Showing papers on "Pentacene published in 2022"

High-performance five-ring-fused organic semiconductors for field-effect transistors.

Abstract: Organic molecular semiconductors have been paid great attention due to their advantages of low-temperature processability, low fabrication cost, good flexibility, and excellent electronic properties. As a typical example of five-ring-fused organic semiconductors, a single crystal of pentacene shows a high mobility of up to 40 cm2 V-1 s-1, indicating its potential application in organic electronics. However, the photo- and optical instabilities of pentacene make it unsuitable for commercial applications. But, molecular engineering, for both the five-ring-fused building block and side chains, has been performed to improve the stability of materials as well as maintain high mobility. Here, several groups (thiophenes, pyrroles, furans, etc.) are introduced to design and replace one or more benzene rings of pentacene and construct novel five-ring-fused organic semiconductors. In this review article, ∼500 five-ring-fused organic prototype molecules and their derivatives are summarized to provide a general understanding of this catalogue material for application in organic field-effect transistors. The results indicate that many five-ring-fused organic semiconductors can achieve high mobilities of more than 1 cm2 V-1 s-1, and a hole mobility of up to 18.9 cm2 V-1 s-1 can be obtained, while an electron mobility of 27.8 cm2 V-1 s-1 can be achieved in five-ring-fused organic semiconductors. The HOMO-LUMO levels, the synthesis process, the molecular packing, and the side-chain engineering of five-ring-fused organic semiconductors are analyzed. The current problems, conclusions, and perspectives are also provided.

Azulene-Fused Acenes.

Abstract: Non-alternant non-benzenoid π-conjugated polycyclic hydrocarbons (PHs) are expected to exhibit very different electronic properties from the all-benzenoid PHs. Herein, we report the synthesis and physical properties of three azulene-fused acene molecules ( 1 , 2 and 3 ), which are isoelectronic to the pentacene, hexacene and heptacene, respectively. X-ray crystallographic analysis, NMR spectra, and theoretical calculations reveal a localised aromatic backbone comprising of all the six- and five-membered rings while the seven-membered ring remains non-aromatic. They display properties of both azulene and acenes and are much more stable than the respective acenes. The dications of 1 , 2 and 3 were formed by chemical oxidation. Notably, 3 2+ exhibited an open-shell diradical character (y 0 = 30.2%) as confirmed by variable-temperature NMR and ESR measurements, which can be explained by recovery of aromaticity of an 2,6-anthraquinodimethane unit annulated with two aromatic tropylium rings.

Linear Nonalternant Isomers of Acenes Fusing Multiple Azulene Units.

Abstract: A modular approach to azulene building blocks was developed starting from readily available aryl-substituted cyclopentadiene and ortho -haloaryl aldehyde by dehydration condensation followed by palladium-catalyzed C-H coupling. It facilitates the synthesis of four nonalternant isomers of pentacene and hexacene, namely, dibenzo[ e , g ]azulene, benzo[1,2- f :5,4- f' ]diazulene, benzo[1,2- f :4,5- f' ]diazulene, and naphtho[2,3- f :6,7- f' ]diazulene, which exhibit narrow bandgaps with high stability in addition to protonation-caused enhanced near-infrared fluorescence. We discovered that in these isomers, (i) constitutional isomerism influences significantly their photoelectric properties and (ii) the elongation of the conjugation system does not necessarily lead to a narrowing in the bandgap. Due to the easy modifiability of the nonazulene building blocks, this strategy can be extended to modularly prepare numerous multiazulene-fused aromatics.

Molecular Engineering of Sulfur-Bridged Polycyclic Emitters Towards Tunable TADF and RTP Electroluminescence.

