Surface band bending and carrier dynamics in colloidal quantum dot solids

• Published in: Nanoscale Vol. 13; no. 42; pp. 17793 - 1786
• Main Authors: Clark, Pip C. J, Lewis, Nathan K, Ke, Jack Chun-Ren, Ahumada-Lazo, Ruben, Chen, Qian, Neo, Darren C. J, Gaulding, E. Ashley, Pach, Gregory F, Pis, Igor, Silly, Mathieu G, Flavell, Wendy R
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 04.11.2021; Royal Society of Chemistry (RSC)
• Subjects: Bending machines; Contaminants; Current carriers; Depletion; Dynamics; Photoelectric emission; Quantum dots
• ISSN: 2040-3364; 2040-3372
• DOI: 10.1039/d1nr05436h

Band bending in colloidal quantum dot (CQD) solids has become important in driving charge carriers through devices. This is typically a result of band alignments at junctions in the device. Whether band bending is intrinsic to CQD solids, i.e. is band bending present at the surface-vacuum interface, has previously been unanswered. Here we use photoemission surface photovoltage measurements to show that depletion regions are present at the surface of n and p-type CQD solids with various ligand treatments (EDT, MPA, PbI 2 , MAI/PbI 2 ). Using laser-pump photoemission-probe time-resolved measurements, we show that the timescale of carrier dynamics in the surface of CQD solids can vary over at least 6 orders of magnitude, with the fastest dynamics on the order of microseconds in PbS-MAI/PbI 2 solids and on the order of seconds for PbS-MPA and PbS-PbI 2 . By investigating the surface chemistry of the solids, we find a correlation between the carrier dynamics timescales and the presence of oxygen contaminants, which we suggest are responsible for the slower dynamics due to deep trap formation. Evidence for band bending in colloidal quantum dot (CQD) solids is shown using photoemission surface photovoltage measurements, and carrier dynamics for a range of CQD solids are measured, correlating the results to surface chemistry.