title: Quantum dot photovoltaics in the extreme quantum confinement regime: the surface-chemical origins of exceptional air- and light-stability.
abstract: We report colloidal quantum dot (CQDs) photovoltaics having a approximately 930 nm bandgap. The devices exhibit AM1.5G power conversion efficiencies in excess of 2%. Remarkably, the devices are stable in air under many tens of hours of solar illumination without the need for encapsulation. We explore herein the origins of this orders-of-magnitude improvement in air stability compared to larger PbS dots. We find that small and large dots form dramatically different oxidation products, with small dots forming lead sulfite primarily and large dots, lead sulfate. The lead sulfite produced on small dots results in shallow electron traps that are compatible with excellent device performance; whereas the sulfates formed on large dots lead to deep traps, midgap recombination, and consequent catastrophic loss of performance. We propose and offer evidence in support of an explanation based on the high rate of oxidation of sulfur-rich surfaces preponderant in highly faceted large-diameter PbS colloidal quantum dots.
authors.affiliation: Department of Materials Science and Engineering, University of Toronto, Toronto, Ontario M5S 3E4, Canada.
authors.forename: Jiang
authors.initials: J
authors.lastname: Tang
authors.forename: Lukasz
authors.initials: L
authors.lastname: Brzozowski
authors.forename: D Aaron R
authors.initials: DA
authors.lastname: Barkhouse
authors.forename: Xihua
authors.initials: X
authors.lastname: Wang
authors.forename: Ratan
authors.initials: R
authors.lastname: Debnath
authors.forename: Remigiusz
authors.initials: R
authors.lastname: Wolowiec
authors.forename: Elenita
authors.initials: E
authors.lastname: Palmiano
authors.forename: Larissa
authors.initials: L
authors.lastname: Levina
authors.forename: Andras G
authors.initials: AG
authors.lastname: Pattantyus-Abraham
authors.forename: Damir
authors.initials: D
authors.lastname: Jamakosmanovic
authors.forename: Edward H
authors.initials: EH
authors.lastname: Sargent