Organic light emitting devices with enhanced outcoupling via microlenses fabricated by imprint lithography

High efficiency white organic light emitting devices (WOLEDs) with optical outcoupling enhanced by hexagonal polymethylmethacrylate microlens arrays fabricated by imprint lithography on a glass substrate are demonstrated. Monte Carlo and finite difference time domain simulations of the emitted light are used to optimize the microlens design. The measured enhancement of light outcoupling and the angular dependence of the extracted light intensity are in agreement with the simulation. Using microlens arrays, we demonstrate a fluorescent/phosphorescent WOLED with a maximum external quantum efficiency of (14.3±0.3)%(14.3±0.3)% at 900 cd/m2900cd∕m2 and power efficiency of 21.6±0.5 lm/W21.6±0.5lm∕W at 220 cd/m2220cd∕m2. The electroluminescent spectra at viewing angles from normal to the substrate plane, to 60° off normal, remain almost unchanged, giving a color rendering index of 87.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87744/2/073106_1.pd

Thermal analysis of high intensity organic light-emitting diodes based on a transmission matrix approach

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98717/1/JApplPhys_110_124516.pd

White organic light-emitting device based on a compound fluorescent-phosphor-sensitized-fluorescent emission layer

The authors demonstrate a combination fluorescent and phosphor-sensitized-fluorescent white organic light-emitting device (WOLED), employing the conductive host material, 4,4′4,4′-bis(9-ethyl-3-carbazovinylene)-1,1′1,1′-biphenyl, doped with the phosphorescent green, and the fluorescent red and blue emitters, fac-tris(2-phenylpyridinato-N,C2′N,C2′) iridium (III), 4-(dicyanomethylene)-2-t2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H4H-pyran, and 4,4′4,4′-bis (9-ethy-3-carbazolvinylene)-1-1′1-1′-biphenyl, respectively. Although two fluorescent dopants are employed along with only a single phosphor, this simple structure can, in principle, achieve 100% internal quantum efficiency. In the prototype, the phosphor-sensitized WOLED exhibits total external quantum and power efficiencies of ηext,tot = 13.1±0.5%ηext,tot=13.1±0.5% and ηp,tot = 20.2±0.7 lm/Wηp,tot=20.2±0.7lm∕W, respectively, at a luminance of 800 cd/m2800cd∕m2 with Commission Internationale de L’Eclairage chromaticity coordinates of (x = 0.38(x=0.38, y = 0.42y=0.42) and a color rendering index of 79.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87798/2/143516_1.pd

Mechanisms for current-induced conductivity changes in a conducting polymer

A layer of polyethylene dioxythiophene:polystyrene sulfonic acid (PEDT:PSS) spun onto the surface of an inorganic semiconductor forms a highly asymmetric rectifying junction when a small current is applied and can be permanently open circuited with application of a high current density. This allows the polymer/semiconductor junction to function as a write-once-read-many-times memory element. We use x-ray photoelectron spectroscopy and temperature induced conductivity measurements to study the morphological and chemical changes responsible for the large current-induced conductivity changes. It is found that by applying a large current to the organic-inorganic semiconductor rectifying heterojunction structure Au/PEDT:PSS/SiAu∕PEDT:PSS∕Si, the ratio of PEDT+PEDT+ to PSS−PSS− near the interface changes due to phase segregation in the presence of both high electric field (>105 V/cm)(>105V∕cm) and temperature. This leads to a decrease in film conductivity by up to six orders of magnitude from its value in the conductive state.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87796/2/142109_1.pd

A Leaf Recognition Algorithm for Plant Classification Using Probabilistic Neural Network

In this paper, we employ Probabilistic Neural Network (PNN) with image and data processing techniques to implement a general purpose automated leaf recognition algorithm. 12 leaf features are extracted and orthogonalized into 5 principal variables which consist the input vector of the PNN. The PNN is trained by 1800 leaves to classify 32 kinds of plants with an accuracy greater than 90%. Compared with other approaches, our algorithm is an accurate artificial intelligence approach which is fast in execution and easy in implementation.Comment: 6 pages, 3 figures, 2 table

25.1: Invited Paper : Achieving Efficient Solid State Lighting Using Organic Light Emitting Devices

A significant challenge facing human kind in the 21st Century is how to address the ever decreasing supply of depletable and renewable energy. One approach to this problem is to decrease our usage. for this reason, considerable attention has been focused on more efficient means for room lighting which currently consumes approximately 20% of the total energy used. Organic light emitting devices (OLEDs) provide a unique opportunity to provide this high efficiency solid state lighting at very low cost. In this talk, I will discuss several strategies for achieving very high efficiency white light emission at high brightnesses for the next generation of efficient solid state lighting sources based on small molecular weight, vapor deposited OLED structures. Key to our approach is the use of electrophosphorescence as a means for converting all electrical into optical energy. We show that the highest luminance efficiencies can be obtained by a combination of fluorescence and phosphorescence in a unique OLED structure. Furthermore, the highest brightnesses are achieved (without a significant loss in power efficiency) by stacking several fluorescent/phosphorescent elements in a single OLED structure (called a SOLED), with each emitting element in the stack separated by a transparent charge generation layer. Prospects for OLEDs as the next practical generation of interior illumination sources will be reviewed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/92000/1/1.2785501.pd

Microfluidic device and method using double anodic bonding

A microfluidic device for use with a microfluidic delivery system, such as an organic vapor jet printing device, includes a glass layer that is directly bonded to a microfabricated die and a metal plate via a double anodic bond. The double anodic bond is formed by forming a first anodic bond at an interface of the microfabricated die and the glass layer, and forming a second anodic bond at an interface of the metal plate and the glass layer, where the second anodic bond is formed using a voltage that is lower than the voltage used to form the first anodic bond. The second anodic bond is formed with the polarity of the voltage reversed with respect to the glass layer and the formation of the first anodic bond. The metal plate includes attachment features that allow removal of the microfluidic device from a fixture

Comparative Evidence for Associative Learning in Task Switching.

Copyright © 2013 Cognitive Science SocietyHumans can perform several different tasks on the same set of stimuli in rapid alternation. Each task, signaled by a distinct task cue, may require the classification of stimuli using a different stimulus attribute. However, such "task switching" performance comes at a cost, as expressed by weaker performance when switching rather than repeating tasks. This cost is often claimed to be the consequence of a mental reorientation away from the previous task and towards the new task, requiring executive control of behavior. Alternatively, task switching could simply be based on the retrieval of different cue-stimulus-response associations. In this experiment, pigeons learned go-left/go-right discriminations between grating patterns according to either their spatial frequency or their orientation, depending on the color of the pattern (the task cue). When humans solved the same tasks on the basis of verbalizable rules, they responded more slowly and made more errors on trials where they had to switch between tasks than when repeating the same task. Pigeons did not show this "switch cost"; but like humans, their performance was significantly worse when the response (left or right) to a given stimulus varied between tasks than when it stayed the same (the “congruency effect”). Larger effects of both switch costs and congruency were observed in humans learning the tasks by trial and error. We discuss the potential driving factors behind these very different patterns of performance for both humans and pigeons