Showing papers on "Pentacene published in 2017"
TL;DR: The ultrafast charge transfer and long-lived charge-separated state in pentacene-MoS2 p-n heterojunctions suggest significant promise for mixed-dimensional van der Waals heterostructures in photovoltaics, photodetectors, and related optoelectronic technologies.
Abstract: van der Waals heterojunctions between two-dimensional (2D) layered materials and nanomaterials of different dimensions present unique opportunities for gate-tunable optoelectronic devices. Mixed-dimensional p–n heterojunction diodes, such as p-type pentacene (0D) and n-type monolayer MoS2 (2D), are especially interesting for photovoltaic applications where the absorption cross-section and charge transfer processes can be tailored by rational selection from the vast library of organic molecules and 2D materials. Here, we study the kinetics of excited carriers in pentacene–MoS2 p–n type-II heterojunctions by transient absorption spectroscopy. These measurements show that the dissociation of MoS2 excitons occurs by hole transfer to pentacene on the time scale of 6.7 ps. In addition, the charge-separated state lives for 5.1 ns, up to an order of magnitude longer than the recombination lifetimes from previously reported 2D material heterojunctions. By studying the fractional amplitudes of the MoS2 decay proces...
180 citations
TL;DR: The use of time-resolved optical and electron paramagnetic resonance spectroscopy is used to probe singlet fission in a pentacene dimer linked by a non-conjugated spacer and a single kinetic model is developed that describes the data over seven temporal orders of magnitude both at room and cryogenic temperatures.
Abstract: When molecular dimers, crystalline films or molecular aggregates absorb a photon to produce a singlet exciton, spin-allowed singlet fission may produce two triplet excitons that can be used to generate two electron-hole pairs, leading to a predicted ∼50% enhancement in maximum solar cell performance The singlet fission mechanism is still not well understood Here we report on the use of time-resolved optical and electron paramagnetic resonance spectroscopy to probe singlet fission in a pentacene dimer linked by a non-conjugated spacer We observe the key intermediates in the singlet fission process, including the formation and decay of a quintet state that precedes formation of the pentacene triplet excitons Using these combined data, we develop a single kinetic model that describes the data over seven temporal orders of magnitude both at room and cryogenic temperatures
169 citations
TL;DR: After a comprehensive analysis on the morphology and electrical properties of the organic films, it is revealed that the ultrahigh performance is largely related to the film charge transport ability, which was less concerned in the studies previously.
Abstract: Organic semiconductor gas sensor is one of the promising candidates of room temperature operated gas sensors with high selectivity. However, for a long time the performance of organic semiconductor sensors, especially for the detection of oxidizing gases, is far behind that of the traditional metal oxide gas sensors. Although intensive attempts have been made to address the problem, the performance and the understanding of the sensing mechanism are still far from sufficient. Herein, an ultrasensitive organic semiconductor NO2 sensor based on 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-petacene) is reported. The device achieves a sensitivity over 1000%/ppm and fast response/recovery, together with a low limit of detection (LOD) of 20 ppb, all of which reach the level of metal oxide sensors. After a comprehensive analysis on the morphology and electrical properties of the organic films, it is revealed that the ultrahigh performance is largely related to the film charge transport ability, which was less concerned in the studies previously. And the combination of efficient charge transport and low original charge carrier concentration is demonstrated to be an effective access to obtain high performance organic semiconductor gas sensors.
162 citations
TL;DR: It is shown that electron transfer to the cluster occurs efficiently from an individual T1 in pentacene but not from the tightly bound 1(TT) state, which might be necessary for the efficient harvesting of triplets from intramolecular singlet fission.
