Filtering by
- Language: English
![187847-Thumbnail Image.png](https://d1rbsgppyrdqq4.cloudfront.net/s3fs-public/styles/width_400/public/2023-06/187847-Thumbnail%20Image.png?versionId=1OBy8QWxlUG7xyVdMIDtJ62Q.WmPBeiS&X-Amz-Content-Sha256=UNSIGNED-PAYLOAD&X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Credential=AKIASBVQ3ZQ42ZLA5CUJ/20240615/us-west-2/s3/aws4_request&X-Amz-Date=20240615T121452Z&X-Amz-SignedHeaders=host&X-Amz-Expires=120&X-Amz-Signature=7f7068920c77f3675c01f14bc6852bbc5302894ea73230886279f7bdfb816e34&itok=HXIAPMaN)
![157441-Thumbnail Image.png](https://d1rbsgppyrdqq4.cloudfront.net/s3fs-public/styles/width_400/public/2021-09/157441-Thumbnail%20Image.png?versionId=PVfFFNU0SVlRiySXYKEfj9p89YjPHKDE&X-Amz-Content-Sha256=UNSIGNED-PAYLOAD&X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Credential=AKIASBVQ3ZQ42ZLA5CUJ/20240616/us-west-2/s3/aws4_request&X-Amz-Date=20240616T191200Z&X-Amz-SignedHeaders=host&X-Amz-Expires=120&X-Amz-Signature=7b2ecefe79840896c239b41aa97ded439496fdef778158f05c220fc1ce39dcc2&itok=52S8rjKU)
OLEDs employing step-wide graded-doped emissive layers were designed to improve charge balance and center the exciton formation zone leading to improved device performance. A red OLED with a peak efficiency of 16.9% and an estimated LT97 over 2,000 hours at 1,000 cd/m2 was achieved. Employing a similar structure, a sky-blue OLED was demonstrated with a peak efficiency of 17.4% and estimated LT70 over 1,300 hours at 1,000 cd/m2. Furthermore, the sky-blue OLEDs color was improved to CIE coordinates of (0.15, 0.25) while maintaining an efficiency of 16.9% and estimated LT70 over 600 hours by incorporating a fluorescent sensitizer. These devices represent literature records at the time of publication for efficient and stable platinum phosphorescent OLEDs.
A newly developed class of emitters, metal-assisted delayed-fluorescence (MADF), are demonstrated to achieve higher-energy emission from a relatively low triplet energy. A green MADF device reaches a peak efficiency of 22% with an estimated LT95 over 350 hours at 1,000 cd/m2. Additionally, a blue charge confined OLED of PtON1a-tBu demonstrated a peak efficiency above 20%, CIE coordinated of (0.16, 0.27), and emission onset at 425 nm.
High triplet energy hosts are required for the realization of stable and efficient deep blue emission. A rigid “M”-type carbazole/fluorene hybrid called mDCzPF and a carbazole/9-silafluorene hybrid called mDCzPSiF are demonstrated to have high triplet energies ET=2.88 eV and 3.03 eV respectively. Both hosts are demonstrated to have reasonable stability and can serve as a template for future material design. The techniques presented here demonstrate alternative approaches for improving the performance of OLED devices and help to bring this technology closer to widespread commercialization.
