Controlling bucking structure by UV/ozone treatment for light extraction from organic light emitting diodes

• Published in: Organic electronics Vol. 12; no. 7; pp. 1177 - 1183
• Main Authors: Koo, Won Hoe, Boo, SamYul, Jeong, Soon Moon, Nishimura, Suzushi, Araoka, Fumito, Ishikawa, Ken, Toyooka, Takehiro, Takezoe, Hideo
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.07.2011
• Subjects: Buckle; Extraction; OLED; Ultraviolet/ozone treatment; Waveguide; OLED; Extraction; Buckle; Waveguide; Ultraviolet/ozone treatment
• ISSN: 1566-1199; 1878-5530
• DOI: 10.1016/j.orgel.2011.03.031

Most of light emitted from organic light emitting diodes (OLEDs) is trapped into ITO/organic layers as waveguide modes. In order to effectively extract the waveguide modes, Bragg diffraction gratings with 300∼400 nm periodicity should be required, because the periodicity in those ranges determines the extracted wavelength for visible EL light. We controlled the periodicity of the buckling patterns as gratings by the UVO treatment. With the UVO treatment time, the periodicity of the buckles decreased from 460 nm to 300 nm and the outcoupled emission wavelengths by buckles in the devices were shifted toward the shorter wavelengths. [Display omitted] ► Spontaneously formed buckling patterns were able to be controlled by the UVO treatment time; the periodicity and depth of the buckle decreased with increasing UVO treatment time. ► An underlying buckling mechanism according to UVO treatment was inferred for the first time. ► We succeeded in shifting the wavelength showing the highest enhancement ratio toward the shorter wavelengths using the device with buckles of the shorter periodicity by UVO treatment. We describe a simple and effective method to control the periodicity of the buckling structure by thermal evaporation and ultraviolet/ozone (UVO) treatment so as to effectively extract the waveguide modes in organic light emitting diode (OLED) devices, inferring an underlying buckling mechanism. The periodicity of the buckles decreased from 460 to 300 nm with the UVO treatment time, shifting the emission wavelength showing the highest enhancement ratio toward the shorter wavelengths in the device with buckles. We exemplified the outcoupling characteristics of the waveguide modes by the buckles with different periodicities.