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Successful synthesis of glyconanoparticles has attracted much attention due to their various biointeractive capabilities, but it is still a challenge to understand different single-cell responses to exogenous particles among cell populations. Herein, we designed polyaniline-containing galactosylated gold nanoparticles (Au@PGlyco NPs) via in situ polymerization of ortho-nitrophenyl-β-galactoside assisted by Au nucleation. The nanogold-carrying polyaniline block produced electromagnetic enhancement in surface-enhanced Raman scattering (SERS). The underlying polymerization mechanism of ortho-nitrophenyl compounds via the formation of Au nanoparticles was investigated. Depending on how the galactoside moiety reacted with β-galactosidase derived from bacteria, the Au@PGlyco NPs-mediated SERS biosensor could detect low amounts of bacteria (∼1 × 102 CFU/mL). In addition, a high accumulation of Au@PGlyco NPs mediated the immune response of tumor-associated M2 macrophages to the immunogenic M1 macrophage transition, which was elicited by reactive oxygen levels biostimulation using single-cell SERS-combined fluorescence imaging. Our study suggested that Au@PGlyco NPs may serve as a biosensing platform with the labeling capacity on galactose-binding receptors expressed cell and immune regulation.

In this study, the multimode photoresponse (PR) features of low-voltage-driven pentacene-based organic phototransistors (OPTs) are reported by utilizing poly(4-vinylphenol) (PVP)-based gate dielectrics containing spiropyran-merocyanine (SP-MC) photochromic materials. In general, pentacene-based OPTs respond to visible light but cannot sense ultraviolet (UV) light. Incorporating SP-MC molecules provides pentacene-based OPTs with the functions of not only sensing UV light but also exhibiting different response modes to UV and visible light and thus can be used to distinguish UV and visible light sources. When the as-prepared OPTs are exposed to UV light, they can simulate the characteristics of typical paired-pulse facilitation and long-term potentiation properties as observed in photonic synaptic devices. The corresponding UV photovoltaic effects in the as-prepared OPTs are investigated in joint experimental measurements and theoretical calculations. We found large amounts of MC molecules in the prepared PVP:SP blend-based dielectrics in the dark, showing that pentacene-based OPTs have unique PR features in contrast to gate dielectrics that contained only SP. MC is an isoform of SP that is typically triggered by irradiation with UV light. Theoretical calculation results indicate that the MC form has large dipole moment features during photoexcitation and several charge transfer states exist, leading to easy separation of photogenerated charges. By contrast, SP does not have the above characteristics. Accordingly, a unique PR mechanism between UV and visible light of the present OPTs is drawn. Several distinct PR types of the as-prepared pentacene-based OPTs expand the functionality of the devices, enhancing their potential for further diverse applications.

The microstructure-dependent charge capturing and releasing behavior of dielectrics influences the memory characteristics of organic thin-film transistors (OTFTs). We use polyimide (PI) as the char...

Organic thin-film transistors (OTFTs) often exhibit significant nonideal, unstable, and fast decaying electrical characteristics, especially in a moisture-containing ambient air environment, which hinders their practical applications. These characteristics are particularly true for OTFTs based on the widely studied poly(3-hexylthiophene) (P3HT) active layer. This study reports that dynamic operational stability of P3HT-based OTFTs even in ambient air can be achieved through the preparation of a semiconducting/insulating polyblend-based pseudo-bilayer configuration with embedded source and drain electrodes. The pseudo-bilayer active layer with desired phase-separated morphology, which consists of insulating poly(methyl methacrylate)-rich round domains and a highly connected network of conducting P3HT channels, was specifically developed and optimized for OTFTs. The present OTFTs can perform with strong endurance against gate-bias stress even under dynamic continuous operation in ambient air, and thus show unexpected nondecaying current features. We investigated the possible origins behind the excellent operational and environmental stability of the pseudo-bilayer-based OTFTs in terms of atomic force microscopy, electrostatic force microscopy, X-ray diffractometry, absorption spectroscopy, Raman spectroscopy, in situ photoluminescence spectroscopy, and quantum chemical calculations. Finally, a gas-induced electrical response mechanism of polymeric OTFTs at the microscopic level was also proposed on the basis of the charge delocalization variation in the semiconducting component. Thus, insight into the impact of ambient gases on the electrical stability of OTFTs was realized. The results provide insight into the solution for the long-standing electrical stability problem of OTFTs under continuous operation through the development of improved fabrication techniques.

