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

Abstract

The organic semiconductor 2,7‐dioctyl[1]benzothieno[3,2‐b][1]benzothiophene (C8‐BTBT) is deposited on a single crystal (0001) Al2O3 (C‐sapphire) by a vacuum thermal evaporation, and effects of the layer thickness and preparation temperature on structural, morphological, optical, and electrical characteristics are investigated with X‐ray diffraction, atomic force microscopy observation, optical absorption measurement, and resistivity measurement with and without light irradiation. The C8‐BTBT layers possess the (001) out‐of‐plane orientation irrespective of the layer thickness and preparation temperature. The C8‐BTBT grains are growing up in direction parallel to the substrate surface keeping almost constant height, and the continuous layer is formed by the coalescence of the C8‐BTBT grains. The grain size of the continuous C8‐BTBT layer increases with raise in preparation temperature. The optical band gap energy could be estimated to be 3.32–3.35 eV regardless of the layer thickness and preparation temperature. The electrical resistivity decreases from 2.1 × 106 to 1.2 × 102 Ω cm with increase in the preparation temperature due to the increase in the grain size, and the light irradiation induce the drastical decrease to 42–28 Ω cm.

Surface State of Thermally Evaporated PTCDI-C8/C8-BTBT Bi-Layer

“…3 shows the topography and surface potential images of the PTCDI-C8 and C8-BTBT single layers and bi-layers with different stacking sequences. The C8-BTBT layer was formed by the lateral growth after the formation of continuous layer by the coalescence of the islands, as already reported, 10) and the 100-nmthick-layer was composed of 2～2.7 μm-size-granular grains with the surface roughness (Ra) with 16.8 nm. The surface potential was almost constant over the entire the surface.…”

“…The C8-BTBT layer showed three peaks at 6.1, 9.1, and 12.3 degrees, and the peaks were assigned as (002) , (003) , and (004) planes of the C8-BTBT layer with the characteristic monoclinic lattice, indicating the formation of (001) -out-of-plane orientation, as already reported. 10) The C8-BTBT / PTCDI-C8 bi-layers showed 5 peaks composed of the 2 peaks and 3 peaks originated from the PTCDI-C8 and C8-BTBT layers irrespective of the stacking sequence, and the peak angles agreed with those of both single layers, indicating the formation of (001) -outof-plane orientation even for the bi-layers. The lattice relationship of (001) -C8-BTBT// (001) -PTCDI-C8// (0001) -Al2O3 was developed for the bi-layer structures, in spite of the large lattice mismatch of -23.5% for PTCDI-C8 b-axis//C8-BTBT a-axis, and -12.2% for C8-BTBT b-axis//PTCDI-C8 a-axis, respectively.…”

“…7) -9) And, we reported the growth of the (001) -oriented-C8-BTBT layer on (0001) Al2O3 (C-sapphire) substrate by the thermal evaporation. 10) In this study, we prepared bi-layers of C8-BTBT and PTCDI-C8 with a different stacking sequence and report the effect on the surface morphology and potential homogeneity on the resultant bilayers. The (001) -C8-BTBT/ (001) -PTCDI-C8 bi-layer showed an excellent performance in the surface morphology and potential homogeneity compared with the (001) -PTCDI-C8/ (001) -C8-BTBT bi-layer.…”

Lateral Alternating Donor/Acceptor Multilayered Junction for Organic Solar Cells

“…C8-BTBT (50 nm) was deposited on C-sapphire substrates since C8-BTBT films with high crystallinities grown by vacuum deposition have been reported . The c -axis of the C8-BTBT molecules was confirmed to be oriented perpendicular to the substrate by X-ray diffraction (Figure S9a).…”

Aggregation‐Dependent Dielectric Permittivity in 2D Molecular Crystals

“…The calculation result shows that the imaginary part is approximately zero and matches the experimental data well, so the complex refractive index ñ ≈ n . [ 43 ] The relative permeability is ≈1, and ε b is estimated to be the square of the refractive index in the C 8 ‐BTBT molecular crystal. [ 42 ] Here, we are mainly concerned with the real part of the dielectric constant in organic molecular crystals, which may be affected by electric dipoles in molecular aggregation.…”