Low-density band-gap states in pentacene thin films probed with ultrahigh-sensitivity ultraviolet photoelectron spectroscopy

Sueyoshi, Tomoki; Fukagawa, Hirohiko; Ono, Masaki; Kera, Satoshi; Ueno, Nobuo

doi:10.1063/1.3258351

Cited by 131 publications

(131 citation statements)

References 20 publications

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“…19,27,30,163 A method to visualize gap states is to plot the leading edge on a semilogarithmic scale, since band tails can be described by exponential functions. 172,173 This is illustrated in Figure 6a for organic small molecules. By using a semilogarithmic plot, the gap states and valence band density of states may be distinguished.…”

Section: Fitting the Leading Edge In Photoemission Spectroscopy Measumentioning

confidence: 99%

Perovskite-Inspired Photovoltaic Materials: Toward Best Practices in Materials Characterization and Calculations

et al. 2017

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ABSTRACT:Recently, there has been an explosive growth in research based on hybrid lead-halide perovskites for photovoltaics owing to rapid improvements in efficiency. The advent of these materials for solar applications has led to widespread interest in understanding the key enabling properties of these materials. This has resulted in renewed interest in related compounds and a search for materials that may replicate the defect-tolerant properties and long lifetimes of the hybrid lead-halide perovskites. Given the rapid pace of development of the field, the rises in efficiencies of these systems have outpaced the more basic understanding of these materials. Measuring or calculating the basic properties, such as crystal/electronic structure and composition, can be challenging because some of these materials have anisotropic structures, and/or are composed of both heavy metal cations and volatile, mobile, light elements. Some consequences are beam damage during characterization, composition change under vacuum, or compound effects, such as the alteration of the electronic structure through the influence of the substrate. These effects make it challenging to understand the basic properties integral to optoelectronic operation. Compounding these difficulties is the rapid pace with which the field progresses. This has created an ongoing need to continually evaluate best practices with respect to characterization and calculations, as well as to identify inconsistencies in reported values to determine if those inconsistencies are rooted in characterization methodology or materials synthesis. This article describes the difficulties in characterizing hybrid lead-halide perovskites and new materials, and how these challenges may be overcome. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 2 challenges discussed. The focus in this article is on crystallography, composition measurements, photoemission spectroscopy and calculations on perovskites and new, related absorbers. We suggest how some of the important artifacts could be avoided and how the reporting for each technique could be streamlined between groups to ensure reproducibility as the field progresses.

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Section: Fitting the Leading Edge In Photoemission Spectroscopy Measumentioning

confidence: 99%

Perovskite-Inspired Photovoltaic Materials: Toward Best Practices in Materials Characterization and Calculations

et al. 2017

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“…higher quality have a lower density of gap states (charge trapping states), which may shift the E F closer to the HOMO [12,16,17]. SC #2 did not show any clear density of occupied states in the energy gap [ Fig.…”

Section: Fig 3: (A)mentioning

confidence: 99%

“…SC #2 did not show any clear density of occupied states in the energy gap [ Fig. S2(c) of the Supporting Information], although it was measured with an experimental set-up which is designed to measure tiny gap states [12], suggesting an extremely low density of defects in the crystal.…”

Section: Fig 3: (A)mentioning

confidence: 99%

Accessing Surface Brillouin Zone and Band Structure of Picene Single Crystals

et al. 2012

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We have experimentally revealed the band structure and the surface Brillouin zone of insulating picene single crystals (SCs), the mother organic system for a recently discovered aromatic superconductor, with ultraviolet photoelectron spectroscopy (UPS) and low-energy electron diffraction with laser for photoconduction. A hole effective mass of 2.24 m0 and the hole mobility µ h ≥ 9.0 cm 2 /Vs (298 K) were deduced in Γ-Y direction. We have further shown that some picene SCs did not show charging during UPS even without the laser, which indicates that pristine UPS works for high-quality organic SCs.

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“…Note that in the ME model, we construct the band-tail states using a superposition of a half-Gaussian and an exponential distribution. We attribute the overall fitting distribution widths of 2 to 5 k B T, indicated in Table 1, to structural defects and chemical impurities 1 , previously reported for small organic molecules 3,53,54 . A recent study 55 , and compared it to the evolution observed in the UPS measurements.…”

mentioning

confidence: 99%

Role of band states and trap states in the electrical properties of organic semiconductors: Hopping versus mobility edge model

2013

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We compare the merits of a hopping model and a mobility edge model in the description of the effect of charge-carrier concentration on the electrical conductivity, carrier mobility, and Fermi energy of organic semiconductors. We consider the case of a composite electronic density of states (DOS) that consists of a superposition of a Gaussian DOS and an exponential DOS. Using kinetic Monte Carlo simulations, we apply the two models in order to interpret the recent experimental data reported for n-doped C 60 films. While both models are capable of reproducing the experimental data very well and yield qualitatively similar characteristic parameters for the density of states, some discrepancies are found at the quantitative level.

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Low-density band-gap states in pentacene thin films probed with ultrahigh-sensitivity ultraviolet photoelectron spectroscopy

Cited by 131 publications

References 20 publications

Perovskite-Inspired Photovoltaic Materials: Toward Best Practices in Materials Characterization and Calculations

Perovskite-Inspired Photovoltaic Materials: Toward Best Practices in Materials Characterization and Calculations

Accessing Surface Brillouin Zone and Band Structure of Picene Single Crystals

Role of band states and trap states in the electrical properties of organic semiconductors: Hopping versus mobility edge model

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