2023 Rising Stars

WEDNESDAY, MAY 31, 2023

TIME	EVENT	LOCATION
6:00 pm - 8:30 pm	Welcome Reception	Frog & Firkin, 874 E. University Blvd.

---

THURSDAY, JUNE 1, 2023

TIME	EVENT	LOCATION
8:00 pm - 9:00 am	Breakfast	ENR2, Cafe Commons
9:00 pm - 10:30 pm	Elevator pitch practice	ENR2, S107
10:30 am - 11:00 am	Break	ENR2, Cafe Commons
11:00 am - 12:00 pm	Hybrid Career Panel with Existing Navel Workforce	ENR2, S107 & https://arizona.zoom.us/j/83526996367 password: stars
12:00 pm - 1:30 pm	Lunch	ENR2, Cafe Commons
1:30 pm - 2:00 pm	Plenary/Research Talk from Naval Workforce: Dr. Chase Ellis "Low-Loss Nanophotonics in the Mid- and Long-Wave Infrared"	ENR2, S107
2:00 pm - 2:25 pm	Anna Roche, University of Arizona "Near-Field Imaging of Excitons in Transition Metal Dichalcogenides"	ENR2, S107
2:25 pm - 2:50 pm	Justin Bonner, UT Dallas "Flexible Transparent Conducting Electrode Fabricated by Blade Coating and Photonic Curing"	ENR2, S107
2:50 pm - 3:15 pm	Joseph Romo, Purdue University "All-Polymeric Flexible and Transparent Joule Heater"	ENR2, S107
3:15 pm - 3:45 pm	Break	ENR2, Cafe Commons
3:45 pm - 4:10 pm	Aaron Woeppel, Purdue University "Outlining Molecularly Imprinted Polymer Organic Electrochemical Transistors as Flexible and Scalable Energetics' Trace Detection Solution"	ENR2, S107
4:10 pm - 4:35 pm	Spencer Yeager, University of Arizona "Using Scanning Electrochemical Cell Microscopy to Understand Nanoscale Electrochemistry of Printable Electronic Materials	ENR2, S107
4:35 pm - 5:00 pm	Garrett Collins, University of Utah "Tracking the Initial Stages of Electrochemical Doping of Organic Mixed Conductors with Photoluminescence Spectroscopy"	ENR2, S107
5:30 pm	Dinner	University of Arizona Sands Club

---

FRIDAY, JUNE 2, 2023

TIME	EVENT	LOCATION
8:00 am - 9:00 am	Breakfast	ENR2, Cafe Commons
9:00 am - 9:30 am	Plenary/Research Talk from Naval Workforce: Dr. Janice Boercker "Coupling Infrared Excitons and Plasmons in Hybrid Nanostructures"	ENR2, S107 & https://arizona.zoom.us/j/81934112003 password: stars
9:30 am - 9:55 am	Patrick Lohr, University of Arizona "Characterizing Molecular Additives for Metal Halide Perovskites using Density Functional Theory"	ENR2, S107
9:55 am - 10:20 am	Hannah Contreras, University of Washington "Does Improving Energy Alignment Lower Voc Loss in High Efficiency Wide Gap Perovskite Solar Cells?"	ENR2, S107
10:20 am - 10:50 am	Break	ENR2, Cafe Commons
10:50 am - 11:15 am	Roxanne Balany, University of Hawaii "Field-Assisted Aerosol Jet Printing for Printed Electronics"	ENR2, S107
11:15 am - 11:40 am	Julia Huddy, Dartmouth "Rapid 2D Patterning of High-Performance Perovskites Using Large Area Flexography"	ENR2, S107
11:40 am - 12:05 pm	Jonathan Nguyen, University of Minnesota "Applying Solution-Processing Principles Towards Self-Aligned Printed Diodes"	ENR2, S107
12:05 pm - 1:30 pm	Lunch	ENR2, Cafe Commons
1:30 pm - 2:00 pm	Plenary/Research Talk from Naval Workforce: Dr. Adam Colbert "Enhanced Infrared Photodiodes Based on PbS/PbClx Core/Shell Nanocrystals"	ENR2, S107
2:00 pm - 2:25 pm	William Hartnett, University of Minnesota "Reducing Variance in Self-Aligned Inkjet-Printed Resistors"	ENR2, S107
2:25 pm - 2:50 pm	Nathan Woodward, NC State "Autonomous, Closed-Loop Optimization of Hybrid Perovskite Anti-Solvent Drip"	ENR2, S107
2:50 pm - 3:15 pm	Jacob Mauthe, NC State "Accelerated Photodegradation Study of Multi-Component Organic Photovoltaic Blends Using Robotic Palletization and High-Throughput Experimentation"	ENR2, S107
3:15 pm - 3:45 pm	Break	ENR2, Cafe Commons
3:45 pm - 4:10 pm	Yeena Ng, University of Minnesota "Transparent Inkjet-Printed Neural Interface Devices for Large-Area Multi-Modal Recording from the Mouse Cortex"	ENR2, S107
4:10 pm - 4:35 pm	Harry Schrikx, NC State  "Lightweight and Flexible Self-Powered Organic Photodetectors for Plant Health Monitoring"	ENR2, S107
5:30 pm	Dinner	Gentle Ben's Restaurant

