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Abstract The quantification of the lowest unoccupied molecular orbital level (LUMO) for molecular semiconductors is of great importance, because it determines the charge transport process and hence the performances of diverse electronic devices. Unfortunately, there is always lack of a convenient technique to determine the intrinsic LUMO. This work provides a reliable electrical spectroscopy by employing an easy-operating hot electron transistor, to make an accurate measurement. By taking advantage of a novel method, named the first derivative-assisted linear fitting method, the determination of the intrinsic LUMO becomes more scientific. Here, four kinds of molecular semiconductors are selected as the research objects and the values can be precisely decided even with a quite small difference in LUMO, which demonstrate the universality and the accuracy of our method. As expected, all the measured values are highly repeatable and it further confirms that we have provided a practical technique for the LUMO detection.

The quantification of the lowest unoccupied molecular orbital level (LUMO) for molecular semiconductors is of great importance, because it determines the charge transport process and hence the performances of diverse electronic devices. Unfortunately, there is always lack of a convenient technique to determine the intrinsic LUMO. This work provides a reliable electrical spectroscopy by employing an easy-operating hot electron transistor, to make an accurate measurement. By taking advantage of a novel method, named the first derivative-assisted linear fitting method, the determination of the intrinsic LUMO becomes more scientific. Here, four kinds of molecular semiconductors are selected as the research objects and the values can be precisely decided even with a quite small difference in LUMO, which demonstrate the universality and the accuracy of our method. As expected, all the measured values are highly repeatable and it further confirms that we have provided a practical technique for the LUMO detection. [ABSTRACT FROM AUTHOR]

Abstract A precise quantification of energy gap for a molecular semiconductor is crucial. However, there has always been a lack of a suitable method which results in an inaccurate measurement. In this research, a three-terminal vertical structure (Al/AlO X /Au/ molecular semiconductor/Al), named hot electron transistor has been designed to be the most powerful method for energy gap determination. By analysing the IC-hot–VEB curves, the electron injected barrier and hole injected barrier can be extracted. In combination of the both, the energy gap of four objects, including PBDB-T-2Cl, C60, PTCDA, and Alq3, has been determined finally.

A precise quantification of energy gap for a molecular semiconductor is crucial. However, there has always been a lack of a suitable method which results in an inaccurate measurement. In this research, a three-terminal vertical structure (Al/AlOX/Au/ molecular semiconductor/Al), named hot electron transistor has been designed to be the most powerful method for energy gap determination. By analysing the IC-hot–VEB curves, the electron injected barrier and hole injected barrier can be extracted. In combination of the both, the energy gap of four objects, including PBDB-T-2Cl, C60, PTCDA, and Alq3, has been determined finally. [ABSTRACT FROM AUTHOR]

Combining a transition metal dichalcogenide monolayer (ML) and molecular semiconductors is an attractive route for forming nanoscale hybrid van der Waals heterostructures with potentially novel (opto‐)electronic properties. The energy level alignment at the hybrid interface governs these properties, but precise determination of the interfacial electronic structure is challenging due to the pronounced excitonic nature of both components and the non‐trivial band structure of the inorganic ML. For instance, dielectric screening by the supporting substrate of such a heterostructure may impact the energy levels, but very few experiments have attended to this important issue to date. Here, it is shown how photoelectron spectroscopy can be used to unravel the energy level line‐up at the C60/ML‐WS2 interface supported on an insulating (sapphire) and a semi‐metallic (graphite) substrates. On both substrates, an almost identical staggered type‐II level alignment is determined. However, C60/ML‐WS2 exhibits stronger n‐type characteristics on sapphire, which is suggested to be due to native donor‐type defects of ML‐WS2. While these remain occupied and active on the insulating substrate, they are emptied into the charge reservoir of the conductive substrate. These insights should be considered in the future design of functional heterostructures of inorganic ML and molecular semiconductor materials. [ABSTRACT FROM AUTHOR]

