Estimation of charge-carrier mobility and trap energy from a space-charge-limited-current measurement is a well-established technique for the characterization of electronic materials. However, classical solid-state theories referenced for parameter extraction are based on simplistic assumptions that may not be strictly valid for a new generation of devices from unconventional materials and processing. In this study, we show that contact-limited currents dominate the entire operating regime in thin-film or nanoscale diodes even at a small charge-injection barrier. This assessment can make many reported values and analysis routines debatable, because they do not generally take any contact effects into consideration. Physical origins of the validity problem and guidelines for holistic parameterization are detailed through systematic correlation of analytical models, numerical simulation, and an experimental investigation into an organic diode with a graphene contact.

Solution processing of OLED is desirable because it allows for large area OLED displays with low manufacturing cost. Historically the device performance achievable with solution processing lagged that of evaporation. DuPont has focused on developing OLED materials for soluble technologies, as well as working with our partners on our proprietary printing process. Our performance data shows that with our latest generation materials and process steps, ink‐jet printed device performance suitable for TV application can now be achieved.

DuPont Displays recently leveraged its nozzle printing experience to develop high performance inkjet materials with a focus on mass production challenges. We will discuss the status of key developments in ink containment, pixel wetting and drying, integrated process/material considerations, ink formulation and rheology, particularly for HIL/HTL materials. A summary of the latest printed performance metrics and future material considerations will be discussed.

Field-effect transistors based on a graphene-organic semiconductor vertical hybrid hold great promise for applications that require a minimal driving voltage, a high current density, and a large transconductance gain. Despite impressive performances reported up to date, their working principles are still not well understood, and therefore a widely applicable functional model is now deemed essential. Here, we report on a physical current-voltage model based on the macroscopic footprints of charge transport and injection associated with the energetic asymmetry within the active diode part of a transistor. The model is composed of separate descriptions of negative and positive drain-biased circuits, which are added to build a single set of equations valid for a broad sweep range. The proposed model is validated by simulating a high-performance fullerene-based device, of which the extracted physical parameters are discussed in detail.

We present a novel logic family alternative to classic CMOS logic and its experimental demonstration for digital application of organic electronics. The proposed logic family is a modified version of the complementary pass-transistor logic (mCPL), which allows use of a stronger transistor (in our case the p-FET) to provide more of the current required to switch the capacitance in the device. We report the integration and characterization of this new class of gates and compare them with the equivalent CMOS structures. The characterization of inverters shows improved tolerance to process variation, up to 2.5× better delay, and 1.7× smaller area for the mCPL devices. Comparison of NOR and NAND gates shows 1.8× and 4.1× reduced gate delay. A 3× reduced energy consumption per operation is also simulated. The improved performance of the mCPL design makes it an alternative architecture for logic application of organic electronics.

In this work, we have used synchrotron-based grazing incidence X-ray scattering to measure the molecular orientation and morphology of nanostructured thin films of blended poly(3-hexylthiophene)/[6,6]-phenyl C61-butyric acid methyl ester blends patterned with nanoimprint lithography. Imprinting the blend films at 150 degrees C results in significant polymer chain orientational anisotropy, in contrast to patterning the film at only 100 degrees C. The temperature-dependent evolution of the X-ray scattering data reveals that the imprint-induced polymer reorientation remains at high temperatures even after the patterned topographic features vanish upon melting. Photovoltaic devices fabricated from the blend films imprinted at 150 degrees C exhibit a similar to 21% improvement in power conversion efficiency compared to those imprinted at 100 degrees C, consistent with a polymer chain configuration better suited to charge carrier collection.

Molecular self-assembly is a key to wide-ranging nano- and microscale applications in numerous fields. Understanding its underlying molecular level science is therefore of prime importance. This study resolves the angstrom-scale structure of the earliest and simplest self-assembled monolayer (SAM), octadecanol on amorphous-SiO2-terminated Si(001) substrate, and determines the structures temperature evolution. At low temperatures lateral hexagonal order exists, with close-packed, surface-normal molecules. At similar to 12 degrees C above the alkanols bulk melting, a fully reversible disordering transition occurs to a novel stretched liquid phase, laterally disordered, but only similar to 15% thinner SAM than in the crystalline phase. The SAM persists to >= 100 degrees C. A thermodynamic model yields here a headgroup-substrate bond energy similar to 40% lower than on crystalline sapphire, highlighting the importance of the substrates order, and near-epitaxy, for the SAMs ordering and stability.

