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Advanced hybrid solar cell approaches for future generation ultra-high efficiency photovoltaic devices

Description

Increasing the conversion efficiencies of photovoltaic (PV) cells beyond the single junction theoretical limit is the driving force behind much of third generation solar cell research. Over the last half century, the experimental conversion efficiency of both single junction and tandem solar cells has plateaued as manufacturers and researchers have optimized various materials and structures. While existing materials and technologies have remarkably good conversion efficiencies, they are approaching their own limits. For example, tandem solar cells are currently well developed commercially but further improvements through increasing the number of junctions struggle with various issues related to material interfacial defects. Thus, there is a need for novel theoretical and experimental approaches leading to new third generation cell structures. Multiple exciton generation (MEG) and intermediate band (IB) solar cells have been proposed as third generation alternatives and theoretical modeling suggests they can surpass the detailed balance efficiency limits of single junction and tandem solar cells. MEG or IB solar cell has a variety of advantages enabling the use of low bandgap materials. Integrating MEG and IB with other cell types to make novel solar cells (such as MEG with tandem, IB with tandem or MEG with IB) potentially offers improvements by employing multi-physics effects in one device. This hybrid solar cell should improve the properties of conventional solar cells with a reduced number of junction, increased light-generated current and extended material selections. These multi-physics effects in hybrid solar cells can be achieved through the use of nanostructures taking advantage of the carrier confinement while using existing solar cell materials with excellent characteristics. This reduces the additional cost to develop novel materials and structures. In this dissertation, the author develops thermodynamic models for several novel types of solar cells and uses these models to optimize and compare their properties to those of existing PV cells. The results demonstrate multiple advantages from combining MEG and IB technology with existing solar cell structures.

ContributorsLee, Jongwon (Author) / Honsberg, C. (Christiana B.) (Thesis advisor) / Bowden, Stuart (Committee member) / Roedel, Ronald (Committee member) / Goodnick, Stephen (Committee member) / Schroder, Dieter (Committee member) / Arizona State University (Publisher)

Created2014

Depression and Anxiety One Month After Stroke

Description

Depression and anxiety after stroke negatively affect patient outcomes; however, health care professionals may overlook poststroke depression and anxiety while they focus on the physical disabilities of patients soon after a stroke. The purpose of this study was to investigate the prevalence and predictors of depression, anxiety, or both concurrently at one month after stroke. We conducted a cross-sectional, descriptive study in a sample of 231 hospitalized patients with ischemic stroke in Korea. Data were collected by interviews using a series of structured questionnaires in addition to clinical data retrieved from patients’ medical records. More than 70% were identified as depressed, 45.9% experienced anxiety, and 43.7% had concurrent depression and anxiety. Using a multiple logistic regression analysis, we identified anxiety as a predictor of depression; depression as a predictor of anxiety; and female sex, headaches, and swallowing difficulty as predictors of the comorbidity of depression and anxiety. Periodical screenings for poststroke depression and anxiety from an early stage in a hospital to years after stroke in a community are recommended to provide better chances for early identification of patients at risk because depression and anxiety may manifest at any stage of recovery. Special attention should be given to individuals with culture-bound somatic symptoms in addition to female patients and those who have difficulty swallowing among Korean stroke patients.

ContributorsShin, Cha-Nam (Author) / Sin, Mo-Kyung (Author) / Lee, Eunice (Author) / Lee, Jongwon (Author) / An, Kyungeh (Author) / Sim, Jeongha (Author) / Arizona State University. College of Nursing & Healthcare Innovation (Contributor)

Created2016