Rearrangement of the molecular orientation of Alq3 in organic light-emitting diodes under constant current aging investigated using sum frequency generation spectroscopy

Miyamae, Takayuki; Takada, Noriyuki; Yoshioka, Toshihiro; Miyaguchi, Satoshi; Ohata, Hiroshi; Tsutsui, Tetsuo

doi:10.1016/j.cplett.2014.10.027

Cited by 15 publications

(11 citation statements)

References 28 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…One is a decrease of SOP because of the randomization of Alq 3 molecules during continuous operation, which was proved using sum frequency generation spectroscopy. [ 40 ] Another one is the compensation of polarization charges by trapped holes in the α‐NPD layer near the interface. [ 41 ] DCMs and carrier trap measurements, such as, thermally stimulated currents, on OLEDs before and after degradation will clarify the detailed relationship between the SOP and the OLED degradation in the future.…”

Section: Resultsmentioning

confidence: 99%

“…In actual OLED architectures, a difference in SOP among stacked organic layers is known to cause a charge accumulation at an organic/organic heterointerface. [ 37 ] Then, the SOP and SOP‐induced accumulated charges cause some critical issues, such as low carrier injection efficiency [ 38 ] and device degradation, [ 39–42 ] in OLEDs. Recently, SOP has been revealed to affect exciton dissociation as an internal electric field in solid‐state organic films.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Active Control of Spontaneous Orientation Polarization of Tris(8‐hydroxyquinolinato)aluminum (Alq₃) Films and Its Effect on Performance of Organic Light‐Emitting Diodes

Esaki

Tanaka

Matsushima

et al. 2021

Adv Elect Materials

View full text Add to dashboard Cite

Vacuum‐deposited amorphous organic films with an anisotropic amorphous structure are known to exhibit spontaneous orientation polarization (SOP). In this study, amorphous structures of tris(8‐hydroxyquinolinato)aluminum (Alq3) films are controlled by substrate temperature (Tsub) during vacuum deposition. The effect of density, molecular orientation, and SOP of Alq3 films on the performance of organic light‐emitting diodes (OLEDs) is comprehensively investigated. The SOP of Alq3 films is significant at low Tsub and becomes weaker as Tsub increases. The presence of SOP certainly improves electron injection from a metal cathode and, therefore, increases the current in OLEDs. External quantum efficiencies (EQEs) of OLEDs are increased by ≈40% when Tsub for the Alq3 deposition is increased from 260 to 328 K. The increased EQEs are attributed to several factors, which include not only increased photoluminescence quantum yields and light outcoupling efficiencies but also suppressed singlet‐polaron annihilation originating from the reduced SOP. Operational stability of OLEDs is also affected by Tsub and becomes the highest when Alq3 layers are vacuum‐deposited at Tsub = 299 K. These findings indicate the importance of controlling organic amorphous structures and SOP in films to maximize OLED performance and contribute to a better understanding of working mechanisms of OLEDs.

show abstract

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Active Control of Spontaneous Orientation Polarization of Tris(8‐hydroxyquinolinato)aluminum (Alq₃) Films and Its Effect on Performance of Organic Light‐Emitting Diodes

Esaki

Tanaka

Matsushima

et al. 2021

Adv Elect Materials

View full text Add to dashboard Cite

show abstract

“…The holes captured at such traps compensate the negative polarization charge due to SOP of TPBi, as the result, the apparent interface charge density decays [18,73]. On the other hand, the molecular orientation, consequently SOP, can be also changed possibly by the high temperature during the device operation due to the Joule's heating and non-radiative recombination [76].…”

Section: Sop and Device Degradationmentioning

confidence: 99%

Spontaneous orientation polarization in organic light-emitting diodes

Noguchi

Brütting

Ishii

2019

Jpn. J. Appl. Phys.

