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Self-doping organic semiconductors provide a promising route to avoid instabilities and morphological issues associated with molecular n-type dopants. Structural characterization of a naphthalenetetracarboxylic diimide (NDI) semiconductor covalently bound to an ammonium hydroxide group is presented. The dopant precursor was found to be the product of an unexpected base catalyzed hydrolysis, which was reversible. The reversible hydrolysis had profound consequences on the chemical composition, morphology, and electronic performance of the doped films. In addition, we investigated the degradation mechanism of the quaternary ammonium group and the subsequent doping of NDI. These findings reveal that the products of more than one chemical reaction during processing of films must be considered when utilizing this promising class of water-soluble semiconductors.

In the search for high performance n-type organic semiconductors (OSCs) a simple strategy might be substitution of aromatic CH groups for nitrogen heteroatoms. Here, we report the synthesis and characterisation of two novel N-heteroacene compounds, namely, 1,5,12-triazatetracene (TrAT1) and 2,5,12-triazatetracene (TrAT2). Their potential as n-type materials is evaluated against 5,12-diazatetracene (DAT) by UV/vis and EPR spectroscopy, cyclic voltammetry, DFT, single crystal X-ray diffraction and thin film characterisation. Increasing the number of N-heteroatoms was found to stabilise the HOMO and LUMO leading to electron affinities for TrAT1 and TrAT2 of ca. −4 eV. Both compounds were found to exhibit columns of co-facial π-stacked molecules. For TrAT1, molecules are also linked by hydrogen bonding, while the crystal structure of TrAT2 was found to be inherently disordered. Thin films of DAT, TrAT1 and TrAT2 were grown by organic molecular beam deposition (OMBD) and found to form discontinuous films, where TrAT1 exhibited a preferential orientation.

A new material platform for boron nitride (BN) as a heterogeneous photocatalyst for solar fuels synthesis has recently emerged. One of the bottlenecks of this material is the lack of photoactivity under visible light, which hinders its rate performance. Theoretical studies have predicted that tuning the oxygen content in oxygen-doped BN (BNO) might be used to lower and vary the band gap. However, this is yet to be verified experimentally. We present herein a systematic experimental route facilitating simultaneous tuning of the chemical, magnetic and optoelectronic properties of BNO using a multivariate synthesis parameter space. Deep visible range band gaps (1.50 – 2.90 eV) were experimentally achieved and tuned over an oxygen composition of 2 – 14 at. %, and specific paramagnetic OB3 content of 7 – 294 a.u. g-1, thus supporting theoretical predictions. Through designing a response surface via a design of experiments (DOE) process, the key synthesis parameters influencing the chemical, magnetic and optoelectronic properties of BNO were identified. In addition, model prediction equations relating the aforementioned properties to the synthesis parameter space are presented. Accurate model predictions for the oxygen content and band gap were conducted and validated experimentally. Such a methodology is valuable for further advances in tailoring and optimising BN materials for heterogeneous photocatalytic reactions.

Celebrating the life of Alasdair Campbell.

Developing robust, multifunctional photocatalysts that can facilitate both hydrogen evolution via photoreforming of water and gas phase CO2 photoreduction is highly desirable with the long-term vision of integrated photocatalytic setups. Here, we present a step-change in the family of boron oxynitride materials by introducing the first example of a B-doped boron oxynitride (B-BNO). This material resolves an on-going bottleneck associated with BN-based materials, i.e. the lack of photoactivity under visible light. Detailed EPR studies revealed distinct hyperfine interactions between the free oxygen radicals and 3 neighbouring boron nuclei. This confirmed isolated OB3 sites, which contribute to band gap narrowing, as the radical species and origin of paramagnetism in BNO materials. We show that B-BNO can facilitate both liquid phase H2 evolution and gas phase CO2 photoreduction, using UV-Vis and deep visible irradiation (λ > 550 nm), without any co-catalysts. The evolution rates, quantum efficiencies, and selectivities observed for both reactions with B-BNO exceed those of its porous BNO counterpart, P25 TiO2 and bulk g-C3N4.

