Color Control in π-Conjugated Organic Polymers for Use in Electrochromic Devices

Head-worn display design is inherently an interdisciplinary subject fusing optical engineering, optical materials, optical coatings, electronics, manufacturing techniques, user interface design, computer science, human perception, and physiology for assessing these displays. This paper summarizes the state-of-the-art in head-worn display design (HWD) and development. This review is focused on the optical engineering aspects, divided into different sections to explore principles and applications. Building on the guiding fundamentals of optical design and engineering, the principles section includes a summary of microdisplay or laser sources, the Lagrange invariant for understanding the trade-offs in optical design of HWDs, modes of image presentation (i.e., monocular, biocular, and stereo) and operational modes such as optical and video see-through. A brief summary of the human visual system pertinent to the design of HWDs is provided. Two optical design forms, namely, pupil forming and non-pupil forming are discussed. We summarize the results from previous design work using aspheric, diffractive, or holographic elements to achieve compact and lightweight systems. The applications section is organized in terms of field of view requirements and presents a reasonable collection of past designs

Head-worn displays: a review

Color in Business, Science, and Industry

The field of organic electrochromics is reviewed here, with particular focus on how the “electrochromic” as a functional material can be brought from the current level of accurate laboratory synthesis and characterization to the device and application level through a number of suited roll-to-roll methods compatible with upscaling and manufacture The successful approaches to operational devices are presented in detail, as well as areas where future research would have a high impact and accelerate the development such as highly conducting and transparent substrates, electrolytes adapted for multilayer application and morphologically stable conjugated polymers

Development and Manufacture of Polymer-based Electrochromic Devices

We report the synthesis and characterization of three new poly(2,7-carbazole) derivatives, namely, poly[N-9-heptadecanyl-2,7-carbazole-alt-5,7-di(3-octylthien-2-yl)-2,3-di(thien-3-yl)-thieno[3,4-b]pyrazine (P1), poly[N-9-heptadecanyl-2,7-carbazole-alt-5,7-di(3-octylthien-2-yl)-2,3-di(phen-1-yl)-thieno[3,4-b]pyrazine (P2), and poly[N-9-heptadecanyl-2,7-carbazole-alt-5,7-di(3-octylthien-2-yl)-2,3-di(4-octylphen-1-yl)-thieno[3,4-b]pyrazine (P3), which reflect green light in their neutral state and show transmissive brown when oxidized. These two colors are compatible for adaptive camouflage for military assets. All solid-state electrochromic cells were prepared using spray-coated films of electrochromic conjugated polymer (P1−P3) as active layer. We report the development of multicolored electrochromic cells (MEC) based on the additive color mixing theory. MEC of various sizes were prepared from 2.5 × 2.5 cm, and up to 12.5 × 12.5 cm. Finally, we also describe the fabrication of a multicolored electrochromic...

Multicolored Electrochromic Cells Based On Poly(2,7-Carbazole) Derivatives For Adaptive Camouflage

Optimization, preparation, and electrical short evaluation for 30 cm2 active area dual conjugated polymer electrochromic windows

Active Matrix Organic Light Emitting Diode (AMOLED) displays are known to exhibit high levels of performance, and these levels of performance have continually been improved over time with new materials and electronics design. eMagin Corporation developed a manually adjustable temperature compensation circuit with brightness control to allow for excellent performance over a wide temperature range. Night Vision and Electronic Sensors Directorate (US Army) tested the performance and survivability of a number of AMOLED displays in a temperature chamber over a range from -55°C to +85°C. Although device performance of AMOLEDs has always been its strong suit, the issue of usable display lifetimes for military applications continues to be an area of discussion and research. eMagin has made improvements in OLED materials and worked towards the development of a better understanding of usable lifetime for operation in a military system. NVESD ran luminance degradation tests of AMOLED panels at 50°C and at ambient to characterize the lifetime of AMOLED devices. The result is a better understanding of the applicability of AMOLEDs in military systems: where good fits are made, and where further development is needed.

