Browsing by Subject "RIR-MAPLE"
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Item Open Access A Semi-Empirical Monte Carlo Method of Organic Photovoltaic Device Performance in Resonant, Infrared, Matrix-Assisted Pulsed Laser Evaporation (RIR-MAPLE) Films(2015) Atewologun, AyomideUtilizing the power of Monte Carlo simulations, a novel, semi-empirical method for investigating the performance of organic photovoltaics (OPVs) in resonant infrared, matrix-assisted pulsed laser evaporation (RIR-MAPLE) films is explored. Emulsion-based RIR-MAPLE offers a unique and powerful alternative to solution processing in depositing organic materials for use in solar cells: in particular, its usefulness in controlling the nanoscale morphology of organic thin films and the potential for creating novel hetero-structures make it a suitable experimental backdrop for investigating trends through simulation and gaining a better understanding of how different thin film characteristics impact OPV device performance.
The work presented in this dissertation explores the creation of a simulation tool that relies heavily on measureable properties of RIR-MAPLE films that impact efficiency and can be used to inform film deposition and dictate the paths for future improvements in OPV devices. The original nanoscale implementation of the Monte Carlo method for investigating OPV performance is transformed to enable direct comparison between simulation and experimental external quantum efficiency results. Next, a unique microscale formulation of the Dynamic Monte Carlo (DMC) model is developed based on the observable, fundamental differences between the morphologies of RIR-MAPLE and solution-processed bulk heterojunction (BHJ) films. This microscale model enables us to examine the sensitivity of device performance to various structural and electronic properties of the devices. Specifically, using confocal microscopy, we obtain an average microscale feature size for the RIR-MAPLE P3HT:PC61BM (1:1) BHJ system that represents a strategic starting point for utilizing the DMC as an empirical tool.
Building on this, the RIR-MAPLE P3HT:PC61BM OPV system is studied using input simulation parameters obtained from films with different material ratios and overall device structures based on characterization techniques such as grazing incidence-wide angle X-ray scattering (GI-WAXS) and X-ray photoelectron spectroscopy (XPS). The results from the microscale DMC simulation compare favorably to experimental data and allow us to articulate a well-informed critique on the strengths and limitations of the model as a predictive tool. The DMC is then used to analyze a different RIR-MAPLE BHJ system: PCPDTBT:PC71BM, where the deposition technique itself is investigated for differences in the primary solvents used during film deposition.
Finally, a multi-scale DMC model is introduced where morphology measurements taken at two different size scales, as well as structural and electrical characterization, provide a template that mimics the operation of OPVs. This final, semi-empirical tool presents a unique simulation opportunity for exploring the different properties of RIR-MAPLE deposited OPVs, their effects on OPV performance and potential design routes for improving device efficiencies.
Item Open Access Design Rules for Complex Emulsion Targets in Resonant Infrared, Matrix-Assisted Pulsed Laser Evaporation of Polymer Thin Films(2021) Ferguson, SpencerPolymer thin films used in many modern technologies, such as light emitting diodes, solar cells, flexible electronics, and sensors, are fabricated in numerous ways. Of these methods, solution-based processing techniques are the most common with established commercial manufacturing and high throughput. However, these approaches face multiple disadvantages when applied to device heterostructures that are essential for optoelectronic devices. In contrast, vacuum-based techniques are amenable to multi-layer films with varying composition, regardless of polymer solubility. Resonant infrared, matrix-assisted pulsed laser evaporation (RIR-MAPLE) allows for the deposition of finely tuned polymer structures, such as uniquely graded heterostructures, which solution processing techniques cannot achieve. The primary contribution of this dissertation is to bring to light general design rules for complex emulsions that comprise the targets used in RIR-MAPLE to deposit polymer thin films containing crystalline domains.
Initially, design rules are discussed that lead to the formation of pinhole-free polymer films that also contain crystalline domains. This work addresses a fundamental challenge to promote the crystalline phase, as opposed to the more prevalent amorphous phase, while also maintaining high-quality film surfaces. These design rules are then expanded to include the effects of overall emulsion composition on the resulting emulsion morphology. In order to maximize the content of the crystalline polymer phase in thin films, the use of various surfactants (not yet applied to RIR-MAPLE emulsion targets) is investigated due to the unique interactions that occur, thereby determining the emulsion morphology. As a result, the impact of surfactant molecular structure on the resultant film properties is described for the first time. Finally, the design rules identified for complex emulsions are used in a fundamentally different emulsion chemistry to verify the extent to which these rules are generally applicable.
Item Open Access Investigation of 2D Hybrid Organic-Inorganic Perovskite Thin Films Deposited by RIR-MAPLE for Heterostructure Integration(2023) Phillips, Niara ElyssaThe power conversion efficiency of perovskite solar cells has increased significantly in the past 10 years from around 13% to over 25%. However, the most common perovskite absorber materials, three-dimensional (3D) perovskites, are challenged by moisture stability which hinders their more widespread commercialization. One approach to increase moisture stability is to incorporate a layer of hydrophobic ligands on top of the absorber layer in the form of a two-dimensional (2D) perovskites, thereby forming a 2D-on-3D heterostructure, however there are significant processing challenges. This dissertation conducts a careful investigation of n = 1 2D perovskite thin films deposited using a technique called resonant infrared, matrix-assisted pulsed laser evaporation (RIR-MAPLE) to better understand and then improve the heterostructure. The major conclusions of this work are that any halide mixing likely occurs in the 3D layer only at the heterostructure interface due to the site preferences that bromine and iodine have in the octahedra. Several supplemental processing parameters – deposition scheme, growth temperature, and solvent ratio (DMSO:MEG) – were used to successfully increase the average grain size, increase the amount of vertically oriented grains, modify the morphology, and decrease the Stokes shift in (PEA)2PbI4 thin films. Ultimately, out-of-plane conductivity in (PEA)2PbI4 thin films was successfully improved using the sequential deposition scheme, elevated growth temperature, and decreased amount of matrix solvent. The structural improvements and improved out-of-plane conductivity were also demonstrated for the heterostructure when modified processing conditions were used to deposit the 2D layer. The process-structure-property relationships investigated in this work serve as guidelines for tailoring 2D-on-3D heterostructures.
