Crystal structure oriented carrier transport characteristic of triphenylamine derivative single crystal

Abstract

Organic electronic materials used in organic photoreceptors for electrophotography are expected to be employed in many functional organic devices. Regarding the inferior mobility compared to inorganic semiconductors, in this study, an organic single crystal was prepared at a high rate and characterized. First, solubility and supersolubility curves of α-phenyl-4’-[(4-methoxyphenyl)phenylamino]stilbene (TPA) were measured. According to the data, the rapid crystal growth has been succeeded. Polarization microscope observation and XRD result confirmed that a single crystal is obtained. The results of a cyclic voltammogram and molecular orbital calculations showed that hole transport takes place in the crystal. On the surface of the obtained single crystal, Au parallel electrodes were vacuum deposited to measure its electric conductivity. Higher currents were observed on the long and short axes of the single crystal than that of the amorphous layer. Moreover, an anisotropic conductivity, in which the current in the long axis is greater than that in the short axes, was remarked. Consequently, the molecular stack of the crystal clarified by an XRD analysis and molecular electronic structure assessed by molecular orbital calculation well explain the anisotropic conductivity of the crystal.

Electrochemical Characteristics of a Triphenylamine Derivative by Microelectrode Voltammetry

“…Triphenylamine derivatives have the following three important advantages: (i) they are low‐cost materials, (ii) a wide range of molecular designs is possible according to requirements, and (iii) their hole mobility is relatively high among representative hole transport materials. Moreover, we previously reported the successful preparation of single crystals of the triphenylamine derivative molecules, 4‐(2,2‐diphenylethenyl)‐ N , N ‐bis(4‐methylphenyl)‐benzenamine (TPA) and α‐phenyl‐4′‐[(4‐methoxyphenyl)phenylamino]stilbene, using a solution method based on their solubility and supersolubility curves, and demonstrated that their conductivities were ∼10 times greater than those of the amorphous forms .…”

Deciphering the Multifarious Charge‐Transport Behaviour of Crystalline Propeller‐Shaped Triphenylamine Analogues

“…High hole mobility of the HTM and electron mobility of ETM layers are preferred for the fabrication of high‐performance OLEDs. The process of crystallisation is one method for regulating the charge‐carrier characteristics of organic materials because molecular ordering and the packing arrangement of the molecules in crystals play a huge role in modulating the charge‐transport abilities . The crystalline architectures that encompass higher degrees of intermolecular orbital overlap enhance the mobility of charges throughout the organic charge transporters .…”

“…The propeller‐shaped triphenylamine (TPA) core has gained immense interest for HTMs in OLEDs, owing to good thermal stability, a high glass transition temperature, and efficient hole‐transporting ability coupled with low ionisation potential . Functionalisation of the TPA molecule would result in diverse crystalline packing arrangements, which, in turn, could fine‐tune the optoelectronic properties of the core TPA moiety by enhancing the π–π interorbital interaction between phenyl rings . Thus, a thorough understanding of the interconnection between the molecular structure, packing arrangement and transport properties is indispensable in designing efficient and economical organic materials that are pertinent for optoelectronic devices …”

“…High hole mobility of the HTM and electron mobility of ETM layers are preferredf or the fabrication of high-performance OLEDs.T he process of crystallisation is one method for regulating the charge-carrier characteristics of organic materials becausem olecular ordering and the packing arrangement of the molecules in crystals play ah uge role in modulating the charge-transport abilities. [9] The crystalline architectures that encompass higherd egreeso fi n-termolecular orbital overlap enhancet he mobility of charges throughout the organic charge transporters. [10][11][12][13][14][15] The propeller-shaped triphenylamine (TPA) core has gained immense interestf or HTMs in OLEDs, owing to good thermal stability,a high glass transition temperature, and efficient hole-transporting ability coupled with low ionisation potential.…”

“…[8,[16][17][18][19][20] Functionalisationo ft he TPAm olecule would result in diverse crystallinep acking arrangements, [21] which, in turn, couldf ine-tune the optoelectronic properties of the core TPAm oiety by enhancing the p-p interorbital interaction between phenyl rings. [9] Thus, at horough understandingo ft he interconnection betweent he molecular structure, packing arrangementa nd transport properties is indispensable in designing efficient and economical organic materialst hat are pertinent for optoelectronicd evices. [22,23] Herein, we have attempted to perform ac omprehensive computational evaluation of the charge-transport characteristics of ac ollection of crystalline para-substituted TPAa nalogues.…”