 

Abstracts are in the order of presentation date and time.

Thursday June 1, 2023

 

            Plenary/Research Talk from Naval Workforce: Dr. Chase Ellis

Low-Loss Nanophotonics in the Mid- and Long-Wave Infrared

The high optical losses of metal-based plasmonic materials in the infrared have driven an extensive search for alternative lower-loss materials that can support plasmonic effects, such as sub-diffraction confinement of optical fields. One promising alternative employs polar-dielectric materials (e.g., SiC) that are capable of supporting phonon-mediated, collective oscillations of bound lattice charges (surface phonon polaritons), which result in low-loss, plasmonic-like, sub-diffractional excitations over the mid- to far-infrared spectral range. In addition to outlining the basic physics of surface phonon polariton resonances, I will also discuss our research group’s latest advances in manipulating light at the nanoscale with low-loss polar dielectric materials (e.g., SiC and calcite). This work includes our efforts to actively tune resonances, further decrease losses by tailoring resonator interactions, inverse design metamaterials, and realize hyperbolic volume confined states within nanostructured calcite crystals.

 

            Anna Roche, University of Arizona

Near-Field Imaging of Excitons in Transition Metal Dichalcogenides

Atomically thin monolayer transition metal dichalcogenides (TMDs) exhibit remarkable physical properties resulting from their reduced dimensionality. These materials give rise to an especially promising platform for fundamental studies of two-dimensional (2D) systems with wide reaching applications in optoelectronics. A direct consequence of this reduced dimensionality is the formation of strongly bound electron-hole pairs, or excitons, which govern the material's optical properties. Previous measurements of excitons in these systems have primarily relied on far-field optical spectroscopy techniques which are diffraction limited to several hundred nanometers. Here, we present a study of the exciton spectra of TMD heterostructures using a cryogenic scattering-type scanning near-field optical microscope (s-SNOM). Using a tunable visible source, we map the exciton resonances in the TMD materials with sub 100 nm spatial resolution at both room temperature and 10 K. As the temperature is lowered to 10 K, the exciton resonance spectrally blueshifts and narrows by at least an order of magnitude. These preliminary results demonstrate cryogenic visible s-SNOM to be an effective nanoscale excitonic probe. 

