Loss spectroscopy of molecular solids: combining experiment and theory

Roth, Friedrich; Cudazzo, Pierluigi; Mahns, Benjamin; Gatti, Matteo; Bauer, Johannes; Hampel, Silke; Nohr, Markus; Berger, H.; Knupfer, M.; Rubio, Ángel

doi:10.1088/1367-2630/15/12/125024

Cited by 18 publications

(30 citation statements)

References 51 publications

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“…These results are in good agreement with previous Hückel-model and DFT-based studies of the TIPS-PEN crystal. [ 17,18 ] Our current study, along with prior work on other π-conjugated molecular crystals, indicates that the nature of excitons within organic crystals is strongly structure-depen dent, [21][22][23][24][25][44][45][46] and is highly sensitive to π-orbital stacking. This suggests that the excitonic properties of TIPS-PEN can be modifi ed for improved functionality because, as mentioned in Section 1, the inter-molecular arrangement of TIPS-PEN is highly tunable via changes in processing conditions.…”

Section: Tuning Low-energy Excitons By Solid-state Structurementioning

confidence: 53%

Relating the Physical Structure and Optoelectronic Function of Crystalline TIPS‐Pentacene

Sharifzadeh

Wong

et al. 2014

Adv Funct Materials

154

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order provide an opportunity to understand many fundamental physical properties relevant to solar energy conversion. Additionally, organic crystals are promising in their own right due to the effi cient carrier and energy transport properties associated with their long-range order.In particular, crystalline and polycrystalline fi lms of pentacene (PEN) and its derivatives have high carrier mobility for charge transport (≈1−10 cm 2 /Vs hole mobility) [ 1 ] and signifi cant photoconductivity. [ 2,3 ] Moreover, PEN and many of its derivatives display a propensity for singlet fi ssion (SF), [ 4,5 ] a phenomenon that results in greater than 100% internal quantum effi ciency in organic photovoltaics. Numerous possible molecular functionalizations may modify solid-state structural and optoelectronic properties. [ 6 ] Therefore, elucidating the structure-property relation is important for the design of new functional molecular materials. 6,13-bis(triisopropylsilylethynyl)-pentacene (TIPS-PEN), [ 7 ] shown in Figure 1 , has recently attracted much interest. The bulky groups functionalizing PEN enable solubility in organic solvents and allow for solution-processing of polycrystalline TIPS-PEN thin fi lms with high carrier mobility and photoconductivity. [ 2,3,7 ] While TIPS-PEN apparently retains optical properties similar to PEN, its enhanced carrier mobility [ 8 ] and Relating the Physical Structure and Optoelectronic Function of Crystalline TIPS-PentaceneSahar Sharifzadeh , * Cathy Y. Wong , Hao Wu , Benjamin L. Cotts , Leeor Kronik , Naomi S. Ginsberg , and Jeffrey B. Neaton * Theory and experiment are combined to investigate the nature of low-energy excitons within ordered domains of 6,13-bis(triisopropylsilylethynyl)-pentacene (TIPS-PEN) polycrystalline thin fi lms. First-principles density functional theory and many-body perturbation theory calculations, along with polarizationdependent optical absorption spectro-microscopy on ordered domains, show multiple low-energy absorption peaks that are composed of excitonic states delocalized over several molecules. While the fi rst absorption peak is composed of a single excitonic transition and retains the polarization-dependent behavior of the molecule, higher energy peaks are composed of multiple transitions with optical properties that can not be described by those of the molecule. The predicted structure-dependence of polarization-dependent absorption reveals the exact inter-grain orientation within the TIPS-PEN fi lm. Additionally, the degree of exciton delocalization can be signifi cantly tuned by modest changes in the solid-state structure and the spatial extent of the excitations along a given direction is correlated with the degree of electronic dispersion along the same direction. These fi ndings pave the way for tailoring the singlet fi ssion effi ciency of organic crystals by solid-state structure.