The interfaces between dielectric films and organic semiconductors are used as carrier traps in organic memory devices. The trapping and release capabilities of carriers must be controlled in memory devices. However, the memory windows of these devices are limited by the carriers' erasing capability. In this work, a series of nano-pentacene films were inserted into n-type dioctyl perylene tetracarboxylic diimide (PTCDI-C13) semiconductor layers near the interface of a dielectric film and an organic semiconductor to form field-effect type memory devices with nano-p–n junctions. The presence of nano-p–n junctions near the interface increased minorities (i.e., holes), which could effectively erase accumulated electrons at the interface during erasing. We achieved a maximum memory window of 48.9 V when a 5 nm-thick pentacene film was inserted into the PTCDI-C13 layer and the memory device was operated under a programming process of 90 V and an erasing process of −90 V. Kelvin probe force and noncontact atomic force microscopy were used to investigate the monolayer growth of pentacene and PTCDI-C13 as well as their interface properties. Although the thickness of the pentacene film reached 10 nm, an incomplete layer was formed. This layer supported minorities during erasing and transmitted electrons during programming. A wide memory window was achieved by the nano-p–n heterojunction field-effect memory transistor. This high-performance organic memory device has potential applications in fresh-type memory devices.

Organic thin film transistors (OTFTs) are a promising technology for the application of photosensors in smart wearable devices. Light-induced electrical behavior of OTFTs is explored to achieve diverse functional requirements. In most studies, OTFTs show an increased drain current (ID) under light irradiation. Here, we use an ultraviolet (UV) light absorption top layer, tris(8-hydroxyquinoline) aluminum (Alq3), to improve the UV light response of poly(3-hexylthiophene-2,5-diyl) (P3HT)-based OTFTs. Unexpectedly, the Alq3-covered device operated at the accumulation mode demonstrates a decreased ID during the UV light irradiation. N,N'-Ditridecyl-3,4,9,10-perylene tetracarboxylic diimide (PTCDI, electron acceptor), pentacene (electron donor), and lithium fluoride (LiF, insulator) as an interlayer were inserted between the P3HT and the Alq3 layers. The PTCDI/Alq3-covered device also shows an unusual decrease in ID under the UV light but an increase in ID under the green light. The pentacene/Alq3-covered device shows an increased ID during the UV light irradiation and, unexpectedly, a memory effect in ID after removing the UV light. The LiF/Alq3-covered device exhibits an electrical behavior similar to the bare P3HT-based device under the UV light. Results of spectroscopic analyses and theoretical calculations have shown that the occurrence of charge transfer at heterojunctions during the UV light irradiation causes charge modulation in the multilayered P3HT-based OTFTs and then results in an unusual decrease or memory effect in ID. In addition, the unexpected ID reduction can be observed in the Alq3-covered poly[2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene]-based OTFTs under UV light. The features, including opposite electrical responses to different wavelengths of light and optical memory effect, provide the multilayered P3HT-based OTFTs with potential for various optical applications, such as image recognition devices, optical logic gates, light dosimeters, and optical synapses.

Ferromagnetic semiconductors with structural flexibility are an indispensable feature for future flexible spin-electronic applications. In this case, we introduce magnetic ingredients into an organic semiconductor, namely, pentacene, to form a ferromagnetic organic semiconductor (FOS). The first observation for ferromagnetic Ni-doped pentacene semiconductors at room temperature in the field of semiconductor spintronics is reported in this article. To date, the mechanism of FOSs with ferromagnetism is not understood yet, especially when their Curie temperature is enhanced above room temperature. Here, we demonstrate dopants of Ni atoms and the modulation of the growth temperature in the FOS films to achieve room-temperature ferromagnetic properties in a series of FOS films, one of which has a maximum coercivity of 257.6 Oe. The spin-exchange interaction between a Ni atom and a pentacene molecule is detected through the magnetic hysteresis obtained using a superconducting quantum interference device magnetometer. We verify the effectiveness of this spin coupling through magnetic force microscopy, Raman spectroscopy, scanning Kelvin probe microscopy, and theoretical simulation. A model for the indirect spin coupling between Ni atoms is proposed for the mechanism of room-temperature ferromagnetic ordering of spins due to the exchange force indirectly. We believe that the π-electrons of pentacene molecules at the triple state for this model can support the spin coupling of electrons of Ni atoms. Our findings facilitate the development of brand-new spintronic devices with structural flexibility and room-temperature ferromagnetism.

Efficient and balanced pentacene-based ambipolar organic thin-film transistors (AmOTFTs) were prepared and ready for use to achieve simple fabrication of complementary-like inverters with high gains. We examined the effect of temperature on the electrical characteristics of pentacene-based AmOTFTs and corresponding complementary-like inverters. Such complementary-like inverters can perform nonpolar operations, such as first and third quadrant operations, and can work normally up to nearly 110 °C. In situ measurements demonstrated the excellent thermal stability of pentacene active layer at the corresponding temperatures. The operating principle of the ambipolar-based complementary-like inverters was also discussed. Given the ambipolar nature of pentacene active channel, the dual-carrier recombination and release processes governed the temperature-dependent switch behaviors of the inverters. A temperature-dependent linearity function was derived using the hysteresis switch voltage, thereby highlighting that pentacene-based ambipolar complementary-like inverters could potentially be employed in temperature sensors.