 

            Justin Bonner, UT Dallas

Flexible Transparent Conducting Electrode Fabricated by Blade Coating and Photonic Curing

Flexible solar cells require a transparent conducting electrode (TCE) to achieve high performance. An ideal TCE needs low sheet resistance, high transmittance, and low surface roughness. Most common TCEs are vacuum-deposited ITO films that are annealed at > 300°C. Plastic substrates cannot withstand processing at such high temperatures. Hence, we explore photonic curing (PC), which utilizes a high-intensity xenon flash lamp to rapidly heat films at µs to ms time scale through light absorption. While the intensity of the light pulse is high, the short duration ensures the energy deposited is low and will not damage the substrate below and cause a thermal expansion mismatch. Because the conductivity of metal oxide film by itself is too low, we first blade coat AgNWs, then IZO on a PET substrate containing Ag lines. The AgNWs bridge the Ag lines while the IZO makes the TCE smoother and prevents Ag from reacting with layers deposited on top. Since PC has many parameters such as pulse length, number of micro pulses, duty cycle, number of pulses, repetition rate, and voltage, a machine learning approach consisting of Latin hyper square sampling and Bayesian optimization is used to optimize the photonic curing parameters. SEM, EDX, AFM, and 4-point probe are used to further evaluate the morphology, uniformity, and sheet resistance of the TCE. We fabricate perovskite solar cells (PSCs) on top of these TCEs and compare them to PSCs made on commercially available TCEs.

 

          Joseph Romo, Purdue

All-Polymeric Flexible and Transparent Joule Heater

Transparent heaters (THs) are devices that produce heat through the Joule effect when a voltage is applied, and they are mainly made from transparent conductive materials (TCMs). The first use of TCMs was during World War II when they were used for defrosting airplane windows at high altitudes. Since then, Indium Tin Oxide (ITO) has remained the most used TCM for THs, particularly for defoggers and defrosters in vehicles, displays, avionics, advertisement boards, etc., owing particularly to its excellent optical transmittance (T550 ∼80−85%) and low sheet resistance (Rs<100 Ω/sq). However, due to the increasing demand for flexible devices, the mechanical fragility of ITO, the scarcity of indium, and the toxicity of the upstream mining processes, alternative materials have been investigated.  Recently, our group has invented a new n-doped conducting polymer (n-PBDF) which is synthesized from a simple and scalable route that features both oxidative polymerization and reductive doping in one-pot under ambient conditions. The n-PBDF ink can be solution processed with ease, and features excellent stability under ambient conditions, as well as high transmittance and low sheet resistance that can rival ITO. Moreover, it is highly compatible with scalable printing methods such as ultrasonic spray coating to produce highly conductive, transparent, and durable thin films at large scales. In my project, I am focused on studying both the underlying thermal properties of n-PBDF, as well as developing n-PBDF into an all-polymer based TH. I will highlight some of the findings from my in-progress work and offer perspectives on future steps.

 

            Aaron Woeppel, Purdue University

Outlining Molecularly Imprinted Polymer Organic Electrochemical Transistors as Flexible and Scalable Energetics’ Trace Detection Solution

Organic Electrochemical Transistors (OECTs) have established a strong presence in the nexus of solution-phase electronic and sensing applications (ex., biosensing); their appeal stems from their high flexibility, low fabrication cost and scalability. These devices contain a conductive polymer active layer which is electrochemically modulated by an electrolyte and controlled by a gate bias. This electrolyte gating operation can be applied to new applications via by supplementing the base polymer/electrolyte structure with either chemically selective or functionalized components. Here, we propose utilizing a poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) OECT, supplemented with a molecularly imprinted polymer (MIPs) barrier, to create a scalable and disposable sensor to detect explosives. MIPs are polymerized containing a template molecule that is, later, removed to form complementary pores. In sensing applications, as MIPs re adsorb template molecules, their bulk porosity decreases. When applied to a MIP-OECT, the MIP porosity can be monitored by efficiency of electrolyte gating. Importantly, MIPs can be polymerized in bulk, then ground in to powders and deposited with a binder. This particle binder system can be processed in many manners analogues to common solution or soft material techniqes(ex., printing, dropcasting, etc.). Our effort aims to create MIP-OECT sensors capable of detecting three demonstrate explosives (TNT, RDX, diethylene glycol dinitrate) and can, later, be scaled and prepared using printable electronic principles.