A large database of known molecular semiconductors is used to define a plausible physical limit to the charge carrier mobility achievable within this materials class. From a detailed study of the desirable properties in a large dataset, it is possible to establish whether such properties can be optimized independently and what would be a reasonably achievable optimum for each of them. All relevant parameters are computed from a set of almost five thousand known molecular semiconductors, finding that the best known materials are not ideal with respect to all properties. These parameters in decreasing order of importance are the molecular area, the nonlocal electron–phonon coupling, the 2D nature of transport, the local electron–phonon coupling, and the highest transfer integral. It is also found that the key properties related to the charge transport are either uncorrelated or "constructively" correlated (i.e., they improve together) concluding that a tenfold increase in mobility is within reach in a statistical sense, on the basis of the available data. It is demonstrated that high throughput screenings, when coupled with physical models of transport produce both specific target materials and a more general physical understanding of the materials space. [ABSTRACT FROM AUTHOR]

This work refers to the synthesis and characterization of new (2E, 4Z)-5, 7-diphenylhepta-2, 4-dien-6-ynoic acids. We describe the nucleophilic addition of bis(trimethylsylil)ketene acetals (TMS) to aryl ynones substituted by halogen groups activated by boron trifluoride diethyl etherate (BF3·Et2O) for the stereoselective synthesis of dienynoic acid. The molecular materials were structurally characterized by IR spectroscopy, NMR spectroscopy and X-ray diffraction. After the characterization the synthesized acids were doped with indium(III) phthalocyanine chloride (In(III)PcCl) in order to generate a organic semiconductor that was characterized by UV–Vis spectroscopy to subsequently obtain their optical bandgap (Eg) values. The Eg value was compared to that obtained for the pure state dienynoic acids in order to evaluate the doping effect with the In(III)PcCl. The Eg diminished from values near 2.6 eV obtained for pure compounds to values around 1.4 eV for the same compounds, but now with doping. With the molecular semiconductors obtained were manufactured structures of disperse heterojunction which later were evaluated in their electric behavior. A behaviour ohmic at low voltages and Space Charge Limited Current (SCLC) at higher voltages was observe from the study J(V) carried out. [ABSTRACT FROM AUTHOR]

Organic light-emitting transistors (OLETs) integrate the functions of light-emitting diodes and field-effect transistors into a unique device, opening a new door for optoelectronics. However, there is still a challenge due to the absence of high quality organic semiconductors for OLETs. Herein, we reported a novel molecule 2,6-di(anthracen-2-yl)naphthalene (2,6-DAN), which exhibited mobility of up to 19 cm2·V−1·s−1 and an absolute fluorescence quantum yield of 37.09%, which are good values for organic semiconductors. Moreover, OLETs based on 2,6-DAN single crystals showed bright yellowish-green emission and well-balanced ambipolar charge transport. The excellent ratio of hole to electron mobility can reach up to 0.86, which is superior to most single-component OLETs in typical device configurations reported so far. [ABSTRACT FROM AUTHOR]

Here, the donor-acceptor organic composites of n-type perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) and p-type cobalt phthalocyanine (CoPc) semiconductors are firstly synthesized and optimized for photocatalytic oxygen evolution (POE) as catalyst. The POE rate of 12.30 mmol·g−1·h−1 with the apparent quantum yield of 4.00 % at 475 nm can be achieved under visible light (> 420 nm), as compared with 1.58 mmol.g−1.h−1 of PTCDA. Under the full UV-Vis light (> 320 nm), the rate is up to 17.65 mmol·g−1·h−1. The systematical experiments clearly reveal the generation of dual-channel energy transfer of fluorescence resonance from CoPc to PTCDA and electron transfer from oxygen groups in PTCDA to Co atom in CoPc under UV-Vis light irradiation. Consequently, the formation of Z-scheme p/n heterojunction in CoPc/PTCDA composite greatly enhances the POE performance due to the lifetime increase of metal-ligand charge transfer exciton in CoPc (44.83 vs. 2.95 ps) and perylene cationic exciton (20.13 vs. 2.13 ps). [Display omitted] • Organic donor-acceptor composite is firstly prepared for photocatalytic water oxidation. • Z-scheme p/n heterojunction of PTCDA/CoPc composite forms due to interaction of Co and O atoms. • POE rate increases to 12.30 (> 420 nm) and 17.65 mmol·g−1·h−1 (> 320 nm) from 1.58 mmol·g−1·h−1. • Dual-channel energy transfer of FRET and ET between PTCDA and CoPc is found and confirmed. • Longer exciton lifetime of MLCT (44.83 vs. 2.95 ps) and Pe+ (20.13 vs. 2.13 ps) is obtained. [ABSTRACT FROM AUTHOR]

