Structural, Optical, and Electrical Properties of Self-Assembled Films of PbSe Nanocrystals Treated with 1,2-Ethanedithiol

TLDR

The study reports on the structural, optical, and electrical properties of high‑quality PbSe nanocrystal films fabricated by a layer‑by‑layer dip‑coating method using 1,2‑ethanedithiol as an insolubilizing agent. The films were produced by a layer‑by‑layer dip‑coating process that employs 1,2‑ethanedithiol to replace oleic acid and render the nanocrystals insoluble. EDT treatment replaces oleic acid, reduces film volume, couples nanocrystals electronically, and while degrading order, yields moderately conductive, ambipolar films that become 30–60× more conductive under illumination, oxidize rapidly to highly conductive p‑type solids, and demonstrate that the LbL process is a versatile route to uniform, conductive nanocrystal films for optoelectronics and solar energy conversion.

Abstract

We describe the structural, optical, and electrical properties of high-quality films of PbSe nanocrystals fabricated by a layer-by-layer (LbL) dip-coating method that utilizes 1,2-ethanedithiol (EDT) as an insolubilizing agent. Comparative characterization of nanocrystal films made by spin-coating and by the LbL process shows that EDT quantitatively displaces oleic acid on the PbSe surface, causing a large volume loss that electronically couples the nanocrystals while severely degrading their positional and crystallographic order of the films. Field-effect transistors based on EDT-treated films are moderately conductive and ambipolar in the dark, becoming p-type and 30–60 times more conductive under 300 mW cm−2 broadband illumination. The nanocrystal films oxidize rapidly in air to yield, after short air exposures, highly conductive p-type solids. The LbL process described here is a general strategy for producing uniform, conductive nanocrystal films for applications in optoelectronics and solar energy conversion.