Thomas Ferron, Victor Murcia, Terry McAfee, and Brian Collins all presented at the 2019 APS March Meeting in Boston, MA. Victor, Terry, and Brian all presented in the Focus Session on “Advanced Morphological Characterization in Polymers” where Brian gave the Invited Talk for the session.
Victor presented his work on combining NEXAFS measurements and DFT of molecules to create more accurate optical models for analysis of polarized resonant soft X-ray scattering (RSoXS). Terry discussed his work with developing in-situ capabilities in RSoXS showing quantitative characterization of polymer micelle structure and dynamics without using chemical labels.
Thomas presented in the Focus Session on Organic Electronics where he discussed his recent paper on charge separation affected by molecular mixing at the donor-acceptor interface in organic photovoltaic devices.
Graduate student Thomas Ferron’s work tying molecular mixing at interfaces to charge generation in organic solar cells (OSC) has been published in Journal of Materials Chemistry A. The work quantifies for the first time both the volume of the mixed phase and the efficiency of separating interfacial Charge Transfer states into free charges. A better than 99% correlation is revealed between these two phenomena in a model OSC system – made possible because both nanostructure and excited state dyanmics were measured on the exact same devices. Thomas’ analysis, furthermore, eliminates all other possible contributing factors to the correlation – implying a causal relationship that sharper interfaces (less mixing) causes higher charge separation efficiencies.
Critical to the study was a relatively new optical pump-electronic probe technique known as Time-Delayed Collection Field (TDCF). Although the technique is increasingly done around the world, the Collins group is the only one capable of the measurement in the US. This is Thomas’ second 1st-Author paper published and includes as coauthors a former Undergraduate physics major Matthew Waldrip and former Masters student Michael Pope. The work was funded by the US Department of Energy as an Early Research Career Award. Congratulations to all involved!
Undergraduate Seniors Michael Anderson [pictured] and Zachary Croft presented their thesis projects at the WSU Showcase for Undergraduate Research and Creative Activities (SURCA). They each put together a poster summarizing their findings and submitted their work for formal judging in the competition.
Obaid Alqahtani’s work on structure-property relationships in small molecule organic solar cells (SM-OSCs) has been officially published online at Advanced Energy Materials. SM-OSC devices convert sunlight into power like commercial solar panels, but this new technology could significantly lower the cost of solar power because it can be printed from inks in a roll-to-roll newspaper fashion, is light-weight and flexible, and is made from earth-abundant, non-toxic materials.
Alqahtani’s work explains how the performance of SM-OSCs depends on the details of the nanostructure, which can be tuned via processing solvent and choice of molecular side-chain. In particular, it is demonstrated that high purity nano-domains results in low/delayed charge generation and severe charge trapping, but that small, mixed domains alleviates such problems to enable high performance in these devices. Future work toward commercialization should target such nanostructure for high solar power conversion efficiencies.
The work involved a large round-robin collaboration with groups across the globe including King Abdullah University of Science and Technology (KAUST, Saudi Arabia), Stanford University (USA), University of Potsdam (Germany), and University of Queensland (Australia).
Terry McAfee has joined the Collins Research Group as postdoctoral researcher. He obtained his PhD in physics from North Carolina State University under Professor Harald Ade. His thesis was titled “Characterization and control of morphology in organic photovoltaic devices.” Recently, he completed postdoctoral work at Tulane University under Professor Wayne Reed developing an Automatic Continuous Online Monitoring of Polymerization (ACOMP) system. Terry joins the Collins group to develop a new Environmental Resonant Soft X-ray Scattering instrument which will enable in-situ/in-operando structural measurement of organic materials.
Thomas Ferron’s work on quantitative spectral RSoXS analysis has been published in Physical Review Letters.
Measurement of buried molecular interfaces enabled by resonant X-ray scattering analysis
We demonstrate a new quantitative X-ray scattering analysis that probes 3D molecular nanostructures and even buried interfaces between those structures. These organic nanomaterials are of increasing impact in bottom-up assembly, electronic devices, and biomimetic applications, but their internal structure is difficult to probe due to light elements and no or low crystallinity. For example, only planar interfaces were previously accessible with laborious and disruptive chemical tagging. This new technique eliminates the need for tagging and can investigate nonplanar interfaces more commonly found in nature. The technique is a leap in X-ray science because the analysis requires absolute scattering intensity at an absorption edge where low sample penetration depths preclude the use of calibration standards. Each molecule has a unique fingerprint encoded as a function of photon energy, which the technique uses to chemically separate components of the nanostructure. Through our new spectral analysis, complex molecular structures composed of any number of unique molecular species can now be fully analyzed.
The Collins Group has received the DOE Early Career Award, a 5 year competitive grant that includes tenure track faculty at all US universities and national laboratories. This year out of approximately 700 submissions, only 59 individuals were awarded. (See release by WSU and DOE). The grant entitled “Polarized resonant X-ray scattering to measure molecular orientation and conformation in organic nanostructures” will enable Collins’ continued state-of-the-art research in developing resonant X-ray techniques to reveal order in molecular materials, structures, and devices.
Keith Hillaire has received his Bachelor of Science in Physics from WSU. His thesis “Color-tuning polymer-based organic light emitting diodes through the addition of a cosolvent” involved research on the how processing can affect the nanomorphology and therefore the color of novel polymer OLEDs. He begins his graduate studies in the North Carolina State University Physics PhD program. Congratulations Keith!
Matthew Waldrip has received his Bachelors in Science with Honors from WSU. He worked with the Collins group developing nanosecond pump-probe methods to investigate charge generation in organic solar cells. His thesis is entitled “Disentangling the effect of pure fullerene nanodomains on charge generation and recombination in organic solar cells.” He starts his graduate studies in the Physics PhD program at Wake Forest University. Congratulations Matthew!
Michael Pope has successfully defended his masters project entitled “Using resonant X-ray scattering to determine how structure controls the charge generation process in PCPDTBT:PC70BM solar cells.” Congratulations Michael!