Abstract: Highly efficient organic thermally activated delayed fluorescence (TADF) and room-temperature phosphorescence (RTP) emitters for organic light-emitting diodes (OLEDs) generally consist of a twisted donor-acceptor skeleton with aromatic amine donors. Herein, through introducing sulfur atoms into isomeric pentaphene and pentacene frameworks, we demonstrate a set of polycyclic luminophores exhibiting efficient TADF and RTP characters. The incorporation of sulfur atoms confirms a folded molecular plane, while intensifies singlet-triplet spin-orbit coupling. Further, the isomeric effect has a significant effect on the electronic structure of excited state, giving rise to the investigated compounds tunable luminescence mechanisms of TADF and RTP. With efficient triplet harvesting ability, maximum external quantum efficiencies up to 25.1% and 8.7% are achieved for the corresponding TADF and RTP OLEDs, verifying the great potential of sulfur-bridged frameworks for highly efficient devices.

Singlet Fission and Triplet Pair Recombination in Bipentacenes with a Twist

Abstract: We investigate triplet pair dynamics in pentacene dimers that have varying degrees of coplanarity (pentacene-pentacene twist angle). The fine-tuning of the twist angle was achieved by alternating connectivity at the 1-position or 2-positions of pentacene. This mix-and-match connectivity leads to tunable twist angles between the two covalently linked pentacenes. These twisted dimers allow us to investigate the subtle effects that the dihedral angle between the covalently linked pentacenes imparts on singlet fission and triplet pair recombination dynamics. We observe that as the dihedral angle between the two bonded pentacenes is increased, the rates of singlet fission decrease, while the accompanying decrease in triplet recombination rates is stark. Temperature-dependent transient optical studies combined with theoretical calculations show that the triplet pair recombination proceeds primarily through a direct multiexciton internal conversion process. Calculations further show that the significant decrease in recombination rates can be directly attributed to a corresponding decrease in the magnitude of the nonadiabatic coupling between the singlet multiexcitonic state and the ground state. These results highlight the importance of the twist angle in designing systems that exhibit rapid singlet fission, while maintaining long triplet pair lifetimes in pentacene dimers.

Singlet fission and triplet pair recombination in bipentacenes with a twist

Abstract: We investigate triplet pair dynamics in pentacene dimers that have varying degrees of coplanarity (pentacene-pentacene twist angle). The fine-tuning of the twist angle was achieved by alternating connectivity at the 1-position or 2-positions of pentacene. This mix-and-match connectivity leads to tunable twist angles between the two covalently linked pentacenes. These twisted dimers allow us to investigate the subtle effects that the dihedral angle between the covalently linked pentacenes imparts on singlet fission and triplet pair recombination dynamics. We observe that as the dihedral angle between the two bonded pentacenes is increased, the rates of singlet fission decrease, while the accompanying decrease in triplet recombination rates is stark. Temperature-dependent transient optical studies combined with theoretical calculations show that the triplet pair recombination proceeds primarily through a direct multiexciton internal conversion process. Calculations further show that the significant decrease in recombination rates can be directly attributed to a corresponding decrease in the magnitude of the nonadiabatic coupling between the singlet multiexcitonic state and the ground state. These results highlight the importance of the twist angle in designing systems that exhibit rapid singlet fission, while maintaining long triplet pair lifetimes in pentacene dimers.

Multifunctional Flexible Organic Transistors with a High-k/Natural Protein Bilayer Gate Dielectric for Circuit and Sensing Applications

Abstract: Organic field-effect transistors (OFETs) have opened up new possibilities as key elements for skinlike intelligent systems, due to the capability of possessing multiple functionalities. Here, multifunctional OFET devices based on gelatin, a natural biopolymer gate dielectric, and TIPS-pentacene as an organic semiconductor are extensively explored. Gelatin is combined with a thin high-k HfO2 dielectric layer deposited by atomic layer deposition (ALD) to achieve a low leakage current and low-voltage operation. The natural biopolymer offers a better semiconductor:dielectric interface, leading to better charge conduction in the devices, along with an enhancement of sensing capabilities giving additional functionality. These fabricated flexible OFET devices exhibit excellent electrical characteristics with a high field-effect mobility reaching over 2 cm2/(V s) (extracted with Ci at 1 kHz), a low subthreshold swing (SS) of ∼200 mV/dec, and a high current on–off (Ion/Ioff) ratio at a low operating voltage of −5 V with excellent electrical and mechanical stability. Moreover, circuit and multiparameter sensing capabilities for visible and UV light, as well as for humidity and breath rate, have been successfully demonstrated for these devices. Our results indicate that these multifunctional OFET devices can open up a plethora of opportunities for practical applications such as real-time health and environmental monitoring.

