Composition and Interface Engineering of Organic-Inorganic Hybrid Perovskites to Improve Photovoltaic Performance and Stability

Faced with the growing demands for energy in modern society, organic-inorganic metal halide perovskite materials have recently fascinated the photovoltaics (PV) research community due to a combination of their high quality optoelectronic properties and their ease in the fabrication proceed. As a result, solar cells employing the perovskite materials have been researched exponentially on their way and now the power conversion efficiency (PCE) of perovskite solar cells have been improved over 23% since the first report showing the PCE of 3% in 2009. In this thesis, I investigate compositional modification of perovskite materials and optimization of the charge transporting materials to produce high efficiency, stable and reproducible perovskite solar cells. First of all, after the reasonable performance was achieved, we have innovated a new approach of interface engineering in a perovskite layer to boost efficiency of devices. Engineering a compositional gradient with formamidinium bromide (FABr) at the rear interface between a pristine mixed perovskite ((FAPbI3)0.85(MAPbBr3)0.15) film and a hole transporting material (spiro-OMeTAD) demonstrated that charge collection is improved and charge recombination is reduced at the interface, which leads to a striking enhancement in open-circuit voltage (VOC). This result shed light on the importance of the passivation engineering on the rear surface of perovskite layers. However, beyond the improvement of efficiency, a long-term stability under moisture and continuous illumination is still remained as another challenge for market deployment of the perovskite solar cells. To develop the stability, we have developed the engineering by the surface growth of a two-dimensional (2D) perovskite, the crystal structure of A2BX4, on top of a bulk three-dimensional (3D) perovskite ABX3 film. It is well-known that the 2D perovskite has the superior stability, but suffered because of their low efficiency in the application of photovoltaics. The formation of a distinct 2D perovskite on top of the 3D perovskite (Cs0.1FA0.74MA0.13PbI2.48Br0.39) layer was proved by investigation of structural and optical properties of the stack. This embodying two different type of perovskite layer in one film had never been shown. Finally, this innovative approach led to the PCE of 21% and enhanced stability sustaining 85% of the initial value after 800 hours under full illumination. Thus, my approach of coating 2D perovskite layer make the perovskite solar cells more effective and stable for commercialization. Besides, to avoid the toxic chemical the lead free perovskite (Cs2AgBiBr6) was explored as photovoltaics and the further improvement can be expected. The last results presented in this thesis are related to optimization of the electron transporting layer (ETL) and hole-transporting materials (HTM) for efficient perovskite solar cells. It is shown that the ETL and the HTMs are playing a significant role in realizing efficient and stable perovskite solar cells

Sex- and Age-Related Changes in Connexin 43 Expression in Normal Rat Bladder

Purpose Gap junctions are intercellular channels to facilitate electrical and metabolic communication between adjacent cells. Connexin 43 is the most predominant type of connexin expressed on rat detrusor muscle cells. We investigated the connexin 43 expressions in various age groups of either sex in normal rats. Methods Eighty Sprague-Dawley rats were used for analysis. Each group was quantified by 8 rats at 1 week, 2 weeks, 1 month, 3 months, and 6 months of age in either sex. In each animal, bladder was removed without any kind of intervention and fresh-frozen in liquid nitrogen. Total RNA extraction was done with easy-BLUE total RNA extraction kit. Reverse transcription polymerase chain reaction was done for connexin 43 and glyceraldehyde-3-phosphate dehydrogenase as an internal control using ImProm-II Reverse Transcription System. Results In female rats, no age-related change was detected in connexin 43 expressions. In male rats, connexin expression at 3 months of age showed significant decrease compared with 1 week, 2 weeks, and 6 months of age (P<0.05). When connexin expression at the same age in male and female were compared, only 3 months group in male showed significant decrease than the same age group in female. Conclusions Our data suggest that the expressions of connexin 43 mRNA in normal detrusor muscle cell showed age-related changes especially in male rats. Although it is difficult to interpret these findings at this stage, age should be considered as a possible compounding factor affecting connexin 43 expressions in male rats

Recurrent True Brachial Artery Aneurysm

True aneurysm of the brachial artery is a rare disease entity. The mechanism of aneurysm formation is considered to be compression of the arterial wall, producing contusion of the media and subsequent weakness of the wall and fusiform dilatation. It can be caused by arteriosclerotic, congenital, and metabolic disorders, and can be associated with diseases such as Kawasaki's disease. Doppler ultrasonography, computed tomography, arteriography, and selective upper extremity angiography may be performed for establishing the diagnosis of aneurysm. The best therapeutic option is operative repair, and it should be performed without any delay, in order to prevent upper extremity ischemic or thrombotic sequelae. Here, we report a case of recurrent brachial artery aneurysm with review of the literature

PowerCore: a program applying the advanced M strategy with a heuristic search for establishing core sets

AbstractMotivation: Core sets are necessary to ensure that access to useful alleles or characteristics retained in genebanks is guaranteed. We have successfully developed a computational tool named 'PowerCore' that aims to support the development of core sets by reducing the redundancy of useful alleles and thus enhancing their richness.Results: The program, using a new approach completely different from any other previous methodologies, selects entries of core sets by the advanced M (maximization) strategy implemented through a modified heuristic algorithm. The developed core set has been validated to retain all characteristics for qualitative traits and all classes for quantitative ones. PowerCore effectively selected the accessions with higher diversity representing the entire coverage of variables and gave a 100% reproducible list of entries whenever repeated.Availability: PowerCore software uses the .NET Framework Version 1.1 environment which is freely available for the MS Windows platform. The files can be downloaded from http://genebank.rda.go.kr/powercore/. The distribution of the package includes executable programs, sample data and a user manual.Contact: [email protected]