Abstract: Singlet fission, the conversion of a singlet exciton (S1) to two triplets (2 × T1), may increase the solar energy conversion efficiency beyond the Shockley-Queisser limit. This process is believed to involve the correlated triplet pair state 1(TT). Despite extensive research, the nature of the 1(TT) state and its spectroscopic signature remain actively debated. We use an end-connected pentacene dimer (BP0) as a model system and show evidence for a tightly bound 1(TT) state. It is characterized in the near-infrared (IR) region (~1.0 eV) by a distinct excited-state absorption (ESA) spectral feature, which closely resembles that of the S1 state; both show vibronic progressions of the aromatic ring breathing mode. We assign these near-IR spectra to 1(TT)→Sn and S1→Sn′ transitions; Sn and Sn′ likely come from the antisymmetric and symmetric linear combinations, respectively, of the S2 state localized on each pentacene unit in the dimer molecule. The 1(TT)→Sn transition is an indicator of the intertriplet electronic coupling strength, because inserting a phenylene spacer or twisting the dihedral angle between the two pentacene chromophores decreases the intertriplet electronic coupling and diminishes this ESA peak. In addition to spectroscopic signature, the tightly bound 1(TT) state also shows chemical reactivity that is distinctively different from that of an individual T1 state. Using an electron-accepting iron oxide molecular cluster [Fe8O4] linked to the pentacene or pentacene dimer (BP0), we show that electron transfer to the cluster occurs efficiently from an individual T1 in pentacene but not from the tightly bound 1(TT) state. Thus, reducing intertriplet electronic coupling in 1(TT) via molecular design might be necessary for the efficient harvesting of triplets from intramolecular singlet fission.
115 citations
TL;DR: This study presents a comprehensive analysis of the phenomenon of charge transfer promoted by a dielectric interlayer with a comparative study of pentacene adsorbed on Ag(001) with and without an ultrathin MgO interlayer.
Abstract: It is becoming accepted that ultrathin dielectric layers on metals are not merely passive decoupling layers, but can actively influence orbital energy level alignment and charge transfer at interfaces. As such, they can be important in applications ranging from catalysis to organic electronics. However, the details at the molecular level are still under debate. In this study, we present a comprehensive analysis of the phenomenon of charge transfer promoted by a dielectric interlayer with a comparative study of pentacene adsorbed on Ag(001) with and without an ultrathin MgO interlayer. Using scanning tunneling microscopy and photoemission tomography supported by density functional theory, we are able to identify the orbitals involved and quantify the degree of charge transfer in both cases. Fractional charge transfer occurs for pentacene adsorbed on Ag(001), while the presence of the ultrathin MgO interlayer promotes integer charge transfer with the lowest unoccupied molecular orbital transforming into a s...
82 citations
TL;DR: The improvement in graphene phototransistor performances is dominated by the efficient electron-hole pair dissociation due to interfacial built-in field rather than bulk absorption, which opens new possibilities for high-performance graphene-based optoelectronics.
Abstract: Interfacing light-sensitive semiconductors with graphene can afford high-gain phototransistors by the multiplication effect of carriers in the semiconductor layer. So far, most devices consist of one semiconductor light-absorbing layer, where the lack of internal built-in field can strongly reduce the quantum efficiency and bandwidth. Here, we demonstrate a much improved graphene phototransistor performances using an epitaxial organic heterostructure composed of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) and pentacene as the light-absorbing layer. Compared with single light-absorbing material, the responsivity and response time can be simultaneously improved by 1 and 2 orders of magnitude over a broad band of 400–700 nm, under otherwise the same experimental conditions. As a result, the external quantum efficiency increases by over 800 times. Furthermore, the response time of the heterostructured phototransistor is highly gate-tunable down to sub-30 μs, which is among the fastest in the sensiti...
79 citations
TL;DR: The outstanding performance of pentacene‐based molecules in molecular electronics, as well as the predicted enhanced semiconducting properties of extended acenes, have stimulated the development of new synthetic methods and functionalization strategies for the preparation of stable and soluble acenes larger than tetracene with the aim of obtaining improved functional materials.
68 citations
TL;DR: It is demonstrated that poly(amic acid) (PAA), a facilely deposited and annealing-free dielectric layer, can tailor the growth of organic semiconductor films with large area and high crystallinity toward efficient charge transport and high mobility in their thin film transistors.
Abstract: Efficient charge transport in organic semiconductors is essential for construction of high performance optoelectronic devices. Herein, for the first time, we demonstrate that poly(amic acid) (PAA), a facilely deposited and annealing-free dielectric layer, can tailor the growth of organic semiconductor films with large area and high crystallinity toward efficient charge transport and high mobility in their thin film transistors. Pentacene is used as a model system to demonstrate the concept with mobility up to 30.6 cm2 V–1 s–1, comparable to its high quality single crystal devices. The structure of PAA has corrugations with OH groups pointing out of the surface, and the presence of an amide bond further allows adjacent polymer strands to interact via hydrogen bonding, leading to a self-rippled surface perpendicular to the corrugation. On the other hand, the strong polar groups (−COOH/–CONH) of PAA could provide repulsive forces between PAA and pentacene, which results in the vertical orientation of pentace...
