X-ray Structural Investigation of Nonsymmetrically and Symmetrically Alkylated [1]Benzothieno[3,2-b]benzothiophene Derivatives in Bulk and Thin Films

Abstract

A detailed structural study of the bulk and thin film phases observed for two potential high performance organic semi conductors has been carried out. The molecules are based on [1]benzothieno[3,2 b]benzothiophene (BTBT) as conjugated core and octyl side groups, which are anchored either symmetrically at both sides of the BTBT core (C 8 −BTBT−C 8 ) or nonsymmetrically at one side only (C 8 −BTBT). Thin films of different thickness (8−85 nm) have been prepared by spin coating for both systems and analyzed by combining specular and grazing incidence X ray diffraction. In the case of C 8 −BTBT−C 8 , the known crystal structure obtained from single crystal investigations is observed within all thin films, down to a film thickness of 9 nm. In the case of C 8 −BTBT, the crystal structure of the bulk phase has been determined from X ray powder diffraction data with a consistent matching of experimental and calculated X ray diffraction patterns (Rwp = 5.8%). The packing arrangement of C 8 −BTBT is similar to that of C 8 −BTBT−C 8 , that is, consisting of a lamellar structure with molecules arranged in a "herringbone" fashion, yet with lamellae composed of two head to head (or tail to tail as the structure is periodic) superimposed molecules instead of only one molecule for C 8 −BTBT−C 8 . As for C 8 −BTBT−C 8 ,we demonstrate that the same phase is observed in bulk and thin films for C 8 −BTBT whatever the film thickness investigated.

Understanding the Meniscus‐Guided Coating Parameters in Organic Field‐Effect‐Transistor Fabrications

“…The formation of the organic thin film actually involves a number of different parameters and here we pay particular attention on the v , c , T , and T b . Among them, v and c are correlated to the conservation of mass described in Equation where d m/ d t is the mass transfer rate, ρ osc is the density of organic semiconductor C 8 ‐BTBT (1133 kg m −3 ), a is the width of the substrate, t osc is the apparent thickness of the organic semiconductor and d ∀/ d t is the instant solvent evaporation rate. It is important to mention that Equation is only valid in the evaporation region as discussed in ref.…”

Organic Single‐Crystal Semiconductor Films on a Millimeter Domain Scale

“…[ 18,19 ] Typically, this C8-BTBT forms a monoclinic crystal structure through weak van der Waals interactions between the molecules and exhibits a characteristic crystallization layer structure with a step-andterrace formation (Figure 1 a). [ 20,21 ] The alkylated BTBT has nonbonding electron pairs of sulfur atoms in the thiophene units, where the protonation of acidic dopants in the PSS can occur. Therefore, based on the electrostatic interaction between BTBT and PSS, as shown in the inset of Figure 1 a, we expect that it would form TMCSs.…”

“…The compressive lattice strain of the C8-BTBT:PSS crystal fi lm might cause the presence of a new diffraction peak at q x,y = 2.13 Å −1 , as indicated by the black arrow in Figure 2 c. In addition, a new diffraction spot, (001)*, at q z = 0.23 Å −1 for GISAXS (white arrow) indicates a shifted structure of C8-BTBT:PSS at the interface between the molecules and substrate (see Figure S11 in the Supporting Information). [ 21 ] This shift is indicative of the role of TMCSs, which promote more effi cient molecular packing of the C8-BTBT molecules because of the slow crystal growth at lower undercooling, leading to compressive lattice strain in the single-crystal C8-BTBT:PSS fi lm. …”

“…[ 19,21 ] However, the C8-BTBT:PSS fi lm has a more compressed molecular packing structure than the C8-BTBT fi lm, as indicated in Figure 3 b. Because of the molecular lattice strain induced by the TMCSs, the distance of π-π stacking decreases from 3.29 Å for the C8-BTBT crystal fi lm to 3.22 Å for the C8-BTBT:PSS crystal fi lm, which might be interpreted as suggesting an oblique molecular packing structure.…”

Growth and Characteristics of C8‐BTBT Layer on C‐Sapphire Substrate by Thermal Evaporation

“…The π‐conjugated organic semiconductors have been technologically great impact in fields of organic electronics; organic thin layer transistors (OTFT), organic field effect transistors (OFETs), organic light‐emitting diodes (OLEDs), and organic photovoltaics (OPVs) . The electrical characteristics including the charge transportation property strongly affects the performance of electronic devices and relates to the structure, molecular orientation, morphology, grain size, and defect density of organic semiconductor layers . The surface defects such as steps and vacancies of the underlying substrate could influence the structure of the molecular ordering and subsequent growth of the organic layers.…”