 

            Spencer Yeager, University of Arizona

Using Scanning Electrochemical Cell Microscopy to Understand Nanoscale Electrochemistry of

Printable Electronic Materials

Printable electronic materials encompass a category of materials that can be formulated into an ink rapidly printed. The scale of production that is unlocked through the solution processability of these materials allows for the cost of energy generation and storage technologies to be drive down. One such class of printable electronic materials, organic semiconductors (OSCs), are of particular interest due to their applications to photovoltaics and for use as photoelectrodes. Processing conditions and choice of polymer affect the electronic properties of OSCs, but these minute changes are rarely captured in bulk electrochemical analyses. To probe surface electrochemical heterogeneity in OSCs, a technique with nanoscale spatial resolution is required. Scanning electrochemical microscopy (SECCM) can satisfy these requirements, due to the use of an electrolyte-filled capillary that acts as a nanoscale electrochemical cell. In addition to performing electrochemical measurements, the capillary can be translated in the X and Y direction over the sample surface, allowing for electrochemical heterogeneity to be probed. Using OSCs as the model system, SECCM and its underlying theory will be introduced and will be used to highlight the unique capability it possesses for printable electronic material characterization.

 

            Garrett Collins, University of Utah

Tracking the Initial Stages of Electrochemical Doping of Organic Mixed Conductors with Photoluminescence Spectroscopy

Organic Mixed Ionic-Electronic Conductors (OMIECs) are a novel class of conjugated polymers possessing the unique capability of conducting both ions and electrons. This dual conductivity, coupled with their solution processibility, biological compatibility, and volumetric capacitance, makes them active materials for various technological applications, including bioelectronics, electrochemical energy storage, and neuromorphic computing.

The underlying functionality of OMIECs arises from the process of electrochemical doping, in which an electrical charge is injected into the polymer matrix. This event prompts ions from a nearby liquid electrolyte to enter the polymer matrix, thus offsetting the induced electronic charge. As the use of OMIECs becomes more widespread, the development of new characterization techniques becomes crucial to comprehending the intricate structure-function relationships inherent within these materials.

We introduce the application of in situ photoluminescence spectroscopy as a practical method of characterizing the initial steps of electrochemical doping of OMIECs. We compare photoluminescence to other widely accepted characterization techniques, such as absorption spectroelectrochemistry, electrochemical quartz crystal microbalance (EQCM), and ion density measurements, thereby emphasizing the sensitive nature of this technique.

Further, by fitting each spectral data set with a mix of a Franck-Condon progression and the amorphous components of the spectrum, we separately track electrochemical doping in crystalline and amorphous regions of the polymer matrix.

 

 

Friday June 2, 2023

 

 

            Plenary/Research Talk from Naval Workforce: Dr. Janice Boercker

Coupling Infrared Excitons and Plasmons in Hybrid Nanostructures

Semiconductor nanocrystals are an exciting material for optoelectronic devices; however, their performance is constrained due to limited carrier diffusion lengths and fast non-radiative decay rates.  Hybrid excitonic/doped-plasmonic semiconductor nanostructures have the potential to circumvent these limitations by coupling excitons and plasmons, and are optically active in the DoD relevant infrared region. Due to the Purcell effect, the exciton/plasmon coupling will increase the nanocrystal radiative rate which will bring about better performing emitting devices (e.g. infrared displays and single-photon emitters), and the close proximity of the plasmon to the exciton in the hybrid nanostructures will concentrate the electric field around the exciton and increase the nanocrystal absorption, which will ease the carrier diffusion length requirements and lead to greater performance in light-absorbing devices (e.g. hand-held infrared detectors). We have made three significant discoveries towards realizing nanoscale infrared exciton-plasmon coupling, 1) an unexpected way to increase the radiative rate in PbS nanocrystals, 2) the realization of the first binary superlattices of excitonic PbS and plasmonic Cu_2-xS nanocrystals, and 3) a solution to the major roadblock preventing the coupling of excitonic PbS nanocrystals to plasmonic Cu_2-xS nanocrystals in binary superlattices. These findings pave the way for the further study of nanoscale infrared exciton-plasmon coupling for DoD relevant optoelectronics.  

