Layer-by-Layer Assembly of Thin Film Zener Diodes from Conducting Polymers and CdSe Nanoparticles

Ultrathin films have been prepared by self-assembling trioctylphosphine oxide, TOPO, capped n-type 20−40 Å diameter CdSe nanoparticles and 1,6-hexadecanethiol, HDT, onto p-doped semiconducting polymers, chemically deposited poly(3-methylthiophene), PMeT (for Device A), and electrochemically deposited poly(pyrrole), Ppy (for Device B). The semiconducting polymers have, in turn, been electrochemically layered (for Device A) or layer-by-layer chemically assembled (for Device B) onto derivatized conducting substrates. The ultrathin films have been characterized by absorption and emission spectroscopy, transmission electron microscopy, scanning force microscopy, X-ray photoelectron spectroscopy, and by electrochemical measurements. By controlling the level of doping into the p-type junction, it was possible to prepare dissymmetrical junctions and observe a rectifying behavior in the forward direction and a Zener breakdown in the reverse direction for Au/PMeT/(HDT/CdSe)3, Device A, and for Au/MEA/Ppy/(HDT/CdSe)3, Device B. Additionally, Au/MeA/PAH/CdSe (PAH = poly(allylamine hydrochloride)), Au/MEA/Ppy/PSS/CdSe (PSS = polystyrene sulfonate), and Au/MEA/Ppy/α-ZrP/CdSe (α-ZrP = α zirconium phosphate) films have been prepared and characterized.