![154499-Thumbnail Image.png](https://d1rbsgppyrdqq4.cloudfront.net/s3fs-public/styles/width_400/public/2021-09/154499-Thumbnail%20Image.png?versionId=DHPayV_MCxorC4yGHZNVaKmWwP2YhmuT&X-Amz-Content-Sha256=UNSIGNED-PAYLOAD&X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Credential=AKIASBVQ3ZQ42ZLA5CUJ/20240617/us-west-2/s3/aws4_request&X-Amz-Date=20240617T115735Z&X-Amz-SignedHeaders=host&X-Amz-Expires=120&X-Amz-Signature=5ae96e19b9ff24e97860852253c849ff5013d8281e23d2951aae588902947aae&itok=KLkloDjm)
![152677-Thumbnail Image.png](https://d1rbsgppyrdqq4.cloudfront.net/s3fs-public/styles/width_400/public/2021-09/152677-Thumbnail%20Image.png?versionId=mnB.37jjI3aLFdlSMXUnjz7FMCpA8l0t&X-Amz-Content-Sha256=UNSIGNED-PAYLOAD&X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Credential=AKIASBVQ3ZQ42ZLA5CUJ/20240617/us-west-2/s3/aws4_request&X-Amz-Date=20240617T060749Z&X-Amz-SignedHeaders=host&X-Amz-Expires=120&X-Amz-Signature=887a311436680b995a659d3946927d3308b8ba0d19607e09092f53a60672b4fb&itok=nCWdpQWk)
![152846-Thumbnail Image.png](https://d1rbsgppyrdqq4.cloudfront.net/s3fs-public/styles/width_400/public/2021-08/152846-Thumbnail%20Image.png?versionId=Rj_3lDZREHUnQiLDfqzedAaIBs4fPeTM&X-Amz-Content-Sha256=UNSIGNED-PAYLOAD&X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Credential=AKIASBVQ3ZQ42ZLA5CUJ/20240617/us-west-2/s3/aws4_request&X-Amz-Date=20240617T142928Z&X-Amz-SignedHeaders=host&X-Amz-Expires=120&X-Amz-Signature=c27ccd2eb2794d5db459a4e23523d20e2b6bb1fb8b4d0c1d7d302c112bfd9cde&itok=fIkYADq-)
![152950-Thumbnail Image.png](https://d1rbsgppyrdqq4.cloudfront.net/s3fs-public/styles/width_400/public/2021-08/152950-Thumbnail%20Image.png?versionId=hVZ2qKXQInYwr95eHkPZqRJQ.3_oOW_W&X-Amz-Content-Sha256=UNSIGNED-PAYLOAD&X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Credential=AKIASBVQ3ZQ42ZLA5CUJ/20240617/us-west-2/s3/aws4_request&X-Amz-Date=20240617T111610Z&X-Amz-SignedHeaders=host&X-Amz-Expires=120&X-Amz-Signature=6313445856ffc72b8f4ef2d8f00a962b84459bd4f48b7de474ff7e13af088db3&itok=Y-05uM1s)
In addition to demonstrating excellent device performance in OLEDs, platinum based complexes exhibit unique photophysical properties including the ability to form excimer emission capable of generating broad white light emission from a single emitter and the ability to form narrow band emission from a rigid, tetradentate molecular structure for select cases. These unique photophysical properties were exploited and their optical and electrical properties in a device setting were elucidated.
Utilizing the unique properties of a tridentate Pt complex, Pt-16, a highly efficient white device employing a single emissive layer exhibited a peak EQE of over 20% and high color quality with a CRI of 80 and color coordinates CIE(x=0.33, y=0.33). Furthermore, by employing a rigid, tetradentate platinum complex, PtN1N, with a narrow band emission into a microcavity organic light emitting diode (MOLED), significant enhancement in the external quantum efficiency was achieved. The optimized MOLED structure achieved a light out-coupling enhancement of 1.35 compared to the non-cavity structure with a peak EQE of 34.2%. In addition to demonstrating a high light out-coupling enhancement, the microcavity effect of a narrow band emitter in a MOLED was elucidated.