Dual-gate organic thin-film transistors (DG-OTFTs) with enhanced functionality, including large current enhancement behavior, highly efficient threshold voltage controllability, and self-contained dual-mode logic gate features, are reported. These DG-OTFTs are based on a semiconducting/insulating polyblend-based active layer with asymmetric top and bottom charge modulation layers (atb-CMLs). The atb-CMLs are automatically generated through the preparation of multilayer stacks of phase-separated semiconducting poly(3-hexylthiophene) (P3HT):insulating poly(methylmethacrylate) (PMMA) polyblend layer, poly(vinylidene fluoride) (PVDF) layer, and cross-linked-poly(4-vinylphenol) (cPVP) layer. They consist of a thin PMMA bottom layer and an uneven-shaped PMMA:PVDF miscible mixture-based top layer. The presence of the polarizable insulating PMMA, PVDF, and PMMA:PVDF mixture regions causes the bottom and top CMLs to experience electrical polarization, which induces the dipole field to achieve efficient charge modulation functions in DG-OTFTs. Owing to the presence of atb-CMLs, the DG-OTFTs exhibit unprecedented electrical characteristics, such as the easy depletion of the bottom channel by the top gate potential. However, the top channel can work properly only when given a bottom gate potential (either positive or negative). Given these unusual electrical features, the design of the fundamental dual-mode logic gates (e.g., AND and OR gates) can be achieved with just one DG transistor. This finding opens an interesting direction for the preparation of DG-OTFTs with diverse operating modes and increasing functionality, thereby widening the application potential of such transistors.

In organic electronic/photonic devices, numerous types of interfaces and their properties exhibit profound correlation with device performance. For optimizing the performance of organic electronic/photonic devices, appropriate and effective interface engineering needs to be developed. In this study, a high dielectric constant material, hafnium dioxide (HfO2), and an organic semiconductor, N,N′-ditridecyl-3,4,9,10-perylene tetracarboxylic diimide (PTCDI-C13) were adopted as the dielectric and active layers, respectively, to fabricate low-voltage-driven organic thin-film transistors. Three kinds of insulating polymers were selected to serve as buffer layers (BLs) to modify HfO2. After the addition of BLs onto HfO2, the insulating properties of HfO2 and the microstructures of PTCDI-C13 active layers improved, resulting in considerably enhanced electrical characteristics and stability of the devices. Among different polymeric BLs, the BL polymer exhibiting smaller interfacial tension with PTCDI-C13 can induce PTCDI-C13 to form better microstructures and generate lower interfacial trap density despite the rougher topography of polymeric BL, leading to improved electrical characteristics of the corresponding device. However, we observed that BL polymer with larger dipole moment of side groups can yield better electrical stability of the corresponding device under continuous operation compared with polymers with smaller interfacial tension. During long-term operation, the dipoles can be aligned by an electric field and form a strong dipole layer to facilitate charge accumulation and alleviate device degradation caused by bias-stress-induced trap/defect states. We further adopted a BL polymer with both small interfacial tension and large dipole moment to fabricate low-voltage-driven organic complementary inverters. The inverter can exhibit high electrical characteristics and stability during continuous operation. Interfacial tension and molecular dipole moment are possible important issues for effective interface engineering.

Ideal molecular features and microstructural properties of organic semiconducting thin films are being explored to achieve high-performance organic thin-film transistors (OTFTs). We prepared and processed hexamethylbenzene (HMB)/poly(3-hexylthiophene) (P3HT) mixtures using a thermal gradient system to fabricate P3HT-based OTFTs. In the thermal gradient system, the HMB separated from the HMB/P3HT mixtures and crystallized along the sample movement direction. The crystallized HMB affected and guided the growth behavior of P3HT at the molecular level. Observations from joint microscopic and spectroscopic analyses revealed that the HMB-processed P3HT (H-P3HT) thin film possessed anisotropic and improved microstructures, particularly in crystalline domains. The improved molecular features and microstructural properties of the H-P3HT thin film enhanced the intramolecular and intermolecular charge transport by extending the π-conjugation, decreasing the reorganization energy, and strengthening the π–π overlaps. ...

Conducting poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) films have high potential as flexible transparent conductive electrodes in various devices. In this study, two simple robust methanol-based treatment methods, namely, dipping process (DP) and solvent vapor annealing (SVA), were used to improve the electrical conductivity of PEDOT:PSS films in order to make them suitable as electrodes in organic solar cells (OSCs). Then, the characteristics of the methanol-treated PEDOT:PSS films were investigated. After the methanol treatments, the sheet resistance of the PEDOT:PSS films (ca. 100 Ω/Sq) were improved by more than 200 times, and the work function (~5.0 eV) was nearly unchanged in both methods. Two completely different possible origins of the improved conductivity of the methanol-treated PEDOT:PSS films were addressed for DP and SVA approaches. Both methods were suitable for preparing methanol-treated PEDOT:PSS films that can be used as anodes for polymer–fullerene-based OSCs. The photovoltaic performance of the modified PEDOT:PSS-based devices was comparable to that of indium tin oxide (ITO)-based devices, thus demonstrating their practicality. The methanol-treated PEDOT:PSS films show great potential as flexible transparent conductive electrodes for ITO-free and metal-free devices.

