Probing of Electric Field Distribution and Carrier Behavior in Double-Layer Organic Light-Emitting Diodes by a Novel Microscopic Electric-Field-Induced Optical Second-Harmonic Generation Measurement system

Abstract

To analyze carrier behaviors leading to electroluminescence (EL) of double-layer organic lightemitting diodes (OLEDs), we used a novel microscopic electric-field-induced optical secondharmonic generation measurement system equipped with a radially polarized pulsed laser beam, which can probe two-dimensional electric field distributions in OLEDs. We showed a relationship between EL emission distribution and interfacial accumulated charge distribution.

Modeling and visualization of carrier motion in organic films by optical second harmonic generation and Maxwell-displacement current

“…Noteworthy that EFISHG experiment is employed in the same way for sandwiched-type devices with two electrodes, by using laser beam that obliquely incident onto the devices [28,[89][90][91][92]. Further we have recently developed a novel method that can detect electric field along the direction of incident laser beam by introducing a radial polarized beam into the EFISHG measurement system, and this system also makes us easy to study carrier transport in sandwiched-type devices [93,94].…”

“…Probing carrier behaviors in combination with charge accumulation at the interface is particularly important, because the Maxwell-Wagner effect suggests carrier accumulation at the interface of layers, and this accumulation contributes to form space charge field. Consequently, EFISHG measurement coupled with the Maxwell-Wagner model analysis is very helpful for this purpose [28,29,89,134,135]. layers, and non-reversal charging and discharging processes resulted from the different carrier behaviors accompanied by ordinary green EL [29,89].…”

A Novel Microscopic Analyzing System for Characterizing Organic Light‐Emitting Diodes Using EFISHG and LBIC Measurements

“…In addition, aiming at a more detailed exploration of real-space carrier behaviors inside MIM devices, we developed a microscopic EFISHG system using radially polarized pulsed laser as a modification of conventional EFISHG measurement [13]. Besides, using this method, we reported on relationships between electric field distribution, interfacial charge distribution, and EL intensity in fullerene single-layer devices and double-layer OLEDs [13,14]. Besides, using this method, we reported on relationships between electric field distribution, interfacial charge distribution, and EL intensity in fullerene single-layer devices and double-layer OLEDs [13,14].…”

“…Thus, we analyzed internal electric fields and carrier behaviors in OLEDs, OSCs, organic transistors, and other devices by means of electric-field-induced optical secondharmonic generation (EFISHG) measurement method that is focused on induced polarization phenomena due to electric field formed in organic materials [7,8,[11][12][13][14]. For example, we measured electric field strength in organic layers along light-emitting surface and electric charge accumulated at organic/organic interface of double-layer OLED, and demonstrated existence of two light emission modes that bring about interfacial charge accumulation in case of ac-driven OLED [8].…”

“…This system makes possible direct measurement of electric field strength in the thickness direction of organic films in MIM devices such as OLEDs and OSCs; local in-plane electric field distributions and interfacial charge distributions can be evaluated by sweeping a laser beam across the surface. Besides, using this method, we reported on relationships between electric field distribution, interfacial charge distribution, and EL intensity in fullerene single-layer devices and double-layer OLEDs [13,14].…”