![155773-Thumbnail Image.png](https://d1rbsgppyrdqq4.cloudfront.net/s3fs-public/styles/width_400/public/2021-08/155773-Thumbnail%20Image.png?versionId=n7_ORUDYOkyuY65wwPBlQmbrgjC5lbbM&X-Amz-Content-Sha256=UNSIGNED-PAYLOAD&X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Credential=AKIASBVQ3ZQ42ZLA5CUJ/20240616/us-west-2/s3/aws4_request&X-Amz-Date=20240616T203749Z&X-Amz-SignedHeaders=host&X-Amz-Expires=120&X-Amz-Signature=f745705d77732e6e7b5eddb422af482e3c9112501f096208f0bdfe10f07c900a&itok=TX0POwzs)
![155609-Thumbnail Image.png](https://d1rbsgppyrdqq4.cloudfront.net/s3fs-public/styles/width_400/public/2021-09/155609-Thumbnail%20Image.png?versionId=rLr4p4PvtCnt6mQ0Qfj_un2b3a1ugLhQ&X-Amz-Content-Sha256=UNSIGNED-PAYLOAD&X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Credential=AKIASBVQ3ZQ42ZLA5CUJ/20240617/us-west-2/s3/aws4_request&X-Amz-Date=20240617T154720Z&X-Amz-SignedHeaders=host&X-Amz-Expires=120&X-Amz-Signature=6a1d4b70fa18672c64cfe6d4f00c40f45b3d8c5fbdfc256d1c6c9337044e5d78&itok=WU82m8lO)
![155413-Thumbnail Image.png](https://d1rbsgppyrdqq4.cloudfront.net/s3fs-public/styles/width_400/public/2021-09/155413-Thumbnail%20Image.png?versionId=qrHoewdGxkR3I6ZgUQgM_g4IwysGSXgq&X-Amz-Content-Sha256=UNSIGNED-PAYLOAD&X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Credential=AKIASBVQ3ZQ42ZLA5CUJ/20240617/us-west-2/s3/aws4_request&X-Amz-Date=20240617T160019Z&X-Amz-SignedHeaders=host&X-Amz-Expires=120&X-Amz-Signature=ad63a4531907cf134111254497600d540c45edc989e081f3e8565681772fafcb&itok=RvfeKD6g)
Worldwide energy demand is increasing as the population grows and the standard of living in developing countries improves. Some studies estimate as much as 20% of annual energy usage is consumed by lighting. Improvements are being made in lightweight, flexible, rugged panels that use organic light emitting diodes (OLEDs), which are particularly useful in developing regions with limited energy availability and harsh environments.
Displays also benefit from more efficient materials as well as the lighter weight and ruggedness enabled by flexible substrates. Displays may require different emission characteristics compared with solid-state lighting. Some display technologies use a white OLED (WOLED) backlight with a color filter, but these are more complex and less efficient than displays that use separate emissive materials that produce the saturated colors needed to reproduce the entire color gamut. Saturated colors require narrow-band emitters. Full-color OLED displays up to and including television size are now commercially available from several suppliers, but research continues to develop more efficient and more stable materials.
This research program investigates several topics relevant to solid-state lighting and display applications. One project is development of a device structure to optimize performance of a new stable Pt-based red emitter developed in Prof Jian Li's group. Another project investigates new Pt-based red, green and blue emitters for lighting applications and compares a red/blue structure with a red/green/blue structure to produce light with high color rendering index. Another part of this work describes the fabrication of a 14.7" diagonal full color active-matrix OLED display on plastic substrate. The backplanes were designed and fabricated in the ASU Flexible Display Center and required significant engineering to develop; a discussion of that process is also included.
This essay uses census data from the eighteenth century to examine the leadership role of caciques in the Guaraní missions. Cacique succession between 1735 and 1759 confirms that the position of cacique transitioned from the Guaraníes’ flexible interpretation of hereditary succession to the Jesuits’ rigid idea of primogenitor (father to eldest son) succession. This essay argues that scholars overstate the caciques’ leadership role in the Guaraní missions. Adherence to primogenitor succession did not take into account a candidate's leadership qualities, and thus, some caciques functioned as placeholders for organizing the mission population and calculating tribute and not as active leaders. An assortment of other Guaraní leadership positions compensated for this weakness by providing both access to leadership roles for non-caciques who possessed leadership qualities but not the proper bloodline and additional leadership opportunities for more capable caciques. By taking into account leadership qualities and not just descent, these positions provided flexibility and reflected continuity with pre-contact Guaraní ideas about leadership.