Fluorination has been demonstrated to improve stability and processing in thiophene-containing small-molecule semiconductors. Here, the impact of partial fluorination on these parameters in a pentacene derivative is examined. Although the improvement in photostability is not as dramatic, there is a clear improvement in the stability of the chromophore upon fluorination. The improvement in processability is more dramatic; devices formed by spin-coating with the fluorinated derivative perform substantially better than those formed from the nonfluorinated compound.

In bottom‐contact organic field‐effect transistors (OFETs), the functionalization of source/drain electrodes leads to a tailored surface chemistry for film growth and controlled interface energetics for charge injection. This report describes a comprehensive investigation into separating and correlating the energetic and morphological effects of a self‐assembled monolayers (SAMs) treatment on Au, Ag, and Cu electrodes. Fluorinated 5,11‐bis(triethylsilylethynyl) anthradithiophene (diF‐TES‐ADT) and pentafluorobenzenethiol (PFBT) are employed as a soluble small‐molecule semiconductor and a SAM material, respectively. Upon SAM modification, the Cu electrode devices benefit from a particularly dramatic performance improvement, closely approaching the performance of OFETs with PFBT‐Au and PFBT‐Ag. Ultraviolet photoemission spectroscopy, polarized optical microscopy, grazing‐incidence wide‐angle X‐ray scattering elucidate the metal work function change and templated crystal growth with high crystallinity resulting from SAMs. The transmission‐line method separates the channel and contact properties from the measured OFET current–voltage data, which conclusively describes the impact of the SAMs on charge injection and transport behavior.

The crystallinity of an organic semiconductor film determines the efficiency of charge transport in electronic devices. This report presents a micro-to-nanoscale investigation on the crystal growth of fluorinated 5,11-bis(triethylgermylethynyl)anthradithiophene (diF-TEG-ADT) and its implication for the electrical behavior of organic field-effect transistors (OFETs). diF-TEG-ADT exhibits remarkable self-assembly through spin-cast preparation, with highly aligned edge-on stacking creating a fast hole-conducting channel for OFETs.

Singlet fission, the conversion of a singlet excitation into two triplet excitations, is a viable route to improved solar-cell efficiency. Despite active efforts to understand the singlet fission mechanism, which would aid in the rational design of new materials, a comprehensive understanding of mechanistic principles is still lacking. Here, we present the first study of singlet fission in crystalline hexacene which, together with tetracene and pentacene, enables the elucidation of mechanistic trends. We characterize the static and transient optical absorption and combine our findings with a theoretical analysis of the relevant electronic couplings and rates. We find a singlet fission time scale of 530 fs, which is orders of magnitude faster than tetracene (10-100ps) but significantly slower than pentacene (80-110 fs). We interpret this increased time scale as a multiphonon relaxation effect originating from a large exothermicity and present a microscopic theory that quantitatively reproduces the rates in the acene family.

The vertical integration of graphene with inorganic semiconductors, oxide semiconductors, and newly emerging layered materials has recently been demonstrated as a promising route toward novel electronic and optoelectronic devices. Here, we report organic thin film transistors based on vertical heterojunctions of graphene and organic semiconductors. In these thin heterostructure devices, current modulation is accomplished by tuning of the injection barriers at the semiconductor/graphene interface with the application of a gate voltage. N-channel devices fabricated with a thin layer of C60 show a room temperature on/off ratio >10(4) and current density of up to 44 mAcm(-2). Because of the ultrashort channel intrinsic to the vertical structure, the device is fully operational at a driving voltage of 200 mV. A complementary p-channel device is also investigated, and a logic inverter based on two complementary transistors is demonstrated. The vertical integration of graphene with organic semiconductors via simple, scalable, and low-temperature fabrication processes opens up new opportunities to realize flexible, transparent organic electronic, and optoelectronic devices.

