title: Role of bond adaptability in the passivation of colloidal quantum dot solids.
abstract: Colloidal quantum dot (CQD) solids are attractive materials for photovoltaic devices due to their low-cost solution-phase processing, high absorption cross sections, and their band gap tunability via the quantum size effect. Recent advances in CQD solar cell performance have relied on new surface passivation strategies. Specifically, cadmium cation passivation of surface chalcogen sites in PbS CQDs has been shown to contribute to lowered trap state densities and improved photovoltaic performance. Here we deploy a generalized solution-phase passivation strategy as a means to improving CQD surface management. We connect the effects of the choice of metal cation on solution-phase surface passivation, film-phase trap density of states, minority carrier mobility, and photovoltaic power conversion efficiency. We show that trap passivation and midgap density of states determine photovoltaic device performance and are strongly influenced by the choice of metal cation. Supported by density functional theory simulations, we propose a model for the role of cations, a picture wherein metals offering the shallowest electron affinities and the greatest adaptability in surface bonding configurations eliminate both deep and shallow traps effectively even in submonolayer amounts. This work illustrates the importance of materials choice in designing a flexible passivation strategy for optimum CQD device performance.
authors.affiliation: Department of Electrical and Computer Engineering, University of Toronto , 10 King's College Road, Toronto, Ontario, M5S 3G4, Canada.
authors.forename: Susanna M
authors.initials: SM
authors.lastname: Thon
authors.forename: Alexander H
authors.initials: AH
authors.lastname: Ip
authors.forename: Oleksandr
authors.initials: O
authors.lastname: Voznyy
authors.forename: Larissa
authors.initials: L
authors.lastname: Levina
authors.forename: Kyle W
authors.initials: KW
authors.lastname: Kemp
authors.forename: Graham H
authors.initials: GH
authors.lastname: Carey
authors.forename: Silvia
authors.initials: S
authors.lastname: Masala
authors.forename: Edward H
authors.initials: EH
authors.lastname: Sargent
mesh_terms: D003198:Computer Simulation; D003460:Crystallization / Q000379:methods; D007854:Lead / Q000737:chemistry* / Q000528:radiation effects; D008027:Light; D008956:Models, Chemical; D008958:Models, Molecular; D045663:Quantum Dots; D018036:Selenium Compounds / Q000737:chemistry* / Q000528:radiation effects
chemical_list: D018036:Selenium Compounds; C088065:lead selenide; D007854:Lead