The discussion of A.C. electric properties of polymeric light emission diode under the change of bias

• Main Authors: Chang-Hong Wei, 魏昌弘
• Other Authors: Gung Chern
• Format: Others
• Language: zh-TW
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/84841675635141990014

碩士 === 國立中正大學 === 物理所 === 94 === This thesis reports the results of frequency and dc-bias dependent dielectric properties of organic polymeric light emission diode (PLED). The main purpose is to understand the influences of the charge carrier injection under different structure of cathode and anode. We produce three luminescent devices which are ITO/PEDOT/PFO/Ca/Al, ITO/PEDOT/PFO/Al and ITO/PFO/Al, respectively. Generally speaking, adding PEDOT and Ca will enhance the injection of holes and electrons because of suitable impedance match. The main measurements include relative dielectric constant and ac-conductivity as a function of frequency (100-1 MHz) and dc Bias (0-18 V). The intensity of light emission was also measured for a comparison with dc I-V curves. The measurement of the intensity of light emission show that only the first two devices have significant light emission phenomena under direct forward of dc bias. Moreover, the light emission intensity is much weaker for the device lacking Ca electrode. Comparing with I-V curves, the first two devices also show non-linear electrical transport also corresponded to forward bias more than 4V. This difference is further resolved by the measurements of the capacitance of these two devices. A significant enhancement of dielectric constant is only observed in ITO/PEDOT/PFO/Ca/Al (from 4.9nF to 140nF). This observation indicates that the forward bias introduce space charge (or interface polarization) so the charge carrier can not inject effectively into PFO. Therefore, the light emission of the device with PEDOt but without Ca is not effective although it shows pronouncedly induced electric current.