Developing robust, multifunctional photocatalysts that can facilitate both hydrogen evolution via photoreforming of water and gas phase CO2 photoreduction is highly desirable with the long-term vision of integrated photocatalytic setups. Here, we present a new addition to the boron nitride (BN) photocatalyst material platform, boron-doped boron oxynitride (B-BNO), capable of fulfilling this goal. Detailed EPR studies revealed hyperfine interactions between free charges located on discrete OB3 sites, exhibiting an out-of-plane symmetry, and the nuclei of neighbouring boron atoms. This material resolves two long-standing bottlenecks associated to BN-based materials concomitantly: instability in water and lack of photo activity under visible light. We show that B-BNO maintains prolonged stability in water for at least three straight days and can facilitate both liquid phase H2 evolution and gas phase CO2 photoreduction, using UV-Vis and deep visible irradiation (λ > 550 nm), without any cocatalysts. The evolution rates, apparent quantum yields, and selectivities observed for both reactions with B-BNO exceed those of its porous BNO counterpart, P25 TiO2 and bulk g-C3N4. This work provides scope to expand the BN photocatalyst platform to a wider range of reactions.

Recent studies have identified the 8C alkyl chain methylimidazolium ionic liquid 1-octyl-3-methylimidazolium in the environment and its potential to trigger the auto-immune liver disease primary biliary cholangitis. The toxicity of a range of methylimidazolium ionic liquids were therefore examined. Oxygen consumption was rapidly inhibited, with potency increasing with alkyl chain length. This preceded caspase 3/7 induction and DNA fragmentation. Time- and dose-dependent loss of dye reduction capacities reflected these effects, with a >700 fold difference in potency between 2C and 10C alkyl chain liquids. None of the ionic liquids directly inhibited mitochondrial complexes I-IV or complex V (F0F1-ATPase). However, dithionite reduction and ESR spectroscopy studies indicate a one electron reduction of oxygen in the presence of a methylimidazolium ionic liquid, suggesting methylimidazolium ionic liquids function as mitochondrial electron acceptors. However, only longer chain ionic liquids form a non-aqueous phase or micelle under aqueous physiological conditions and lead to increases in reactive oxygen species in intact cells. These data therefore suggest that the longer chain methylimidazolium liquids are toxic in sensitive liver progenitor cells because they both readily integrate within the inner mitochondrial membrane and accept electrons from the electron chain, leading to oxidative stress.

Interactions between iron surfaces and hydrocarbons are the basis for a wide range of materials synthesis processes and novel applications, including sensing. However, in diesel engines these interactions can lead to deposit formation that reduces performance, lowers efficiency, and increases emissions. Here, we present a global study to understand deposition at iron-hexadecane interfaces. We use a combination of spectroscopy, microscopy, and mass spectrometry to investigate surface reactions, bulk chemistry, and deposition processes. A dynamic equilibrium between the oxidation products, both at the surface and in solution, determines the deposition at the surface. Considering the solution and the surface in parallel, we find that the iron speciation affects the morphology, composition, and quantity of the deposit at the surface, as well as the oxidation of hexadecane. Fe(II) and Fe(III) both promote the decomposition of peroxides-intermediates in the oxidation of hexadecane-but through noncatalytic and catalytic mechanisms, respectively. In contrast, Fe(0) is proposed to initiate hexadecane autoxidation during its oxidation to Fe(III). We find that in all cases, the surfaces exclusively contain Fe(III) following heat treatment with hexadecane. Upon subsequent exposure at room temperature, Fe(III) species are found to promote oxidation; this finding is particularly concerning for hybrid vehicles where longer time periods are expected between engine operation. Our work provides a foundation for the development of strategies that disrupt the role of iron in the degradation of hexadecane to ultimately reduce oxidation and deposition in diesel engines.

We report on a new approach for the fabrication of ferromagnetic molecular thin films. Co-evaporated films of manganese phthalocyanine (MnPc) and tetracyanoquinodimethane (TCNQ) have been produced by organic molecular beam deposition (OMBD) on rigid (glass, silicon) and flexible (Kapton) substrates kept at room temperature. The MnPc:TCNQ films are found to be entirely amorphous due to the size mismatch of the molecules. However, by annealing while covering the samples highly crystalline MnPc films in the β-polymorph can be obtained at 60 °C lower than when starting with pure MnPc films. The resulting films exhibit substantial coercivity (13 mT) at 2 K and a Curie temperature of 11.5 K.

