s−1 was attained with the corresponding single‐crystal organic field‐effect transistor (OFET) device. The vacuum‐deposited OFET device consisting of a polycrystalline sample exhibited high electron mobility of up to 0.27 cm2 V−1 s−1 even in air. This study demonstrates that dual incorporation of both imide substituents and imine‐type nitrogen atoms is an effective strategy to create novel electron‐deficient π‐systems. [ABSTRACT FROM AUTHOR]

Abstract A new n -type organic semiconductor (n -OS) acceptor with (E)-5-(2-(5-(2-ethylhexyl)thiophen-2-yl)vinyl)-thiophene-2-yl (TVT) functional group as π-bridge to link indacenodithiophene (IDT) core and 3-(dicyanomethylidene)indan-1-one (IC) terminals, named ITVT, was synthesized and applied in polymer solar cells (PSCs). It is the first time employing TVT unit in n -OS small molecule acceptor. Benefited from the conjugated TVT side groups, the small molecule ITVT shows a strong absorption at the short wavelength range (300–500 nm). In addition, ITVT exhibits a low optical band gap (E g opt) of 1.48 eV and a medium electron mobility of 1.85 × 10−4 cm2 V-1 s-1. A wide band gap polymer PBZ was chosen as donor to fabricate an inverted BHJ PSCs because of the complementary absorption and matched molecular energy levels. The as-cast PSCs yield a power conversion efficiency (PCE) of 5.84% with an open-circuit voltage (V oc) of 0.96 V and a short-circuit current density (J sc) of 14.22 mA cm−2 under the illumination of AM 1.5 G at 100 mW cm−2. Graphical abstract A new small molecule acceptor ITVT containing Alkylthienylenevinylene thiophene unit was synthesized. The as-cast PSCs yield a power conversion efficiency (PCE) of 5.84% under the illumination of AM 1.5 G at 100 mW cm−2. Image 1 Highlights • A new molecule with thienylenevinylene thiophene as π bridge was synthesized. • ITVT exhibits appropriate optoelectronic properties used as an electron acceptor. • The as-cast solar cells based on ITVT yield a power conversion efficiency of 5.84%. [ABSTRACT FROM AUTHOR]

Dopants, i.e., electronically active impurities, are added to organic semiconductor materials to control the material's Fermi level and conductivity, to improve injection at the device contacts, or to fill trap states in the active device layers and interfaces. In contrast to bulk doping as achieved by blending or co-deposition of dopant and semiconductor, surface doping has a lower propensity to introduce additional traps or scattering centers or to even alter the layer morphology relative to the undoped active material layers. In this study, the electrical effects of a very simple, post-device-fabrication surface doping process involving various amine group-containing alkoxysilanes on the performance of organic field-effect transistors (OFETs) made from the well-known n-type materials PTCDI-C8 and N2200 are researched. It is demonstrated that OFETs doped in such a way generally show enhanced characteristics (up to 10 times mobility increase and a significant reduction in threshold voltage) without any adverse effects on the devices' on/off ratio. It is also shown that the efficiency of the doping process is linked to the number of amine groups. [ABSTRACT FROM AUTHOR]

Abstract: Two n‐type organic semiconductor (n‐OS) small molecules m‐ITIC‐2F and m‐ITIC‐4F with fluorinated 2‐(2,3‐dihydro‐3‐oxo‐1H‐inden‐1‐ylidene)propanedinitrile (IC) terminal moieties are prepared, for the application as an acceptor in polymer solar cells (PSCs), to further improve the photovoltaic performance of the n‐OS acceptor 3,9‐bis(2‐methylene‐(3‐(1,1‐dicyanomethylene) indanone) ‐5,5,11,11‐tetrakis(3‐hexylphenyl)‐dithieno[2,3‐d:2′,3′‐d′]‐sindaceno[1,2‐b:5,6‐b′]‐dithiophene (m‐ITIC). Compared to m‐ITIC, these two new acceptors show redshifted absorption, higher molecular packing order, and improved electron mobilities. The power conversion efficiencies (PCE) of the as‐cast PSCs with m‐ITIC‐2F or m‐ITIC‐4F as an acceptor and a low‐cost donor–acceptor (D–A) copolymer PTQ10 as a donor reach 11.57% and 11.64%, respectively, which are among the highest efficiency for the as‐cast PSCs so far. Furthermore, after thermal annealing treatment, improved molecular packing and enhanced phase separation are observed, and the higher PCE of 12.53% is achieved for both PSCs based on the two acceptors. The respective and unique advantage with the intrinsic high degree of order, molecular packing, and electron mobilities of these two acceptors will be suitable to match with different p‐type organic semiconductor donors for higher PCE values, which provide a great potential for the PSCs commercialization in the near future. These results indicate that rational molecular structure optimization is of great importance to further improve photovoltaic properties of the photovoltaic materials. [ABSTRACT FROM AUTHOR]