Organic thin-film transistor (OTFT) devices with polyimide (PI) layers of various solid contents were fabricated. In OTFT devices, the factor of interface between modification and active layers exhibits profound correlation with electrical stability of devices. To improve the performance of stability of OTFTs during long-term operation, effective interface engineering needs to be utilized. Herein, this study demonstrated the relevance about interface properties and microstructures of N,N′-ditridecyl-3,4,9,10-perylene tetracarboxylic diimide (PTCDI-C 13 H 27 ) grown the PI layers of various solid content. Moreover, the microstructure of PTCDI-C 13 H 27 affects the trap state in the channel, leading to the enhancement of electrical stability of the devices. Consequently, we further adopted an appropriate solid content of PI with smooth surface and lower trap state to fabricate low voltage-driven organic devices.

Upon the tuning of solvent composition, the unfavorable solvation of adsorbed polyhexylthiophene is found able to drive graphene sheets to scroll steadily in solutions, resulting in nanoscrolls with a central void and regular stacking of internal layers. For theses steadily evolved graphene nanoscrolls, the interlayer distance is subject to the average radius of adsorbed molecular coils and the bending rigidity of graphene hexagonal structural units restricts the reachable curvature of central voids. When the unfavorable solvation is progressively lessened upon slow crystallization of adsorbed polyhexylthiophene molecules, the reverse unwrapping ensues accordingly. On the other hand, the solvent evaporation initiates the dense growth of crystalline whiskers outward from graphene nanoscrolls and thus results in comb-like superstructures. With mutual impingement effects associated with present superstructures, oriented assembly and growth behaviors of crystalline whiskers are able to occur, creating nematic fields of crystalline whiskers.

Perovskite microwires have a larger surface-to-volume ratio and better photoelectric conversion efficiency than perovskite films. The degree of crystallization also affects the optoelectrical performances of perovskite microwires. Laser annealing was regarded as a tool for crystallization. High light absorption induced fast heating process. A 405 nm violet laser located near the absorption peak of typical perovskite films was employed as the annealing laser. In an in situ experimental design, the annealing laser beam was combined into the micro Raman measurement system. Real-time information of the annealing and crystallization was provided. Many excellent works were done, and typically needed offline optoelectronic measurements. An mW-level continuous-wave laser beam can provide enough kinetic energy for crystalline in perovskite microwires. The thermal distribution of the perovskite microwire under the annealing laser beams was considered here. Polarized Raman signals can provide evidence of the perovskite microwires crystallization. This work offered the novel approach of an on-site, real-time laser-induced thermal annealing design for perovskite microwires. This approach can be used in other material procedures. Intensity-dependent conditions were crucial for the annealing processes and analyzed in detail. The substrate effect was found. This proposed scheme provided integrated novel, scalable, and highly effective designs of perovskite-based devices.

Low-operating-voltage organic inverters using bilayer cross-linked poly(4-vinylphenol)/Al2O3 dielectrics were fabricated on polyimide substrates. The flexible inverters could be operated at a supply voltage of as low as 2 V and achieve a gain of over 50 at 2 V. The organic inverters exhibited good mechanical and electrical stabilities after 104 times of bending due to the superior microstructural stabilities of the organic semiconductors, as confirmed by in situ 2D grazing incidence X-ray diffraction (GIXRD). Analysis of GIXRD spectra showed that the variation in the width of the diffraction peak was less than 1.5% after different bending times. The proposed inverters maintained stable gains of above 50 after 104 times of bending and had a maximum transition voltage shift of 0.31 V during the bending process. These findings imply that our inverters could be commercially applied to low-voltage flexible electronics.

The power conversion efficiency of solar cells can be optimized via an efficient charge collection by electrodes. In this study, a simple linear polyethylenimine (LPEI), which is an insulating polymer, was adopted as the cathode interfacial layer of poly(3-hexylthiophene) (P3HT):[6,6]-phenyl-C 61 -butyric acid methyl ester (PCBM)-based bulk-heterojunction organic solar cells (OSCs) with a non-inverted configuration. All photovoltaic parameters of the OSCs were significantly enhanced by depositing LPEI onto the oxygen plasma-treated P3HT:PCBM active layers. The causes of performance enhancement in OSCs were studied. Results revealed that the microstructure and morphology of the P3HT:PCBM layer were almost unaffected by the oxygen plasma treatment and the subsequent LPEI deposition. The X-ray photoelectron spectra of the specimens demonstrated that with the aid of oxygen plasma treatment, the linked LPEI molecules formed a well-aligned dipole layer on top of the P3HT:PCBM layer through the bonding of nitrogen (N) with oxygen (O). The results from quantum chemical calculations showed that the LPEI molecule with an N–O bond had a larger dipole moment at an appropriate direction than that without an N–O bond. By contrast, the LPEI molecules can form a dipole layer with a random orientation in the absence of N–O bonds. The conductive atomic force microscopy images of the specimens showed that the well-aligned dipole layer could facilitate electron transfer and could block hole transfer from the P3HT:PCBM to the cathodes. The well-aligned and augmented interface dipoles improved the charge selectivity at the cathodes and the photovoltaic performance of the devices.