Organic Field‐Effect Transistors Based on Ternary Blends Including a Fluorinated Polymer for Achieving Enhanced Device Stability

Abstract: The stability of organic semiconductors (OSCs) is strongly hampered by the presence of water molecules. One approach that has been proved to lead to organic field‐effect transistors with an enhanced performance is the use of blends of OSCs with insulating binding polymers. In this work, the fabrication of OSC thin films based on polymeric ternary blends including a hydrophobic fluorinated polymer is reported as a novel route to engineer long‐term reliable organic field‐effect transistors (OFET) devices. In particular, OFETs based on blends of bis(triisopropylsilylethynyl)pentacene (TIPS) with polystyrene (PS) and poly(pentafluorostyrene) (PFS) are explored. The PS:PFS ratio is tuned in order to find the optimum formulation. It is shown that films including 20% of PFS in the polymeric blend exhibit an improved device performance, which is reflected by a low bias stress and an exceptional environmental stability, without significantly hampering the OFET mobility. This work advocates that adding a small percentage of fluorinated polymers in OSC blends is a promising route to realize more reliable and stable devices without importantly compromising the device mobility.

Review of the Common Deposition Methods of Thin-Film Pentacene, Its Derivatives, and Their Performance

Abstract: Pentacene is a well-known conjugated organic molecule with high mobility and a sensitive photo response. It is widely used in electronic devices, such as in organic thin-film transistors (OTFTs), organic light-emitting diodes (OLEDs), photodetectors, and smart sensors. With the development of flexible and wearable electronics, the deposition of good-quality pentacene films in large-scale organic electronics at the industrial level has drawn more research attention. Several methods are used to deposit pentacene thin films. The thermal evaporation technique is the most frequently used method for depositing thin films, as it has low contamination rates and a well-controlled deposition rate. Solution-processable methods such as spin coating, dip coating, and inkjet printing have also been widely studied because they enable large-scale deposition and low-cost fabrication of devices. This review summarizes the deposition principles and control parameters of each deposition method for pentacene and its derivatives. Each method is discussed in terms of experimentation and theory. Based on film quality and device performance, the review also provides a comparison of each method to provide recommendations for specific device applications.

High‐Performance Pentacene‐Based Field‐Effect Transistor Memory Using the Electrets of Polymer Blends

Abstract: Organic field‐effect transistor (OFET) memory based on pentacene has attracted a lot of attentions due to its promising prospect of application in flexible electronics, while the high programming/erasing (P/E) gate voltages due to the existence of hole barrier at pentacene/polymer interface leaves great challenges for its commercial applications. A high‐performance pentacene‐based OFET nonvolatile memory (ONVM) with polymer blends is reported here as the charge‐trapping layer containing poly(2‐vinyl naphthalene) (PVN) and poly{[N,N'‐bis(2‐octyldodecyl)naphthalene‐1,4,5,8‐bis(dicarboximide)‐2,6‐diyl]‐alt‐5,5'‐(2,2'‐bithiophene)} (N2200). The presence of N2200, an n‐type semiconductor, in blends significantly improves the memory performance of pentacene‐based memory devices based on the static‐electric effect. The electrons in N2200 are aggregated near the pentacene/polymer interface due to the electric attraction from the positively charged defects in pentacene. Furthermore, those electrons reduce the height of hole barrier and produce local easy‐transportation paths for holes between pentacene and PVN, which enables the electret‐based ONVM device with low P/E voltages, fast P/E speeds, large mobility and stable multilevel data‐storage ability in ambient air.

Quantifying Exciton Transport in Singlet Fission Diblock Copolymers.