In this work, a new non-fused small molecule acceptor Ph-IC based on alkoxyl benzene and IC units was synthesized for photovoltaic applications. The small molecule Ph-IC has a very simple chemical structure and is easily synthesized. Benefited from the coplanar conjugated structure, the O-H and S-H non-covalent interactions, Ph-IC exhibits a narrow optical bandgap of 1.62 eV and a medium electron mobility of 1.84 × 10 −4 cm 2 V −1 s −1 . When using Ph-IC as acceptor and a wide-bandgap polymer PBFTZ as donor, the devices show a maximum PCE of 5.68% with V oc of 0.89 V, J sc of 12.37 mA cm −2 and FF of 51.5% under the illumination of AM 1.5 G at 100 mW/cm 2 . This work demonstrates that the simple-structured and low cost non-fused group can also be used as building blocks in high performation n -OS acceptors. [ABSTRACT FROM AUTHOR]

A family of novel highly π-extended tetracyano-substituted acene diimides, named as tetracyanodiacenaphthoanthracene diimides (TCDADIs), have been synthesized using a facile four-fold Knoevenagel condensation strategy. Unlike conventional cyano substitution reactions, our approach enables access to a large π-conjugated backbone with the in-situ formation of four cyano substitutents at room temperature while avoiding extra cyano-functionalization reactions. TCDADIs decorated with different N-alkyl substituents present good solubility, near-coplanar backbones, good crystallinity, and low-lying lowest unoccupied molecular orbital energies of -4.33 eV, all of which contribute to desirable electron-transport performance when applied in organic field-effect transistors (OFET). The highest electron mobility of an OFET based on a 2-hexyldecyl-substituted TCDADI single crystal reaches 12.6 cm 2  V -1  s -1 , which is not only among the highest values for the reported n-type organic semiconductor materials (OSMs) but also exceeds that of most n-type OSMs decorated with imide units., (© 2023 Wiley-VCH Verlag GmbH.)

Understanding two mesomerism-like forms (quinoid vs. benzenoid structures) over organic semiconductors (OSCs) is essential for achieving high electronic device performance. Herein, we report the synthesis as well as the comparative physicochemical, microstructural, and charge-transporting analysis of dicyanomethylene-quinoid versus dicyanovinyl-benzenoid OSCs based on benzo[1,2 -b :4,5 -b′ ]dithiophene (BDT) units (DCM- Q -BDT and DCV- B -BDT). The electron-deficient nature of the quinoid structure in DCM- Q -BDT can lower the LUMO level and bandgap relative to the benzenoid analogy DCV- B -BDT. Top-gate/bottom-contact (TG/BC) field-effect transistors (OFETs) based on DCM- Q -BDT show not only the maximum electron mobility up to 0.23 cm 2 /V.s without requiring post-annealing treatments, but also demonstrate excellent air stability (half-life times of drain current ≈ 35 h) without any encapsulation. The superior n -channel performance for DCM- Q -BDT is due to the anisotropic orientation, high degree of the crystallinity, and low-lying LUMO induced by the quinoid structure. Our study shows underlying structure–property relationships in quinoid over benzenoid OSCs while demonstrating promise in n -channel OFETs. [ABSTRACT FROM AUTHOR]

n-Doped small molecular organic thermoelectric materials (OTMs) hold advantages of high Seebeck coefficient and better performance reproducibility over their polymeric analogues; however, high-performance n-type small molecular OTMs are severely lacking. We report here a class of small molecular OTMs based on terminal cyanation of a bithiophene imide-based ladder-type heteroarene BTI2. It was found that the cyanation could effectively lower the lowest unoccupied molecular orbital (LUMO) level from -2.90 eV (BTI2) to -4.14 eV (BTI2-4CN) and thus lead to significantly improved n-doping efficiency. Additionally, terminal cyano-functionalization can maintain the close packing and efficient intermolecular charge transfer between these cyanated molecules, thus yielding high electron mobilities of up to 0.40 cm 2 V -1 s -1 . Benefiting from its low LUMO-enabled efficient n-doping and high electron mobility, an encouraging n-type electrical conductivity of 0.43 S cm -1 and power factor (PF) of 6.34 μW m -1 K -2 were achieved for tetracyanated BTI2-4CN, significantly outperforming those of its noncynated BTI2 (<10 -7 S cm -1 , PF undetectable) and dicyanated BTI2-2CN (0.24 S cm -1 , 1.78 μW m -1 K -2 ). These results suggest the great potential of the terminal cyanation strategy of ladder-type heteroarenes for developing high-performance small molecular OTMs.

