Adam J Moulé

Adam J Moulé
University of California, Davis | UCD · Department of Chemical Engineering and Materials Science

PhD in Physical Chemistry from UC Berkeley

About

102
Publications
22,783
Reads
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5,520
Citations
Additional affiliations
July 2007 - present
University of California, Davis
Position
  • Professor (Associate)
January 2004 - June 2007
University of Cologne
Position
  • Alexander von Humboldt Postdoctoral Fellow

Publications

Publications (102)
Article
Knowledge of the full phonon spectrum is essential to accurately calculate the dynamic disorder (σ) and hole mobility (μh) in organic semiconductors (OSCs). However, most vibrational spectroscopy techniques under-measure the phonons, thus limiting the phonon validation. Here, we measure and model the full phonon spectrum using multiple spectroscopi...
Article
Molecular doping of conjugated polymers causes bleaching of the neutral absorbance and results in new polaron absorbance transitions in the mid and near infrared. Here, the concentration dependent changes in the spectra for a series of molecularly doped diketopyrrolopyrrole (DPP) co-polymers with a series of ultra-high electron affinity cyanotrimet...
Article
Patterned semiconductors are essential for the fabrication of nearly all electronic devices. Over the last two decades, semiconducting polymers (SPs) have received enormous attention due to their potential for creating low-cost flexible electronic devices, while development of scalable patterning methods capable of producing sub-μm feature sizes ha...
Article
Atomic vibrations can inform about materials properties from hole transport in organic semiconductors to correlated disorder in metal-organic frameworks. Currently, there are several methods for predicting these vibrations using simulations, but the accuracy-efficiency tradeoffs have not been examined in depth. In this study, rubrene is used as a m...
Article
We describe an automated workflow that connects a series of atomic simulation tools to investigate the relationship between atomic structure, lattice dynamics, materials properties, and inelastic neutron scattering (INS) spectra. Starting from the atomic simulation environment (ASE) as an interface, we demonstrate the use of a selection of calculat...
Article
Full-text available
Inelastic neutron scattering (INS) provides a weighted density of phonon modes. Currently, INS spectra can only be interpreted for perfectly crystalline materials because of high computational cost for electronic simulations. INS has the potential to provide detailed morphological information if sufficiently large volumes and appropriate structural...
Article
Doping-induced solubility control (DISC) patterning is a recently developed technique that uses the change in polymer solubility upon doping, along with an optical dedoping process, to achieve high-resolution optical patterning. DISC patterning can produce features smaller than predicted by the diffraction limit; however, no mechanism has been prop...
Article
High electron affinity (EA) molecules p-type dope low ionization energy (IE) polymers, resulting in an equilibrium doping level based on the energetic driving force (IE-EA), reorganization energy, and dopant concentration. Anion exchange doping (AED) is a process whereby the dopant anion is exchanged with a stable ion from an electrolyte. We show t...
Article
New organic-soluble dopants have record high electron affinity values and show outstanding doping performance with high ionization energy co-polymers.
Article
Recent development of dopant induced solubility control (DISC) patterning of polymer semiconductors has enabled direct‐write optical patterning of poly‐3‐hexylthiophene (P3HT) with diffraction limited resolution. Here, the optical DISC patterning technique to the most simple circuit element, a wire, is applied. Optical patterning of P3HT and P3HT d...
Article
Merocyanines (MC) are a versatile class of small molecule dyes. Their optoelectronic properties are easily tunable by chemically controlling their donor-acceptor strength, and their structural properties can be tuned by simple side chain substitution. This manuscript demonstrates a novel series of MC featuring an indoline donor with varying hydroca...
Article
Charge mobility of crystalline organic semiconductors (OSC) is limited by local dynamic disorder. Recently, the charge mobility for several high mobility organic semiconductors, including TIPS-Pentacene, were accurately predicted from a density functional theory (DFT) simulation constrained by the crystal structure and the inelastic neutron scatter...
Article
Organic semiconductors (OSCs) offer a new avenue to the next-generation electronics, but the lack of a scalable and inexpensive nanoscale patterning/deposition technique still limits their use in electronic applications. Recently, a new lithographic etching technique was introduced that uses molecular dopants to reduce semiconducting polymer solubi...
