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    Surface band bending and carrier dynamics in colloidal quantum dot solids

    Year: 2021

    Journal: Nanoscale, Volume 13, NOV 4, page 17793–17806

    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.

    Organizations: National Renewable Energy Laboratory [DE-AC36-08GO28308]; EPSRC (UK) [EP/K008544/1]; Director's Fellowship within NREL's Laboratory Directed Research and Development (LDRD) program

    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, PbI2, MAI/PbI2). 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/PbI2 solids and on the order of seconds for PbS-MPA and PbS-PbI2. 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.
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