Impact of dithiol treatment and air annealing on the conductivity, mobility, and hole density in PbS colloidal quantum dot solids

Abstract

Crosslinking molecules have recently been combined with colloidal quantum dots to build robust, closely packed, conductive solid-state devices. Ethanedithiol ͑EDT͒ has been used in PbS quantum dot photovoltaic devices to assist in film formation during fabrication. However, there is evidence that EDT influences the electronic properties of the colloidal quantum dot ͑CQD͒ films. We fabricate thin film field-effect transistors and find that EDT treatment increases the majority carrier mobility by a factor of 10. We attribute this increase to a reduction in interparticle spacing which we observe using transmission electron microscopy. However, this increase is accompanied by a decrease in the majority carrier concentration. Using x-ray photoelectron microscopy, we find that EDT reduces the extent of the surface oxidation which is acting as a p-type dopant in these materials. We find that by lightly reoxidizing, we can redope the CQD films and can do so without sacrificing mobility gains.

Molecular Oxygen Induced in-Gap States in PbS Quantum Dots

“…54 V eff is the effective average volume occupied by each QD. Assuming that the QDs have a spherical shape, with a volume fill fraction of 0.5 and an inter-QD distance of 1.6 nm for PbS-EDT, 51 we have V eff = 3.75 Â 10 À19 cm 3 . Thus, n v = 2.1 Â 10 19 cm À3 .…”

Inorganic-ligand exchanging time effect in PbS quantum dot solar cell

“…Micro-and nano-scale cracks have been frequently observed in ligand-exchanged CQD devices due to the considerable volume shrink of the films when long oleic acids were substituted by short organic and/or inorganic ligands. [15][16][17] Furthermore, the crack formation results in severe problems such as highly inducing short circuit or leakage current in CQD-based device applications. 18 Therefore, careful control of the ligand exchange process is essential for producing crack-free CQD films.…”

A tunable colloidal quantum dot photo field-effect transistor

“…Aluminum-doped zinc oxide (AZO) serves as the electron-accepting channel. We employ no conductivity-enhancing treatments to the CQD films-instead of employing crosslinking treatments using short dithiols, 2 we leave the quantum dots capped with oleic acid. This, combined with our use of a submonolayer of CQDs, ensures that our study focuses on electron injection into the channel, followed by conduction within the channel, since the photogate material has negligible conductance compared to the channel.…”