AMOLED (active matrix OLED) functionality and usable lifetime at temperature

The U.S. Army and eMagin Corporation established a Cooperative Research and Development Agreement (CRADA) to
characterize the ongoing improvements in the lifetime of OLED displays. This CRADA also called for the evaluation of
OLED performance as the need arises, especially when new products are developed or when a previously untested
parameter needs to be understood. In 2006, eMagin Corporation developed long-life OLED-XL devices for use in their
AMOLED microdisplays for head-worn applications. Through Research and Development programs from 2007 to 2012
with the U.S. Government, eMagin made additional improvements in OLED life and developed the first SXGA (1280 X
1024 with triad pixels) and WUXGA (1920 X 1200 with triad pixels) OLED microdisplays. US Army RDECOM
CERDEC NVESD conducted life and performance tests on these displays, publishing results at the 2012, 2011, 2010,
2009, 2008, and 2007 SPIE Defense, Security and Sensing Symposia. Life and performance tests have continued
through 2013, and this data will be presented along with a comparison to previous data. This should result in a better
understanding of the applicability of AMOLEDs in military and commercial head mounted systems, where good fits are
made, and where further development might be desirable.

Active matrix organic light emitting diode (AMOLED) performance and life test results

Complementary coloring conducting polymer based electrochromic devices have been designed, fabricated and tested for possible application as a variable attenuation combiner element for a see-through head mounted display or a variable trasnsmissive sand wind dust goggle lens. Electrochromic cells fabricated on both glass and polycarbonate substrates have been demonstrated to meet closely the desired goals of low power consumption, wide transmission range, fast switching speeds and long lifetime. Photopic transmissions of 34% in colored state and 67% in bleached state were achieved in a reproducible manner. The measured switching times are 0.6 sec (colored to bleached state) and 1.9 sec (bleached to colored state). The life cycle testing showed stability up to 92,000 switches. The measured power consumption of the fabricated devices was < 1 mW/cm . The electrochromic technology design effort has identified processes for obtaining the optimum layer thickness and selecting polymers and gel electrolytes necessary to obtain the widest transmission range, fastest switching speed and longest lifetime. Early environmental testing has been performed by subjecting prototype electrochromic cells to temperatures varying from -30°C to + 40°C with the results reported herein. Follow on work includes further optimization of electronic drive schemes as well as field testing of electrochromic lens equipped sand, wind dust goggles.

Electrochromic variable transmission optical combiner

Image intensifiers (I2) have gained wide acceptance throughout the Army as the premier nighttime mobility sensor for the individual soldier, with over 200,000 fielded systems. There is increasing need, however, for such a sensor with a video output, so that it can be utilized in remote vehicle platforms, and/or can be electronically fused with other sensors. The image-intensified television (I2TV), typically consisting of an image intensifier tube coupled via fiber optic to a solid-state imaging array, has been the primary solution to this need. I2TV platforms in vehicles, however, can generate high internal heat loads and must operate in high-temperature environments. Intensifier tube dark current, called "Equivalent Background Input" or "EBI", is not a significant factor at room temperature, but can seriously degrade image contrast and intra-scene dynamic range at such high temperatures. Cooling of the intensifier's photocathode is the only practical solution to this problem. The US Army RDECOM CERDEC Night Vision & Electronic Sensors Directorate (NVESD) and Ball Aerospace have collaborated in the reported effort to more rigorously characterize intensifier EBI versus temperature. NVESD performed non-imaging EBI measurements of Generation 2 and 3 tube modules over a large range of ambient temperature, while Ball performed an imaging evaluation of Generation 3 I2TVs over a similar temperature range. The findings and conclusions of this effort are presented.

Michael V. Wood

Papers

Optimization, preparation, and electrical short evaluation for 30 cm2 active area dual conjugated polymer electrochromic windows

AMOLED (active matrix OLED) functionality and usable lifetime at temperature

Active matrix organic light emitting diode (AMOLED) performance and life test results

Electrochromic variable transmission optical combiner

Characterization of photocathode dark current vs. temperature in image intensifier tube modules and intensified televisions