Molecules and atoms at material interfaces have properties that are distinct from those found in the bulk. Distinguishing the interfacial species from the bulk species is the inherent difficulty of interfacial analysis. For organic photovoltaic devices, the interface between the donor and acceptor materials is the location for exciton dissociation. Dissociation is thought to occur via a complex route effected by microstructure and the electronic energy levels. The scale of these devices and the soft nature of these materials create an additional level of difficulty for identification and analysis at these interfaces. The transmission electron microscope (TEM) and the spectroscopic techniques it incorporates can allow the properties of the donor-acceptor interfaces to be revealed. Cross-sectional sample preparation, using modern focused ion beam instruments, enables these buried interfaces to be uncovered with minimal damage for high resolution analysis. This powerful instrument combination has the ability to draw conclusions about interface morphology, structure and electronic properties of organic donor-acceptor interfaces at the molecular scale. Recent publications have demonstrated these abilities, and this article aims to summarise some of that work and provide scope for the future.

Manganese porphyrins are of interest due to the optical, electronic and magnetic properties of the central metal ion, coupled to the low bandgap of the polyaromatic ring. These attractive characteristics are harnessed in solutions or in ultra-thin films, such as, for example, self-assembled monolayers. However, for devices, thicker films deposited using a controlled and reproducible method are required. Here we present the morphological, structural, chemical and optical properties of manganese(III) tetraphenylporphyrin chloride (MnTPPCl) thin films deposited using organic molecular beam deposition, typically employed to process analogue molecules for applications such as organic photovoltaics. We find, using a combination of UV-vis and X-ray photoelectron spectroscopies, that the sublimation process leads to the scission of the Mn–Cl bond. The resultant film is a Mn(II)TPP:Mn(III)TPPCl blend where approximately half the molecules have been reduced. Following growth, exposure to air oxidizes the Mn(II)TPP molecule. Through quantitative analysis of the time-dependent optical properties, the oxygen diffusion coefficient (D) [Formula: see text] is obtained, corresponding to a slow bulk oxidation following fast oxidation of a 8-nm-thick surface layer. The bulk diffusion D is lower than for analogous polycrystalline films, suggestion that grain boundaries, rather than molecular packing, are the rate-limiting steps in oxidation of molecular films. Our results highlight that the stability of the axial ligands should be considered when depositing metal porphyrins from the vapor phase, and offer a solvent-free route to obtain reproducible and smooth thin films of complex materials for engineering film functionalities.

Thin films of pentacene and p-terphenyl were grown via organic molecular beam deposition to enable solid-state dilution of functional molecules (pentacene) in an inert matrix (p-terphenyl) at higher concentrations than permitted by traditional crystal growth methods, such as melts. Growth rates were first optimised for single component films to ensure a precise control over the dopant/host concentrations when the mixed films were deposited. Both thin film and bulk phases can be identified in pentacene growths, with the precise lattice parameters dependent on the deposition rates. The effect on the microstructure, resulting from progressive dilution of pentacene in a p-terphenyl host, was then investigated. Although disorder increases and the crystallite size decreases in the mixture, with a minimum at a 1 : 1 ratio, phase segregation is not observed on the length scale (limit) that can be probed in our measurements. This indicates that the mixed films form homogeneous solid-solutions that may be employed for the investigation of solid-state phenomena. Our methodology can be extended to other compatible host-dopant systems used in optoelectronic and spintronic devices.

Correction for ‘Comparison of organic and inorganic layers for structural templating of pentacene thin films’ by Dong Kuk Kim et al., Mater. Horiz., 2019, DOI: 10.1039/c9mh00355j. The authors wish to amend the Acknowledgements section of the originally published manuscript. The correct Acknowledgements section is shown below.

Pentacene is a key organic semiconductor, which has achieved prominence in transistor applications and as an archetypal material for singlet fission, the process whereby the absorption of one photon leads to the formation of two triplet states. Functional properties of molecules are highly anisotropic, and control over the molecular orientation in thin films with structural templating is commonly implemented as a route for governing the morphology and structure of organic films. Among the structural templating layers, 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) and copper(I) iodide (CuI) have been shown to effectively template aromatic systems such as phthalocyanines. Here, we extend their use to pentacene thin films and find that a successful transition to a flat-lying arrangement is achieved with CuI films grown at high temperatures, but not with PTCDA. As a result, we postulate a model based on quadrupole interactions as the driving force behind the molecular orientation of pentacene. A 0.25 eV increase in work function and a two-fold increase in visible light absorption are recorded for the induced flat-lying orientation. Therefore, our templating methodology provides design opportunities for optoelectronic devices that require a predominantly flat-lying orientation.

