Influences of Out-Of-Plane Lattice Alignment on the OFET Performance of TIPS-PEN Crystal Arrays

Abstract

In organic field-effect transistors (OFETs), the quality of chargetransport pathway, controlled by crystal structures of organic semiconductors (OSCs), strongly affects the performance of the device. To achieve higher charge mobility, solution-processed single-crystal (SPSC) techniques have been used to decrease crystal defects by aligning the crystals of OSCs in the in-plane direction. Nonetheless, through SPSC techniques, whether the crystalline lattices are wellaligned in the out-of-plane direction and how the out-of-plane lattice misorientaion affects OFET performances remain unclear. Here, a characterization protocol based on polarized optical microscope, X-ray diffraction, and electron diffraction is established to identify the lattice structure, the in-plane and out-of-plane lattice alignment in the crystal array of 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-PEN). Regardless of the solvents used in the PDMS-assisted crystallization, the characterization protocol confirms that all the crystal arrays share the same lattice structure (form I phase), and have similar in-plane lattice alignment. However, TIPS-PEN molecules have sufficient time to unify their out-of-plane orientation and prevent the formation of low angle grain boundary (LAGB) during crystal growth if high boiling temperature solvents are used. The improved out-of-plane lattice alignment increases the hole mobility and decreases the performance fluctuations of devices. The results confirm that the out-of-plane lattice alignment significantly impacts the performance of the devices and the reproducibility of the solution-processed TIPS-PEN OFETs.

Enhancement of charge transfer in thermally-expanded and strain-stabilized TIPS-pentacene thin films

“…2(a) that the twin boundary is along the [100] direction. This conclusion is also supported by evidence from several other groups [37,38].…”

“…Establishing clear structure-property relationships for TIPS-pentacene is challenging, and we have noticed that there are discrepancies and even contradictory results reported in the literature. Several of these issues include: (1) Multiple groups have reported that the twin boundary of TIPS-pentacene twin grains are along [210] directions [27,61], but our previous report [28] and others [37,38] have found that the boundary is along the [100] direction. It is not yet clear whether these differences are a result of different thin film deposition conditions or due to spurious experimental results.…”

Molecularly aligned films of [1]benzothieno[3,2‐b][1]benzothiophene derivatives by solution shearing: Effect of alkyl substitution on morphology and charge transporting property

“…The polycyclic acenes and heteroacenes such as pentacene, S , N ‐heteropentacene (DTPT), dinaphtho[2,3‐b:2′,3′‐f]thieno[3,2‐b]thiophene (DNTT), dibenzothiopheno[6,5‐b:6′,5′‐f]thieno[3,2‐b]thiophene (DBTTT), and [1]benzothieno[3,2‐b][1]benzothiophene (BTBT) have become the benchmark materials in organic field‐effect transistor (OFET) fabrication to deliver high charge mobilities. [ 1–7 ] However, the generally low solubility of these parent compounds limits their processing to vacuum deposition. To adapt to the trend of easy processing using techniques such as solution‐coating, alkyl substituents at various positions of the polycyclic structures are required to render them sufficient solubility and processability.…”

Tuning Luminescence and Conductivity through Controlled Growth of Polymorphous Molecular Crystals

“…The performance of these transistors was very stable and highly reproducible in air. These results suggest that the electrical performance of a compound, especially one exhibiting polymorphism, can be improved by changing the crystallization factors to reach the desired molecular packings; this approach provides a novel means of developing new electrical materials …”