68 citations
TL;DR: The synergistic effects of charge trapping in the discontinuous P13 and the charge‐trapping property of the poly(4‐vinylphenol) (PVP) layer remarkably improve the memory performance.
Abstract: Nonvolatile organic field-effect transistor (OFET) memory devices based on pentacene/N,N′-ditridecylperylene-3,4,9,10-tetracarboxylic diimide (P13)/pentacene trilayer organic heterostructures have been proposed. The discontinuous n-type P13 embedded in p-type pentacene layers can not only provide electrons in the semiconductor layer that facilitates electron trapping process; it also works as charge trapping sites, which is attributed to the quantum well-like pentacene/P13/pentacene organic heterostructures. The synergistic effects of charge trapping in the discontinuous P13 and the charge-trapping property of the poly(4-vinylphenol) (PVP) layer remarkably improve the memory performance. In addition, the trilayer organic heterostructures have also been successfully applied to multilevel and flexible nonvolatile memory devices. The results provide a novel design strategy to achieve high-performance nonvolatile OFET memory devices and allow potential applications for different combinations of various organic semiconductor materials in OFET memory.
67 citations
TL;DR: In this paper, the properties of six recently synthesized rubrene derivatives (with substitutions on the side phenyl rings) were examined and compared to known singlet fission materials [tetracene, pentacene, 5,12-diphenyltetricene (DPT), and rubrene itself].
Abstract: We examine the properties of six recently synthesized rubrene derivatives (with substitutions on the side phenyl rings) that show vastly different crystal structures. In order to understand how packing in the solid state affects the excited states and couplings relevant for singlet fission, the lowest excited singlet (S1), triplet (T1), multiexciton (TT), and charge-transfer (CT) states of the rubrene derivatives are compared to known singlet fission materials [tetracene, pentacene, 5,12-diphenyltetracene (DPT), and rubrene itself]. While a small difference of less than 0.2 eV is calculated for the S1 and TT energies, a range of 0.50 to 1.2 eV in the CT energies and nearly 3 orders of magnitude in the electronic couplings are computed for the rubrene derivatives in their crystalline packings, which strongly affects the role of the CT state in facilitating SF. To rationalize experimental observations of singlet fission occurring in amorphous phases of rubrene, DPT, and tetracene, we use molecular dynamics ...
58 citations
TL;DR: In this paper, the integration of a thin layer of an organic polymer (pentacene) on a quartz crystal microbalance (QCM) used for pollutant detection at room temperature was reported.
Abstract: In this work we report the results concerning the integration of a thin layer of an organic polymer (pentacene) on a quartz crystal microbalance (QCM) used for pollutant detection at room temperature. Volatile organic compounds (VOC) are one of the major air pollutants. They are directly involved in the photochemistry of the ozone layer and can affect human health. Exposure to VOC may happen in indoor or outdoor environments, both for short or longer period of time in domestic or working conditions. Among VOCs, mono aromatic compounds such as benzene, toluene or xylenes (often referred as BTX) have carcinogenic, narcotic and neurotoxic properties. Thin films of pentacene were obtained by thermal physical vapor deposition both on transducers and silicon substrates. Structural and morphological characterizations by FTIR and AFM analysis confirm analogy between layered material before and after BTX exposition. QCM was chosen as a transducer due to the kind of interactions involved between material and the target gases. The device was exposed to BTX both in dry and wet conditions. The measurements results where compared also with those collected during the exposure toward humidity and ethanol. A clear discrimination between the different analytes was found.
TL;DR: "dragging mode" electrohydrodynamic jet printing that can simultaneously achieve direct writing and aligning of 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-PEN) crystals is reported and the feasibility of controlling pattern shapes of the crystals as well as the fabrication of printed flexible OFET arrays is demonstrated.