The electric field of ferroelectric materials has been used as a driving force to promote molecular adsorption and control the orientation of small dipolar molecules. This approach has not been investigated on larger polyaromatic molecules, such as those used in organic electronic devices, even though the physical and electronic properties of thin films are strongly dependent on molecular structure and orientation, ultimately affecting device performance. Here we investigate the effects of model ferroelectric surfaces on a dipolar organic semiconducting molecule. Thin films of vanadyl phthalocyanine (VOPc) deposited on to (0001) and (2[1 with combining macron][1 with combining macron]0) lithium niobate were subjected to structural and morphological analysis. Whilst thin films could be grown on these surfaces, no obvious change to their structure or morphology was observed suggesting there was no influence of a surface electrical field or surface chemistry on the film structure, and that the substrate is more complex than previously thought.

In the present work, the templating effect of thin layers of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) on the growth of cobalt tetrakis(thiadiazole)porphyrazine (CoTTDPz) thin films was examined. X-ray diffraction and optical absorption spectra indicate that while CoTTDPz forms amorphous thin films on the bare substrates, it forms crystalline thin films on the PTCDA templates, in which the molecular planes of CoTTDPz are considered to be parallel to the substrates. Magnetic measurements reveal a significantly enhanced antiferromagnetic interaction of CoTTDPz in the templated thin films, with values reaching over 13 K. The ability to generate crystalline films and to control their orientation using molecular templates is an important strategy in the fields of organic electronics and spintronics in order to tailor the physical properties of organic thin films to suit their intended application.

The optical and electronic properties of organic materials influence the functionality of all organic electronics. These properties can be measured in bulk materials easily, but determining the opto-electronic properties in thin films and at interfaces is challenging. In this report we describe how these properties can be measured with high spatial resolution using an optimized electron energy-loss spectroscopy (EELS) method in the scanning transmission electron microscope (STEM). EELS spectra were collected for poly(3-hexylthiophene) (P3HT), [6,6]phenyl-C61 butyric acid methyl ester (PCBM), copper phthalocyanine (CuPc), and C60. These organic materials are both susceptible to electron beam damage and commonly utilized in organic photovoltaics (OPVs). In order to prove that these spectra are representative of the pure materials and that the samples have not undergone any significant beam damage, the real and imaginary parts of the complex dielectric function obtained from these spectra have been compared to the same functions obtained using variable angle spectroscopic ellipsometry (VASE), a technique that should not induce any beam damage to the samples. Comparisons of these two data sets reveal good agreement in both measured peak intensities and their corresponding peak energies, thus validating this low-damage EELS acquisition method. EELS spectrum images were acquired from a CuPc/C60 bilayer structure to demonstrate that it is possible to collect spatially resolved EELS data from device-related structures comprised of these beam-sensitive materials.

Metal oxide thin films are increasingly utilized in small molecular organic photovoltaic devices to facilitate electron transport and injection. Despite this there is little understanding of the influence these layers have on the structure of adjacent organic semiconductor layers. Here we use both O- and Zn-terminated (0001) single crystal zinc oxide (ZnO) as a model system to investigate the effect of a metal oxide surface on the growth of a molecular semiconductor, vanadyl phthalocyanine (VOPc). The surface reconstructions of these model surfaces are determined and the properties of thin films of VOPc deposited atop are investigated. The nature of the bulk truncation of the surface is found to have pronounced effects on both the morphology and crystal structure of these molecular films. This work highlights the importance of considering the effects of the chemical composition and surface termination of metal oxide films on the structure of adjacent molecular semiconductor films.

The morphological and structural properties of films based on the strong electron acceptor molecule, 7,7,8,8,-tetracyanoquinodimethane (TCNQ) are presented and the influence of growth rate and the nature of the substrate are investigated. On weakly-interacting substrates, TCNQ films grown by Organic Molecular Beam Deposition (OMBD) exhibit randomly oriented micron-sized islands with significant curvature and three preferential orientations suggested by diffraction from (022), (021) and (020) planes. Pre-coating with 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) is shown to result in morphological and structural modifications to the TCNQ films, characterized by uniform rectangular-shaped micron-sized islands, with the preferential molecular orientation reduced to only (020), compared to the films on bare substrates. We rationalise the interactions between TCNQ and PTCDA based on the match between the displacement of the perylene-H atoms/anhydride groups in PTCDA and that of the CN groups in TCNQ. These results suggest an alternative approach for using templating to control the molecular orientation in organic heterostructures.