 

            Patrick Lohr, University of Arizona

Characterizing Molecular Additives for Metal Halide Perovskites using Density Functional Theory

Metal halide perovskite semiconductors exhibit exceptional optoelectronic properties, including high carrier lifetime, high carrier mobility, and extraordinary power conversion efficiencies (PCE) in photovoltaic devices. Despite these favorable characteristics, the thermomechanical and chemical stability of these devices is insufficient to provide robust performance in most real-world scenarios, a significant roadblock to technological relevancy. A key driver of these instabilities are defects that form on the surface of grains during crystallization in polycrystalline perovskite films. Additive engineering – the addition of organic molecules during perovskite manufacturing – has been demonstrated to inhibit the formation of defect sites in perovskite films and reduce ion migration, enhancing PCE retention. However, the molecular features and properties that determine an organic additive’s ability to passivate defects and coordinate precursors during crystallization in perovskite materials are not well-understood on the atomic scale. Through the application of density functional theory (DFT) calculations, we have begun systematically docking candidate additives to the surface of methylammonium lead iodide (MAPbI₃) perovskite starting with a class of multifunctional additives known as 5-aminovaleric acid (5-AVA) halide derivatives. Combined with experimental evidence, we believe that our results clarify the role of halides in these additives.

 

            Hannah Contreras, University of Washington

Does Improving Energy Alignment Lower V_oc Loss in High Efficiency Wide Gap Perovskite Solar Cells?

In the last decade, lead halide perovskite solar cells have experienced a significant increase in research interest due to their high efficiency coupled with their low-cost, facile, solution-processible synthesis, making them promising candidates to address the growing energy crisis. While perovskite solar cells exhibit a range of favorable electronic characteristics due to their unique chemistry, traditional charge transport layers are energetically mismatched with the perovskite active layer. This mismatch increases nonradiative recombination, restricting the quasi-Fermi level splitting and limiting open circuit voltage (VOC). A major challenge is finding novel charge transport layer materials that are closely aligned with wide bandgap perovskites (Eg ≥ 1.7 eV) used in tandem solar cells. In this work, we modulate the anode work function using novel self-assembled monolayer (SAM) molecules and demonstrate suppressed nonradiative recombination.

We first use drift diffusion simulations to identify the ideal energy offset between the hole extraction and perovskite layers. We screened SAMs with different functional groups and identified those with the ideal work function to align with 1.7 eV perovskite active layer used in silicon-tandem solar cells. Improvement in non-radiative recombination at the SAMs/perovskite interface was tested through steady state and time resolved photoluminescence spectroscopy. The SAMs were then incorporated into a whole device stack that is characterized by measuring the current-voltage curve under 1 sun equivalent illumination. In the future, these interface modifiers will be used in perovskite-on-silicon tandem devices to minimize energy offset.

 

            Roxanne Balanay, University of Hawaii

Field-Assisted Aerosol Jet Printing for Printed Electronics

The additive manufacture of production-grade flexible, large area electronics is of intense interest to rapidly design, prototype, and fabricate electronics without reliance upon traditional electronics fabrication pathways. Such additive processes enable the direct integration of electronics on arbitrary, non-planar surfaces, expanding the potential form-factors and application spaces. Aerosol Jet Printing (AJP) is emerging as a powerful printing approach for high-resolution fabrication of printed high-quality electronic circuits, antennas, and sensors with design geometries not possible via other additive manufacturing technologies. AJP precisely deposits an aerosolized, liquid ink into prescribed electronic traces. Ink formulations typically utilize specialized material formulations to adhere to deposition surfaces and maintain the prescribed print resolution. Here, we describe a new type of AJP print process that controls aerosol spatial position via acoustic field (‘acoustophoretic’) focusing for printing high-fidelity, high-resolution print lines. The acoustophoretic focusing relies upon differences in material properties between the ink and surrounding medium (air), rather than the material itself, enabling a “material agnostic” approach that is extensible to a broad array of established and nascent AJP ink chemistries. Acoustic forces offer the possibility to control the width of the printed material by focusing the aerosol jet to a narrower region than would be possible with a physical orifice. As the acoustic focusing effect is dependent on the ink droplet size, the utilization of acoustic focusing provides a means to “refine” the jet such that the deposited material has a smaller line width and exhibits a reduction in the typically observed particle overspray.