Item Open Access Matrix-Assisted Pulsed Laser Evaporation of Conjugated Polymer and Hybrid Nanocomposite Thin Films: A Novel Deposition Technique for Organic Optoelectronic Devices(2011) Pate, Ryan JaredThis dissertation develops a novel application of the resonant-infrared matrix-assisted pulsed laser evaporation (RIR-MAPLE) technique toward the end goal of conjugated-polymer-based optoelectronic device fabrication. Conjugated polymers are attractive materials that are being investigated in the development of efficient optoelectronic devices due to their inexpensive material costs. Moreover, they can easily be combined with inorganic nanomaterials, such as colloidal quantum dots (CQDs), so as to realize hybrid nanocomposite-based optoelectronic devices with tunable optoelectronic characteristics and enhanced desirable features. One of the most significant challenges to the realization of optimal conjugated polymer-CQD hybrid nanocomposite-based optoelectronics has been the processes by which these materials are deposited as thin films, that is, conjugated polymer thin film processing techniques lack sufficient control so as to maintain preferred optoelectronic device behavior. More specifically, conjugated-polymer-based optoelectronics device operation and efficiency are a function of several attributes, including surface film morphology, internal polymer chain morphology, and the distribution and type of nanomaterials in the film bulk. Typical conjugated-polymer thin-film fabrication methodologies involve solution-based deposition, and the presence of the solvent has a deleterious impact, resulting in films with poor charge transport properties and subsequently poor device efficiencies. In addition, many next-generation conjugated polymer-based optoelectronics will require multi-layer device architectures, which can be difficult to achieve using traditional solution processing techniques. These issues direct the need for the development of a new polymer thin film processing technique that is less susceptible to solvent-related polymer chain morphology problems and is more capable of achieving better controlled nanocomposite thin films and multi-layer heterostructures comprising a wide range of materials. Therefore, this dissertation describes the development of a new variety of RIR-MAPLE that uses a unique target emulsion technique to address the aforementioned challenges.
The emulsion-based RIR-MAPLE technique was first developed for the controlled deposition of the conjugated polymers poly[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) and poly[2-methoxy-5-(2'ethylhexyloxy)-1,4-(1-cyanovinylene) phenylene] (MEH-CN-PPV) into homogenous thin films. Therein, it was identified that target composition had the most significant influence on film surface morphology, and by tuning the concentration of hydroxyl bonds in the target bulk, the laser-target absorption depth could be tuned so as to yield more or less evaporative deposition, resulting in films with tunable surface morphologies and optical behaviors.
Next, the internal morphologies of emulsion-based RIR-MAPLE-deposited MEH-PPV thin films were investigated by measuring their hole drift mobilities using the time-of-flight (TOF) photoconductivity method in the context of amorphous materials disorder models (Bässler's Gaussian Disorder model and the Correlated Disorder model) in order to provide a quantitative measure of polymer chain packing. The polymer chain packing of the RIR-MAPLE-deposited films was demonstrated to be superior and more conducive to charge transport in comparison to spin-cast and drop-cast MEH-PPV films, yielding enhanced hole mobilities.
The emulsion-based RIR-MAPLE technique was also developed for the deposition of different classes of inorganic nanoparticles, namely un-encapsulated nanoparticles and ligand-encapsulated nanoparticles. These different classes of nanoparticles were identified to have different film growth regimes, such that either rough or smooth films were obtained, respectively. The ligand-encapsulated nanoparticles were then co-deposited with MEH-PPV as conjugated polymer-CQD hybrid nanocomposites, wherein the distributions of the constituent materials in the film bulk were identified to be tunable, from homogeneous to highly clustered. The RIR-MAPLE deposition regime determined the said distributions, that is, if the polymer and CQDs were sequentially deposited from a sectioned target or simultaneously deposited from a single target, respectively. The homogeneous conjugated polymer-CQD nanocomposites were also investigated in terms of their charge transport properties using the TOF photoconductivity technique, where it was identified that despite the enhanced dispersion of CQDs in the film bulk, the presence of a high concentration of CQDs degraded hole drift mobility, which indicates that special considerations must be taken when incorporating CQDs into conjugated-polymer-based nanocomposite optoelectronics.
Finally, the unique capability of RIR-MAPLE to enable novel conjugated polymer-based optical heterostructures and optoelectronic devices was evaluated by the successful demonstration of a conjugated polymer-based distributed Bragg reflector (DBR), a plasmonic absorption enhancement layer, and a conjugated polymer-based photovoltaic solar cell featuring a novel electron-transporting layer. These optical heterostructures and optoelectronic devices demonstrate that all of the constituent polymer and nanocomposite layers have controllable thicknesses and abrupt interfaces, thereby confirming the capability of RIR-MAPLE to achieve multi-layer, conjugated polymer-based heterostructures and device architectures that are appropriate for enhancing specific desired optical behaviors and optoelectronic device efficiencies.