Charge Transport Properties of Perylene–TCNQ Crystals: The Effect of Stoichiometry

Abstract

In this work we have revisited the charge-transfer crystal system perylene− TCNQ and found that this complex can crystallize with a 2:1 stoichiometric ratio in addition to the 1:1 and 3:1 stoichiometries previously observed. The vibrational and electronic properties of these perylene−TCNQ charge-transfer crystals have been investigated by means of Raman scattering measurements and density functional theory calculations. Electrical measurements were also performed by preparing organic field-effect transistors (OFETs) from the crystals. The Raman spectra in the low-frequency range (below 200 cm −1 ) are found to be unique to the specific crystal structure and can therefore be used to determine the stoichiometry. The Raman data and the X-ray diffraction measurements indicate that at room temperature the amount of charge transferred to the TCNQ molecule is less than 0.2e for all three compounds, and is nearly the same in P1T1 and P2T1 but is slightly larger in P3T1. The electronic structure calculations suggest good intrinsic charge transport properties for both holes and electrons in P1T1 and P2T1 and only for holes in P3T1. Ambipolar charge transport characteristics were found for P2T1 and hole and electron charge transport characteristics were found in P3T1 and P1T1, respectively.

Polymorphism in the 1:1 Charge‐Transfer Complex DBTTF–TCNQ and Its Effects on Optical and Electronic Properties

“…Within experimental error, this result confirms that each polymorph has a 1:1 donor-to-acceptor ratio. While the α-polymorph is known to have a 1:1 ratio from X-ray diffraction, this finding is not trivial, as we have shown that different D:A ratios can be obtained for other systems by tuning the growth conditions [34] .…”

Phenomenology of the Neutral-Ionic Valence Instability in Mixed Stack Charge-Transfer Crystals

“…Yet, the formation of stacks and their packing is determined by more subtle, sometimes difficult to control, interactions. Letting aside the possibility of D:A ratios different from 1:1 [73], there are cases of a DA pair growing in either segregated or mixed stack, like tetramethyl-tetraselenofulvalene-TCNQ [79,80], or of the growth of different polymorphs with ms motif, as DBTTF-TCNQ [81,82]. Even the prototypical TTF-CA has at least two polymorphs, with quite different electronic properties [10,83].…”

“…Table 2), among others, has been found to exhibit such a property, although with limited mobility values [72]. Mainly for these reasons, several studies have appeared aimed at exploring the phase space of ms CT crystals at ambient conditions [73][74][75][76][77], tuning the band gap, and at the same time moving towards the N-I borderline, where the stack dimerizes and becomes potentially ferroelectric.…”

Uniaxially oriented polycrystalline thin films and air-stable n-type transistors based on donor-acceptor semiconductor (diC8BTBT)(FnTCNQ) [n = 0, 2, 4]

“…[4][5][6] Such unique characteristics are promising for providing functional organic electronics or optoelectronic devices, although studies on device applications have been limited, so far, to those for prototypical single-crystal devices. [6][7][8][9][10] Because semiconducting CT compounds have a high tendency to form needle crystals along the donor-acceptor molecular stacks, manufacturing high quality thin films on substrate surfaces is difficult. For example, polycrystals obtained using vacuum deposition or solution cast techniques usually have large boundary potentials or discontinuity between microcrystal grains.…”