Abstract: Patterning and aligning of organic small-molecule semiconductor crystals over large areas is an important issue for their commercialization and practical device applications. This Letter reports “dragging mode” electrohydrodynamic jet printing that can simultaneously achieve direct writing and aligning of 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-PEN) crystals. Dragging mode provides favorable conditions for crystal growth with efficient controls over supply voltages and nozzle-to-substrate distances. Optimal printing speed produces millimeter-long TIPS-PEN crystals with unidirectional alignment along the printing direction. These crystals are highly crystalline with a uniform packing structure that favors lateral charge transport. Organic field-effect transistors (OFETs) based on the optimally printed TIPS-PEN crystals exhibit high field-effect mobilities up to 1.65 cm2/(V·s). We also demonstrate the feasibility of controlling pattern shapes of the crystals as well as the fabrication of printed ...
TL;DR: In this paper, a theoretical model based on dielectrophoresis is developed to guide the selection of the optimal conditions (frequency and amplitude) of the electric field applied through the solution-shearing blade during coating of OSC thin films.
Abstract: Recent improvements in solution-coated organic semiconductors (OSCs) evidence their high potential for cost-efficient organic electronics and sensors. Molecular packing structure determines the charge transport property of molecular solids. However, it remains challenging to control the molecular packing structure for a given OSC. Here, the application of alternating electric fields is reported to fine-tune the crystal packing of OSC solution-shearing coated at ambient conditions. First, a theoretical model based on dielectrophoresis is developed to guide the selection of the optimal conditions (frequency and amplitude) of the electric field applied through the solution-shearing blade during coating of OSC thin films. Next, electric field-induced polymorphism is demonstrated for OSCs with both herringbone and 2D brick-wall packing motifs in 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene and 6,13-bis(triisopropylsilylethynyl) pentacene, respectively. Favorable molecular packing can be accessible in some cases, resulting in higher charge carrier mobilities. This work provides a new approach to tune the properties of solution-coated OSCs in functional devices for high-performance printed electronics.
TL;DR: In this paper, the potential of black phosphorene (BP) as a platform to fabricate two-dimensional crystals through van der Waals epitaxy of organic molecules was revealed.
Abstract: Phosphorene, a monolayer of elemental phosphorus, has emerged as the most important 2D atomic crystal post graphene. As a consequence of its suitable direct band gap, it has high carrier mobility, thereby making it suitable for potential applications in nanoelectronic devices. In this article, we have performed molecular dynamics simulations for the first time to unveil the potential of black phosphorene (BP) as a platform to fabricate two-dimensional crystals through van der Waals epitaxy of organic molecules. Eight molecules (benzene, 1,3,5-trimethylbenzene, 1,3,5-trifluorobenzene, 1,3,5-trihydroxybenzene, 7,7′,8,8′-tetracyanoquinodimethane (TCNQ), pentacene, coronene, and fullerene) of various size, shape, and polarity are shown to form highly periodic 2D monolayers on BP. We show that self-assembly proceeds through a hierarchy of steps, beginning with adsorption on the surface followed by interplay between the kinetic energy and intermolecular interactions. Crystalline 2D layers are obtained through t...
TL;DR: High quality organic single crystals are adopted instead of polycrystalline films to construct a pentacene/MoS2 p-n vdWHs, which show a much higher current density and better anti-ambipolar characteristics and a mechanism of a gate bias modulated vertical space charge zone existing at the vertical p- n vd WHs interface is proposed.
Abstract: Recently, van der Waals heterostructures (vdWHs) have trigged intensive interest due to their novel electronic and optoelectronic properties. The vdWHs could be achieved by stacking two dimensional layered materials (2DLMs) on top of another and vertically kept by van der Waals forces. Furthermore, organic semiconductors are also known to interact via van der Waals forces, which offer an alternative for the fabrication of organic–inorganic p–n vdWHs. However, the performances of organic–inorganic p–n vdWHs produced so far are rather poor, owing to the unmatched electrical property between the 2DLMs and organic polycrystalline films. To make improvements in such novel heterostructure architectures, here we adopt high quality organic single crystals instead of polycrystalline films to construct a pentacene/MoS2 p–n vdWH. The vdWHs show a much higher current density and better anti-ambipolar characteristics with a highest transconductance of 211 nS. Moreover, device configuration-dependent transfer characteristics are demonstrated and a mechanism of a gate bias modulated vertical space charge zone existing at the vertical p–n vdWHs interface is proposed. These findings provide a new route to optimize the organic–inorganic p–n vdWHs and a guideline for studying the intrinsic properties of vdWHs.