π-Extended porphyrins represent an attractive class of organic compounds because of their unique photophysical, optoelectronic, and physicochemical properties. Herein, cross-conjugated (Ace-PQ-Ni) and linear-conjugated (AM6) porphyrins are used to build double-layer heterojunction devices by combining them with a lutetium bisphthalocyanine complex (LuPc 2 ). The heterojunction effect at the porphyrin-phthalocyanine interface plays a key role in the charge transport properties. Both devices exhibit exceptionally high ammonia sensitivity at room temperature and under ambient relative humidity, with limit of detection values of 156 and 115 ppb for Ace-PQ-Ni/LuPc 2 and AM6/LuPc 2 sensors, respectively. Interestingly, the Ace-PQ-Ni/LuPc 2 and AM6/LuPc 2 sensors display opposite effects upon light illumination. While the former sensors show largely decreased ammonia sensitivity under light illumination, the current variation of the latter under ammonia is remarkably enhanced with a multiplication factor of 13 and a limit of detection (LOD) of 83 ppb. The striking difference in their sensing properties upon light illumination is attributed to their different π-conjugation pathways (cross-conjugation versus linear conjugation).

An unprecedented molecular polyanionic metal oxide cluster of eleven-Fe III substituted antimoniotungstate Na 27 [Fe 11 (H 2 O) 14 (OH) 2 (W 3 O 10 ) 2 (α-SbW 9 O 33 ) 6 ]·103H 2 O( 1 ) based on earth abundant elements has been successfully synthesized. A careful physical investigation of this molecule reveals that VB=−6.34 eV/CB=−4.39 eV, this unique physical properties ensures that 1 can be defined as a new type of nanoscale molecular semiconductor. This compound showed remarkable catalytic property for light driven H 2 evolution activity. A H 2 evolution rate of 820 μmol h −1 g −1 was achieved in the presence of 1 without adding any co-catalyst at neutral condition, which is a very high rate among all polyoxotungstate photocatalysts reported thus far. Six evidences proved that 1 is a true stable molecular catalyst during the photocatalytic hydrogen evolution. [ABSTRACT FROM AUTHOR]

Modulation of charge transport in an organic heterojunction sensor is a promising strategy to enhance its gas sensing properties. Herein, a heterostructure consisting of a bilayer assembly of perfluorinated copper phthalocyanine and lutetium bis-phthalocyanine is investigated for ammonia sensor development in two different electrode geometries and in a wide range of applied bias. The microstructure of the heterostructure retains the bulk electronic and structural properties of the individual components and shows granular distribution of phthalocyanine crystallites on the surface. The charge transport of the heterojunction devices depends on the electrode geometry and the applied bias. Notably, interfacial charge transport gets faster, while bulk charge transport remains constant with increasing bias in both devices. But, the small gap between the electrodes fastens the bulk and the interfacial charge transport by 75 and 5 times, respectively, compared to the big gap electrodes. The implication of faster charge transport in the small gap electrodes-based sensor is demonstrated on its ammonia sensing properties, exhibiting higher response and shorter response time. Moreover, the response of the sensor exponentially increases with increasing bias. The high sensitivity and stability of the sensor at different relative humidity make it a suitable NH 3 sensor for real environment applications. [Display omitted] • Organic heterojunction sensors for NH 3 detection are realized. • Electrode geometry has strong influence on charge transport and sensor performance. • Smaller gap between electrodes fasten the charge transport in sensors. • Small electrode based sensor displays high NH 3 sensitivity and short response time. • Gas-material interaction mechanism based on adsorption and diffusion is proposed. [ABSTRACT FROM AUTHOR]