109

View full text Add to dashboard Cite

Spontaneous orientation polarization (SOP) is inherent in evaporated films of many organic semiconducting molecules with a permanent dipole moment. A significant electric field is formed in the film due to SOP. Consequently, the properties of organic light-emitting diodes (OLEDs) incorporating such films are influenced. The polarization charge appearing at heterointerfaces dominates the charge injection and accumulation properties.Moreover, SOP correlates to device degradation. In this article, we review SOP of organic semiconductor films and its influences on the device properties of OLEDs.

show abstract

“…For the time-resolved experiments, multilayer OLEDs were operated with the application of a square wave pulse voltage using a pulse delay generator and a highspeed bipolar amplifier. 12 Transient EL emission from the OLEDs was also monitored using a photomultiplier and was stored by an oscilloscope.…”

Section: Methodsmentioning

confidence: 99%

“…Furthermore, we have reported the direct observation of the real-time carrier behavior in OLEDs by timeresolved EFI-DR-SFG technique. 12 The use of these new techniques allows us to observe the carrier behavior at the buried organic interfaces of OLEDs varied with time in response to the applied bias voltage non-destructively.…”

Section: Introductionmentioning

confidence: 99%

Operando sum‐frequency generation spectroscopy of high‐efficiency OLEDs for probing the charge carrier behavior

Miyamae

Sato

2021

J Soc Info Display

Self Cite

View full text Add to dashboard Cite

Operando analysis of organic devices is crucial for understanding the device operation mechanism and intrinsic degradation mechanism. Buried organic layers in OLEDs during operation have been investigated using electric-field-induced doubly resonant sum-frequency generation (EFI-DR-SFG) and time-resolved EFI-DR-SFG experiments. The time-resolved EFI-SFG technique allows us to observe the carrier transportation directly and non-destructively. DC electric field leads to a significant increase in the SFG intensity produced by the charged carriers. Electric-field-induced SFG results clearly show that charge accumulation occurs at the interface between the light emitting layer and the electron-blocking layer in the blue OLED and that this charge accumulation strongly contributes for the light emission. Particularly in the TTA process, high charge accumulation is effective in generating triplet excitons and improving the luminescence efficiency, but at the same time, it reduces the lifetime of the device.

show abstract

Rearrangement of the molecular orientation of Alq3 in organic light-emitting diodes under constant current aging investigated using sum frequency generation spectroscopy

Cited by 15 publications

References 28 publications

Active Control of Spontaneous Orientation Polarization of Tris(8‐hydroxyquinolinato)aluminum (Alq₃) Films and Its Effect on Performance of Organic Light‐Emitting Diodes

Active Control of Spontaneous Orientation Polarization of Tris(8‐hydroxyquinolinato)aluminum (Alq₃) Films and Its Effect on Performance of Organic Light‐Emitting Diodes

Spontaneous orientation polarization in organic light-emitting diodes

Operando sum‐frequency generation spectroscopy of high‐efficiency OLEDs for probing the charge carrier behavior

Contact Info

Product

Resources

About

Rearrangement of the molecular orientation of Alq3 in organic light-emitting diodes under constant current aging investigated using sum frequency generation spectroscopy

Cited by 15 publications

References 28 publications

Active Control of Spontaneous Orientation Polarization of Tris(8‐hydroxyquinolinato)aluminum (Alq3) Films and Its Effect on Performance of Organic Light‐Emitting Diodes

Active Control of Spontaneous Orientation Polarization of Tris(8‐hydroxyquinolinato)aluminum (Alq3) Films and Its Effect on Performance of Organic Light‐Emitting Diodes

Spontaneous orientation polarization in organic light-emitting diodes

Operando sum‐frequency generation spectroscopy of high‐efficiency OLEDs for probing the charge carrier behavior

Contact Info

Product

Resources

About

Active Control of Spontaneous Orientation Polarization of Tris(8‐hydroxyquinolinato)aluminum (Alq₃) Films and Its Effect on Performance of Organic Light‐Emitting Diodes

Active Control of Spontaneous Orientation Polarization of Tris(8‐hydroxyquinolinato)aluminum (Alq₃) Films and Its Effect on Performance of Organic Light‐Emitting Diodes