Article
Molecular dopants are increasingly studied to enhance the conductivity of semiconducting polymers. Most available p-type dopants have low solubility in common solvents and moderate electron affinities (EA), which makes solution processing difficult and limits the range of semiconducting polymers that can be doped. Here, we describe the synthesis an...
Article
Full-text available
Molecular doping is a crucial tool for controlling the charge-carrier concentration in organic semiconductors. Each dopant molecule is commonly thought to give rise to only one polaron, leading to a maximum of one donor:acceptor charge-transfer complex and hence an ionization efficiency of 100%. However, this theoretical limit is rarely achieved be...
Article
Many organic electronic devices require vertically layered structures to operate. This manuscript demonstrates an additive solution process for depositing multiple layers of semiconducting polymer (SP) films by controlling film solubility with molecular dopants. During multi-layer deposition the bottom layers are exposed to a series of solvent envi...
Article
{There is a critical need to develop a method to pattern semiconducting polymers for device applications on the sub-micrometer scale. Dopant induced solubility control (DISC) patterning is a recently published method for patterning semiconductor polymers that has demonstrated sub-micron resolution. DISC relies on the sequential addition of molecula...
Article
Recent theories suggest that low frequency dynamic intra- and molecular intermolecular motions in organic semiconductors (OSCs) are critical to determining the hole mobility. So far, however, it has not been possible to probe these motions directly experimentally and therefore no unequivocal and quantitative link exists between molecular-scale ther...
Article
When an organic semiconductor (OSC) is blended with an electron acceptor molecule that can act as a p-type dopant, there should ideally be complete (integer) transfer of charge from the OSC to the dopant. However, some dopant-OSC blends instead form charge transfer complexes (CTCs), characterized by fractional charge transfer (CT) and strong orbita...
Article
Conformational and energetic disorder in organic semiconductors (OSCs) reduces charge and exciton transport due to structural defects thus reducing efficiency in devices such as organic photovoltaics and organic light-emitting diodes. The main structural heterogeneity is due to the twisting of the polymer backbone that occurs even in polymers that...
Article
Mixtures of conjugated polymers and quantum dot nanocrystals present an interesting solution-processable materials system for active layers in optoelectronic devices, including solar cells. We use scanning transmission electron microscopy to investigate the effects of exchanging the capping ligand of quantum dots on the three-dimensional morphology...
Article
1,8-diiodooctane (DIO) is a high boiling point solvent additive commonly used to control the active layer morphology of bulk-heterojuction organic photovoltaic (OPV) films. OPV devices fabricated using DIO often show improved efficiency, but recent studies have suggested that light exposure may cause residual DIO to react with OPV materials. We use...
Article
The field of organic electronics thrives on the hope of enabling low-cost, solution-processed electronic devices with mechanical, optoelectronic, and chemical properties not available from inorganic semiconductors. A key to the success of these aspirations is the ability to controllably dope organic semiconductors with high spatial resolution. Here...
Article
Full-text available
Recent advances in efficiency of organic photovoltaics are driven by judicious selection of processing conditions that result in a “desired” morphology. An important theme of morphology research is quantifying the effect of processing conditions on morphology and relating it to device efficiency. State-of-the-art morphology quantification methods p...
Article
Understanding the nature of dopant dynamics in the solid state is critical for improving the longevity and stability of organic electronic devices and for optimizing the doping-induced solubility control (DISC) patterning method. In this work, we use quasi-elastic neutron scattering (QENS) and fluorescence quenching techniques to develop a comprehe...
Article
The greatest advantage of organic materials is the ability to synthetically tune desired properties. However, structural heterogeneity often obfuscates the relationship between chemical structure and functional properties. Inelastic neutron scattering (INS) is sensitive to both local structure and chemical environment and provides atomic level deta...
Article
Organic electronics is a popular and rapidly growing field of research. The optical, electrical and mechanical properties of organic molecules and materials can be tailored using increasingly well controlled synthetic methods. The challenge and fascination with this field of research is derived from the fact that not only the chemical identity, but...
