Research

The Moulé group chooses research projects in areas that will have maximal long term impact on future science. We focus on development of characterization techniques, data analysis, and model building. Our research efforts can be roughly divided into four larger projects:   

Organic Semiconductors (OSCs) have received widespread attention due to their promising qualities like superior absorbance/emission, easy chemical tunablity, low-temperature solution processing, lightweight and flexible substrates, and low environmental toxicity. A significant obstacle for the industrial development of OSCs is the lack of a patterning technology that is inexpensive, rapid and viable. Photomask lithography is impossible because the OSC cannot withstand the processing steps. The Moule group recently developed a new photopatterning concept that enables nanopatterning of OSC polymers. The principle concept is to turn the OSC into a negative resist and to directly photo-pattern the OSC. We have studied resolution and write speed as functions of the solvent quality, polymer identity, and with various patterning light sources. The patterning rate is proportional light intensity squared, which comes from a highly non-linear etch rate as a function of temperature. This nonlinear rate can be modeled using a single activation energy. Photothermal patterning is a new disruptive paradigm for OSC device processing.

Jacobs, Ian E; Bedolla-Valdez, Zaira I; Rotondo, Brandon T; Bilsky, David J; Lewis, Ryan; Oviedo, Alejandra N Ayala; Gonel, Goktug; Armitage, John; Li, Jun; Moulé, Adam J

Super-Resolution Photothermal Patterning in Conductive Polymers Enabled by Thermally Activated Solubility Journal Article

In: ACS nano, vol. 15, no. 4, pp. 7006–7020, 2021.

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Bedolla-Valdez, Zaira I; Xiao, Rui; Cendra, Camila; Fergerson, Alice S; Chen, Zekun; Gonel, Goktug; Salleo, Alberto; Yu, Dong; Moulé, Adam J

Reversible Doping and Photo Patterning of Polymer Nanowires Journal Article

In: Advanced Electronic Materials, vol. 6, no. 10, pp. 2000469, 2020.

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Molecular doping is the process of adding a molecule to a OSC that adds or removes an electron to the polymer backbone, and thereby greatly increases the charge conductivity. Unlike inorganic doping, a molecular dopant is in equilibrium with the lattice and only has a probability to ionize based on energetics. The Moule group invented a process called sequential solution doping that enables separate processing of the polymer and dopant and more efficient dopant ionization. This discovery led to new research on soluble molecular dopants with increased doping potential. Unfortunately, soluble dopant diffuse in the polymer matrix. We developed an optical microscopy based technique to quantify dopant diffusion. Another project in molecular doping is to quantify the doping level as a function of the solution dopant concentration. We also focus on exchange reactions that replace molecular dopants with non-reversible ions that lead to doping levels of >70% for many polymers.

Murrey, Tucker L; Riley, Margaret A; Gonel, Goktug; Antonio, Dexter D; Filardi, Leah; Shevchenko, Nikolay; Mascal, Mark; Moulé, Adam J

Anion Exchange Doping: Tuning Equilibrium to Increase Doping Efficiency in Semiconducting Polymers Journal Article

In: The journal of physical chemistry letters, vol. 12, no. 4, pp. 1284–1289, 2021.

Links | BibTeX

Jacobs, Ian E; Moulé, Adam J

Controlling molecular doping in organic semiconductors Journal Article

In: Advanced Materials, vol. 29, no. 42, pp. 1703063, 2017.

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Jacobs, Ian E; Aasen, Erik W; Oliveira, Julia L; Fonseca, Tayane N; Roehling, John D; Li, Jun; Zhang, Gwangwu; Augustine, Matthew P; Mascal, Mark; Moulé, Adam J

Comparison of solution-mixed and sequentially processed P3HT: F4TCNQ films: effect of doping-induced aggregation on film morphology Journal Article

In: Journal of Materials Chemistry C, vol. 4, no. 16, pp. 3454–3466, 2016.