Pancreatic serous cystadenocarcinoma with invasive growth into the colon and spleen

Serous cystic neoplasms of the pancreas are almost always benign lesions. However, there are some case reports of malignant serous neoplasms of the pancreas. It is very difficult to distinguish malignant and benign tumors. Indeed, only clinicopathologic findings of locoregional invasion and metastasis represent a malignancy. We report a serous cystadenocarcinoma of the pancreas that was initially considered to be colon cancer. Post-operatively, the tumor was confirmed to be a malignant serous cystic tumor of the pancreas. One year later, the patient remains disease-free

Selective Growth of Layered Perovskites for Stable and Efficient Photovoltaics

Perovskite solar cells (PSCs) are promising alternatives toward clean energy because of their high-power conversion efficiency (PCE) and low materials and processing cost. However, their poor stability under operation still limits their practical applications. Here we design an innovative approach to control the surface growth of a low dimensional perovskite layer on top of a bulk three-dimensional (3D) perovskite film. This results in a structured perovskite interface where a distinct layered low dimensional perovskite is engineered on top of the 3D film. Structural and optical properties of the stack are investigated and solar cells are realized. When embodying the low dimensional perovskite layer, the photovoltaic cells exhibit an enhanced PCE of 20.1% on average, when compared to pristine 3D perovskite. In addition, superior stability is observed: the devices retain 85% of the initial PCE stressed under one sun illumination for 800 hours at 50 1 C in an ambient environment

Optical Shaping of Plasma Cavity for Controlled Laser Wakefield Acceleration

Laser wakefield accelerators rely on relativistically moving micron-sized plasma cavities that provide extremely high electric field >100GV/m. Here, we demonstrate transverse shaping of the plasma cavity to produce controlled sub-GeV electron beams, adopting laser pulses with an axially rotatable ellipse-shaped focal spot. We showed the control capability on electron self-injection, charge, and transverse profile of the electron beam by rotating the focal spot. We observed that the effect of the elliptical focal spot was imprinted in the profiles of the electron beams and the electron energy increased, as compared to the case of a circular focal spot. We performed 3D particle-in-cell (PIC) simulations which reproduced the experimental results and revealed dynamics of a new asymmetric self-injection process. This simple scheme offers a novel control method on laser wakefield acceleration to produce tailored electron beams and x-rays for various applications.Comment: 5 pages, 5 figure

A Pulmonary Nodule due to Pulmonary Infarction Diagnosed by Video-Assisted Thoracoscopy

We report a pulmonary infarction in 68-year-old man who was referred for an asymptomatic pulmonary nodule in chest radiography. Computed tomography (CT), positron emission tomography (PET), and transthoracic needle aspiration suggested suspicion for malignancy. Video-assisted thoracoscopic surgery (VATS) was performed for histologic diagnosis. Our case is a pulmonary nodule due to pulmonary infarction diagnosed by VATS in Korea

Phenotyping of rice in salt stress environment using high-throughput infrared imaging

Phenotyping of rice (Oryza sativa L. cv. Donggin) in salt stress environment using infrared imaging was conducted. Results were correlated with the most frequently used physiological parameters such as stomatal conductance, relative water content and photosynthetic parameters. It was observed that stomatal conductance (R2 = –0.618) and relative water content (R2 = –0.852) were significantly negatively correlated with average plant temperature (thermal images), while dark-adapted quantum yield (Fv/Fm, R2 = –0.325) and performance index (R2 = –0.315) were not consistent with plant temperature. Advantages of infrared thermography and utilization of this technology for the selection of stress tolerance physiotypes are discussed in detail

The potent protective effect of wild ginseng (Panax ginseng C.A. Meyer) against benzo[alpha]pyrene-induced toxicity through metabolic regulation of CYP1A1 and GSTs

Wild Panax ginseng C.A. Meyer (WG) is a well-known medicinal herb. In this study, the protective effects of a water extract from the root of WG on benzo[alpha]pyrene (BP)-induced hepatotoxicity and the mechanism of these effects were investigated for the first time. The effects of WG on liver toxicities induced by BP were assessed by blood biochemical and histopathological analyses. BP caused severe liver injury in rats, as indicated by elevated plasma ALT, AST and LPO levels. Pretreatment with WG for 4 weeks completely abrogated increases in the ALT, AST and LPO levels when challenged with BP. Reductions in GSH content and GST activity by BP were reversed by WG. These protective effects of WG against BP-induced toxicity were consistent with the results of histopathological examinations. We next examined the effects of WG on the gene expression of the enzymes that metabolize BP in H4IIE cells. CYP1A1 mRNA and protein expression were increased by BP. WG moderately inhibited BP-induced CYP1A1 gene expression. Moreover, GSTA2, GSTA3 and GSTM2 gene expressions were significantly increased by WG through the Nrf2/antioxidant responsive element pathway for enzyme induction. In summary, WG is efficacious in protecting against BP-induced hepatotoxicity as results of metabolic regulations through both the inhibition of metabolic enzyme activation and the enhancement of electrophilic detoxification, implying that WG should be considered a potential chemopreventive agent