 

            Julia Huddy, Dartmouth

Rapid 2D Patterning of High-Performance Perovskites Using Large Area Flexography

Solution processing of perovskite solar cell (PSC) materials makes PSC fabrication highly amenable to roll-based fabrication methods, allowing for high-speed manufacturing of photovoltaics (PV) at lower cost than achievable with silicon PV. However, current PSC fabrication methods are limited in their ability to rapidly produce highly uniform perovskite absorbers and rely on post-deposition scribing for module integration. Here we present a method for flexographic printing of the perovskite absorber at the highest reported speed (60 m/min) for any absorber material deposition while integrating high-resolution patterning (< 3 μm line edge roughness). Precise ink design allows for control over the film thickness (100 – 500 nm) by modulating the viscosity (4.7 to 17.4 mPa·s) of the inks used. Patterning of the films over large areas (140 cm2) shows the ability to print intentional gaps under 50 μm width, suitable for obviating damaging scribing steps and applications in perovskite LED or photodetector fabrication. We combine this printing method with 2D scanning photoluminescence (PL) to spatially resolve PL emission intensity and evaluate optoelectronic quality of the printed films. Interestingly, both the uniformity of PL emission and the device performance for printed perovskite films are heavily influenced by the thickness uniformity of the perovskite. Integrating printed films into n-i-p planar perovskite solar cells, we achieve efficiencies over 20%, matching that of spin-coated counterparts. Together these processes improve our understanding of large-area perovskite fabrication and provide opportunities for inline monitoring and quality control for module manufacture.

 

            Jonathan Nguyen, University of Minnesota

Applying Solution-Processing Principles Towards Self-Aligned Printed Diodes

The prospect of fully integrating electronic systems into everyday items has garnered considerable attention, with the coinage of the ‘Internet of Things’. Potential applications of interest include wearable electronics, flexible displays, and sensors for smart packaging. To keep up with this demand, there is a critical need for a cheap, highly scalable manufacturing method to fabricate electronic devices. Printed electronics is a rapidly growing field that provides a low-cost, additive route to fabricating electronic devices on a roll-to-roll production scale. We present a manufacturing process that combines UV microimprinting, inkjet printing, and capillary flow to fabricate organic Schottky diodes. Using a new design, we address the geometrical limitations of previous diodes by Cao et al.1 that limited the minimum semiconductor thickness to 1 μm. The new design incorporates solution-processing principles, namely, droplet drying and planarization, in combination with a novel mesa geometry, to allow for deposition of thinner device active layers down to 500 nm. Functional diodes with 103 rectification ratio and little hysteresis were demonstrated using this mesa design. Devices were characterized using two-point probe measurements in combination with cross-sectional SEM and scanning profilometry to investigate the layer thicknesses and uniformity throughout the device. This work demonstrates the synergistic potential of combining processing fundamentals and electronics towards improving device performance through greater control over materials deposition and layer uniformity.

 

            Plenary/Research Talk from Naval Workforce: Dr. Adam Colbert

 Enhanced Infrared Photodiodes Based on PbS/PbCl_x Core/Shell Nanocrystals

Improved passivation strategies to address the more complex surface structure of large-diameter nanocrystals are critical to the advancement of infrared photodetectors based on colloidal PbS. In this contribution, the performance of short-wave infrared (SWIR) photodiodes fabricated with PbS/PbCl_x (core/shell) nanocrystals vs their PbS-only (core) counterparts are directly compared. Devices using PbS cores suffer from shunting and inefficient charge extraction, while core/shell-based devices exhibit greater external quantum efficiencies and lower dark current densities. To elucidate the implications of the shell chemistry on device performance, thickness-dependent energy level offsets and interfacial chemistry of nanocrystal films with the zinc oxide electron-transport layer are evaluated. The disparate device performance between the two synthetic methods is attributed to unfavorable interface dipole formation and surface defect states, associated with inadequate removal of native organic ligands in core-only films. The core/shell system offers a promising route to manage the additional nonpolar (100) surface facets of larger nanocrystals that conventional halide ligand treatments fail to sufficiently passivate.