A series of polyimides (PIs) containing different weight ratios of polar piperazinyl and cholesterol side chains, denoted as PCPI, was synthesized in this study. These PIs were used as gate dielectrics of n-type organic field-effect transistors (OFETs) and as electrets of photo-assisted organic memories. The thermal properties of the PI/PCPI composite films were improved by increasing the spatial distribution of the PCPI molecules to form a thermally stable dielectric film. The performances of OFETs with PIs used as gate dielectrics, were gradually enhanced by increasing the mixture ratios of the PCPI molecules. A dipole field, which originated from the PCPI molecules into the OFETs, was introduced to observe the special phenomenon of output current growth over a long operation time. The application of these superior transistors with PCPI- and PI-mixed electrets to the field of organic memory resulted in a photo-assisted memory window of more than 38 V. The mechanisms of the carriers trapped in and released from the PI electrets were elucidated. Results showed that our devices possess excellent stability for OFETs and an extra-large memory window for organic memory devices.

A molecular design for the electret material of n-operating organic field-effect transistor-based (OFET) memories is introduced. A large memory window and high operating speed were achieved while the polar groups are connected to the polymer chain of polyimide, which plays the role of electret of a transistor memory device. The phase variation of electrical force microscopy images showed that polarization field induces charge trapping states on the surface of electret layer and accumulates charged carriers within the conducting channel of OFET to achieve high-performance memory and transistor simultaneously. An extra-large memory window was also obtained by introducing photo-induced charge transfer effect.

The temperature-dependent electrical and charge transport characteristics of pentacene-based ambipolar thin-film transistors (TFTs) were investigated at temperatures ranging from 77 K to 300 K. At room temperature (RT), the pentacene-based TFTs exhibit balanced and high charge mobility with electron (μe) and hole (μh) mobilities, both at about 1.6 cm2/V s. However, at lower temperatures, higher switch-on voltage of n-channel operations, almost absent n-channel characteristics, and strong temperature dependence of μe indicated that electrons were more difficult to release from opposite-signed carriers than that of holes. We observed that μe and μh both followed an Arrhenius-type temperature dependence and exhibited two regimes with a transition temperature at approximately 210–230 K. At high temperatures, data were explained by a model in which charge transport was limited by a dual-carrier release and recombination process, which is an electric field-assisted thermal-activated procedure. At T

Conjugated polymer-fullerene-based bulk-heterojunction (BHJ) organic solar cells (OSCs) have attracted tremendous attention over the past two decades because of their potential to develop low-cost and easy methods to produce energy from light. The complicated microstructure and morphology with randomly organized architecture of these polymer-fullerene-based active layers (ALs) is a key factor that limits photovoltaic performance. In this study, a binary-solvent annealing (BSA) approach was established to improve the poly(3-hexylthiophene):indene-C60 bisadduct-based AL for efficient BHJ-type OSCs by varying the second solvents with different boiling points (BP). Thus, we were able to change the evaporation behavior of cosolvents and consequently obtain the various microstructural properties of the AL. An in-depth study was conducted on the solvent-evaporation driven morphology of the active layer under various cosolvent conditions and its effect on the photovoltaic parameters of OSCs. Under the BSA processes, we found that the specimens with low-BP second solvents allows us to observe a more ideal AL for increasing photon absorption and efficient charge transport and collection at the respective electrodes, resulting in enhanced PCE of the corresponding OSCs. By contrast, the specimens with high-BP second solvents exhibit random microstructures, which are detrimental to charge transport and collection and lead to diminished PCE of the corresponding OSCs. By appropriately selecting the composition of a binary solvent, BSA can be employed as an easy method for the effective manipulation of the microstructures of ALs. BSA is a promising technique for the performance enhancement of not only OSCs but also other organic/polymeric-based electronic devices.

We demonstrate semiconducting polymer-based thin-film transistors (PTFTs) with fast switching performance and an uncommon nondecaying feature. These PTFTs based on widely studied poly(3-hexylthiophene) are developed by incorporating the insulating polymer into the active channel and subjecting the compound to specific, spontaneous multiple-scale phase separation (MSPS). An in-depth study is conducted on the interfacial and phase-separated microstructure of the semiconducting/insulating blending active layer and its effect on the electrical characteristics of PTFTs. The polyblends exhibit a confined crystallization behavior with continuously semiconducting crystalline domains between scattered insulator-rich domains. The insulator-rich domains can block leakage current and strengthen the gate control of the channel. A small amount of the insulating polymer penetrates the bottom of the active channel, resulting in effective interface modification. We show specific MSPS morphology of the present blending films to reduce charge trapping effects, enhance charge accumulation, and create a high-seed switching channel. The findings enable us to develop the required morphological conceptual model of the ideal-like field-effect-modulated polymer-based active channel. The polyblend-based PTFTs with MSPS morphology also have promising sensing functions. This study offers an effective approach for overcoming the major drawbacks (instability and poor switching) of PTFTs, thus allowing such transistors to have potential applications.

