Effect of chemical interaction at modification layer/substrate interface on molecular orientation of dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene thin films

Abstract

The molecular orientation of dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (DNTT) thin films on modified silicon dioxide (SiO2) and copper oxide (CuOx) substrates whose surfaces were treated by 6-[(3-trisilanol)propylamino]-1,3,5-triazine-2,4-bis(2-aminoethylamine) (TAS) was investigated using near-edge X-ray absorption fine structure and ultraviolet/X-ray photoelectron spectroscopy. The standing orientation of DNTT was obtained in DNTT/TAS/SiO2 and DNTT/TAS/CuOx. The amount of amorphous region in DNTT/TAS/SiO2 was larger than that in DNTT/TAS/CuOx. The TAS treatment on the substrates formed interfacial dipoles at TAS/SiO2 and TAS/CuOx interfaces by chemical interaction, resulting in the vacuum level shift by −0.9 and −1.2 eV, respectively. Functional groups at the outermost TAS surface were amino groups in TAS/SiO2 and silanol groups in TAS/CuOx. The intermolecular distance of DNTT was widened in DNTT/TAS/SiO2 because of an electrostatic repulsion with nitrogen. The interfacial dipole at the modification layer/substrate interface and functional groups at the modified surface affect the molecular orientation of DNTT thin films on the modification layer.

Experimental Observation of Anisotropic Valence Band Dispersion in Dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (DNTT) Single Crystals

“…In addition, the present value of the threshold ionization energy was verified by PYS on both the single crystal and thin-film samples of DNTT, as shown in Figure S2. Also, this ionization energy value for the peak position was fairly consistent with previous reports for the DNTT thin films. , Note that the present ionization energy value is still greater than those of the single crystals of rubrene (4.85 eV) and pentacene (4.95 eV) and is thought to be moderately high in connection with the work function values of ordinary anode materials.…”