Unlike universally applicable fullerene derivatives, current nonfullerene electron acceptors are rarely effective with more than one donor polymer in bulk heterojunction (BHJ) solar cells. A novel class of nonfullerene electron acceptors, bis(naphthalene imide)-3,6-diphenyl- trans-anthrazolines (BNIDPAs), that is applicable and yields efficient photovoltaic devices with multiple donor polymers, including a thiazolothiazole-dithienosilole copolymer (PSEHTT) and benzodithiophene copolymers (PBDTT-FTTE and PTB7) is reported. Photovoltaic devices composed of the BNIDPA-butyloctyl (BO) acceptor with PSEHTT, PBDTT-FTTE, and PTB7, respectively, have power conversion efficiencies of 3.0%-3.1% with high open-circuit voltages of ≈1.0 V. In contrast, BHJ devices composed of BNIDPA-DT acceptor with larger 2-decyltetradecyl chains and the same donor polymers have substantially reduced bulk electron mobility and reduced photovoltaic efficiencies of 1.3%-1.7%, which highlight the critical role of the size of alkyl chains appended onto nonfullerene electron acceptors. The present results provide a rare example of nonfullerene electron acceptors that are capable of pairing with multiple donor polymers to achieve efficient BHJ solar cells. [ABSTRACT FROM AUTHOR]

Electron mobilities of two pentacenquinone derivatives as n-type organic semiconductors, 5,7,12,14-tetraaza-6,13-pentacenquinone (TAPQ5) and 1,4,8,11-tetraaza-6,13-pentacenquinone (TAPQ7), have been investigated at the molecular and crystal levels by means of the density functional theory (DFT) calculations and the incoherent charge-hopping model. It was found that these materials have lower LUMO energy levels, which can easily function as n-type organic semiconductors. The reorganization energy and transfer integral are the two important factors for tuning the electron transfer. The small reorganization energy and the large transfer integral for electron transport suggested that they have relatively high electron mobilities. The transfer integral among the dominant hopping pathways showed that the electron transport processes occur in parallel dimers between two neighboring molecules with π-stacking interactions. On the basis of the angular resolution anisotropic mobility investigation, TAPQ5 and TAPQ7 exhibit remarkable angular dependence of mobilities and anisotropic behaviors. The results are helpful for experimentalists to choose the candidate materials and to design novel organic semiconductors. [ABSTRACT FROM AUTHOR]

A series of dicyanomethylene-substituted 2,5-di(thiophen-2-yl)thieno[3,2-b]thieno-quinoids, in which soluble alkyl chains (2-decyltetradecyls) are substituted at different positions (namely, 2,2′-positions (Compound 1); 3,3′- positions (Compound 2); 6,6′-positions (Compound 3)), are strategically designed and successfully synthesized. The photophysical and electrochemical properties as well as molecular packing of these new compounds are thoroughly investigated. Thin film transistor measurements reveal that Compounds 1-3 display markedly different charge transport performance. The solution processed thin film transistors of Compound 2 exhibits the highest electron mobility of up to 0.22 cm2 V−1 s−1 under ambient conditions, one and three orders of magnitude higher than those of Compounds 3 and 1, respectively, demonstrating the strong impact of alkyl chain orientations on transistor performance. [ABSTRACT FROM AUTHOR]

The transfer of heat energy in organic semiconductors (OSCs) plays an important role in advancing the applications of organic electronics, especially for lifetime issues. However, compared with crystalline inorganic semiconductors, the thermal transport of OSCs is less efficient and a relevant understanding is very limited. In this contribution, we show that the heat conduction of OSCs can be enhanced by blending with a "commodity" insulator (both thermal and electrical). PC 71 BM, a well-known electron transporter but poor thermal conductor, was selected as the host OSC material. The blending of a small amount of polystyrene (PS), a commonly used insulating polymer, can facilitate the heat transfer of PC 71 BM films, as substantiated by the scanning photothermal deflection technique and an infrared thermal camera. The phase thermodynamics of PC 71 BM/PS blends indicates that the efficient heat transfer preferably occurs in the OSC/insulator blends with better intimate mixing, where isolated PC 71 BM domains can be effectively bridged by PS that thread through the regions. The applicability of this approach can be observed in blends with another host material─ITIC. This work provides a facile strategy for designing thermally durable organic electronic devices.