In the optimization of organic solar cells (OSCs), a key problem lies in the maximization of charge carriers from the active layer to the electrodes. Hence, this study focused on the interfacial molecular configurations in efficient OSC charge extraction by theoretical investigations and experiments, including small molecule-based bilayer-heterojunction (sm-BLHJ) and polymer-based bulk-heterojunction (p-BHJ) OSCs. We first examined a well-defined sm-BLHJ model system of OSC composed of p-type pentacene, an n-type perylene derivative, and a nanogroove-structured poly(3,4-ethylenedioxythiophene) (NS-PEDOT) hole extraction layer. The OSC with NS-PEDOT shows a 230% increment in the short circuit current density compared with that of the conventional planar PEDOT layer. Our theoretical calculations indicated that small variations in the microscopic intermolecular interaction among these interfacial configurations could induce significant differences in charge extraction efficiency. Experimentally, different interfacial configurations were generated between the photo-active layer and the nanostructured charge extraction layer with periodic nanogroove structures. In addition to pentacene, poly(3-hexylthiophene), the most commonly used electron-donor material system in p-BHJ OSCs was also explored in terms of its possible use as a photo-active layer. Local conductive atomic force microscopy was used to measure the nanoscale charge extraction efficiency at different locations within the nanogroove, thus highlighting the importance of interfacial molecular configurations in efficient charge extraction. This study enriches understanding regarding the optimization of the photovoltaic properties of several types of OSCs by conducting appropriate interfacial engineering based on organic/polymer molecular orientations. The ultimate power conversion efficiency beyond at least 15% is highly expected when the best state-of-the-art p-BHJ OSCs are combined with present arguments.

Photovoltaic characteristics of organic solar cells (OSCs) are correlated with microstructural qualities of active layers (ALs). Numerous efforts focused on improving process conditions of ALs to attain effective microstructures to achieve high-efficiency OSCs. Aside from AL process conditions, layer properties under AL can also influence microstructural qualities of AL. In this study, we adopted poly(3-hexylthiophene) (P3HT):(6,6)-phenyl C61-butyric acid methyl ester (PCBM) mixture as AL, poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) as hole extraction layer, and branched polyethyleneimine (BPEI) as electron extraction layer to prepare OSCs with different device structures, that is, normal type (PEDOT:PSS/P3HT:PCBM/BPEI) and inverted type (BPEI/P3HT:PCBM/PEDOT:PSS) structures. We discovered that although devices have similar layer components, they have different photovoltaic characteristics. Inverted devices demonstrated higher power conversion efficiency than normal devices. Various methods, including absorption spectroscopy and microscopy, were used to study AL microstructures of different devices. We observed that P3HT crystallites grown on BPEI had longer vertical size and shorter horizontal size compared with those grown on PEDOT:PSS; these properties could result from larger interfacial tension of P3HT with BPEI than with PEDOT:PSS. Observed shape of P3HT crystallites in inverted devices facilitated efficient charge transport to electrodes and suppressed current leakage. As a result, inverted devices generated improved photovoltaic performance.

In this study, In2O3 films were prepared by three methods and resulted in three different film structures. We firstly produced In2O3 polycrystal films by the evaporation of In source under oxygen ambient. In the second attempt, In2O3(111) films were fabricated by oxidation of In films. The surface scattering contributed to the resistivity of the oxidized In film and resulted a poor conductivity. As the third approach, a combination of the first and the second way, we prepared an ultrathin In film, oxidized it, and made it served as a seeding layer in the evaporation of In source under oxygen ambient. Due to the specific fabrication, we obtained the In2O3(111) films, in which a better conductivity and a smooth surface were observed in the In2O3(111) film through the third approach.

Control of the operating voltage in organic thin-film transistor (OTFT) based photosensors is a very important issue, which can effectively enhance photosensitivity by reducing the contribution of the field-effect current to the output current under darkness. In this study, we show a highly sensitive flexible organic photosensor, which is made by the use of cross-linked poly(4-vinylphenol) as a polymer dielectric layer and N,N′-ditridecyl-3,4,9,10-perylenetetracarboxylic diimide (PTCDI-C13H27) as an n-type active layer on a transparent polyethersulfone (PES) substrate, by tuning both source–drain and source–gate voltages to around the threshold voltage (Vt = 3.0 V). Interestingly, a maximum photocurrent/dark current ratio was obtained when the operating voltage was reduced to around Vt. The time-response characteristics and sensitivity of the PTCDI-C13H27-based photosensor were investigated. Considerable interest has been focused on developing a flexible in-cell remote touch screen that should comprise photosensitive OTFTs and switch OTFTs simultaneously. In this work, both switch-OTFTs and photo-OTFTs can be formed on the flexible PES substrate by use of the same fabrication process. The electrical characteristics of switch-OTFTs under bending states are discussed in terms of photoluminescence and time-resolved photoluminescence measurements, as well as quantum theory calculations.