While organic semiconductors provide tantalizing possibilities for low-cost, light-weight, flexible electronic devices, their current use in transistors-the fundamental building block-is rather limited as their speed and reliability are not competitive with those of their inorganic counterparts and are simply too poor for many practical applications. Through self-assembly, highly ordered nanostructures can be prepared that have more competitive transport characteristics; however, no simple, scalable method has been discovered that can produce devices on the basis of such nanostructures. Here, we show how transistors of self-assembled molecular nanowires can be fabricated using a scalable, gradient sublimation technique, which have dramatically improved characteristics compared to those of their thin-film counterparts, both in terms of performance and stability. Nanowire devices based on copper phthalocyanine have been fabricated with threshold voltages as low as -2.1 V, high on/off ratios of 105, small subthreshold swings of 0.9 V/decade, and mobilities of 0.6 cm2/V s, and lower trap energies as deduced from temperature-dependent properties, in line with leading organic semiconductors involving more complex fabrication. High-performance transistors manufactured using our scalable deposition technique, compatible with flexible substrates, could enable integrated all-organic chips implementing conventional as well as neuromorphic computation and combining sensors, logic, data storage, drivers, and displays.

The processes that generate current in organic photovoltaics are highly dependent on the micro‐ and nano‐structure in the semiconductor layers, especially at the donor‐acceptor interface. Elucidating film properties throughout the thickness of the devices is therefore key to their further development. Here, a methodology is developed to gain unprecedented insights into the structure and composition of the molecular layers within the depth of device structure using high resolution transmission electron microscopy (HRTEM). The technique was applied to three archetypical solar cell configurations consisting of copper phthalocyanine (CuPc) and C60, which have been cross‐sectioned using a focused ion beam method optimized to minimize sample damage. The HRTEM images exhibit lattice fringes in both CuPc and C60, confirming the crystallinity and texture of both materials, and offering novel insight into the growth of C60 onto molecular materials. The donor‐acceptor interface morphology is further studied using scanning transmission electron microscopy (STEM) in combination with energy dispersive X‐ray (EDX) spectroscopy, extending the scope of our methodology to amorphous heterostructures.

The magnetic, thin-film structural, conductivity, and magnetoresistance properties of [Ni(quinoline-8-thiolate)2] ([Ni(qt)2]) are studied. The conducting and magnetoresistance properties are studied in single crystals and in evaporated thin films through deposition on an interdigitated electrode array. Non-linear conductivity interpreted through a space-charge limited conduction mechanism with charges injected from the electrodes is observed. Under applied magnetic field, the material displays giant negative magnetoresistance above 50% at 2 K in both single crystals and in evaporated thin films. The effect can still be observed at 200 K and is interpreted in terms of a double exchange mechanism with the shape of the curve determined by the magnetic anisotropy. The unique observation of giant magnetoresistance (GMR) as an intrinsic effect in an evaporated thin film of paramagnetic molecules opens up new possibilities in organic spintronics.

Organic semiconductors are studied intensively for applications in electronics and optics, and even spin-based information technology, or spintronics. Fundamental quantities in spintronics are the population relaxation time (T1) and the phase memory time (T2): T1 measures the lifetime of a classical bit, in this case embodied by a spin oriented either parallel or antiparallel to an external magnetic field, and T2 measures the corresponding lifetime of a quantum bit, encoded in the phase of the quantum state. Here we establish that these times are surprisingly long for a common, low-cost and chemically modifiable organic semiconductor, the blue pigment copper phthalocyanine, in easily processed thin-film form of the type used for device fabrication. At 5 K, a temperature reachable using inexpensive closed-cycle refrigerators, T1 and T2 are respectively 59 ms and 2.6 μs, and at 80 K, which is just above the boiling point of liquid nitrogen, they are respectively 10 μs and 1 μs, demonstrating that the performance of thin-film copper phthalocyanine is superior to that of single-molecule magnets over the same temperature range. T2 is more than two orders of magnitude greater than the duration of the spin manipulation pulses, which suggests that copper phthalocyanine holds promise for quantum information processing, and the long T1 indicates possibilities for medium-term storage of classical bits in all-organic devices on plastic substrates.