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Li, Jun; Rochester, Chris W; Jacobs, Ian E; Friedrich, Stephan; Stroeve, Pieter; Riede, Moritz; Moulé, Adam J

Measurement of small molecular dopant F4TCNQ and C60F36 diffusion in organic bilayer architectures Journal Article

In: ACS applied materials & interfaces, vol. 7, no. 51, pp. 28420–28428, 2015.

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Molecular vibrations play an important role in scientific areas ranging from charge transport in organic semiconductors to correlated disorder in MOFs and beyond. We are known for producing the highest-quality predictions of molecular vibrations in organic semiconductors. Recently, we’ve worked with collaborators in the department and at Lawrence Livermore National Lab (LLNL) to expand our simulations to larger, more complex systems using machine learning methods. This work is known as the Davis Computational Spectroscopy (DCS) project and includes a computational workflow (Welcome to DCS-Flow’s documentation! — DCS-Flow documentation) as well as a repository of past calculations https://dcs-discover.web.app/

Harrelson, Thomas F; Dettmann, Makena; Scherer, Christoph; Andrienko, Denis; Moulé, Adam J; Faller, Roland

Computing inelastic neutron scattering spectra from molecular dynamics trajectories Journal Article

In: Scientific reports, vol. 11, no. 1, pp. 1–12, 2021.

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Harrelson, Thomas F; Dantanarayana, Varuni; Xie, Xiaoyu; Koshnick, Correy; Nai, Dingqi; Fair, Ryan; nez, Sean A Nu; Thomas, Alan K; Murrey, Tucker L; Hickner, Michael A; others,

Direct probe of the nuclear modes limiting charge mobility in molecular semiconductors Journal Article

In: Materials Horizons, vol. 6, no. 1, pp. 182–191, 2019.

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Harrelson, Thomas; Dantanarayana, Varuni; Bonilla, Alejandro; Troisi, Allesandro; Faller, Roland; Moule, Adam

Towards Novel Organic Electronics: Integrating Simulation and Neutron Scattering Inproceedings

In: APS March Meeting Abstracts, pp. P56–009, 2018.

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The Moule group uses Electron tomography to study the structure of three-dimensional functional materials. First we studied organic  photovoltaic devices made with various polymers and a fullerene acceptor with a metal cluster in the fullerene. The metal cluster made an excellent contrast agent for the microscopy. Found that a BHJ layer required three phases, polymer rich, fullerene rich, and mixed and that the composition of these phases could be quantified. Using tomography we studied the effects of annealing, polymer/fullerene ratio, vertical segregation at metal electrodes, and blade coated vs spin coated films. We also used the tomograms to create 3D charge transport models. The best publication in this area was recently completed in collaboration with Jean Luc Bredas

Li, Haoyuan; Sini, Gjergji; Sit, Joseph; Moulé, Adam J; Bredas, Jean-Luc

Understanding charge transport in donor/acceptor blends from large-scale device simulations based on experimental film morphologies Journal Article

In: Energy & Environmental Science, vol. 13, no. 2, pp. 601–615, 2020.

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The current material we are working on is Quantum dot super lattices. QDs are versatile building blocks whose interactions (electronic and excitonic) in self-assembled solids can be tuned by changing QD size, size distribution, shape, inter-QD spacing, spatial ordering, surface chemistry, and QD-QD bridging. We are developing advanced experimental and analytical tomographic tools to study and draw correlations between these microscopic and mesoscopic structural features aiming for establishing better charge transport model and better material fabrications.

Chu, Xiaolei; Heidari, Hamed; Abelson, Alex; Unruh, Davis; Hansen, Chase; Qian, Caroline; Zimanyi, Gergely; Law, Matt; Moulé, Adam J

Structural characterization of a polycrystalline epitaxially-fused colloidal quantum dot superlattice by electron tomography Journal Article

In: Journal of Materials Chemistry A, vol. 8, no. 35, pp. 18254–18265, 2020.

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