Displacement Current Measurement for Exploring Charge Carrier Dynamics in Organic Semiconductor Devices

Noguchi, Yutaka; Tanaka, Yuya; Miyazaki, Yukimasa; Sato, Naoki; Nakayama, Yasuo; Ishii, Hisao

doi:10.1002/9783527654949.ch5

Cited by 8 publications

(15 citation statements)

References 96 publications

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“…This result indicates that the electron charging to the hetero interface is delayed because of a long RC time constant (s RC ) of the test device. 7,26,27 Because the carrier of the device in this bias range is an electron, s RC can be attributed to the high resistance to the electron injection and transport in the Al(7-Prq) 3 layer, as suggested by the J-V characteristics (Fig. 2).…”

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confidence: 97%

“…2 The polarity of GSP in the previous studies has been mostly positive with respect to the substrate potential, indicating that the direction of the permanent dipole moment of the molecules points to the surface normal on average (a positive polarization charge appears on the film surface), and the mechanism of the formation of the spontaneous orientation polarization in the film remains to be clarified. 2,7,8 However, Isoshima et al recently reported that the attachment of a propyl group to Alq 3 leads to an inverted polarity of GSP. 9 This result strongly suggests that the molecular shape is critical to form the orientation polarization in the evaporated film.…”

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confidence: 99%

“…DCM is a type of capacitance-voltage (C-V) measurement that uses a triangular waveform as the applied voltage and measures both the actual and displacement current responses. 7 Because of the constant sweep rate of the applied voltage (dV=dt), i dis is proportional to the apparent capacitance of the test device (C app ). The accumulation charge density can be estimated by integrating the measured C app along the V axis if the sweep rate is sufficiently slow (i.e., the quasi-static regime).…”

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confidence: 99%

“…4(a), respectively]. 7 In the forward sweep, the onset of the charge injection appears at approximately À8 V [V inj in Fig. 4(a)], and the injected charge accumulates at the a-NPD/Al(7-Prq) 3 interface.…”

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confidence: 99%

“…4(a)], which indicates the presence of positive interface charge in the Al(7-Prq) 3based device. 7,13 We estimate the positive interface charge density to be approximately 3.1 mC/m 2 by integrating the current during the discharging process [ Fig. 4(a)].…”

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confidence: 99%

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Influence of the direction of spontaneous orientation polarization on the charge injection properties of organic light-emitting diodes

Noguchi

Lim

Isoshima

et al. 2013

Applied Physics Letters

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A tris(7-propyl-8-hydroxyquinolinato) aluminum [Al(7-Prq) 3 ] film shows negative giant surface potential (GSP) because of spontaneous orientation polarization. The polarity of this film is opposite to those of tris-(8-hydroxyquinolate) aluminum films. In Al(7-Prq) 3-based organic light-emitting diodes, negative GSP leads to the positive interface charge and governs the electron injection and accumulation properties. In addition, a high resistance to the electron injection at the Al(7-Prq) 3 /Ca interface is suggested possibly because of the negative polarization charge at the interface. These results show the importance of orientation polarization in controlling the charge injection and accumulation properties and potential profile of the resultant devices. V

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confidence: 99%

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Influence of the direction of spontaneous orientation polarization on the charge injection properties of organic light-emitting diodes

Noguchi

Lim

Isoshima

et al. 2013

Applied Physics Letters

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Spontaneous Orientation Polarization in Organic Light‐Emitting Diodes and its Influence on Charge Injection, Accumulation, and Degradation Properties

Noguchi¹,

Ishii²,

Jäger³

et al. 2021

Organic Semiconductors for Optoelectronics

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Controlling Polarization‐Induced Polaron Accumulation in OLEDs via Device Design

Pakhomenko,

Martin,

et al. 2024

Adv Funct Materials

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Spontaneous alignment of molecular electric dipole moments, known as spontaneous orientation polarization (SOP), is present in many organic electronic materials. The SOP‐induced field changes the internal voltage distribution within the device, altering polaron injection and accumulation. The important role of SOP in organic light‐emitting devices (OLEDs) has recently been emphasized with clear links between dipole alignment and device efficiency and operational lifetime. Prior work has thus sought to engineer SOP via changes in thin film composition or processing conditions. These efforts have generally been directed at the OLED electron transport layer, which can show strong SOP. This work takes a different approach, focusing instead on how changes in device architecture can be applied to tune the magnitude and dynamics of polaron accumulation in response to SOP. In this work, it is demonstrated that the introduction of SOP into the device emissive layer offers control over the spatial location of accumulation. In parallel, insertion of a spacer layer between the hole transport and emissive layers can be used to tune the polaron accumulation rate and density during device operation. Both of these architectural changes permit an increase in OLED efficiency and a pathway around the deleterious impact of SOP‐induced polaron accumulation.

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Displacement Current Measurement for Exploring Charge Carrier Dynamics in Organic Semiconductor Devices

Cited by 8 publications

References 96 publications

Influence of the direction of spontaneous orientation polarization on the charge injection properties of organic light-emitting diodes

Influence of the direction of spontaneous orientation polarization on the charge injection properties of organic light-emitting diodes

Spontaneous Orientation Polarization in Organic Light‐Emitting Diodes and its Influence on Charge Injection, Accumulation, and Degradation Properties

Controlling Polarization‐Induced Polaron Accumulation in OLEDs via Device Design

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