Chemicals are ubiquitous, from the food we eat to the composition of our own bodies. Different chemicals can give us information about ourselves or our surroundings. For example, chemicals in the body can give information about the state of a person's health, while chemicals in the atmosphere can give information about pollution. Chemical sensors are necessary to gain this information. Electrochemical sensors can use electrical signal output to indicate the presence and amount of chemicals. This is done two ways: amperometric sensors output current, and potentiometric sensors output potential. The magnitude of the signal indicates the amount of chemical present. Printing is useful for fabricating these sensors in flexible form factors and for disposable uses.

This thesis discusses the development of several different printed electrochemical sensors. An overview is first given of the developments in printed electrochemical sensors which enabled this work. Printed amperometric sensors for determination of lactate in sweat are optimized for sensing the transition from aerobic to anaerobic metabolism. These sensors are printed to accommodate form factors closely matching that of skin. These sensors have a sensitivity of 4.8 uA/mM and a linear range up to 25 mM lactate. However, an investigation into the selectivity of these sensors determines they are susceptible to interference from the salt present in sweat, making them less useful as sensors and more useful as indicators. Potentiometric sensors are proposed as an alternative for sensing metabolites in sweat, due to their selectivity in sweat. Potentiometric sensors cannot be made for sensing lactate, but ammonium sensors are demonstrated instead for determining levels of carbohydrates and metabolic condition. Potentiometric ammonium sensors show a near-Nernstian response of 57.5 mV/decade +/- 0.3 mV/decade. Sweat is not the only application for printed sensors. Printed potentiometric sensors for nitrate in soil are also demonstrated, where printing enables the use of degradable materials. The nitrate sensors have near-Nernstian sensitivity of -53.3 mV/decade +/- 1.1 mV/decade, and the printed reference developed shows relative insensitivity to nitrate in solution. The work discussed here indicates a step toward distributed networks of sensors.

Organic electronics is an emerging technology with advantages of mechanical flexibility,

solution-processability, and high-throughput manufacturing at low temperatures on inexpensive

and light-weight substrates such as plastic, paper, and fiber in large-scales not possible

with high-temperature processing techniques. While the performance of devices cannot rival

the silicon counterpart, the performance should be tuned to meet the required specifications

of the application in mind. This thesis will overview the performance of the organic thin

transistors (OTFTs) and organic phototransistors (OPTs) optimized and used for circuits

and large area sensing applications. The work first covers the printing techniques employed

for the fabrication of organic devices on the flexible substrate. There have been device-level

optimizations for scale ratio tuning and power improvement by using a bilayer gate dielectric

structure. We also introduce a novel technique for rapid and digital modulation of the scale

ratios. Interconnection is done with the screen printing method for the fabrication of printed

flexible logic circuits and an OTFT weak classifier for data classification. The OPTs, with

a good dual performance as both transistor and photodetector, are capable of merging the

sensing and function generation in one substrate, which can reduce system complexity.

Light and image sensors are ubiquitous and used in a wide variety of applications ranging from consumer products to healthcare and industrial applications. The signal-to-noise ratio (SNR) from a photodetector element increases with larger photoactive area, which is costly to scale up using silicon wafers and wafer-based microfabrication. On the other hand, the performance of solution-processed photodetectors and transistors is advancing considerably. It is proposed that the printability of these devices on plastic substrates can enable low-cost areal scaling for high SNR light and image sensors.

This thesis advances the performance of printed organic thin film transistor (OTFT), pho- todiode (OPD), and phototransistor (OPT) devices optimized for light and image sensing applications by developing novel printing techniques and creating new device architectures. An overview is first given on the essential figures of merit for each of these devices and the state of the art in solution-processed image sensors. A novel surface energy-patterned doc- tor blade coating technique is presented to fabricate OTFTs on flexible substrates over large areas. Using this technique, OTFTs with average mobility and on-off ratios of 0.6 cm^(2)/Vs and 10^(5) are achieved, which is competitive with amorphous silicon TFTs. High performance OPDs are also fabricated using doctor blade coating and screen printing. These printing processes give high device yield and good controllability of photodetector performance, enabling an average specific detectivity of 3.45×10^(13) cm·Hz^(0.5)·W^(-1) that is higher than silicon photo- diodes (10^(12-13)). Finally, organic charge-coupled devices (OCCDs) and a novel OPT device architecture based on an organic heterojunction between a donor-acceptor bulk heterojunction blend and a high mobility semiconductor that allows for a wide absorption spectrum and fast charge transport are discussed. The OPT devices not only exhibit high transistor and photodetector performance, but are also able to integrate photogenerated charge at video frame rates up to 100 frames per second with external quantum efficiencies above 100%. Applications of these devices include screen printed OTFT backplanes, large-area OPDs for pulse oximeter applications, and OPT-based image sensors.