Abstract: Perylene diimides are known as promising n-type semiconductor building blocks. Here we report the synthesis and characterization of a set of three soluble poly(perylene diimide)s and their preliminary characterization in organic photovoltaic cells. These polymers are made through the polycondensation of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) with a variety of poly(ethylene glycol) (PEG)- or poly(propylene glycol) (PPG)-based diamine comonomers. The flexible spacer offers increased solubility in organic solvents and allows the perylene core to assume a conformation that promotes favorable cofacial π–π interactions. Mixtures of these polymers with the hole-transporting polymer, poly(3-hexylthiophene) (P3HT) result in significant fluorescence quenching. However, the phase separation occurs on a scale too large for a bulk heterojunction solar cell. The PPGylated poly(perylene diimide) shows an unusually low free electron concentration (∼1.0×1012 cm−3) and therefore makes an excellent model system for future doping studies. These new polymers may have promise as stable electron-conductive layers with large light-absorptivities in solution-processable applications of organic electronics. [Copyright &y& Elsevier]

[Display omitted] • Development of two new naphthalene diimide-based n -type conjugated copolymers. • Studied the effects of conjugated side chains on optoelectronic properties. • Very high absorption coefficient induced by conjugated side chains. • Weak morphological effect because of the large size of naphthalene diimide moiety. Two poly(naphthalene diimide)s (PNDIs) have been developed using p -phenylene ethynylene-based comonomers with either thiophene side chains (P(NDI-BT)) or bithiophene side chains (P(NDI-BBT)), and the effects of the length of conjugated side chains on electrochemical, optical, and morphological properties were investigated. Both polymers showed additional vibronic peaks due to the interchain π-π* transition, and a high absorption coefficient (α) of the order of 105 cm−1 was observed. P(NDI-BBT) gave higher α with narrower optical energy band gaps and lower lying the lowest unoccupied molecular orbital (LUMO) energy levels compared to those in P(NDI-BT). Interestingly, lower crystallinity was observed in P(NDI-BBT) than P(NDI-BT), which is the opposite of trends shown for reported polymers with conjugated side chains. Their charge carrier mobilities and photovoltaic properties were also investigated, and provide insight of designing NDI based n -type polymer semiconductors with conjugated side chians. [ABSTRACT FROM AUTHOR]

In this work we report on fully operational sub-micrometric low voltage OFETs by using graphene as the source-drain electrodes pair and a high- κ ultra-thin dielectric in a local gate architecture. The impact of the graphene electrodes on the miniaturization of the organic devices has been assessed, with particular attention to the influence of the contact resistances as well as the parasitic overlap gate capacitance on the device bandwidth. By the use of a modified Transmission-Line-Method, contact resistances have been analyzed as function of the applied voltages, revealing characteristic functional trends that follow the doping state of graphene electrodes. Through impedance spectroscopy of the electrodes, cut-off frequencies as high as 105 Hz have been estimated, highlighting the peculiar role of quantum capacitance of graphene in such architectures. • Short channel, local gate n-type organic transistors with graphene electrodes are demonstrated. • The impact of the graphene on the miniaturization of the devices has been assessed. • Contact resistances have been analyzed by the Modified Transmission Line method. • Impedance spectroscopy highlighted the quantum capacitance contribution of graphene. • Cut-off frequencies as high as 100 kHz are obtained for 200 nm channels. [ABSTRACT FROM AUTHOR]

Compared to inorganic semiconductors and/or fullerene derivatives, nonfullerene n‐type organic semiconductors present some advantages, such as low‐temperature processing, flexibility, and molecule structure diversity, and have been widely used in perovskite solar cells (PSCs). In this research news article, the recent advances in nonfullerene n‐type organic semiconductors which function as electron‐transporting, interface‐modifying, additive, and light‐harvesting materials in PSCs are summarized. The remaining challenges and promising future directions of nonfullerene‐based PSCs are also discussed. [ABSTRACT FROM AUTHOR]