 

            William Hartnett, University of Minnesota

  Reducing Variance in Self-Aligned Inkjet-Printed Resistors

Flexible electronics (FE) is an emerging field of research that is enabling many novel technologies such as wearable medical sensors, large-area distributive sensing, RFID tags, and more. The flexibility and stretchability of FE allow them to conform to any surface and withstand large amounts of strain. Printed-FE (PFE) is a subfield of FE where devices are printed using additive roll-to-roll (R2R) compatible processes such as inkjet printing, gravure printing, aerosol jet printing, etc. Of these techniques, inkjet printing has been favored for its many advantages including simultaneous deposition of multiple materials, high-resolution, non-contact printing, and commercial availability. While good resolution has been achieved using inkjet printing, precise layer-to-layer alignment for multilayered devices remains a challenge. This becomes further problematic when processing devices at a R2R level, as the substrate velocity needs to be taken into account. Self-aligned Capillarity-Assisted Lithography for Electronics (SCALE) is a patented process that solves this registration issue while also improving upon resolution. SCALE utilizes traditional photolithographic and etching techniques to pattern microfluidic channels and ink reservoirs into silicon wafers. The wafers act as master templates for the creation of poly(dimethylsiloxane) PDMS stamps, which are used to imprint into UV-curable resin. Relatively large ink reservoirs act as targets for ink deposition, while spontaneous capillary flow through the microfluidic channels creates self-aligning devices. Resolution using this process is no longer limited by ejected droplet size, rather, the photolithographic minimum feature size. This project addresses variability and yield of SCALE devices to improve performance of multicomponent circuits.   

 

          Nathan Woodward, NC State

Autonomous, Closed-Loop Optimization of Hybrid Perovskite Anti-Solvent Drip

Hybrid metal-halide perovskites are a promising material for photovoltaics that have made large strides in power conversion efficiency (PCE) in the past decade due to being a compositionally tunable, solution-processible, direct bandgap semiconductor with defect tolerant properties. Spin coating is a widely adopted technique for fabricating solution-processible thin films; however, it is a very strenuous, manual process that can vary person-to-person in a given lab. Optimization of one-step spin coating of a hybrid perovskite system with an anti-solvent drip is a multiparametric problem that requires many human hours and resources.
We have developed the RoboCoater, which allows precise control of processing conditions like spin speed, anti-solvent drip timing, and drip volume to achieve accurate and reproducible results that are not feasible by humans. Bayesian Optimization has been implemented to reduce the time spent varying multiple process parameters of perovskite thin films for different anti-solvents in a high-throughput, closed-loop manner to reduce the time and material cost. This platform is integrated with a sensor suite, including in-situ absorbance and photoluminesce measurement capabilities synchronized with the spin coating experiment.
Overall, we have built an autonomous spin coater that integrates multimodal spectroscopies and which can learn to coat solution processible thin films without prior knowledge. The RoboCoater is small, modular, and 3D printed and helps define standardized processing conditions in different researchers to achieve repeatable, peer-executed experimentation to help the community advance together.