Abstract: Singlet fission (SF) is a mechanism of exciton multiplication in organic chromophores, which has potential to drive highly efficient optoelectronic devices. Creating effective device architectures that operate by SF critically depends on electronic interactions across multiple length scales─from individual molecules to interchromophore interactions that facilitate multiexciton dephasing and exciton diffusion toward donor-acceptor interfaces. Therefore, it is imperative to understand the underpinnings of multiexciton transport and interfacial energy transfer in multichromophore systems. Interestingly, block copolymers (BCPs) can be designed to control multiscale interactions by tailoring the nature of the building blocks, yet SF dynamics are not well understood in these macromolecules. Here, we designed diblock copolymers comprising an inherent energy cleft at the interface between a block with pendent pentacene chromophores and an additional block with pendent tetracene chromophores. The singlet and triplet energy offset between the two blocks creates a driving force for exciton transport along the BCP chain in dilute solution. Using time-resolved optical spectroscopy, we have quantified the yields of key energy transfer steps, including both singlet and triplet energy transfer processes across the pentacene-tetracene interface. From this modular BCP architecture, we correlate the energy transfer time scales and relative yields with the length of each block. The ability to quantify these energy transfer processes provides valuable insights into exciton transport at critical length scales between bulk crystalline systems and small-molecule dimers─an area that has been underexplored.

X‐ray Detectors With Ultrahigh Sensitivity Employing High Performance Transistors Based on a Fully Organic Small Molecule Semiconductor/Polymer Blend Active Layer

Abstract: The implementation of organic semiconductor (OSC) materials in X‐ray detectors provides exciting new opportunities for developing a new generation of biocompatible devices with high potential for the fabrication of sensitive and low‐cost X‐ray imaging systems. Here, the fabrication of high performance organic field‐effect transistors (OFETs) based on blends of 1,4,8,11‐tetramethyl‐6,13‐triethylsilylethynyl pentacene (TMTES) with polystyrene is reported. The films are printed employing a low cost and high‐throughput deposition technique. The devices exhibit excellent electrical characteristics with a high mobility and low density of hole traps, which is ascribed to the favorable herringbone packing (different from most pentacene derivatives) and the vertical phase separation in the blend films. As a consequence, an exceptional high sensitivity of (4.10 ± 0.05) × 1010 µC Gy–1cm–3 for X‐ray detection is achieved, which is the highest reported so far for a direct X‐ray detector based on a tissue equivalent full organic active layer, and is higher than most perovskite film‐based X‐ray detectors. As a proof of concept to demonstrate the high potential of these devices, an X‐ray image with sub‐millimeter pixel size is recorded employing a 4‐pixel array. This work highlights the potential exploitation of high performance OFETs for future innovative large‐area and highly sensitive X‐ray detectors for medical dosimetry and diagnostic applications.

Ultrafast orbital tomography of a pentacene film using time-resolved momentum microscopy at a FEL

Abstract: Abstract Time-resolved momentum microscopy provides insight into the ultrafast interplay between structural and electronic dynamics. Here we extend orbital tomography into the time domain in combination with time-resolved momentum microscopy at a free-electron laser (FEL) to follow transient photoelectron momentum maps of excited states of a bilayer pentacene film on Ag(110). We use optical pump and FEL probe pulses by keeping FEL source conditions to minimize space charge effects and radiation damage. From the momentum microscopy signal, we obtain time-dependent momentum maps of the excited-state dynamics of both pentacene layers separately. In a combined experimental and theoretical study, we interpret the observed signal for the bottom layer as resulting from the charge redistribution between the molecule and the substrate induced by excitation. We identify that the dynamics of the top pentacene layer resembles excited-state molecular dynamics.

Integrated, Stretched, and Adiabatic Solid Effects.