Efficient synthesis of silicon phthalocyanines (SiPc) eliminating the strenuous reaction conditions and hazardous reagents required by classical methods is described. Implementation into organic thin-film transistors (OTFTs) affords average electron field-effect mobility of 3.1 × 10−3 cm2 V−1 s−1 and threshold voltage of 25.6 V for all synthetic routes. These results demonstrate that our novel chemistry can lead to high performing SiPc-based n-type OTFTs. [ABSTRACT FROM AUTHOR]

The control over aggregation pathways is a key requirement for present and future technologies, as it can provide access to a variety of sophisticated structures with unique functional properties. In this work, we demonstrate an unprecedented control over the supramolecular self-assembly of a semiconductive material, based on a naphthalenediimide core functionalized with phenyl-thiophene moieties at the imide termini, by trapping the molecules into different arrangements depending on the crystallization conditions. The control of the solvent evaporation rate enables the growth of highly elaborated hierarchical self-assembled structures: either in an energy-minimum thermodynamic state when the solvent is slowly evaporated forming needle-shaped crystals (polymorph α) or in a local energy-minimum state when the solvent is rapidly evaporated leading to the formation of nanofibers (polymorph β). The exceptional persistence of the kinetically trapped β form allowed the study and comparison of its characteristics with that of the stable α form, revealing the importance of molecular aggregation geometry in functional properties. Intriguingly, we found that compared to the thermodynamically stable α phase, characterized by a J-type aggregation, the β phase exhibits (i) an unusual strong blue shift of the emission from the charge-transfer state responsible for the solid-state luminescent enhancement, (ii) a higher work function with a "rigid shift" of the electronic levels, as shown by Kelvin probe force microscopy and cyclic voltammetry measurements, and (iii) a superior field-effect transistor mobility in agreement with an H-type aggregation as indicated by X-ray analysis and theoretical calculations.

Planar backbone, locked conformation, and low lowest unoccupied molecular orbital level provide polymer F4 BDOPV-2T with ultrahigh electron mobilities of up to 14.9 cm(2) V(-1) s(-1) and good air stability. It is found that the nonlinear transfer curves can be tuned to near-ideal ones by changing fabrication conditions, indicating that film morphology largely contributes to the nonlinear transfer curves in high-mobility conjugated polymers., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The furan-thiophene-based quinoidal organic semiconductor, TFT-CN, is designed and synthesized. TFT-CN displays a high electron mobility of 7.7 cm(2) V(-1) s(-1) , two orders of magnitude higher than the corresponding thiophene-based derivative., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A strong, electron-deficient small molecule, F4 -BDOPV, has a lowest unoccupied molecular orbital (LUMO) level down to -4.44 eV and exhibits cofacial packing in single crystals. These features provide F4 -BDOPV with good ambient stability and large charge-transfer integrals for electrons, leading to a high electron mobility of up to 12.6 cm(2) V(-1) s(-1) in air., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A series of thiophene-diketopyrrolopyrrole-based quinoidal small molecules (TDPPQ-2-TDPPQ-5) bearing branched alkyl chains with different side-chain lengths and varied branching positions are synthesized. Field-effect transistor (FET) measurement combined with thin-film characterization is utilized to systematically probe the influence of the side-chain length and branching position on the film microstructure, molecular packing, and, hence, charge-transport property. All of these TDPPQ derivatives show air-stable n-channel transporting behavior in spin-coated FET devices, which exhibit no significant decrease in mobility even after being stored in air for 2 months. Most notably, TDPPQ-3 exhibits an outstanding n-channel semiconducting property with electron mobilities up to 0.72 cm(2) V(-1) s(-1), which is an unprecedented value for spin-coated DPP-based n-type semiconducting small molecules. A balance of high crystallinity, satisfactory thickness uniformity and continuity, and strong intermolecular interaction accounts for the superior charge-transport characteristics of TDPPQ-3 films. Our study demonstrates that tuning the length and branching position of alkyl side chains of semiconducting molecules is a powerful strategy for achieving high FET performance.

Arylene linkers in a series of new tetraaza-benzodifluoranthene diimide dimers enable tuning of the 3D molecular structure of nonfullerene electron acceptors, facilitating observation of dramatic variation of the power conversion efficiency from 2.6% to 6.4% as the twist angle between the monomeric building blocks in the dimer is varied., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)