 

            Jacob Mauthe, NC State

Accelerated Photodegradation Study of Multi-Component Organic Photovoltaic Blends Using Robotic Palletization and High-Throughput Experimentation

Multi-component OPV blends have been used to improve the performance and stability of devices. However, there is a lack of understanding of the fundamental mechanisms that cause improved performance and stability in these devices. Investigating photodegradation of a vast library of materials and their multi-component combinations is a demanding problem that currently requires considerable effort in terms of time and resources. In this work, we describe a robotic platform, the RoboMapper, which formulates and prints miniature OPV active layers which enables rapid evaluation of photodegradation Printing 1/15th of the size of traditional samples consumes a fraction of materials, whereas robotic micro-UV-Vis characterization enables high throughput evaluation of photobleaching. Using the RoboMapper, we conducted photodegradation campaigns on PM6, Y6, and PC71BM binary and multi-component blends. The photodegradation analysis allows us to identify donor-acceptor combinations for optimal photostability. By preparing devices with photostable blends, we can identify the overlap of stability and efficiency. The ability to prepare multiple samples simultaneously from a small amount of stock materials also considerably reduces the waste generated for the same quantity and quality of data. Importantly, these gains translate to data intensity, allowing quantitative models of performance and stability to be created and mapped to the active layer composition. In addition, thanks to combination of the RoboMapper photodegradation campaigns with inline spectroscopic analyses, we also derive insight into the aggregation of the active layer, as well as singlet oxygen phosphorescence, which reveals mechanistic insights into the triplet population and photostability of the blends.

 

            Yeena Ng, University of Minnesota

Transparent Inkjet-Printed Neural Interface Devices for Large-Area Multi-Modal Recording from the Mouse Cortex

 Flexible electronics have enabled a new class of neural interface devices that can provide
long-term chronic access to neural tissue for electrophysiological recording. Soft, flexible
devices cause less tissue damage than traditional rigid neural probes; therefore, they do not elicit the same foreign-body response that often limits the long-term stability of neural recordings. In our work, flexible and transparent inkjet-printed PEDOT:PSS electrodes are used to interface directly with the cortex in multi-modal opto-electrophysiological neuroscience experiments. Inkjet-printing allows for electrodes of varying patterns to be quickly fabricated and modified on-demand. Transparent inkjet-printed electrode arrays were integrated with transparent polymer skulls (eSee-Shells) and implanted on transgenic GCaMP6f mice for simultaneous mesoscale calcium imaging, electrocorticography, and stimulation. The PEDOT:PSS provides a low-impedance interface to the cortical surface and is sufficiently transparent such that calcium imaging is not obstructed by the electrodes. These electrodes can record neural signals and stimulate cortical tissue chronically in both anesthetized and awake mice. Multi-modal capabilities can reveal how electrocorticography and calcium signals are affected by the behavior of mice.

 

            Harry Schrikx, NC State

Lightweight and Flexible Self-Powered Organic Photodetectors for Plant Health Monitoring

Ultrathin organic photodetectors (OPDs) can be made lightweight, flexible, and mechanically resilient, opening up opportunities for novel applications. More specifically, ultrathin OPDs can be used as wearable optical sensors for both human and plant health monitoring. Photodetectors are an effective tool to capture plant health indicators including chlorophyll fluorescence, which can unveil metabolic processes and stress responses in plants. Here, we develop a high performance ultrathin self-powered OPD designed for on-plant optical sensing. The OPD employs an electrode consisting of Ag nanowires embedded in a UV-curable resin to achieve a flexible and thin form factor. In addition, the OPD active layer consisting of D18-Cl and Y6 was sequentially cast to optimize vertical segregation and reduce dark current. The flexible OPD was sensitive to wavelengths from 400-950 nm and exhibited photodetector characteristics comparable to state-of-the-art rigid OPDs. Along with excellent photodetector characteristics, the detectivity and bending stability showed great promise for extended on-plant health monitoring. The photocurrent maintained steady values above 95% over the course of 600 hours. Similarly, the photocurrent remained steady across 4,000 cycles with a bending radius of 2 mm. The flexible OPD was then demonstrated to effectively sense time-dependent chlorophyll fluorescence as well as detect plant up-take of rare-earth metals (with applications in soil remediation), highlighting its utility for on-plant fluorescence measurements. Thus, we show that OPDs are a promising approach for on-plant health monitoring that can ultimately drive precision agriculture to achieve higher yields and a more sustainable agriculture industry.