Electronic density tailing outside π-conjugated polymer surface

Abstract

A systematic density functional theory study of the electronic structure of bulk and (001) surface of transitionmetals carbides Penning ionization electron spectroscopy ͑PIES͒ was adopted to examine surface electronic property of conjugated poly͑3-hexylthiophene͒ ͑P3HT͒ aiming to detect the electronic density tailing outside a polymer surface. The electronic wave function of the highest occupied molecular orbital ͑HOMO͒ state is shielded by side hexyl chain for a P3HT film with edge-on conformation and was not detected by PIES, while it is tailing outside the polymer surface for face-on conformation and was observed clearly by PIES. The presence of HOMO electronic wave function outside the polymer surface makes it possible to form HOMO-HOMO overlapping with overlayer materials, and therefore more efficient charge transfer is expected in a heterojunction structure for device application.

Interfacial properties of free-standing poly(3-hexylthiophene) films

“…51 Near-edge x-ray absorption fine structure spectroscopy (NEXAFS) (Refs. [22][23][24] can also be used to determine the orientation of thiophene ring and hexyl groups at the interface. It is therefore possible to directly compare our simulation results with experiment.…”

“…Using NEXAFS for regioregular P3HT thin films at air/film interfaces, several average tilt-angle measurements of thiophene ring have been reported. [22][23][24] Ho et al 24 found tilt angles for spin-casted thin film, using different solvents, of 57 • -60 • and drop-cast thin-film P3HT of 59 • . Hao et al 22,23 investigated the orientation of the thiophene ring for different thin-film samples.…”

“…However, there are relatively few reported experimental studies on the surface and interfacial properties of P3HT. These experimental studies have primarily focused on the orientation of the thiophene-ring backbone of the P3HT at the polymer/air and polymer/substrate interfaces, [22][23][24][25] but less attena) Electronic mail: mtsige@uakron.edu. tion has been given to the orientations of the hexyl side chains at interfaces.…”

Origins of Improved Hole‐Injection Efficiency by the Deposition of MoO3 on the Polymeric Semiconductor Poly(dioctylfluorene‐alt‐benzothiadiazole)

“…On polymer samples, MAES has been used as a powerful method to determine the molecular orientation at the surface because the obtained spectra directly reflect the electron density distributed at the outermost surface of the specimens. [28][29][30] In the present study, we carried out X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and MAES integrally on the MoO 3 -on-F8BT interfaces for the sake of clarifying the mechanism for the improvement of hole-injection characteristics from the top anodes being realized by the MoO 3 interlayers. Figure 1 shows the UPS and MAES spectra of the F8BT film plotted together with the ab initio molecular orbital (MO) calculation results (GAMESS [31] with B3LYP/6-31G Ã basis set) for the monomer of F8BT as a reference.…”

“…Taking into consideration that MAES is an extremely surface sensitive method, the absence of MAES intensity at the top-valence region suggests that the backbones of F8BT are not exposed to the outermost surface of the film, probably because they lie beneath the octyl side-groups. [29,30] It is interesting to note that the spectral shape of the MAES resembled that of normal alkanes standing upright in their crystalline phase. [34] This fact also supports the idea that the MAES signals predominantly came from the methyl terminals of the octyl side chains.…”