Electric-field-induced optical second-harmonic generation in poly(phenylene vinylene) light-emitting diodes (original) (raw)
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Applied Physics Letters, 2009
By using the electric field induced optical second-harmonic generation ͑EFISHG͒ measurements, we probed the transient electric field in a double-layer indium zinc oxide ͑IZO͒/N, NЈ-di-͓͑1-naphthyl͒-N, NЈ-diphenyl͔-͑1,1Ј-biphenyl͒-4, 4Ј-diamine͑␣-NPD͒ / tris ͑8-hydroxy-quinolinato͒aluminum͑III͒ ͑Alq3͒/Al electroluminescent ͑EL͒ diode. Results evidently showed that EL was initiated by the injected hole transport across ␣-NPD layer, and holes accumulated at the ␣-NPD/ Alq3 interface while EL was enhanced. Analysis based on the Maxwell-Wagner effect model well accounted for the hole accumulation. EFISHG measurement is useful as a tool for probing carrier behavior in organic EL devices.
Applied Physics Express, 2011
By using time-resolved electric-field-induced optical second-harmonic generation (EFISHG) measurement, we directly probed photovoltaic effect generated in double-layer (pentacene/C 60 ) organic solar cells (OSCs). The electric field in C 60 layer was selectively probed by using incident laser with a wavelength of 1,000 nm. Results showed that excess positive charges Q s ¼ 1:5 Â 10 À8 C/cm 2 accumulated at the pentacene/C 60 interface under photoillumination. These charges generated the interfacial voltage V s ¼ 0:16 V and deformed a potential profile in the OSCs. The EFISHG measurement is an effective way for directly catching carrier behavior at the double-layer interface in OSCs in terms of the photovoltaic effect.
physica status solidi (c), 2005
We apply electric field induced second harmonic (EFISH) to polymer light emitting diodes (PLEDs) and demonstrate the ability to determine the diffusion voltage in PLED devices. The EFISH signal is proportional to the square of the effective field, which is the sum of the diffusion voltage and the applied voltage. By minimizing the EFISH-signal as a function of the applied voltage, the diffusion voltage is determined by measuring the applied voltage that cancels out the diffusion voltage. The PLEDs are fabricated with indium tin oxide (ITO) as the hole injecting contact and two different electron injecting contacts, namely aluminum and calcium. The diffusion voltage originates from the rearranged charges caused by the difference in Fermi levels in the materials in the PLEDs. Different contacts will thus cause different diffusion voltages. We demonstrate here that the EFISH signal is proportional to the square of the effective field in both reverse and forward bias, and discuss the dependence on contact materials.
Applied Surface Science, 2014
We observed phase shift in optical second harmonic generation (SHG) from interfaces of indium tin oxide (ITO)/copper phthalocyanine (CuPc) and ITO/pentacene. Phase correction due to Fresnel factors of the sample was taken into account. The phase of SHG electric field at the ITO/pentacene interface, with respect to the phase of SHG of bare substrate ITO was 160°, while the interface of ITO/CuPc had a phase of 140˚.
Applied Physics Letters, 2010
We have observed optical second harmonic generation (SHG) from a space charge layer (SCL) in a stacked indium tin oxide (ITO)/molybdenum trioxide (MoO3)/N−N′-diphenyl-N−N′-bis(1-naphthly)-1,1′-biphenyl-4,4′-diamine (α-NPD) system. When the MoO3 thicknesses were increased, the SHG signals from this system decreased sharply at smaller MoO3 thicknesses, and were saturated at MoO3 thicknesses larger than 1 nm. These results prove the vital role of SCL in improvement of drive voltages of organic light-emitting diodes.
Japanese Journal of Applied Physics, 2011
By using electric-field-induced second-harmonic generation (EFISHG) measurement, we probed charging and discharging in an -NPD/Alq3 organic light-emitting diode N,-N,N 0 -diphenyl]-(1,1 0 -biphenyl)-4,4 0 -diamine; Alq3, tris(8-hydroxy-quinolinato)aluminum(III)] while electroluminescence response was monitored. The EFISHG measurement showed that excessive positive charges accumulated at the -NPD/Alq3 interface in the charging process, accompanying electroluminescence (EL) radiation, and the accumulated excess positive charges disappeared in the discharging process before the EL decayed. Note that the EL radiation was smooth and strong under the high voltage application, while the EL decayed in a similar way. The Maxwell-Wagner model analysis showed no-dependence of the accumulated excessive positive charge on the applied external voltage, suggesting that electrons and holes injected from the opposite electrodes for EL radiation balanced at the interface. The EFISHG measurement will be useful as a direct way to probe carrier behaviors in organic EL devices.