Article
Doping-induced solubility control (DISC) is a patterning technique for semiconducting polymers that utilizes the reduction in polymer solubility upon p-type doping to provide direct, optical control of film topography and doping level with sub-diffraction-limited resolution. In article 1603221, A. J. Moulé and co-workers demonstrate the optical ded...
Article
Although doping is a cornerstone of the inorganic semiconductor industry, most devices using organic semiconductors (OSCs) make use of intrinsic (undoped) materials. Recent work on OSC doping has focused on the use of dopants to modify a material's physical properties, such as solubility, in addition to electronic and optical properties. However, i...
Article
Doping-induced solubility control (DISC) is a recently introduced photolithographic technique for semiconducting polymers, which utilizes reversible changes in polymer solubility upon doping to allow the polymer to function as its own photoresist. Central to this process is a wavelength sensitive optical dedoping reaction, which is poorly understoo...
Article
Doping-induced solubility control is a patterning technique for semiconducting polymers, which utilizes the reduction in polymer solubility upon p-type doping to provide direct, optical control of film topography and doping level. In situ direct-write patterning and imaging are demonstrated, revealing sub-diffraction-limited topographic features. P...
Article
Full-text available
High efficiency polymer:fullerene photovoltaic device layers self-assemble with hierarchical features from ångströms to 100’s of nanometers. The feature size, shape, composition, orientation, and order all contribute to device efficiency and are simultaneously difficult to study due to poor contrast between carbon based materials. This study seeks...
Article
As organic electronics improve, there is increased research interest on the longevity and stability of both the device and individual material components. Most of these studies focus on post deposition degradation and aging of the film. In this article, we examine the stability of polyelectrolyte dispersions before film coating. We observe substant...
Article
Solution-processed organic electronic devices often consist of layers of polar and non-polar polymers. In addition, either of these layers could be doped with small molecular dopants. It is extremely important for device stability to understand the diffusion behavior of these molecular dopants under the thermal stress and whether the dopants have p...
Article
Doping polymeric semiconductors often drastically reduces the solubility of the polymer, leading to difficulties in processing doped films. Here, we compare optical, electrical, and morphological properties of P3HT films doped with F4TCNQ, both from mixed solutions and using sequential solution processing with orthogonal solvents. We demonstrate th...
Article
The diffusion of molecules through and between organic layers is a serious stability concern in organic electronic devices. In this work, the temperature-dependent diffusion of molecular dopants through small molecule hole transport layers is observed. Specifically we investigate bilayer stacks of small molecules used for hole transport (MeO-TPD) a...
Conference Paper
Organic electronics promise to provide flexible, large-area circuitry such as photovoltaics, displays, and light emitting diodes that can be fabricated inexpensively from solutions. A major obstacle to this vision is that most conjugated organic materials are miscible, making solution-based fabrication of multilayer or micro- to nanoscale patterned...
Article
To overcome the poor solubility of the widely used p-type dopant 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ), a series of structure-modified, organic p-type dopants have been synthesized to include alkyl ester groups designed to enable solubility and miscibility control. UV-vis-NIR and cyclic voltammetry measurements show increase...
Article
Organic electronics promise to provide flexible, large-area circuitry such as photovoltaics, displays, and light emitting diodes that can be fabricated inexpensively from solutions. A major obstacle to this vision is that most conjugated organic materials are miscible, making solution-based fabrication of multilayer or micro- to nanoscale patterned...
Article
Full-text available
Poly(3,4-ethylenedioxythiophene)-- poly(styrenesulphonate) (PEDOT:PSS) is the most used organic hole injecting or hole transporting material. The hole carrying matrix PEDOT is highly doped by the acidic dopant PSS. When coated onto a substrate, PEDOT:PSS makes a highly uniform conductive layer and a thin (<5 nm) overlayer of PSS covers the air inte...
Article
The morphology in mixed bulk-heterojunction films are compared using three different quantitative measurement techniques. We compare the vertical composition changes using high-angle annular dark-field scanning transmission electron microscopy with electron tomography and neutron and x-ray reflectometry. The three measurement techniques yield quali...
Article
Full-text available
To meet the huge demand for renewable energy, significant research effort focuses on creating efficient organic photovoltaic (OPV) devices. In comparison to silicon-based semiconductors, OPB materials have many superior properties such as cost effectiveness, being lightweight, and flexibility, which lead to a high potential for the replacement of s...