Organic electronics have gained popularity due to their potential to revolutionize electronic technologies with improved performance, low cost, and unique applications in flexible and wearable systems. A significant advantage of organic electronics is their solution solubility, which enables cost-effective and additive printing processes, reducing material waste and facilitating large-area manufacturing. This thesis will present work towards developing eco- friendly and scalable organic optoelectronic sensors. Organic light-emitting diodes (OLEDs) and organic photodiodes (OPDs) are demonstrated as photoplethysmography (PPG) sensors, representing steps toward lightweight and flexible pulse oximeters. A scalable blade coating method is used to simultaneously print OLEDs and OPDs on a single substrate, simplifying fabrication while maintaining device performance of both devices. Finally, solution and film optimizations are used to replace toxic solvents with a greener solvent in organic photovoltaics (OPVs), demonstrating critical steps towards eco-friendly fabrication of organic electronics.

Recently, form factors of electronics have been changing from conventional rigid electronics to more novel and complex form factors including soft, flexible, and even stretchable forms. These unique form factors are lightweight and enable conformal interfaces between electronics and the objects they rest upon. Printing is a commercially viable manufacturing technology for fabricating these types of electronics, capable of depositing materials including conducting, insulating, and semiconducting materials. However, printed flexible electronics are not as efficient as silicon integrated circuits (ICs) in certain regimes, such as computation or communication. Flexible hybrid electronics (FHE) leverage the benefits of flexible printed electronics and ICs by combining the two onto flexible substrates.

In this dissertation, I will discuss the various components of an FHE system and the range of printing techniques that are used to fabricate them. This dissertation will also overview specific works highlighting advancements in developing FHE systems. For passive sensing applications, I will focus on our work on screen-printed thermistor arrays, and their applications in battery health monitoring. For active sensing applications, I will discuss our work using doctor-blade coated arrays of organic light-emitting diodes (OLEDs) and organic photodiodes (OPDs) for reflection mode blood oximetry, which accurately measures pulse rate and oxygenation. In addition to the discussion of the flexible sensor composed of OLEDs and OPDs, I will present our work on various unique geometries of optoelectronics and their significance in improving sensor efficiency. For power sources, I will present our work on screen-printed Zn-Ag2O battery arrays, and the scalability of these devices. Finally, I will discuss other techniques to develop robust conformal electronics, using a class of FHE systems called in-mold electronics.

Organic light-emitting diodes (OLEDs) are made from a growing library of man-made semiconductor materials. Unlike inorganic LEDs, OLED materials can be custom-designed and synthesized for desired emission characteristics. The bulk of OLED development to date has been for display and lighting applications, leveraging their tunable color characteristics and high efficiencies. Within display and lighting development, there has been a push to fabricate OLEDs over large areas of flexible substrates compatible with low-cost, high-throughput roll-to-roll printing technology. It is this flexibility and scalable processing that has more recently garnered attention for using OLEDs in wearable optoelectronic biomedical devices. This work focuses on the development of solution-processed, printed OLEDs specifically for biomedical applications.

As a proof of concept that solution processed polymer OLEDs can perform in a wearable biomedical device, green and red OLEDs spin-coated on glass substrates were implmented in an all-organic otoelectronic pulse oximeter to measure heart rate and arterial oxygen saturation. These OLEDs were able to generate a clear photoplethysmogram (PPG), the signal from which heart rate and oxygenation are derived, in conjunction with both inorganic and organic photodiodes. The fully organic opto-electronic sensor was able to accurately measure heart rate and oxygenation within 2% error of a commercially available hospital-grade pulse oximeter.

The next step from a proof of concept device was to develop OLED structures and processing more in line with fabricating flexible and scalable devices. Structurally, most OLEDs employ indium-tin oxide (ITO) as a transparent anode. However, ITO is brittle, and therefore not an ideal material for a flexible device meant to be worn flush with the human body. In this work an ITO-free near-infrared (NIR) OLED was fabricated on a flexible polyethylene napthalate (PEN) substrate. In place of ITO, the anode was thermally evaporated WO3/Ag/WO3. To improve scalability and increase through-put (compared to spin-coating), all polymer layers were printed via blade coating. These OLEDs exhibited a 735 nm emission peak and 2.17% external quantum efficiency (EQE) at 100 mA/cm2.

