Development of efficient, stable organic-inorganic hybrid solar cells

textDeveloping a fundamental understanding of photocurrent generation processes at organic-inorganic interfaces is critical for improving hybrid solar cell efficiency and stability. This dissertation explores processes at these interfaces by combining data from photovoltaic device performance tests with characterization experiments conducted directly on the device. The dissertation initially focuses on exploring how morphologically and chemically modifying the organic-inorganic interface, between poly(3-hexylthiophene) (P3HT) as the electron donating light absorbing polymer and titanium dioxide (TiO₂) as the electron acceptor, can result in stable and efficient hybrid solar cells. Given the heterogeneity which exists within bulk heterojunction devices, stable interfacial prototypes with well-defined interfaces between bilayers of TiO₂ and P3HT were developed, which demonstrate tunable efficiencies ranging from 0.01 to 1.6 %. Stability of these devices was improved by using Cu-based hole collecting electrodes. Efficiency values were tailored by changing TiO₂ morphology and by introducing sulfide layers like antimony trisulfide (Sb₂S₃) at the P3HT-TiO₂ interface. The simple bilayer device design developed in this dissertation provides an opportunity to study the precise role played by nanostructured TiO₂ surfaces and interfacial modifiers using a host of characterization techniques directly on a working device. Examples introduced in this dissertation include X-ray photoelectron spectroscopy (XPS) depth profiling analysis of metal-P3HT and P3HT-TiO₂ interfaces and Raman analysis of bonding between interface modifiers like Sb₂S₃ and P3HT. The incompatibility of TiO₂ with P3HT was significantly reduced by using P3HT derivatives with -COOH moieties at the extremity of a polymer chain. The role of functional groups like -COOH in interfacial charge separation phenomena was studied by comparing the photovoltaic behavior of these devices with those based on pristine P3HT. Finally, for hybrid solar cells discussed in this dissertation to become commercially viable, high temperature processing steps of the inorganic TiO₂ layer must be avoided. Accordingly, this dissertation demonstrates the novel use of electromagnetic radiation in the form of microwaves to catalyze growth of anatase TiO₂ thin films at temperatures as low as 150 °C, which is significantly lower than that used in conventional techniques. This low temperature process can be adapted to a variety of substrates and can produce patterned films. Accordingly, the ability to fabricate TiO₂ thin films by the microwave process at low temperatures is anticipated to have a significant impact in processing devices based on plastics.Materials Science and Engineerin

Laser Powder Bed Fusion of Cemented Carbide Geometries Using Tungsten Carbide-Nickel Agglomerated Powder

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Evaluating the Microwave Sintering Behaviors of Binder-jetted Additively Manufactured Alumina

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The role of defects in microwave-assisted synthesis of cubic ZrO2

Microwave radiation (MWR) is capable of inducing rapid, low-temperature crystallization and potential non-equilibrium phase formation in ceramic oxide materials.1 However, the mechanisms by which MWR influences phase transitions and atomic ordering are not well understood. Theories to explain the influence of MWR range from purely thermal effects (e.g., rapid heating rate) to purely MWR-driven, non-thermal effects (e.g., enhanced defect generation).2 To take full advantage of the opportunities provided by field-assisted methods, it is necessary to understand the underlying mechanisms. One limiting factor in determining how MWR affects phase formation has been the ability to effectively characterize the effects of an applied field on both long range (crystalline) and short range (amorphous/disordered) atomic order. Here, we utilize synchrotron x-ray pair distribution function (PDF) analysis, coupled with molecular dynamics (MD) and density functional theory (DFT) to explore the role of MWR-induced defects and local atomic disorder on low-temperature cubic phase formation in ZrO2 thin films. PDF analysis is an experimental technique capable of quantitatively characterizing both local and long range atomic order, and thus can characterize the effects of MWR on atomic structure beyond the capabilities of conventional x-ray diffraction. We find the application of MWR can stabilize cubic ZrO2 at temperatures as low as 225°C, about 2000°C lower than conventionally required. Our PDF analysis suggests that distortions in the local atomic structure may be responsible for the stabilization of the cubic phase, and these distortions are consistent with increased oxygen vacancy formation (Fig. 1). Interestingly, higher MWR power levels and faster heating rates do not correspond to more crystalline phase formation, suggesting that thermal effects may not be the sole driving force. To further explore the idea of MWR-induced, defect-mediated phase transitions, we utilize MD and DFT simulations to investigate how oxygen vacancy concentrations affect the relative phase stability of various ZrO2 polymorphs, and compare the resultant simulated structures with our experimental PDF data. Through analysis of both crystalline phase formation and local atomic order, we investigate how defects and local atomic distortions are influenced by MWR exposure, and how these structural effects can impact low-temperature phase transitions. Please click Additional Files below to see the full abstract