Chapter
Each year we are bombarded with B.Sc. and Ph.D. applications from students that want to improve the world. They have learned that their future depends on changing the type of fuel we use and that solar energy is our future. The hope and energy of these young people will transform future energy technologies, but it will not happen quickly. Organic p...
Article
Full-text available
http://chemgroups.ucdavis.edu/%7Eosterloh/pubs/ref_70.pdf Living organisms use fractal structures to optimize material and energy transport across regions of differing size scales. Here we test the effect of fractal silver electrodes on light distribution and charge collection in organic semiconducting polymer films made of P3HT and PCBM. The semic...
Article
Full-text available
http://chemgroups.ucdavis.edu/%7Eosterloh/pubs/ref_69.pdf Surface photovoltage (SPV) spectra are reported for separate films of (6,6)-phenyl-C61-butyric acid methyl ester (PCBM) and for regioregular and regiorandom poly(3-hexylthiophene) (P3HT):PCBM bulk heterojunctions, as a function of wavelength, film thickness, thermal annealing, and substrate....
Article
Surface photovoltage spectroscopy (SPS) was used to probe photon induced charge separation in thin films of regioregular and regiorandom poly(3-hexylthiophene) (P3HT) as a function of excitation energy. Both positive and negative photovoltage signals were observed under sub-band-gap (<2.0 eV) and super-band-gap (>2.0 eV) excitation of the polymer....
Article
Full-text available
The hole transport polymer poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) derives many of its favorable properties from a PSS-rich interfacial layer that forms spontaneously during coating. Since PEDOT:PSS is only usable as a blend it is not possible to study PEDOT:PSS without this interfacial layer. Through the use of the se...
Article
Full-text available
Establishing how fabrication conditions quantitatively affect the morphology of organic blends opens the possibility of rationally designing higher efficiency materials; yet such a relationship remains elusive. One of the major challenges stems from incomplete three-dimensional representations of morphology, which is due to the difficulties of perf...
Article
Solvent additives have been explored as a reliable way to control the morphology in bulk-heterojunction (BHJ) layers for improved device performance. We show that the choice of solvent additives has direct implications on morphological evolution, i.e. poly(3-hexylthiophene) (P3HT):[6,6]-phenyl C61-butyric acid methyl ester (PCBM) BHJ films processe...
Article
Full-text available
The effect of the strong electron acceptor, 2,3,5,6-tetra?uoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ), on poly (3-hexylthiophene) (P3HT) aggregates is studied. F4-TCNQ is commonly used as a dopant for P3HT, however, relatively little is currently known about its affect on polymer conformation and packing. Resonance Raman and optical spectra of...
Article
Abstract The three-dimensional morphology of mixed organic layers are quantitatively measured using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) with electron tomography for the first time. The mixed organic layers used for organic photovoltaic applications have not been previously imaged using STEM tomograp...
Article
The composition of polymer-fullerene blends is a critical parameter for achieving high efficiencies in bulk-heterojunction (BHJ) organic photovoltaics. Achieving the “right” materials distribution is crucial for device optimization as it greatly influences charge-carrier mobility. The effect of the vertical concentration profile of materials in spi...
Article
Nanofibers (NFs) of the prototype conjugated polymer, poly(3-hexylthiophene) (P3HT), displaying H- and J-aggregate character are studied using temperature- and pressure-dependent photoluminescence (PL) and transient absorption (TA) spectroscopy. Single J-aggregate NF spectra show a decrease of the 0-0/0-1 vibronic intensity ratio from ~2.0 at 300K...
Article
The directional dependence of electron blocking by poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is investigated in organic photovoltaic devices. In a conventional OPV architecture we find that a doped interlayer forms between poly(3-hexylthiophene) (P3HT) and the PSS-rich top layer of spin-coated PEDOT:PSS films. In an invert...
Conference Paper
The systematic multiscale of heterogeneous soft matter systems is an area of current research. We are first developing models for a variety of fullerenes used as electron acceptors in a solar cell's photo-active layer. The donor (typically thiophene based polymers) and acceptor are generally mixed together to produce a bicontinuous percolating netw...