Molecular templating is an attractive method to improve the crystallinity and control the molecular orientations of organic thin films. Here, we report on the templating effects of an organic [Formula: see text]-type semiconductor, tetrakis(thiadiazole)porphyrazine (H2TTDPz), on the structure and optical absorption of a [Formula: see text]-type semiconductor, copper phthalocyanine (CuPc). X-ray diffraction measurements for the double layer thin films, CuPc/H2TTDPz, indicate a face-on orientation of CuPc, which is replicating the structure of the H2TTDPz thin films, even though the CuPc thin films usually form edge-on-type thin films. The optical absorption measurements show new low-energy transitions in the templated CuPc films.

Metallocenes are a promising candidate for future spintronic devices due to their versatile and tunable magnetic properties. However, single metallocenes, e.g., ferrocene, sublimate below room temperature, and therefore the implementation for future applications is challenging. Here, a method to prepare biferrocene thin films using organic molecular beam deposition (OMBD) is presented, and the effect of substrate and deposition rate on the film structure and morphology as well as its chemical and magnetic properties is investigated. On Kapton and Si substrates, biferrocene interacts only weakly with the substrate, and distinct grains scattered over the surface are observed. By incorporating a 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) seeding layer and depositing biferrocene at high deposition rates of 1.0 Å s–1, it is possible to achieve a well-ordered densely packed film. With spintronic applications in mind, the magnetic properties of the thin films are characterized using superconducting quantum interference device (SQUID) magnetometry. Whereas initial SQUID measurements show weak ferromagnetic behavior up to room temperature due to oxidized molecule fragments, measurements of biferrocene on PTCDA capped with LiF show the diamagnetic behavior expected of biferrocene. Through the successful deposition of biferrocene thin films and the ability to control the spin state, these results demonstrate a first step toward metallocene-based spintronics.

Structural templating is frequently used in organic photovoltaic devices to control the properties of the functional layers and therefore improve efficiencies. Modification of the substrate temperatures has also been shown to impact the structure and morphology of phthalocyanine thin films. Here we combine templating by copper iodide and high substrate temperature growth and study its effect on the structure and morphology of two different non-planar phthalocyanines, chloroaluminium (ClAlPc) and vanadyl (VOPc) phthalocyanine. X-ray diffraction, atomic force microscopy and low energy ion scattering show that both the morphology and the structure of the films are starkly different in every case, highlighting the versatility of phthalocyanine film growth.\ud \ud

The structure of copper phthalocyanine (CuPc) thin films (5-100 nm) deposited on single-crystal ZnO(1100) substrates by organic molecular beam deposition was determined from grazing-incidence X-ray diffraction reciprocal space maps. The crystal structure was identified as the metastable polymorph α-CuPc, but the molecular stacking was found to vary depending on the film thickness: for thin films, a herringbone arrangement was observed, whereas for films thicker than 10 nm, coexistence of both the herringbone and brickstone arrangements was found. We propose a modified structure for the herringbone phase with a larger monoclinic β angle, which leads to intrastack Cu-Cu distances closer to those in the brickstone phase. This structural basis enables an understanding of the functional properties (e.g., light absorption and charge transport) of (opto)electronic devices fabricated from CuPc/ZnO hybrid systems.

Electrodeposition of highly crystalline ZnO nanostructures directly onto copper phthalocyanine and pentacene thin films, from aqueous solutions containing zinc nitrate and dissolved oxygen, has been successfully demonstrated for the first time using a two-step electrochemical deposition process. Importantly, surface activation of the molecular thin film substrates by depositing a thin layer of ZnO nanoparticles at high cathodic overpotentials prior to film growth was found to be crucial for achieving a dense coverage of ZnO nanostructures with uniform morphology. The mechanism for ZnO deposition via electroreduction of hydroxide precursor species (oxygen and NO3– ions) at the organic-electrolyte interface was shown to be analogous to that reported for conventional inorganic and metal electrodes. Comparison of cathodic current density-time curves, measured during deposition, with film orientation and morphology revealed that the cathodic current density and number of nucleation sites are key factors in det...