Synthesis of Novel Flower-Like Zn(OH)F via a Microwave-Assisted Ionic Liquid Route and Transformation into Nanoporous ZnO by Heat Treatment

Zinc hydroxide fluoride (Zn(OH)F) with novel flower-like morphology has been prepared via a microwave-assisted ionic liquid route. The flower-like Zn(OH)F particle has six petals and every petal is composed of lots of acicular nano-structure. Nanoporous ZnO is obtained by thermal decomposition of as-prepared Zn(OH)F in air, and the flower-like morphology is well retained. In the process of synthesis, ionic liquid 1-Butyl-3-methylimidazolium tetrafluoroborate is used as both the reactant and the template

Organophosphonate bridged anatase mesocrystals: low temperature crystallization, thermal growth and hydrogen photo-evolution

The sol-gel co-condensation of organo-phosphonates to titanium alkoxides enables access to novel organic-inorganic hybrids based on phosphonate-bridged titanium dioxide. In this contribution, we bring new perspectives to the long established sol-gel mineralization of titanium alkoxide species, by harnessing the virtues of the well-designed phosphonate-terminated phosphorus dendrimers as reactive amphiphilic nanoreactor, confined medium and cross-linked template to generate discrete crystalline anatase nanoparticles at low temperature (T = 60 degrees C). An accurate investigation on several parameters (dendrimer generation, dendrimer-to-titanium alkoxide ratio, precursor reactivity, temperature, solvent nature, salt effect) allows a correlation between the network condensation, the opening porous framework and the crystalline phase formation. The evolution of the dendrimer skeleton upon heat treatment has been deeply monitored by means of P-31 NMR, XPS and Raman spectroscopy. Increasing the heteroatom content within a titania network provides the driving force for enhancing their photocatalytic water splitting ability for hydrogen production.Brahmi, Y.; Katir, N.; Macia Agullo, JA.; Primo Arnau, AM.; Bousmina, M.; Majoral, J.; García Gómez, H.... (2015). Organophosphonate bridged anatase mesocrystals: low temperature crystallization, thermal growth and hydrogen photo-evolution. Dalton Transactions. 44(35):15544-15556. doi:10.1039/c5dt02367jS1554415556443

Battery Charge Curve Prediction via Feature Extraction and Supervised Machine Learning

Abstract Real‐time onboard state monitoring and estimation of a battery over its lifetime is indispensable for the safe and durable operation of battery‐powered devices. In this study, a methodology to predict the entire constant‐current cycling curve with limited input information that can be collected in a short period of time is developed. A total of 10 066 charge curves of LiNiO2‐based batteries at a constant C‐rate are collected. With the combination of a feature extraction step and a multiple linear regression step, the method can accurately predict an entire battery charge curve with an error of < 2% using only 10% of the charge curve as the input information. The method is further validated across other battery chemistries (LiCoO2‐based) using open‐access datasets. The prediction error of the charge curves for the LiCoO2‐based battery is around 2% with only 5% of the charge curve as the input information, indicating the generalization of the developed methodology for predicting battery cycling curves. The developed method paves the way for fast onboard health status monitoring and estimation for batteries during practical applications