Abstract: This paper presents a theory describing the dynamic nuclear polarization (DNP) process associated with an arbitrary frequency swept microwave pulse. The theory is utilized to explain the integrated solid effect (ISE) as well as the newly discovered stretched solid effect (SSE) and adiabatic solid effect (ASE). It is verified with experiments performed at 9.4 GHz (0.34 T) on single crystals of naphthalene doped with pentacene-d14. It is shown that the SSE and ASE can be more efficient than the ISE. Furthermore, the theory predicts that the efficiency of the SSE improves at high magnetic fields, where the EPR line width is small compared to the nuclear Larmor frequency. In addition, we show that the ISE, SSE, and ASE are based on similar physical principles and we suggest definitions to distinguish among them.

Exciton Dynamics in MoS2-Pentacene and WSe2-Pentacene Heterojunctions

Abstract: We measured the exciton dynamics in van der Waals heterojunctions of transition metal dichalcogenides (TMDCs) and organic semiconductors (OSs). TMDCs and OSs are semiconducting materials with rich and highly diverse optical and electronic properties. Their heterostructures, exhibiting van der Waals bonding at their interfaces, can be utilized in the field of optoelectronics and photovoltaics. Two types of heterojunctions, MoS2-pentacene and WSe2-pentacene, were prepared by layer transfer of 20 nm pentacene thin films as well as MoS2 and WSe2 monolayer crystals onto Au surfaces. The samples were studied by means of transient absorption spectroscopy in the reflectance mode. We found that A-exciton decay by hole transfer from MoS2 to pentacene occurs with a characteristic time of 21 ± 3 ps. This is slow compared to previously reported hole transfer times of 6.7 ps in MoS2-pentacene junctions formed by vapor deposition of pentacene molecules onto MoS2 on SiO2. The B-exciton decay in WSe2 shows faster hole transfer rates for WSe2-pentacene heterojunctions, with a characteristic time of 7 ± 1 ps. The A-exciton in WSe2 also decays faster due to the presence of a pentacene overlayer; however, fitting the decay traces did not allow for the unambiguous assignment of the associated decay time. Our work provides important insights into excitonic dynamics in the growing field of TMDC-OS heterojunctions.

Accurate Polarization-Resolved Absorption Spectra of Organic Semiconductor Thin Films Using First-Principles Quantum-Chemical Methods: Pentacene as a Case Study.

Abstract: Theoretical studies using clusters as model systems have been extremely successful in explaining various photophysical phenomena in organic semiconductor (OSC) thin films. But they have not been able to satisfactorily simulate total and polarization-resolved absorption spectra of OSCs so far. In this work, we demonstrate that accurate spectra are predicted by time-dependent density functional theory (TD-DFT) when the employed cluster reflects the symmetry of the crystal structure and all monomers feel the same environment. Additionally, long-range corrected optimal tuned functionals are mandatory. For pentacene thin films, the computed electronic spectra for thin films then reach an impressive accuracy compared with experimental data with a deviation of less than 0.1 eV. This allows for accurate peak assignments and mechanistic studies, which paves the way for a comprehensive understanding of OSCs using an affordable and easy-to-use cluster approach.

Orbital-resolved observation of singlet fission

Abstract: Singlet fission1-13 may boost photovoltaic efficiency14-16 by transforming a singlet exciton into two triplet excitons and thereby doubling the number of excited charge carriers. The primary step of singlet fission is the ultrafast creation of the correlated triplet pair17. Whereas several mechanisms have been proposed to explain this step, none has emerged as a consensus. The challenge lies in tracking the transient excitonic states. Here we use time- and angle-resolved photoemission spectroscopy to observe the primary step of singlet fission in crystalline pentacene. Our results indicate a charge-transfer mediated mechanism with a hybridization of Frenkel and charge-transfer states in the lowest bright singlet exciton. We gained intimate knowledge about the localization and the orbital character of the exciton wave functions recorded in momentum maps. This allowed us to directly compare the localization of singlet and bitriplet excitons and decompose energetically overlapping states on the basis of their orbital character. Orbital- and localization-resolved many-body dynamics promise deep insights into the mechanics governing molecular systems18-20 and topological materials21-23.

