Highly reproducible alkali metal doping system for organic crystals through enhanced diffusion of alkali metal by secondary thermal activation

Abstract

In this paper, we report an efficient alkali metal doping system for organic single crystals. Our system employs an enhanced diffusion method for the introduction of alkali metal into organic single crystals by controlling the sample temperature to induce secondary thermal activation. Using this system, we achieved intercalation of potassium into picene single crystals with closed packed crystal structures. Using optical microscopy and Raman spectroscopy, we confirmed that the resulting samples were uniformly doped and became K2picene single crystal, while only parts of the crystal are doped and transformed into K2picene without secondary thermal activation. Moreover, using a customized electrical measurement system, the insulator-to-semiconductor transition of picene single crystals upon doping was confirmed by in situ electrical conductivity and ex situ temperature-dependent resistivity measurements. X-ray diffraction studies showed that potassium atoms were intercalated between molecular layers of picene, and doped samples did not show any KH- nor KOH-related peaks, indicating that picene molecules are retained without structural decomposition. During recent decades, tremendous efforts have been exerted to develop high-performance organic semiconductors and superconductors, whereas as little attention has been devoted to doped organic crystals. Our method will enable efficient alkali metal doping of organic crystals and will be a resource for future systematic studies on the electrical property changes of these organic crystals upon doping.

Exfoliated Graphite Electrodes for Organic Single-Crystal Field-Effect Transistor Devices

“…To achieve smooth carrier injection, several methods have been attempted previously, which include insertion of a layer of heteromaterial (such as tetracyanoquinodimethane (TCNQ)) between the contact metal electrodes and the channel region 35 or switching to electrode metals with a large work function such as platinum (5.6 eV). 19 However, these approaches still require complex processes and need direct contact between the target materials achieved by a deposition process. In the graphite electrode case, the work function of the electrode can be easily modulated by surface modification of pristine graphite by a simple oxygen-plasma treatment.…”

“…In order to solve this problem, we attempted to align both energy levels by increasing the work function of graphite by oxygen-plasma treatment. To achieve smooth carrier injection, several methods have been attempted previously, which include insertion of a layer of heteromaterial (such as tetracyanoquinodimethane (TCNQ)) between the contact metal electrodes and the channel region or switching to electrode metals with a large work function such as platinum (5.6 eV) . However, these approaches still require complex processes and need direct contact between the target materials achieved by a deposition process.…”

“…Picene and C 60 single crystals were prepared using the drop-drying method. , The drop-drying method yields organic single crystals upon drying droplets of supersaturated precursor solution on a solid substrate. Therefore, saturated precursor solutions were prepared first.…”

Enhancing multifunctional photocatalysis with acetate‐assisted cesium doping and unlocking the potential of Z‐scheme solar water splitting

“…On the contrary, Kumar et al 26 incorporated Cs into g‐C 3 N 4 and reported the adverse effects on photocatalytic activity. As elaborately reviewed above, these cases adopted the traditional methods to induce the spontaneous diffusion of evaporated alkali metals from stoichiometric mixtures of alkali metal precursors and nitrogen‐rich organic systems, mainly in powder form 36 . A common challenge is that the traditional dopant source such as alkali metal halide (CsCl or CsBr) with high melting points relies heavily on the adding amount to achieve visual doping.…”

“…As elaborately reviewed above, these cases adopted the traditional methods to induce the spontaneous diffusion of evaporated alkali metals from stoichiometric mixtures of alkali metal precursors and nitrogen-rich organic systems, mainly in powder form. 36 A common challenge is that the traditional dopant source such as alkali metal halide (CsCl or CsBr) with high melting points relies heavily on the adding amount to achieve visual doping. The challenge of sluggish bond breaking and diffusion kinetics for alkali metal halides resists the dissemination of metal atoms to establish uniform and ordered doping, which greatly weakens the advantage of easy manipulation of alkali metal doping.…”