Abstract: Elementary arguments are used to show that there is a maximum charge mobility that can be described by sequential hopping between molecules and that this maximum mobility can be expressed in terms of physical quantities that are all experimentally accessible. The evaluation of the maximum hopping mobility with realistic parameters suggests that sequential charge hopping is not the correct transport mechanism for the best molecular materials used for organic transistors. [Copyright &y& Elsevier]

Abstract: A series of new molecular semiconductor-doped insulator (MSDI) heterojunctions as conductimetric transducers to NH3 sensing were fabricated based on a novel semiconducting molecular material, an amphiphilic tris(phthalocyaninato) rare earth triple-decker complex, Eu2[Pc(15C5)4]2[Pc(OC10H21)8], quasi-Langmuir–Shäfer (QLS) film, as a top-layer, and vacuum-deposited and cast film of CuPc as well as copper tetra-tert-butyl phthalocyanine (CuTTBPc) QLS film as a sub-layer, named as MSDIs 1, 2 and 3, respectively. MSDIs 1–3 and respective sub-layers prepared from three different methods were characterized by X-ray diffraction, electronic absorption spectra and current–voltage (I–V) measurements. Depending on the sub-layer film-forming method used, α-phase CuPc film structure, β-phase CuPc crystallites and H-type aggregates of CuTTBPc have been obtained, respectively. An increasing sensitivity to NH3 at varied concentrations in the range of 15–800ppm, follows the order MSDI 2

Abstract: The combination of a sexithiophene and a perylene diimide derivatives, as p-type and n-type materials, respectively, used as sub-layers, to an intrinsic semiconductor, namely the lutetium bisphthalocyanine, allows to obtain a new transducer for gas sensing. These transducers were called molecular semiconductor-doped insulator (MSDI) heterojunctions, were recently designed and reported, but with only phthalocyanines as active materials. p-Type material leads to MSDIs that exhibit a positive response to ozone and a negative response to ammonia, whereas MSDIs prepared from n-type material exhibit a positive response to ammonia and negative response to ozone. The remarkable point is that the only material in contact with the analytes is the lutetium bisphthalocyanine. It means that the inverted responses observed for both p-type and n-type MSDIs come from the modulation of the electronic properties of LuPc2 by the p-type and n-type sub-layers. That study enlarges the potentialities of the MSDIs and opens the way to their promising development in the field of chemical sensors. [Copyright &y& Elsevier]

Abstract: A lithium phthalocyanine radical and the analogous aluminum phthalocyanine radical were synthesized as part of an investigation of isostructural dopants. An improved synthesis of the free base of octa(pentoxy)phthalocyanine (H2Pc*) involves the reduction of 1,2-dicyano-4,5-dipentoxybenzene with hydroquinone. Deprotonation with lithium bis(trimethylsilyl)amide leads to the dilithium derivative Li2Pc* and subsequent oxidation with ferrocenium yields the radical LiPc*. Treatment of H2Pc* with Et2AlCl gives ClAlPc* and reduction with sodium amalgam yields AlPc*, the first reported aluminum phthalocyanine radical. In the solid state LiPc* and AlPc* are electrical conductors with pressed-pellet conductivities of 8×10−11 Ω−1 cm−1 and 5×10−7 Ω−1 cm−1, respectively. [Copyright &y& Elsevier]