We present a new generic method to synthesize nanostructured metal(II) oxide films on a substrate such as silicon. Vacuum ultraviolet (VUV) excimer lamps rupture metal organic precursors, creating volatile organic fragments, while the metal species at the surface form oxides. X-ray photoemission spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) confirm that 172 nm VUV irradiation of manganese and copper phthalocyanines yields manganese(II) and copper(II) oxides, respectively. The morphology of the precursor film provides a template from which metal oxide nanoparticles are formed, which we demonstrate for particles with dimensions 40 x 40 x 10 nm(3). Our procedure is both simple and flexible, with low thermal budget and potential for patterning.

Different growth modes were identified using scanning tunnelling microscopy (STM) in the initial stages of ultra-thin films growth of copper phthalocyanine (CuPc) on Si(0 0 1) surfaces terminated with ammonia (Si(0 0 1):NH3) and hydrogen (Si(0 0 1):H), depending on the surface chemistry. At the onset of the growth, defect sites are saturated with strongly-pinned flat-lying CuPc molecules. Subsequently, molecules arrange in a standing manner, with two macroscopic island directions along the [1 1 0] and [ 1 1 ¯ 0 ] directions. The Si surface termination influences the shape and coverage of the molecular layer before the onset of multilayer formation: on NH3 terminated surfaces, large elongated islands are formed, and nucleation of the second layer begins after the first layer is only 50% complete. This is in contrast to the H passivated surfaces, where a high density of smaller islands form and a higher coverage is reached before second layer nucleation, which we have attributed to a difference in molecular mobility on the substrate. STM shows that the islands contain columns of molecules, which on both surfaces are aligned by 64° with respect to the macroscopic island direction. From these observations, we have derived a model in which the molecular orientation observed in these studies is very similar to the bulk α -phase CuPc. This rationalises the reduced crystallite size characteristic of thicker phthalocyanine films.

Cantilever torque magnetometry is used to elucidate the orientation of magnetic molecules in thin films. The technique allows depth-resolved investigations by intercalating a layer of anisotropic magnetic molecules in a film of its isotropic analogues. The proof-of-concept is here demonstrated with the single-molecule magnet TbPc2 evidencing also an exceptional long-range templating effect on substrates coated by the organic molecule perylene-3,4,9,10-tetracarboxylic dianhydride.

Organic molecular beam deposition (OMBD) is used for co-evaporation of copper phthalocyanine (CuPc) and C60 to form mixed films. Although pure single layers are crystalline, mixing leads to amorphous films in most cases, although phase segregation occurs for high concentrations of C60. An underlying CuPc single layer suppresses the segregation and leads to a homogeneous CuPc/C60 mixed film for all layer compositions. These effects are exploited in photovoltaic (PV) devices, where new architectures to improve device performance are investigated. Mixing the CuPc and C60 improves device performance, with the maximum efficiency (ηp = 1.17%) reached for devices containing 75% CuPc in the mixed layer, surrounded by pure layers at the electrode interfaces.

The growth and characterisation of a non-planar phthalocyanine (vanadyl phthalocyanine, VOPc) on a complete monolayer (ML) of a planar phthalocyanine (Iron(II) phthalocyanine, FePc) on an Au(111) surface, has been investigated using ultra-high vacuum (UHV) scanning tunnelling microscopy (STM) and low energy electron diffraction (LEED). The surface mesh of the initial FePc monolayer has been determined and shown to correspond to an incommensurate overlayer, not commensurate as previously reported. Ordered islands of VOPc, with (1 × 1) epitaxy, grow on the FePc layer at submonolayer coverages. The individual VOPc molecules occupy sites directly atop the underlying FePc molecules, indicating that significant intermolecular bonding must occur. It is proposed that this interaction implies that the V[double bond, length as m-dash]O points down into the surface, allowing a Fe-O bond to form. The detailed appearance of the STM images of the VOPc molecules is consistent with previous studies in other VOPc growth studies in which this molecular orientation has been proposed.