TL;DR: The valence-band structures of single-crystal pentacene and the temperature dependence of their energy-momentum dispersion relations are successfully demonstrated using angle-resolved ultraviolet photoelectron spectroscopy (ARUPS).
Abstract: The electronic structures of the highest occupied molecular orbital (HOMO) or the HOMO-derived valence bands dominate the transport nature of positive charge carriers (holes) in organic semiconductors. In the present study, the valence-band structures of single-crystal pentacene and the temperature dependence of their energy-momentum dispersion relations are successfully demonstrated using angle-resolved ultraviolet photoelectron spectroscopy (ARUPS). For the shallowest valence band, the intermolecular transfer integral and effective mass of the holes are evaluated as 43.1 meV and 3.43 times the electron rest mass, respectively, at room temperature along the crystallographic direction for which the widest energy dispersion is expected. The temperature dependence of the ARUPS results reveals that the transfer integral values (hole effective mass) are enhanced (reduced) by ∼20% on cooling the sample to 110 K.
TL;DR: In this paper, the authors evaluate the validity of the commonly assumed polaron hopping model for some of the most popular organic semiconductors, rubrene, pentacene, and C60.
Abstract: We evaluate the validity of the commonly assumed polaron hopping model for some of the most popular organic semiconductors, rubrene, pentacene, and C60. This model is based on the assumption that the charge carrier is localized, i.e., forms a polaron that hops from one molecule to the next. We have calculated the relevant intermolecular charge transfer parameters that determine whether a polaron forms or not: electronic coupling matrix element and reorganization energy for the above materials using quantum chemical calculations and molecular dynamics simulations. We find that neither for rubrene nor pentancene the hopping model is justified due to the relatively large electronic couplings between molecules in the respective herringbone layers. For C60 the coupling matrix elements are smaller, and a small but finite barrier for charge transport exists in any transport direction. Despite the theoretical problems surrounding the polaron transport model, we find that mobilities based on this model (as obtaine...
TL;DR: In this paper, a set of pentacene-based organic field effect transistor (OFET) memory devices using different thicknesses (ranging from 17.8 to 100.4nm) of poly (N-vinylcarbazole) (PVK) as charge trapping layers were fabricated, and the dependences of thickness on charge trapping behaviors were systematically investigated.
TL;DR: A nonacyclic aromatic hydrocarbon 9,19‐dihydrodinaphtho[3,2,1‐de:3′,2′,1′‐op]pentacene, tethered with four 4‐hexylphenyl solubilizing groups is reported, achieving good power conversion efficiencies in DSCs.
Abstract: Continuous studies on the use of a polycyclic aromatic hydrocarbon as the central block of an organic photosensitizer have brought forth a new opportunity toward efficiency enhancement of dye-sensitized solar cells (DSCs). In this paper, a nonacyclic aromatic hydrocarbon 9,19-dihydrodinaphtho[3,2,1-de:3',2',1'-op]pentacene, tethered with four 4-hexylphenyl solubilizing groups is reported. The novel chromophore 9,9-19-19-tetrakis(4-hexylphenyl)-9,19-dihydrodinaphtho[3,2,1-de:3',2',1'-op]pentacene is further functionalized with diarylamines and 4-(7-ethynylbenzo[c][1,2,5]thiadiazol-4-yl)benzoic acid to produce two donor-acceptor (D-A) organic photosensitizers, achieving good power conversion efficiencies up to 10.2% in DSCs.
TL;DR: The correlations between the molecular vibrations of the complex and the oscillations in the electron-transfer character of its lowest excited state point to vibration-induced coherences between the (pentacene-based) local-excitation (LE) state and the complex charge-transfer (CT) state.
Abstract: We characterize the dynamic nature of the lowest excited state in a pentacene/C60 complex on the femtosecond time scale, via a combination of ab initio molecular dynamics and time-dependent density functional theory. We analyze the correlations between the molecular vibrations of the complex and the oscillations in the electron-transfer character of its lowest excited state, which point to vibration-induced coherences between the (pentacene-based) local-excitation (LE) state and the complex charge-transfer (CT) state. We discuss the implications of our results on this model system for the exciton-dissociation process in organic solar cells.
