Gravure Printed and Solution-Processed Polymer Semiconductor Devices

The idea of printing optoelectronic devices has been developed over the last decade by various printing techniques such as screen printing, transfer printing, and inkjet printing, attributed to the advent of soluble organic semiconducting (OSC) materials. Printing of optoelectronic devices provides economical advantages for its fast and simple processing stages which is conceptually similar to the graphical printing. The advantage is expected to overcome the relatively low performance of organic materials where its charge transport is occurred by hopping process which is limited by its hopping distance and conformation of molecular chains. Printing techniques currently available should be optimized further to attract a huge impact. For example, the inkjet printing has a drawback of its low printing speed although it offers the printing of high definition pixels with its width around 60 μm. In this Thesis, gravure printing, a high throughput printing technique, is discussed to experimentally demonstrate its feasibility as a production method of optoelectronic devices. The targeted device structures are organic light-emitting diodes (OLEDs) and field-effect transistors (OFETs). Both printed OFETs and OLEDs have reached device performance similar to reference devices with the same materials and structures fabricated by spin-coating. Unlike the graphic art printing, such as is used to fabricate newspapers, magazines and posters, the printing of OSC optoelectronic devices is very sensitive to processing conditions attributed to a thickness of very thin layers, usually less than 100 nm. Therefore, the surface uniformity of the printed layers must be very planar, with a surface roughness root mean square (RMS) value typically less than 3 nm. It is found that controlling hydrodynamic forces during the thin film formation, such as the coffee stain convection flow and the surface tension driven Marangoni flow, offer a clear opportunity for achieving devices with high performance in gravure contact printed thin films. Chapter 2 and 3 discuss background theory related to experiments in this thesis. Chapter 4 is an experimental chapter explaining materials used and experimental techniques. In Chapter 5, gravure printing of OLEDs with printed poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT: PSS) hole injection and LUMATION Green 1300 (LG1300) light emissive layers is developed with discussions of wetting of printing formulations and fluidic movements observed during film formation. A mixture of solvent method provides the circulation of hydrodynamic flows inside the printed formulation providing a deposition of highly uniform thin film after solvent evaporation. As a result, high performance of OLEDs with its performance of 8.8 cd/A and 5.4 lm/W with a maximum brightness of 66,000 cd/m2 is reported in OLEDs where both PEDOT: PSS and LG1300 are gravure printed. The performance is the highest up to date among the OLEDs printed by the same printing method. Chapter 6 introduces an inverted structure type OLED where its high work function anode is placed on the top of the device so that it consequently improves device stability as high work function metals such as Au or Ag are less sensitive to ambient dopants. The use of carbonate or oxide layers on the top of a high work function metal at the bottom of the device induced efficient injection of electrons to the device. A very thin layer of caesium carbonate (Cs2CO3) around 5-10 nm was gravure printed onto the ITO electrode. The printed Cs2CO3 layer showed that the surface roughness is highly improved owing to molecular ordering is affected and improved by the mechanical forces such as pressure and thermal energy engaged during the printing. The inverted OLEDs with the printed Cs2CO3 layer recorded the device performance of 10 cd/A and 3 lm/W with a maximum brightness of around 7,500 cd/m2. This is a first report showing that a very thin and inorganic layer can also be gravure printed. Chapter 7 describes charge balancing and position of recombination zone in inverted OLEDs using poly (9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) and poly (9,9-dioctylfluoreneco- N-(4-butylphenyl)-diphenylamine) (TFB) bilayer structure. The two layers are either hole or electron transporting materials and can form a large energy offsets between the HOMO levels and the LUMO levels of the two materials at the interface which confines a large number of injected charge carriers there. It is shown that a position of recombination zone and the charge carrier confinement effect are dependent with the thicknesses of the two polymer layers. The confined charged carriers induce the recombination zone to be positioned close to the interface where charge carrier tunnelling and Föster energy transfer occur more frequently than the bulk. The experimentally optimized thicknesses of the two layers record the highest efficiency of 36 cd/A and 23 lm/W with a bright emission of 51,200 cd/m2 at a low voltage around 4 V. The efficiency is the highest efficiency reported so far to the best of our knowledge using fluorescence materials. Chapter 8 explains gravure printing of OFETs using a thiophene polymer. Poly(3- hexylthiophene)-2,5-diyl (P3HT) OSC, two dielectric layers, and top Ag gate electrode are sequentially gravure printed. The annealing condition of P3HT, choice of dielectric layer and issues related to printing P3HT are discussed. Fully gravure printed OFETs on the pre-patterend ITO source and drain pattern report a high mobility of 3 × 10-2 cm2/Vs and an on/off current ratio of 104.62. The performance is the highest among the printed OFETs using P3HT