Low-power flexible organic memristor based on PEDOT:PSS/pentacene heterojunction for artificial synapse

Abstract: Organic synaptic memristors are of considerable interest owing to their attractive characteristics and potential applications to flexible neuromorphic electronics. In this work, an organic type-II heterojunction consisting of poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT:PSS) and pentacene was adopted for low-voltage and flexible memristors. The conjugated polymer PEDOT:PSS serves as the flexible resistive switching (RS) layer, while the thin pentacene layer plays the role of barrier adjustment. This heterojunction enabled the memristor device to be triggered with low-energy RS operations (V < ± 1.0 V and I < 9.0 μA), and simultaneously providing high mechanical bending stability (bending radius of ≈2.5 mm, bending times = 1,000). Various synaptic properties have been successfully mimicked. Moreover, the memristors presented good potentiation/depression stability with a low cycle-to-cycle variation (CCV) of less than 8%. The artificial neural network consisting of this flexible memristor exhibited a high accuracy of 89.0% for the learning with MNIST data sets, even after 1,000 tests of 2.5% stress-strain. This study paves the way for developing low-power and flexible synaptic devices utilizing organic heterojunctions.

Nanoconfinement of an Otherwise Useless Fluorophore in Metal–Organic Frameworks to Elicit and Tune Emission

Abstract: The rational design of the assembly of fluorophores is highly important for the fabrication of advanced nanomaterials. Here we report the encapsulation of pentacene (PNT) in the nanochannels of metal–organic frameworks (MOFs) as a powerful method to maximize properties of the fluorophore. Despite the nonemissive property of the bulk PNT, the nanoconfinement of PNT in MOFs drastically enhanced the luminescence, which enabled the precise tuning of the emission band approaching to the near-infrared region. The luminescence of PNT was obviously changed concomitant with the adsorption of additional guests, which is beneficial to use the nanocomposites as a vapor sensor. Moreover, we demonstrated that the confined PNT exhibited exceptional stability (>100×) toward heat, in comparison with that in solution. The strong and intrinsic low-energy emission of long acenes together with the porous features of MOFs prompts the application of the MOF/acene hybrids targeting lighting devices, smart sensors, and in vivo imaging.

Tandem Desulfurization/C-C Coupling Reaction of Tetrathienylbenzenes on Cu(111): Synthesis of Pentacene and an Exotic Ladder Polymer.

Abstract: Surface-confined reactions represent a powerful approach for the precise synthesis of low-dimensional organic materials. A complete understanding of the pathways of surface reactions would enable the rational synthesis of a wide range of molecules and polymers. Here, we report different reaction pathways of tetrathienylbenzene (T1TB) and its extended congener tetrakis(dithienyl)benzene (T2TB) on Cu(111), investigated using scanning tunneling microscopy, X-ray photoelectron spectroscopy, and density functional theory calculations. Both T1TB and T2TB undergo desulfurization when deposited on Cu(111) at room temperature. Deposition of T1TB at 453 K yields pentacene through desulfurization, hydrogen transfer, and a cascade of intramolecular cyclization. In contrast, for T2TB the intramolecular cyclization stops at anthracene and the following intermolecular C-C coupling produces a conjugated ladder polymer. We show that tandem desulfurization/C-C coupling provides an adjustable reaction pathway for growing carbon-based nanostructures on metal surfaces.

Excited-State Dynamics of 5,14- vs 6,13-Bis(trialkylsilylethynyl)-Substituted Pentacenes: Implications for Singlet Fission

Abstract: Singlet fission is a process in conjugated organic materials that has the potential to considerably improve the performance of devices in many applications, including solar energy conversion. In any application involving singlet fission, efficient triplet harvesting is essential. At present, not much is known about molecular packing arrangements detrimental to singlet fission. In this work, we report a molecular packing arrangement in crystalline films of 5,14-bis(triisopropylsilylethynyl)-substituted pentacene, specifically a local (pairwise) packing arrangement, responsible for complete quenching of triplet pairs generated via singlet fission. We first demonstrate that the energetic condition necessary for singlet fission is satisfied in amorphous films of the 5,14-substituted pentacene derivative. However, while triplet pairs form highly efficiently in the amorphous films, only a modest yield of independent triplets is observed. In crystalline films, triplet pairs also form highly efficiently, although independent triplets are not observed because triplet pairs decay rapidly and are quenched completely. We assign the quenching to a rapid nonadiabatic transition directly to the ground state. Detrimental quenching is observed in crystalline films of two additional 5,14-bis(trialkylsilylethynyl)-substituted pentacenes with either ethyl or isobutyl substituents. Developing a better understanding of the losses identified in this work, and associated molecular packing, may benefit overcoming losses in solids of other singlet fission materials.