This study presents an approach to design hybrid dielectrics with ultrahigh capacitance density at extremely low supply voltages that behave like supercapacitors and are thus energy efficient. Hybrid dielectrics are fabricated from polymer/metal-oxide bilayer films with real-time and effective internal voltage generated by chemically interlocking interfacial species at the charged state. The designed dielectrics are named charged-state dipole-enhanced (CSDE) dielectrics. We demonstrate their potential use in ultralow voltage driving organic field-effect transistors (FETs) characterized by the high performance and great stability. Using the CSDE dielectrics, organic FETs with a pentacene active layer can deliver adequate performance and excellent operational stability at ultralow operating voltage in air. The linear field-effect mobility of pentacene-based FETs can be as high as 1.5 cm2 V−1 s−1 at only 0.1 V. After long-term storage and continuous operation in air, the FETs still exhibited outstanding electrical performance. Several advantageous features of the designed CSDE dielectrics are presented, thereby providing a glimpse into the future of energy-efficient electronics.

This study presents the developed poly(3-hexylthiophene):indene-C60 bisadduct (P3HT:ICBA)-based organic solar cells, where nanoimprinted poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) gratings successfully functioned as charge transport highways and induced an ICBA-rich surface. The embedded nanostructures improved light harvesting and contact area; however, these two factors were not the primary enhancers of solar cell performance. Atomic force microscopy and conductive atomic force microscopy revealed that the imprinted PEDOT:PSS gratings activated hole- and electron-conducting pathways. This result can be attributed to the enhancement of the π–π orbital overlap between P3HT and PEDOT:PSS polymer chains and to the grating-induced ICBA phase separation. These two effects were the primary factors that increased the short-circuit current of the imprinted devices, which resulted in the increase of power conversion efficiency. In-plane and out-of-plane grazing incident X-ray diffraction revealed that the chain orientation of P3HT on the PEDOT:PSS gratings was the same as that on the plane PEDOT:PSS surface. This study proved the feasibility of nanoimprinting for organic solar cells, as well as for organic field-effect transistors.

The shift of the open-circuit voltage (Voc) of flexible organic solar cells (OSCs) under bending conditions was investigated by fabricating bi-layer heterojunction and polymer-based OSCs on flexible polyethylene terephthalate (PET) substrates. To realize the performance variations of flexible solar cells characterized by important parameters, Voc was measured when the substrate was bent under various curvatures. The Voc was increased and decreased by using tensile and compressive stresses, respectively. The ratio of increase for Voc is larger than the ratio of reduction, thus indicating that the intermolecular distance of an organic semiconductor is difficult to change because of the strong electrostatic repulsive force. A quantitative analysis of energy levels by the photoluminescence spectrum, UV-visible absorption spectrum, and quantum chemical calculation at various bending states was used to explain the Voc as a function of bending curvature. The peak shifts of UV-visible absorption and photoluminescence spectra provide direct evidence of the variation in energy levels when devices are bent, which causes Voc shifts. For bent organic semiconductor films, the bending curvature-dependent intermolecular distance was studied by Raman spectroscopy by analyzing the intermolecular coupling energy. This study shows that the change of Voc cannot be neglected in the application of flexible OSCs on a flexible loading circuit.

Control of the polymorphism of organic semiconductor films is very important in optoelectronic devices, such as organic thin-film transistors, solar cells, and organic light-emitting diodes. Here, we show the use of polyimide nanogratings (PI-NGs) patterned by nanoimprint lithography to control the polymorphism of deposited pentacene films. Interestingly, a new crystalline phase is first found in the pentacene thin-film formed on the PI-NGs. This new phase, with a d-spacing of 1.35 nm, is more stable than the bulk and thin-film phases in the pentacene film, discussed in terms of X-ray diffraction (XRD) measurements and quantum theory calculations. The response mechanism of the formation of this new phase is characterized by XRD and atomic force microscopy; the polymorphism and surface morphology show a strong dependence on the width of PI-NGs. The size-dependent PI-NG responses of the pentacene film can also control the phase transition from the thin-film to the bulk phase.

We demonstrate efficient hybrid inorganic/organic p–i–n photovoltaic (PV) devices with a p -type-doped hydrogenated amorphous silicon (a-Si:H), intrinsic a-Si:H, and an organic semiconductor, pentacene. The correlation between the electrical properties of the PV devices and the morphological properties of the pentacene films were investigated using absorption spectroscopy, X-ray diffraction, and scanning electron microscopy. The maximum power conversion efficiency can be increased by one order with respect to the devices using different thicknesses of a pentacene layer from 0.32% at 10 nm to above 3.0% at 30 nm. Photocarriers in PVs are suggested to be mainly generated in the intrinsic a-Si:H layer. The pentacene layer is used as the exciton-blocking and electron-transport layer. Thus, the structural quality of pentacene films plays an important role in PV performance.

