Deep blue/ultraviolet microcavity OLEDs based on solution-processed PVK:CBP blends |
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| Affiliation: | 1. Ames Laboratory-USDOE and Physics & Astronomy Department, Iowa State University, Ames, IA 50011, USA;2. Ames Laboratory-USDOE and Electrical & Computer Engineering Department, Iowa State University, Ames, IA 50011, USA;3. Ames Laboratory-USDOE and Simpson College, Indianola, IA 50125, USA;4. Microelectronics Research Center and Electrical & Computer Engineering Department, Iowa State University, Ames, IA 50011, USA;1. Department of Physics and Institute of Advanced Materials, Hong Kong Baptist University, Kowloon Tong, Hong Kong, China;2. Institute of Molecular Functional Materials, Department of Chemistry, and Institute of Advanced Materials, Hong Kong Baptist University, Kowloon Tong, Hong Kong, China;3. College of Chemistry and Environmental Engineering, Guangdong Engineering and Technology Research Center for Advanced Nanomaterials, Dongguan University of Technology, Dongguan 523808, China;4. Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640, China;1. Luminous! Center of Excellence for Semiconductor Lighting and Displays, School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore;2. Department of Electrical and Electronics Engineering, Department of Physics, and UNAM - Institute of Materials Science and Nanotechnology, Bilkent University, Ankara 06800, Turkey;1. Department of Chemical Engineering, University of Rochester, Rochester, NY 14627, USA;2. Department of Chemistry, University of Rochester, Rochester, NY 14627, USA |
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| Abstract: | There is an increasing need to develop stable, high-intensity, efficient OLEDs in the deep blue and UV. Applications include blue pixels for displays and tunable narrow solid-state UV sources for sensing, diagnostics, and development of a wide band spectrometer-on-a-chip. With the aim of developing such OLEDs we demonstrate an array of deep blue to near UV tunable microcavity (μc) OLEDs (λ ～373–469 nm) using, in a unique approach, a mixed emitting layer (EML) of poly(N-vinyl carbazole) (PVK) and 4,4′-bis(9-carbazolyl)-biphenyl (CBP), whose ITO-based devices show a broad electroluminescence (EL) in the wavelength range of interest. This 373–469 nm band expands the 493–640 nm range previously attained with μcOLEDs into the desired deep blue-to-near UV range. Moreover, the current work highlights interesting characteristics of the complexity of mixed EML emission in combinatorial 2-d μcOLED arrays of the structure 40 nm Ag/x nm MoOx/～30 nm PVK:CBP (3:1 weight ratio)/y nm 4,7-diphenyl-1,10-phenanthroline (BPhen)/1 nm LiF/100 nm Al, where x = 5, 10, 15, and 20 nm and y = 10, 15, 20, and 30 nm. In the short wavelength μc devices, only CBP emission was observed, while in the long wavelength μc devices the emission from both PVK and CBP was evident. To understand this behavior simulations based on the scattering matrix method, were performed. The source profile of the EML was extracted from the measured EL of ITO-based devices. The calculated μc spectra indeed indicated that in the thinner, short wavelength devices the emission is primarily from CBP; in the thicker devices both CBP and PVK contribute to the EL. This situation is due to the effect of the optical cavity length on the relative contributions of PVK and CBP EL through a change in the wavelength-dependent emission rate, which was not suggested previously. Structural analysis of the EML and the preceding MoOx layer complemented the data analysis. |
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| Keywords: | UV-to-blue OLED arrays UV-to-blue microcavity OLED arrays PVK:CBP OLED arrays Polymer/small molecule mixed emission layer |
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