Electronic density tailing outside π-conjugated polymer surface

Penning ionization electron spectroscopy (PIES) was adopted to examine surface electronic property of conjugated poly(3-hexylthiophene) (P3HT) aiming to detect the electronic density tailing outside a polymer surface. The electronic wave function of the highest occupied molecular orbital (HOMO) 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. (c) 2006 American Institute of Physics.