We have studied the effects of molecular architecture, co-deposition and annealing on the properties and performance of photovoltaic cells based on copper phthalocyanine (CuPc)–fullerene (C 60 ) heterojunctions. Significant improvements in performance are achieved when mixed CuPc:C 60 layers are incorporated into the device structure due to the creation of an intermolecularly mixed donor (D)–acceptor (A) blend that favours efficient exciton dissociation. We utilise the control afforded by organic molecular beam deposition to show that the mixed-layer composition plays an important role in determining device performance and correlate device efficiency to the morphological and spectroscopic properties of the organic layers. A maximum power conversion efficiency of η p = 1.17% is achieved for devices containing a mixed layer of ratio 75:25 CuPc:C 60 surrounded by thin continuous layers of pure organic material at the electrode interfaces. A structure containing a compositional gradient where the CuPc:C 60 composition is varied from purely D to purely A via three mixed layers of increasing A composition leads to a further improvements in efficiency ( η p = 1.36%). Finally, we use thermal annealing to show how structural defects and morphological templating of organic thin films reduces the interfacial area for exciton separation and yields poor device performance.

Surface modification of indium-tin-oxide (ITO)-coated substrates through the use of self-assembled monolayers (SAMs) of molecules with permanent dipole moments has been used to control the ITO work function and device performance in polymer light-emitting diodes based on a polyfluorene hole transporting copolymer. Measured current-voltage characteristics of the devices reveal greatly increased hole injection currents from the SAM-altered electrodes with higher work function, in agreement with an expected reduction in the barrier for hole injection. In particular, it is shown that the SAM-modified electrode with the highest work function provides an ohmic contact for hole injection into the studied polymer. Injection from the widely used poly(2,3-ethylenedioxythiophene)/polystyrenesulphonic acid (PEDOT:PSS)-coated ITO anode system, is less efficient compared with some of the studied SAM-coated ITO anodes despite the significantly higher work function measured by a Kelvin probe. This apparently anomalous situation is attributed to the inhomogenities in the injection processes that occur over the area of the device when the PEDOT:PSS-coated ITO electrode is used.

The effects of film thickness, codeposition and introduction of exciton-blocking layers are investigated for heterojunction photovoltaic devices based on copper phthalocyanine (CuPc) and fullerene (C60). Device performance peaks at low film thicknesses and is improved by the introduction of a mixed layer between continuous pure layers at the electrodes. The control afforded by organic molecular beam deposition enables a detailed analysis of the effects of mixed-layer composition on the device performance. The highest efficiency is reached for devices containing 75% CuPc and is further improved in structures containing multiple mixed layers that lead to the creation of a gradient of donor–acceptor compositions. The mixed-layer properties were assessed using atomic force microscopy and electronic absorption spectroscopy. In most cases, amorphous films with intimate molecular mixing are formed, but several exceptions rationalise the efficiencies observed in corresponding devices. Finally, the degradation of the devices under solar illumination highlights the destructive effects of oxygen, which are found to be particularly severe in mixed-layer devices.

The influence of the growth conditions on the properties of PTCDA thin films deposited by organic molecular beam deposition on glass substrates is presented. Powder X-ray diffraction studies show that only the α polymorph is formed, regardless of the growth conditions. By contrast, the film morphology depends specifically upon the deposition parameters, the observed crystal size increasing with growth temperature or after post-growth annealing. The spectroscopic properties (electronic absorption, fluorescence excitation and emission) are also found to be influenced by heat treatment and these are correlated with the changing crystal size in the PTCDA films. A qualitative model is presented in order to account for the photophysical properties of the films.

Molecular templating is an attractive method to improve the crystallinity of organic thin films and control the molecular orientations in them. Here, we report on the templating effects of an organic n-type semiconductor, tetrakis(thiadiazole)porphyrazine (H2TTDPz), on the structure and optical absorption of a p-type semiconductor, copper phthalocyanine (CuPc). X-ray diffraction measurements for the double layer thin films, CuPc/H2TTDPz, indicate a flat-on structure of CuPc, which is copied by the structure of the H2TTDPz thin films, in spite of that the CuPc thin films usually form edge-on type thin films. The optical absorption measurements show new low-energy transitions in the templated CuPc films.

We fabricate high-performance pentacene thin-film transistors (TFTs) using lithographic processes compatible with industry standard amorphous silicon (a-Si) TFT fabrication. Bottom-contact bottom-gate pentacene TFTs realized with silicon nitride (SiNx) gate dielectric show effective mobility values of 0.59 cm2/Vs, contact resistances as low as 2.4 kΩ·cm , and low threshold voltages. These results demonstrate the viability of using SiNx as a gate dielectric for vacuum-deposited organic TFTs for large-area and flexible electronic applications.