TL;DR: In this article, a multi-level nonvolatile organic transistor-based memory using pentacene semiconductor and a lithium-ion-encapsulated fullerene (Li + @C 60 ) as a charge trapping layer was reported.
TL;DR: In this paper, high quality graphene synthesized directly from sustainable carbon source (M. alternifolia oil) was used as electrode and pentacene/C60 as active layers in carbon-based RRAM.
TL;DR: In this article, a superhydrophobic micropillar flow-coating (SMFC) was used to obtain uniform and homogenous organic single-crystalline arrays with controlled crystal packing, thickness and position.
Abstract: A convenient and controlled organic semiconductor alignment strategy, superhydrophobic micropillar flow-coating (SMFC), is presented. Patterned, large-area (>1 cm2) 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) single-crystalline arrays which show hole mobilities up to 6.8 cm2 V−1 s−1 were obtained via this method. Crucially, the polymorphism of TIPS-pentacene was regulated by tuning the flow rate, solvent and the substrate hydrophobicity. These results indicate that this technique is reliable for creating uniform and homogenous organic single-crystalline arrays with controlled crystal packing, thickness, and position.
TL;DR: The synthesis and characterization of bistetracene derivatives that exhibit a band gap up to 1.71 eV and an increased stability up to 21 times compared to TIPS-PEN are presented and could give rise to organic semiconductors with interesting properties.
Abstract: The benchmark of soluble organic semiconductors based on acenes is the 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS–PEN). However TIPS–PEN still suffers from photoinduced oxidation due to its low degree of aromaticity. Increasing the aromaticity while keeping similar optical and electrochemical properties as well as a shape suitable for good hole transport can be achieved with two-dimensional polycyclic aromatic hydrocarbons (2D-PAHs). Herein, we present an efficient synthesis and characterization of bistetracene derivatives that exhibit a band gap up to 1.71 eV and an increased stability up to 21 times compared to TIPS–PEN and mobility over 0.1 cm2 V−1 s−1 in solution-processed organic field-effect transistors. Based on simple structural consideration, the high stability is attributed to the aromaticity of the bistetracene which is comparable to an anthrancene along each tetracene. According to Clar's sextet rule, the bistetracene should be best regarded as two anthracenes fused at the face bridged by two ethylenic spacers. The synthesis path paves the way towards the preparation of ambipolar and/or longer 2D-PAHs such as bispentacenes and could give rise to organic semiconductors with interesting properties.
TL;DR: Notably, distinct temporal changes of DNTT thin films on SiO2 and the SAM-treated dielectric substrates are observed, which exhibit a pronounced dewetting and island formation on time scales of minutes to hours, even under ambient conditions, leading to a breakup of the initially closed wetting layer.
Abstract: The novel organic semiconductor dinaphthothienothiophene (DNTT) has gained considerable interest because its large charge carrier mobility and distinct chemical robustness enable the fabrication of organic field effect transistors with remarkable long-term stability under ambient conditions. Structural aspects of DNTT films and their control, however, remain so far largely unexplored. Interestingly, the crystalline structure of DNTT is rather similar to that of the prototypical pentacene, for which the molecular orientation in crystalline thin films can be controlled by means of interface-mediated growth. Combining atomic force microscopy, near-edge X-ray absorption fine structure, photoelectron emission microscopy, and X-ray diffraction, we compare substrate-mediated control of molecular orientation, morphology, and wetting behavior of DNTT films on the prototypical substrates SiO2 and graphene as well as technologically relevant dielectric surfaces (SiO2 and metal oxides that were pretreated with self-a...
TL;DR: In this paper, density functional theory computations are performed to investigate the charge transfer and electrostatic potential modulation upon the adsorption of pentacene molecule on the surface of MoS2 monolayer (ML).