Article
Full-text available
We develop a model for charge trapping on conjugated polymer chains using a continuous representation of the polymer. By constraining the motion to along the chain, we find that kinks along the chain serve as points of attraction and can induce localization and spontaneous buckling of the chain. We implement this in a model system of a conjugated p...
Article
Full-text available
Solution-processed tandem polymer solar cells are demonstrated using stacked perovskite, (TBA,H) Ca 2 Nb 3 O 10 (CNO), semiconductor nanosheets as an electron transport layer (ETL) within the recombination layers. Two poly(3-hexylthiophene):(6,6)-phenyl-C 61 -butyric acid methyl ester, P3HT:PCBM, sub-cells connected in series via a CNO–poly(3,4-eth...
Article
P3HT/PCBM bilayer samples were fabricated by spin coating PCBM dissolved in CH2Cl2 onto P3HT films. Dissolution of the P3HT does not occur because CH2Cl2 is a nonsolvent for P3HT. We show using steady-state spectroscopy, neutron reflectometry, and current–voltage measurements that substantial mixing occurs between the P3HT and the PCBM during the P...
Article
Full-text available
We demonstrate the ability to control the microstructural order of self-assembled nanofibers of poly(3-hexylthiophene) (P3HT) and link structure differences with formation conditions. We control the crystallization conditions of the P3HT chains through the use of various solvents and show that distinct differences in overall organization occur betw...
Article
Full-text available
For the last decade, researchers have attempted to construct photovoltaic (PV) devices using a mixture of inorganic nanoparticles and conjugated polymers. The goal is to construct layers that use the best properties of each material e.g., flexibility from the polymer and high charge mobility from the nanoparticles or blue absorbance from the polyme...
Article
Nanofibers (NFs) of poly-3-hexylthiophene (P3HT) assembled in toluene exhibit single-chain J-aggregate character. Absorption, fluorescence emission, and Raman spectroscopy of dilute NF dispersions demonstrate that P3HT chains possess long-range intrachain order (planarity) that suppresses interchain exciton coupling. We demonstrate that a delicate...
Article
We characterize thin films of a new conductive copolymer, sulfonated poly(thiophene-3-[2-(2-methoxyethoxy)ethoxy]-2,5-diyl) (S-P3MEET), with various chemical additives to determine if the films are suitable for use as a hole transport layer in organic electronic devices. Using atomic force microscopy, Kelvin probe, and contact angle measurements, w...
Article
Broadband femtosecond transient absorption spectroscopy is used to explore the mechanisms underlying excited-state and ground-state exciton relaxation in poly(3-hexylthiophene) (P3HT) solution. We focus on the picosecond spectral shifts in the ground and excited states of P3HT, using pump–probe (PP) and pump–dump–probe (PDP) techniques to investiga...
Article
Recombination in poly-3-hexylthiophene (P3HT) blends with five fullerene acceptors was resolved with temperature-dependent transient absorption spectroscopy. Recombination rates were temperature and acceptor dependent with differing timescales originating from acceptor functionalization and fullerene size. Acceptors with increasing numbers of sidec...
Article
Full-text available
The performance of bulk-heterojunction (BHJ) solar cells is strongly correlated with the nanoscale structure of the active layer. Various processing techniques have been explored to improve the nanoscale morphology of the BHJ layer, e.g., by varying the casting solvent, thermal annealing, solvent annealing, and solvent additives. This paper highlig...
Article
Organic bulk-heterojunction solar cells are being developed as a low-cost alternative to inorganic photovoltaics. A key step to producing high-efficiency bulk-heterojunction devices is film curing using either heat or a solvent atmosphere. All of the literature examining the curing process have assumed that improvement of the bulk-heterojunction mo...
Article
Organic photovoltaic devices, which include polymer-based solar cells, show promise as cheap alternatives to silicon-based photovoltaics. Polymer solar cells use a mixture of a light-absorbing conducting polymer as the electron donor and a fullerene derivative as the electron acceptor in the solar cell's photoactive layer. The components are genera...
Presentation
The systematic coarse-graining of heterogeneous soft matter systems is an area of current research. We show how the Iterative Boltzmann Inversion systematically develops models for polymers in different environments. We present the scheme and a few applications. We study polystyrene in various environments and compare the different models from the...