To maximize OLED scalability and reduce manufacturing costs for inexpensive optical biomedical devices, the entire device structure should be printed and high vacuum evaporation processes should be eliminated. Here, efforts were made to replicate the thermally evaporated WO3/Ag/WO3 anode with blade coated layers. Partially printed WO3/Ag/WO3 anode OLEDs with WO3 layers printed from a WO3 nanoparticle ink and thermally evaporated Ag were achieved. The OLEDs had a red, 617 nm emission peak and exhibited 1-10 mW/cm2 forward flux per pixel area, values compatible with the wavelength and irradiance requirements of optical biomedical devices. Further Ag ink development out of the scope of this work is necessary in order to achieve a fully printed WO3/Ag/WO3 electrode, however a step towards fully printed OLEDs suitable for biomedical applications has been made.

In addition to scalability and flexibility, OLEDs for biomedical applications should have optimzied emission spectra. NIR light has the highest penetration depth in human tissue compared to visible light wavelengths. However, the development of solution-processable organic emitters with emission peaks beyond 800 nm has been slow. Here, a printed ITO-free 745 nm NIR OLED with a secondary emission peak at 815 nm is achieved by increasing the thickness of the emissive layer from 150 to 250 nm, affecting the optical interference within the device to alter the emission spectrum.

To show the importance and impact of deeper NIR emission in an optical biomedical device, PPG signals acquired from a subject's forefinger using a NIR OLED with the secondary 815 nm peak and an NIR OLED with only a 745 nm emission peak were compared. The calibrated strength (magnitude) of the PPG acquired with the NIR-shifted OLED was 32.87% higher than the PPG acquired with the 745 nm OLED. What's more, the better PPG was acquired with less light: the 745 nm OLEDs had a maximum 1 mW/cm2 irradiance on the subject's forefinger, while the NIR-shifted OLED's irradiance was only .33 $mWcm^{-2}$. This underscores the value of developing NIR OLEDs with deeper NIR emission for biomedical applications.

For printed and flexible OLEDs to catch on in biomedicine on a wide scale, their improved utility over currently available devices needs to be demonstrated. Flexible organic optoelectronic pulse oximeter patch prototypes developed and fabricated by Cambridge Display Technology and the Arias Group were shown to physicians from a variety of specialties. The physicians provided feedback on how the organic optoelectronic oximeters could aide their practice in ambulatory emergency care, chronic respiratory disease management, intraoperative monitoring, and pediatrics. Strategies for where and how to best interface the sensors with the human body were also developed from the physicians' input. PPG signals were acquired from flexible organic optoelectronic oximeters secured to the abdomen and back, both novel locations for pulse oximetry.

Non-invasive detection of biomarkers in sweat is of great interest for assessing the body’s response to physical activity, as well as for clinical diagnostics. Moreover, if fabricated in a form factor of a wearable device, sweat sensors offer advantages of continuous data acquisition, high performance and low cost. Despite significant progress up to date, major developments in fabrication of reliable sensing components still have to be realized in order to implement the vision of using sweat for continuous health monitoring. Commercially viable sweat sensors should demonstrate fast response, sensitivity to physiologically relevant concentrations of analyte, batch to batch reproducibility, stable performance under continuous operation, specificity, i.e. insensitivity to other analytes present in sweat, long-term storage, and ideally, no calibration requirement.

These sensors are designed to be compliant and nearly imperceptible to the wearer. The need to power these devices while retaining their mechanical properties has been driving active innovation in the field of wearable compliant batteries. Unfortunately, incorporating additional functionalities commonly compromises the energy storage capacity of the wearable devices: they usually show lower gravimetric or volumetric capacity than those of commercially available systems. It remains important to maximize the energy density of wearable batteries. Additionally, despite numerous innovative design strategies for the compliant batteries, there are few reports of batteries that exhibit fatigue resistance satisfactory enough for applications in wearable systems which are likely to undergo thousands of deformation cycles throughout their lifetime. Not to mention, the disposal of batteries becomes a concern with increased worldwide use of these devices. At the same time, the bulk of the demonstrations are based on Li-ion ion battery chemistry, which often relies on toxic and/or flammable components. Designing non-toxic systems comprising more abundant and disposable materials is of great importance.

