The role of gap states on energy level alignment at an α-NPD/HAT(CN) 6 charge generation interface

Yang, Jinpeng; Bussolotti, Fabio; Li, Yanqing; Zeng, Xianghua; Kera, Satoshi; Tang, Jianxin; Ueno, Nobuo

doi:10.1016/j.orgel.2015.05.033

Cited by 23 publications

(29 citation statements)

References 31 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Using the “conventional” method of determining the IE of α‐NPD from UPS measurements is once more demonstrated in Figure (a) and (b), leading to a value of 4.95 eV. This is substantially too low for α‐NPD, for which the established IE is 5.3 ± 0.1 eV . Applying the fitting routine described above, we find a local work function of 4.16 eV for α‐NPD on top of the gold stripes.…”

Section: Resultsmentioning

confidence: 93%

Importance of Substrate Work Function Homogeneity for Reliable Ionization Energy Determination by Photoelectron Spectroscopy

Schultz

Amsalem

Kotadiya

et al. 2018

Physica Status Solidi (b)

View full text Add to dashboard Cite

Ultraviolet photoelectron spectroscopy (UPS) is the most widely used technique to determine the ionization energy (IE) of electronic materials, as this parameter is critically important for the energy level alignment in electronic and optoelectronic devices. For organic semiconductor IE assessment, molecules are typically evaporated and polymers spin-coated onto a conductive substrate, and then measured by UPS. For substrates that possess a constant work function over large area, the determination of IE from the measured UPS data is straight forward. However, if the substrate is heterogeneous (intentionally or unintentionally) in local work function, the conventional method to determine IE yields erroneous results and a more careful data evaluation is necessary. While the secondary electron cutoff (SECO) can exhibit area-averaged values, the valence levels are split in energy according to the local work function. Here, we demonstrate the possible pitfalls of heterogeneous substrates by employing well-controlled model systems, and show how appropriate data analysis can still yield correct IE values.

show abstract

Section: Resultsmentioning

confidence: 93%

Importance of Substrate Work Function Homogeneity for Reliable Ionization Energy Determination by Photoelectron Spectroscopy

Schultz

Amsalem

Kotadiya

et al. 2018

Physica Status Solidi (b)

View full text Add to dashboard Cite

show abstract

“…The carrier ladder effect and carrier transport mechanism resulting from the introduction of HAT(CN)6 led to excellent current density characteristics [11,12]. The carrier transport between HAT(CN)6 and α-NPD is described in Figure 4 [11,12]. The Fermi level is contiguous to the conduction band for HAT(CN)6.…”

Section: Resultsmentioning

confidence: 99%

“…Since the gap between the HOMO (Highest Occupied Molecular Orbital) level of α-NPD and the LUMO level of HAT(CN)6 is under 0.5 eV, the carrier transport between the two materials is easy. The carrier ladder effect and carrier transport mechanism resulting from the introduction of HAT(CN)6 led to excellent current density characteristics [11,12]. [8,9].…”

Section: Resultsmentioning

confidence: 99%

“…Specifically, the HOMO level for α-NPD is about 1.1 eV away from the conduction band of HAT(CN)6. In this regard, the carrier-transport process from the HOMO level The carrier transport between HAT(CN)6 and α-NPD is described in Figure 4 [11,12]. The Fermi level is contiguous to the conduction band for HAT(CN)6.…”

Section: Resultsmentioning

confidence: 99%

“…Figure 6 shows luminance-current density characteristics with a log-log scale with HAT(CN)6 thickness variation. The devices using 1 and 7 nm thin-film HAT(CN)6 as the interlayer showed [11,12]: E F is the Fermi level, V L is a vacuum level, EA (electron affinity.) is electron affinity and Ip is ion potential [11,12].…”

Section: Resultsmentioning

confidence: 99%

See 2 more Smart Citations

Electro-Optical Performance of Organic Thin-Film Using HAT(CN)6 between Anode and Organic Materials

Park

2019

Coatings

View full text Add to dashboard Cite

We report the electro-optical properties of an organic thin-film by varying the thickness of 1,4,5,8,9,11-hexaazatriphenylene-hexacarbonitrile (HAT(CN)6), included therein as an interlayer. Devices with HAT(CN)6, which are 7 nm thin films used as interlayers, exhibited good current density–voltage characteristics due to an improved hole injection barrier resulting from carrier ladder effects and carrier transport phenomena. The device without an interlayer showed the worst driving voltage characteristics due to the hole injection barrier. At low driving voltages, a device using 7 nm HAT(CN)6 as an interlayer exhibited a current density about 9.9 times higher than that of a device using 20 nm HAT(CN)6, and showed a current density about 9600 times higher than that of a device without an interlayer. Due to the proper carrier balance, the device using 7 nm HAT(CN)6 as an interlayer achieved a maximum current efficiency of 10.8 cd/A, which was the highest among the devices studied. This shows that the electro-optical properties of devices using HAT(CN)6 as an interlayer are dominated by the holes.

show abstract

The Interlayer Method: A Universal Tool for Energy Level Alignment Tuning at Inorganic/Organic Semiconductor Heterojunctions

Schultz

Lungwitz

Longhi

et al. 2020

Adv Funct Materials

View full text Add to dashboard Cite

The combination of inorganic and organic semiconductors in a heterojunction is considered a promising approach to overcome limitations of each individual material class. However, to date only few examples of improved (opto‐)electronic functionality have been realized with such hybrid heterojunctions. The key to unraveling the full potential offered by inorganic/organic semiconductor heterojunctions is the ability to deliberately control the interfacial electronic energy levels. Here, a universal approach to adjust the offset between the energy levels at inorganic/organic semiconductor interfaces is demonstrated: the interlayer method. A monolayer‐thick interlayer comprising strong electron donor or acceptor molecules is inserted between the two semiconductors and alters the energy level alignment due to charge transfer with the inorganic semiconductor. The general applicability of this method by tuning the energy levels of hydrogenated silicon relative to those of vacuum‐processed films of a molecular semiconductor as well as solution‐processed films of a polymer semiconductor is exemplified, and is shown that the energy level offset can be changed by up to 1.8 eV. This approach can be used to adjust the energy levels at the junction of a desired material pair at will, and thus paves the way for novel functionalities of optoelectronic devices.

show abstract

The role of gap states on energy level alignment at an α-NPD/HAT(CN) 6 charge generation interface

Cited by 23 publications

References 31 publications

Importance of Substrate Work Function Homogeneity for Reliable Ionization Energy Determination by Photoelectron Spectroscopy

Importance of Substrate Work Function Homogeneity for Reliable Ionization Energy Determination by Photoelectron Spectroscopy

Electro-Optical Performance of Organic Thin-Film Using HAT(CN)6 between Anode and Organic Materials

The Interlayer Method: A Universal Tool for Energy Level Alignment Tuning at Inorganic/Organic Semiconductor Heterojunctions

Contact Info

Product

Resources

About