Control of PbSe Quantum Dot Surface Chemistry and Photophysics Using an Alkylselenide Ligand

Abstract

We have synthesized alkylselenide reagents to replace the native oleate ligand on PbSe quantum dots (QDs) in order to investigate the effect of surface modification on their stoichiometry, photophysics, and air stability. The alkylselenide reagent removes all of the oleate on the QD surface and results in Se addition; however, complete Se enrichment does not occur, achieving a 53% decrease in the amount of excess Pb for 2 nm diameter QDs and a 23% decrease for 10 nm QDs. Our analysis suggests that the Se ligand preferentially binds to the {111} faces, which are more prevalent in smaller QDs. We find that attachment of the alkylselenide ligand to the QD surface enhances oxidative resistance, likely resulting from a more stable bond between surface Pb atoms and the alkylselenide ligand compared to Pb-oleate. However, binding of the alkylselenide ligand produces a separate nonradiative relaxation route that partially quenches PL, suggesting the formation of a dark hole-trap.

Postsynthetic Doping Control of Nanocrystal Thin Films: Balancing Space Charge to Improve Photovoltaic Efficiency

“…37 From a stoichiometric perspective, ICP measurements show that EDT treatments shift films from being cation-rich to anionrich. 44,45 This is in agreement with density functional theory (DFT) calculations on similar nonstoichiometric PbX nanocrystals that suggest such stoichiometry shifts lead to the generation of hole carriers to balance charge. 46,47 Excess unpassivated surface chalcogenides have also been implicated in the creation of midgap states from observations of PL quenching and recovery when switching between anion and cation capped particles.…”

Kinetic analysis of the temperature dependence of PbSe colloidal quantum dot photoluminescence: Effects of synthesis process and oxygen exposure

“…Independent models [8,10,11] have been developed to quantify various aspects of the published PL behavior for subsets of the samples listed in Table I. However, we are unaware of any account of a systematic attempt to fit the entirety of this disparate PbSe nanocrystal temperature-dependent integrated PL data from 5 to 325 K using a single, physically based model.…”

“…Regarding phonon-mediation of nonradiative decay, Chappell et al and Hughes et al assumed a N ph -phonon absorption functional form for their low-energy, nonradiative pathway [10,11], and they reported fits suggested N ph = 4 ± 2. In cases where present, if we replace the severalto-ten meV nonradiative Arrhenius pathway ( e − E/kT ) with a one-phonon emission functional form, ph […”

“…One obstacle that has hindered progress in gaining a quantitative microscopic understanding of the optical emission from this material system has been the lack of consistency of the experimental results reported by different groups. Chappell et al [10] and Hughes et al [11] recently reported temperature-dependent emission spectra from ≈5-nm-diameter oleate-capped PbSe QDs with apparent contributions from two distinct radiative transitions, the integrated strength of which varies nonmonotonically from 13 to 325 K. Their synthesis is performed in an airfree environment and, depending on procedural details, the temperature dependence of their samples' emission can be irreversibly sensitive, in drop-cast form, to even minute exposures to air.…”

“…The near-infrared photoluminescence (PL) from PbSe and PbSe/CdSe colloidal quantum dots (QDs) with diameters on order 4-6 nm has been studied extensively in solution [1][2][3][4][5] but less so out of solution, where significant applications also exist [6][7][8][9][10][11]. One obstacle that has hindered progress in gaining a quantitative microscopic understanding of the optical emission from this material system has been the lack of consistency of the experimental results reported by different groups.…”