Interface-Driven Assembly of Pentacene/MoS2 Lateral Heterostructures

Abstract: Mixed-dimensional van der Waals heterostructures formed by molecular assemblies and 2D materials provide a novel platform for fundamental nanoscience and future nanoelectronics applications. Here we investigate a prototypical hybrid heterostructure between pentacene molecules and 2D MoS2 nanocrystals, deposited on Au(111) by combining pulsed laser deposition and organic molecular beam epitaxy. The obtained structures were investigated in situ by scanning tunneling microscopy and spectroscopy and analyzed theoretically by density functional theory calculations. Our results show the formation of atomically thin pentacene/MoS2 lateral heterostructures on the Au substrate. The most stable pentacene adsorption site corresponds to MoS2 terminations, where the molecules self-assemble parallel to the direction of MoS2 edges. The density of states changes sharply across the pentacene/MoS2 interface, indicating a weak interfacial coupling, which leaves the electronic signature of MoS2 edge states unaltered. This work unveils the self-organization of abrupt mixed-dimensional lateral heterostructures, opening to hybrid devices based on organic/inorganic one-dimensional junctions.

Modulating Singlet Fission by Scanning through Vibronic Resonances in Pentacene-Based Blends.

Abstract: Vibronic coupling has been proposed to play a decisive role in promoting ultrafast singlet fission (SF), the conversion of a singlet exciton into two triplet excitons. Its inherent complexity is challenging to explore, both from a theoretical and an experimental point of view, due to the variety of potentially relevant vibrational modes. Here, we report a study on blends of the prototypical SF chromophore pentacene in which we engineer the polarizability of the molecular environment to scan the energy of the excited singlet state (S1) continuously over a narrow energy range, covering vibrational sublevels of the triplet-pair state (1(TT)). Using femtosecond transient absorption spectroscopy, we probe the dependence of the SF rate on energetic resonance between vibronic states and, by comparison with simulation, identify vibrational modes near 1150 cm-1 as key in facilitating ultrafast SF in pentacene.

Ultrafast and Sensitive Self‐Powered Photodetector Based on Graphene/Pentacene Single Crystal Heterostructure with Weak Light Detection Capacity

Abstract: Organic materials exhibit efficient light absorption and low‐temperature, large‐scale processability, and have stimulated enormous research efforts for next‐generation optoelectronics. While, high‐performance organic devices with fast speed and high responsivity still face intractable challenges, due to their intrinsic limitations including finite carrier mobility and high exciton binding energy. Here an ultrafast and highly sensitive broadband phototransistor is demonstrated by integrating high‐quality pentacene single crystal with monolayer graphene. Encouragingly, the −3 dB bandwidth can reach up to 26 kHz, which is a record‐speed for such sensitized organic phototransistors. Enormous absorption, long exciton diffusion length of pentacene crystal, and efficient interfacial charge transfer enable a high responsivity of >105 A W−1 and specific detectivity of >1011 Jones. Moreover, self‐powered weak‐light detection is realized using a simple asymmetric configuration, and the obvious zero‐bias photoresponses can be displayed even under 750 nW cm−2 light intensity. Excellent response speed and photoresponsivity enable high‐speed image sensor capability in UV‐Vis ranges. The results offer a practical strategy for constructing high‐performance self‐powered organic hybrid photodetectors, with strong applicability in wireless, weak‐light detection, and video‐frame‐rate imaging applications.