The film growth by physical vapour deposition (PVD) and their subsequent conditioning was studied for Chloro[subphthalocyaninato]boron(III) (C24H12N6BCl, “SubPc”) and its perfluorinated derivative Chloro[dodecafluorosubphthalocyaninato]boron(III) (C24F12N6BCl, “F12SubPc”) on a variety of insulating substrates. During preparation in high vacuum the films were characterized in situ by optical absorption spectroscopy (UVvis) and subsequently (ex situ) by atomic force microscopy (AFM) and X-ray diffraction (XRD). Compared to regular phthalocyanines (Pc), these materials showed a decreased intermolecular interaction because of their cone-shaped macrocyclic system. Nevertheless, ordered crystalline growth could be obtained. They therefore represent an example of crystalline molecular layers that already have, however, some characteristics of organic glasses. This may help to overcome the serious problems of grain boundaries dominant in thin Pc films for applications as organic field-effect-transistors (OFET). P-type conduction was indicated for SubPc; n-type conduction is expected for F12SubPc. Perfluorination in phthalocyanines leads to clear n-type characteristics. Implementations for the use of these materials in OFET devices are discussed. [Copyright &y& Elsevier]

Hexane-1,6-diammonium pentaiodobismuth (HDA-BiI5) is one of the narrowest bandgap molecular semiconductor reported in recent years. Through the study of its energy band structure, it can be identified as an N-type semiconductor and is able to absorb most of the visible light, making it suitable to fabricate solar cells. In this paper, SnO2 was used as an electron transport layer in HDA-BiI5-based solar cells, for its higher carrier mobility compared with TiO2, which is the electron transport layer used in previous researches. In addition, the dilution ratio of SnO2 solution has an effect on both the morphology and photophysical properties of HDA-BiI5 films. At the dilution ratio of SnO2:H2O = 3:8, the HDA-BiI5 film has a better morphology and is less defect inside, and the corresponding device exhibited the best photovoltaic performance. [ABSTRACT FROM AUTHOR]

With the development of the semiconductor industry, research on photoelectronic devices has been emphasized. In this paper, a molecular semiconductor material with a narrow bandgap of hexane-1,6-diammonium pentaiodobismuth (HDA-BiI5) was utilized to prepare photodetectors without electron transport layers. Using a single light source, the effects of different wavelengths and different powers on the photoresponsivity, switching ratio, specific detectivity, and external quantum efficiency of the device were investigated. It is demonstrated that this device has excellent responsivity, specific detectivity, stability, and repeatability, and this work will help expand the application of molecular semiconductor materials for photodetection. [ABSTRACT FROM AUTHOR]

Molecular semiconductors, as the core component, determine the performance of different devices. It is essential to gain more knowledge of such materials. Hot electron spectroscopy, by applying a ballistic electron emission microscope and hot-electron transistor, has been demonstrated to be the most powerful method. This review concentrates on the achievements in several emerging fields, such as the interfacial energy level alignment and the charge transport characteristics in molecular film. As a versatile technique, hot electron spectroscopy has been found to be helpful in exploring the metal/molecule interface energy, the molecular levels, the electronic transport gap, and even the group structures. In comparison to the traditional techniques, such as ultraviolet photoemission spectroscopy, inverse photoemission spectroscopy, and scanning tunneling spectroscopy, this method offers in-situ characterizations, which makes the detection much more accurate and convenient. This review contributes to a deep comprehension of the intrinsic characteristics of molecular semiconductors and molecule-based devices. [Display omitted] • Hot electron spectroscopy has recently been employed to determine the intrinsic lowest unoccupied molecular orbital. • Hot electron spectroscopy has been developed to determine the highest occupied molecular orbital. • Hot electron spectroscopy has applied to acquire more informations about molecular levels, such as the LUMO+1 level. • Hot electron spectroscopy provides a powerful approach to achieve a high-efficient spin injection. [ABSTRACT FROM AUTHOR]