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Section: Tuning Low-energy Excitons By Solid-state Structurementioning

confidence: 53%

Relating the Physical Structure and Optoelectronic Function of Crystalline TIPS‐Pentacene

Sharifzadeh

Wong

et al. 2014

Adv Funct Materials

154

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“…The bound excitons represented in figure 9 are mainly related to HOMO-LUMO transitions, with the exception of picene. In fact in picene also higher energy transitions give a remarkable contribution: 14 For the details of the GW calculations we refer to [39,41,128]. the exciton binding energy evaluated including only HOMO-LUMO bands would be 0.3 eV smaller than the value obtained from the full calculation.…”

Section: Excitons and Their Dispersionmentioning

confidence: 95%

“…Also in the experiments the details of the crystal structure of the measured samples are not always fully accessible, in particular concerning the herringbone angle between the molecules in the unit cell (see e.g. [41]). As the electronic and optical properties are highly anisotropic and sensitive to the mutual orientation of the molecules, those differences and uncertanties demand care for a quantitative comparison of the spectra [41].…”

Section: Excitons and Their Dispersionmentioning

confidence: 99%

“…[41]). As the electronic and optical properties are highly anisotropic and sensitive to the mutual orientation of the molecules, those differences and uncertanties demand care for a quantitative comparison of the spectra [41]. In any case an overall agreement between the different BSE calculations and ellipsometry and EELS experiments [41,74,75,128,[134][135][136][137][138] can be verified.…”

Section: Excitons and Their Dispersionmentioning

confidence: 99%

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Exciton dispersion in molecular solids

Cudazzo¹,

Sottile²,

Rubio³

et al. 2015

J. Phys.: Condens. Matter

Self Cite

119

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The investigation of the exciton dispersion (i.e. the exciton energy dependence as a function of the momentum carried by the electron-hole pair) is a powerful approach to identify the exciton character, ranging from the strongly localised Frenkel to the delocalised Wannier-Mott limiting cases. We illustrate this possibility at the example of four prototypical molecular solids (picene, pentacene, tetracene and coronene) on the basis of the parameter-free solution of the many-body Bethe-Salpeter equation. We discuss the mixing between Frenkel and charge-transfer excitons and the origin of their Davydov splitting in the framework of many-body perturbation theory and establish a link with model approaches based on molecular states. Finally, we show how the interplay between the electronic band dispersion and the exchange electron-hole interaction plays a fundamental role in setting the nature of the exciton. This analysis has a general validity holding also for other systems in which the electron wavefunctions are strongly localized, as in strongly correlated insulators.

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“…[15,16] for an overview). In particular, it has proven useful for the investigation of excitonic states in organic semiconductors [17][18][19]. In addition, it is possible to retrieve the complete dielectric function ϵðq; ωÞ ¼ ϵ 1 ðq; ωÞ þ iϵ 2 ðq; ωÞ via a Kramers-Kronig analysis (KKA) of the measured data.…”

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confidence: 99%

Anisotropic Particle-Hole Excitations in Black Phosphorus

et al. 2015

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We report on the energy- and momentum-resolved optical response of black phosphorus (BP) in its bulk form. Along the armchair direction of the puckered layers, we find a highly dispersive mode that is strongly suppressed in the perpendicular (zigzag) direction. This mode emerges out of the single-particle continuum for finite values of momentum and is therefore interpreted as an exciton. We argue that this exciton, which has already been predicted theoretically for phosphorene-the monolayer form of BP-can be detected by conventional optical spectroscopy in the two-dimensional case and might pave the way for optoelectronic applications of this emerging material.

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Loss spectroscopy of molecular solids: combining experiment and theory

Cited by 18 publications

References 51 publications

Relating the Physical Structure and Optoelectronic Function of Crystalline TIPS‐Pentacene

Relating the Physical Structure and Optoelectronic Function of Crystalline TIPS‐Pentacene

Exciton dispersion in molecular solids

Anisotropic Particle-Hole Excitations in Black Phosphorus

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