We present the excimer laser crystallization of amorphous silicon on a low dielectric constant (low-k) insulator for very large scale integration monolithic 3D integration and demonstrate that low dielectric constant materials are suitable substrates for 3D integration through laser crystallization of silicon thin films. We crystallized 100 nm amorphous silicon on top of SiO2 and SiCOH (low-k) dielectrics, at different material thicknesses (1 μm, 0.75 μm, and 0.5 μm). The amorphous silicon crystallization on low-k dielectric requires 35% less laser energy than on an SiO2 dielectric. This difference is related to the thermal conductivity of the two materials, in agreement with one dimensional simulations of the crystallization process. We analyzed the morphology of the material through defect-enhanced microscopy, Raman spectroscopy, and X-ray diffraction analysis. SEM micrographs show that polycrystalline silicon is characterized by micron-long grains with an average width of 543 nm for the SiO2 sample and 570 nm for the low-k samples. Comparison of the Raman spectra does not show any major difference in film quality for the two different dielectrics, and polycrystalline silicon peaks are closely placed around 517 cm−1. From X-ray diffraction analysis, the material crystallized on SiO2 shows a preferential (111) crystal orientation. In the SiCOH case, the 111 peak strength decreases dramatically and samples do not show preferential crystal orientation. A 1D finite element method simulation of the crystallization process on a back end of line structure shows that copper (Cu) damascene interconnects reach a temperature of 70 °C or lower with a 0.5 μm dielectric layer between the Cu and the molten Si layer, a favorable condition for monolithic 3D integration.

Molecular orientation and packing motif governs charge-transport property of organic semiconductor films, especially for planar small molecules. We analyze the surface-induced orientation of copper phthalocyannine (CuPc) molecules deposited on graphene or poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) covered indium-tin-oxide (PEDOT:PSS/ITO). The CuPc films deposited on graphene are templated with preferential face-on stacking, whereas the molecules on PEDOT:PSS/ITO crystallize with edge-on ordering. Static current–voltage measurement and small-signal impedance spectroscopy are combined to elucidate the structural impact on the electrical response when those films are part of a rectifying diode. The graphene-templated diode shows enhanced out-of-plane hole conduction as compared to the diode with a PEDOT:PSS/ITO contact. Equivalent circuits describing charge injection and transport properties are proposed.

The electrophoretic deposition (EPD) of quantum dots (QDs) after ligand exchange is investigated, along with its use as one step in the formation of photovoltaic (PV) device structures. The ligands on CdSe QDs are exchanged to pyridine and these QDs are deposited by EPD in heterojunction PV structures, which are then tested.

Nanostructured grating surfaces with groove widths less than 200 nm impose boundary conditions that frustrate the natural molecular orientational ordering within thin films of blended polymer semiconductor poly(3-hexlythiophene) and phenyl-C-61-butyric acid methyl ester, as revealed by grazing incidence X-ray scattering measurements. Polymer interactions with the grating sidewall strongly inhibit the polymer lamellar alignment parallel to the substrate typically found in planar films, in favor of alignment perpendicular to this orientation, resulting in a preferred equilibrium molecular configuration difficult to achieve by other means. Grating surfaces reduce the relative population of the parallel orientation from 30% to less than 5% in a 400 nm thick film. Analysis of in-plane X-ray scattering with respect to grating orientation shows polymer backbones highly oriented to within 10 degrees of parallel to the groove direction.

Solution-processed organic field-effect transistors (OFETs) using chemically modified copper electrodes are reported. The purpose of this study is to shed light on the use of inexpensive copper electrodes in bottom-contact OFETs, which is consistent with the major goal of organic electronics: the realization of low-cost electronics. 6,13-Bis(triisopropylsilylethynyl)pentacene was used for solution-processed hole-transporting molecular films and pentafluorobenzenethiol was used to form self-assembled monolayers (SAMs) on the contact metals. We conducted a comparative study on copper and gold contacts and realized that, under the same performance improvement schemes, via SAM treatment and controlled crystal growth, the copper electrode device experienced a more significant enhancement than the gold electrode device. We attribute the beneficial effects of SAMs to the improved charge injection and transport properties, which are critical double effects from the fluorinated aromatic SAM structure. Grazing-incidence wide-angle X-ray scattering (GIWAXS) measurements showed that templating property of SAMs promotes the crystallization of TIPS-pentacene films at the metal/organic interface. The presented result indicates that copper can be regarded as a promising candidate for reducing the use of gold in organic-based circuits and systems, where the cost-effective production is an important issue.