This thesis focuses on addressing some of the existing shortcomings in the development of the wearable electrochemical devices: both electrochemical sensors for sweat monitoring and batteries. We demonstrate several unique design strategies to achieve high-performance flexible and stretchable batteries for wearable applications. For example, we develop an electrode composite with interpenetrated binder network to achieve a flexible battery with energy density matching that of the commercial AA alkaline battery. We also show wire-shaped batteries based on helical band springs that are resilient to fatigue and retain electrochemical performance over 17,000 flexure cycles. Both of these innovations address important limitations of existing flexible battery systems. Moreover, we use intrinsically safe, non-toxic silver-zinc (Ag/Zn) and zinc-manganese dioxide (Zn/MnO2) battery chemistries, which are highly desirable for wearable applications. For electrochemical sensors, we outline optimization steps to achieve printed flexible sensors for continuous monitoring of the lactate, Na+ or NH4+ ions and show how different optimization parameters affect the sensor performance. Last but not the least, we point out aspects that remain to be studied and/or addressed before such system can be claimed to be commercially viable.

Emerging wireless and flexible electronic systems such as wearable devices and sensor networks call for a power source that is sustainable, reliable, has high power density, and can be integrated into a flexible package at low cost. These demands can be met using photovoltaic systems, consisting of solar modules for energy harvesting, battery storage to overcome variations in solar module output or load, and often power electronics to regulate voltages and power flows. A great deal of research in recent years has focused on the development of high-performing materials and architectures for individual components such as solar cells and batteries. However, there remains a need for co-design and integration of these components in order to achieve complete power systems optimized for specific applications. To fabricate these systems, printing techniques are of great interest as they can be performed at low temperatures and high speeds and facilitate customization of the components.

This thesis discusses the development of printed and flexible photovoltaic power systems, spanning both device-level and system-level design. Photovoltaic cells and multi-cell modules are designed and manufactured using solution-processed organic materials. The use of carbon nanotube films as a flexible, low-cost, solution-processed transparent electrode for photovoltaics is investigated. Then, photovoltaic modules are integrated with batteries into energy harvesting and storage systems with multiple power levels and form factors, optimized to deliver power to loads such as wearable medical sensors. The energy collecting potentials of these systems are evaluated under indoor and outdoor lighting conditions. Designing the solar module maximum power point to match the battery voltage, as well as optimizing load characteristics such as duty cycle, are shown to enable power systems with long-term wireless operation and high efficiency. Finally, screen-printed passive components are developed and demonstrated in a hybrid flexible voltage regulator circuit. In particular, high-quality printed spiral inductors satisfactory for power electronics applications are achieved through optimization of the geometry and fabrication. Overall, the high-performance devices and integrated system designs demonstrated here have the potential for significant impact in the areas of flexible, portable and large-area electronics.

For Latina school administrators, the movement through the principal pipeline is not easy, as many encounter discrimination and biases rooted in their gender, ethnicity and other intersecting identities. Schools should leverage Latina administrators' cultural knowledge, perspectives, and experience to improve student educational outcomes. A Latina administrator brings these prior experiences to the work and can better understand and support the needs of the growing Latino/a population (Crawford & Fuller, 2017; Elizondo, 2005; Magdaleno, 2006; Méndez-Morse, 2004; Méndez-Morse, & Byrne-Jiménez, 2016; Murakami, Hernandez, 2016; Rodríguez, Martínez, & Falle, 2015). The dissertation highlights four Latina administrators' personal and professional journeys as they navigated the principal pipeline through interviews. Through participant and mentor interviews, the researcher sought to uncover the challenges, triumphs, and support systems the Latinas faced during their trajectory. The dissertation highlights participant stories with the objective of understanding how they overcame challenges and barriers with mentorship support. Latina representation is crucial, yet Latinas are scarce in leadership roles (Bitterman et al., 2013). Importance must be placed on actively developing a diverse group of Latina administrators, to ensure school leaders are better equipped to understand and address the academic challenges and disparities faced by Latino/a students due to their shared cultural backgrounds and experiences. The framework for this dissertation, Latina/o Critical Race Theory, or LatCrit, (Solorzano & Bernal, 2001), encompasses a range of social constructs such as racism, classism, sexism, and other forms of oppression that exist within the lived experiences of Latino/a administrators. As LatCrit is explored, these four Latinas' experiences showcase how social constructs intersect with their individual journeys. The findings revealed that while the four Latinas navigated their pathways to the principalship, they found empowerment through mentorships. They drew strengths from their identity and their mentors, took on a Sí se Puede mindset and pursued their Calling, or Vocación, and became principals.