While regulation of the nanoscale microstructure of the active layers in organic bulk heterojunction (BHJ) solar cells, particularly for conjugated polymer–fullerene blend systems, has been shown to be highly important when maximizing power conversion efficiency, little is known about the role of disordered polymer chains in the photovoltaic (PV) behaviors and electrochemical potential drops of polymer–fullerene interfaces. In this study, the microstructural-dependent PV properties of a series of poly(3-hexylthiophene) (P3HT):fullerene (i.e., [6,6]-phenyl-C61-butyric acid methyl ester, or PCBM) blending films with different compositions have been investigated using several experiments (i.e., absorption spectroscopy, Raman spectroscopy, X-ray diffraction, and atomic force microscopy) and theoretical methods (i.e., spectroscopic simulation and quantum mechanical calculations). A strong correlation exists between amorphous P3HT chain properties, characterized by degree of conjugation (Leff), and PV parameter...

A combined quasi-swelling and recrystallization (QSRC) approach is developed to alter distorted segments of conjugated polymer into highly ordered crystalline domains with super-long effective conjugation lengths (>100mer). These highly extended conjugated chains, at their maximum, are expected to have important implications for photonic and electronic applications and theoretical studies.

A promising and simple method to control the crystal polymorphic transformations of insoluble pentacene through solvent treatments is developed to obtain superior films with stable polymorphs and enhanced intermolecular electronic coupling, as proven by X-ray diffraction, Raman and absorption spectroscopy, and quantum chemical calculations. The degree of polymorphic transformations within films can be managed by the selection of appropriate organic solvents according to the magnitude of the pentacene—solvent interaction. A reaction pathway that could interpret how a metastable polymorph T ("thin film" phase) transforms into a more stable polymorph B ("bulk" or "single-crystal" phase) is proposed. The hypothesis is based on the terms of crystal structural parameters, including separation distance, tile angle, and herringbone edge-to-face angle. With the aid of quantum chemical calculations, we combine the binding energy of pentacene dimers and pentacene—solvent interaction energy to develop a new quantitative criterion for the selection of appropriate organic solvents for the structural improvement of organic crystal/films rather than damage. The proposed solvent post-treatments concepts could provide opportunities for improved vacuum-evaporated organic crystal/films and further expand potential applications in organic electronics and photonics.

This study focuses on the microstructural modifications of regioregular poly(3-hexylthiophene) (rr-P3HT) in the small active channel of thin-film transistors (TFTs) during operations. Polarized abs...

We have studied the current–voltage characteristics and threshold voltage behaviors in polycrystalline pentacene-based organic thin-film transistors (OTFTs) with gold top-contact electrodes for different thickness of the pentacene films. The study uses a number of techniques to measure threshold voltage including: square-root method, constant-current method, maximum transconductance method and capacitance–voltage measurements. The results of our experiments suggest that the space–charge and trapping effects of the pentacene bulk film plays an important role in current–voltage characteristics. In the presence of trapping centers within the polycrystalline pentacene film, we have provided an analytical model explaining the effect of bulk traps on the thickness-dependent threshold voltage. Square-law of threshold voltage versus pentacene thickness in OTFTs was derived during our study providing consistent results with experimental data. Furthermore, using the square-law, we estimated trap density of about 1017 cm−3 in experimental pentacene films. The orders of magnitude in trap density of polycrystalline pentacene films are similar to the values found in other literature source.

Thickness-dependent crystal structure, surface morphology, surface energy, and molecular structure and microstructure of a series of polycrystalline pentacene films with different film thickness ranging from several monolayers to the several hundred nanometers have been investigated using X-ray diffraction (XRD), atomic force microscopy (AFM), contact angle meter, and Raman spectroscopy. XRD studies indicate that thin film polymorphs transformation behaviours are from the orthorhombic phase to the thin-film phase and then to the triclinic bulk phase as measured by the increased tilt angle (θtilt) of the pentacene molecule from the c-axis toward the a-axis. We propose a growth model that rationalizes the θtilt increased along with increasing film thickness in terms of grain size and surface energy varying with film growth using AFM combined with contact angle measurements. The vibrational characterizations of pentacene molecules in different thickness films were investigated by Raman spectroscopy compared to density functional theory calculations of an isolated molecule. In combination with XRD and AFM the method enables us to distinguish the molecular microstructures in different thin film polymorphs. We proposed a methodology to probe the microscopic parameters determining the carrier transport properties based on Davydov splitting and the characteristics of aromatic C–C stretching modes in Raman spectra. When compared to the triclinic bulk phase at a high thickness, we suggest that the first few monolayer structures located at the dielectric surface could have inferior carrier transport properties due to weak intermolecular interactions, large molecular relaxation energy, and more grain boundaries.