Entity Based Sentiment Analysis for Textual Health Advice

This work explores entity based sentiment analysis for textual health advice through deep learning. We fine tuned a pretrained BERT model to analyze sentiments across five different predetermined categories which consist of food, medicine, disease, exercise, and vitality for three different sentiments: positive, negative, and neutral. Original set of annotated medical dataset from Dartmouth College’s Persist Lab was used to conduct the experiments. For the aim of tailoring the data for the purpose of entity based sentiment analysis, we explored data transformation techniques to generate optimum training examples. During the experiments, we were able to discover that the wide variety and complexity of terms for the medicine and the disease category posed difficulty on the BERT model which we utilized masking techniques to mitigate. We also demonstrated that our model struggles to learn neutral sentiments in cases where instances of all labels are balanced(in both training and testing). Our system was able to achieve an overall F1 score of 0.739 when conducting the experiment with masked text on a balanced dataset

Walking and Dwelling: Creating an Atelier in Nature

This paper comprises a description of an exploration of how the author’s daily walking reflected the emergence of an a/r/tographical living inquiry that engendered a profound sense of dwelling and lingering, and a deeper understanding of the nature of artistic invitation through a pedagogical aesthetic provocation

Format blurring: how the advent of the Walmart Supercenter has changed the U.S. grocery industry

This paper develops a game-theoretic model that analyzes how a grocery store responds to the entry of a Walmart Supercenter using its store-format choice. By adopting a set of realistic assumptions, such as the cost advantage of Walmart and differentiated services of grocery stores, we find that the distance to a Walmart Supercenter is a key moderating factor in the store-format choice of grocery stores. Grocery stores would prefer to sell non-food items, but when sufficiently close to Walmart Supercenters they would specialise in food items, as consumers find it less costly to engage in two-stop shopping, making the gain from non-food items smaller. So an asymmetric equilibrium becomes feasible, wherein grocery stores carrying increasingly more non-food products and a new grocery store concept like Whole Foods and Wild Oats emphasising high-quality, organic foods can coexist. Our results yield important managerial implications. Under the specialisation strategy, the quality of its differentiated services should be sufficiently high, at least two to four times the disutility of two-stop shopping. Under the expansion strategy, grocery stores should engage in loss leadership, pricing non-food items below cost to lure large-basket consumers while earning higher margins from food items to compensate for the loss

Haplotype-based score test for linkage in nuclear families

<p>Abstract</p> <p>Background</p> <p>To look for genetic linkage between angiotensin-I converting enzyme(ACE) gene and hypertension in a Korean adolescent cohort, we developed a powerful test using the covariances between marginal differences and their variances in a transmission/non-transmission table.</p> <p>Results</p> <p>We estimated haplotype frequencies using the parental and affected offspring's genotypes and then constructed a transmission/non-transmission table for the parental haplotypes transmitted to the offspring. We then proposed a test for checking the marginal homogeneity in the table. Because the cells in the table were dependent due to the uncertainty of the parental haplotypes, we adopted a randomization procedure to estimate the significance of the observed test statistic. Simulations show that our test performs well on a nominal level and has a monotone power, which increases as the relative risk increases. With our test, there was no evidence of genetic linkage between the ACE gene and hypertension in the Korean adolescent cohort.</p> <p>Conclusion</p> <p>We developed a score test for linkage and used simulations to demonstrate that our test performs well at a nominal level. Under some situations where the diversity of haplotypes is low, the proposed test gained a little power over the method based on only variances between marginal differences in a transmission/non-transmission table.</p