Abstract: Molecular doping of monolayer MoS2 provides a great opportunity to modulate its electronic properties for the potential applications in high performance devices. Density functional theory computations are performed to investigate the charge transfer and electrostatic potential modulation upon the adsorption of pentacene molecule on the surface of MoS2 monolayer (ML). Theoretical calculations indicate that interfacial charge transfer is negligible between pentacene and 2H-MoS2 ML while significant in the pentacene/1T-MoS2 ML complex, which is attributed to the match of energy levels near the Fermi level in the latter case. Moreover, molecular doping of pentacene induces substantial structure changes of the substrate resulting in large adsorption energy, which helps stabilize the 1T-MoS2 ML. Depending on different substrate phases and doping configurations, the interfacial dipole barrier and related work function of MoS2 ML may be modulated in a wide range of the order of about 1 eV. The findings therefore shed light on the possibility of developing the desired organic/inorganic complex for electrical and optoelectronic devices by molecular doping via charge transfer modulation and interface engineering.
TL;DR: The ALD VOx is found to contain a high density of defect states starting from 0.67 eV below the Fermi level, and the energy level of these defect states is in excellent alignment with the HOMO level of pentacene, which allows these VOx defect states to provide an efficient hole-injection pathway at the contact interface.
Abstract: Ultrathin atomic-layer-deposited (ALD) vanadium oxide (VOx) interlayer has recently been demonstrated for remarkably reducing the contact resistance in organic electronic devices (Adv. Funct. Mater. 2016, 26, 4456). Herein, we present an in situ photoelectron spectroscopy investigation (including X-ray and ultraviolet photoelectron spectroscopies) of ALD VOx grown on pentacene to understand the role of the ALD VOx interlayer for the improved contact resistance. The in situ photoelectron spectroscopy characterizations allow us to monitor the ALD growth process of VOx and trace the evolutions of the work function, pentacene HOMO level, and VOx defect states during the growth. The initial VOx growth is found to be partially delayed on pentacene in the first ∼20 ALD cycles. The underneath pentacene layer is largely intact after ALD. The ALD VOx is found to contain a high density of defect states starting from 0.67 eV below the Fermi level, and the energy level of these defect states is in excellent alignment ...
TL;DR: In this paper, an organic field effect transistor (OFET) based gas sensor using polyvinyl alcohol (PVA) as a gas accumulation layer was fabricated, and the results showed that the percentage responses of saturation current (Ion) was 50.3% under 0.5 ppm NH3, which is over one order of magnitude higher than that of pure PMMA dielectric.
Abstract: Ammonia (NH3) gas sensors based on organic field-effect transistor (OFET) using poly(vinyl alcohol) (PVA) as a gas accumulation layer were fabricated. The results showed the percentage responses of saturation current (Ion) was 50.3% under 0.5 ppm NH3, which is over one order of magnitude higher than that of pure PMMA dielectric. Also, it showed that there was a remarkable shift in the field-effect mobility after exposed to NH3 gas. Moreover, the percentage responses of Ion would increase to 66.9% and 30.2% under 0.5 ppm and 0.2 ppm NH3 after applied a gate voltage pulse, respectively. The sensing properties of these OFET gas sensors can realize absorption and desorption with opposite gate bias, exhibiting non-volatile states of Ion and VT under the programming-erasing bias as used for memory elements. By analyzing the morphologies of dielectric and organic semiconductor, and the electrical characteristics of OFET sensors, the interaction between NH3 and PVA will be strengthened under the influence of the applied electrical field on the hydroxyl dipoles. The bias-induced re-orientation of the hydroxyl dipoles can modulate the influence of NH3 on the trapping (absorption) and detrapping (desorption) processes of charge carriers at the pentacene/PVA interface.
TL;DR: Crystalline dioctyl-3,4,9,10-perylenedicarboximide nanowires and 6,13-bis pentacene microplates are integrated into a vertical-yet-open asymmetrical heterojunction for the realization of a high-performance organic photovoltaic detector, which shows fast photoresponse, ultrahigh signal-to-noise ratio, and high sensitivity to weak light.
Abstract: Crystalline dioctyl-3,4,9,10-perylenedicarboximide nanowires and 6,13-bis(triisopropylsilylethynyl) pentacene microplates are integrated into a vertical-yet-open asymmetrical heterojunction for the realization of a high-performance organic photovoltaic detector, which shows fast photoresponse, ultrahigh signal-to-noise ratio, and high sensitivity to weak light.