title: Charge separation in type II tunneling structures of close-packed CdTe and CdSe nanocrystals.
abstract: We report on charge separation between type II aligned CdTe and CdSe nanocrystals. Two types of electrostatically bound nanocrystal structures have been studied: first, clusters of nanocrystals hold together by Ca(II) ions in aqueous solution and, second, thin film structures of nanocrystals created with layer-by-layer deposition in combination with polyelectrolytes. In both types of structures, short interparticle distances of less than 1 nm have been achieved, whereby the isolating organic ligands on the nanocrystal surfaces and/or the polymer monolayers act as tunneling barriers between nanocrystals. We have observed an efficient quenching of photoluminescence and a reduced emission lifetime for CdTe nanocrystals in both types of type II heterostructures. This result is explained by a spatial charge separation of the photoexcited electron-hole pairs due to tunneling of charge carriers through the thin organic layer between CdTe and CdSe nanocrystals. Type II heterostructures demonstrated here may find future applications in photovoltaics.
authors.affiliation: Photonics and Optoelectronics Group, Physics Department and Center for NanoScience (CeNS), Ludwig-Maximilians-Universität München, 80799 Munich, Germany.
authors.forename: Dieter
authors.initials: D
authors.lastname: Gross
authors.forename: Andrei S
authors.initials: AS
authors.lastname: Susha
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Klar
authors.forename: Enrico
authors.initials: E
authors.lastname: Da Como
authors.forename: Andrey L
authors.initials: AL
authors.lastname: Rogach
authors.forename: Jochen
authors.initials: J
authors.lastname: Feldmann
mesh_terms: D019187:Cadmium Compounds / Q000737:chemistry*; D003198:Computer Simulation; D004579:Electron Transport; D008956:Models, Chemical; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure; D036103:Nanotechnology / Q000379:methods*; D010316:Particle Size; D018036:Selenium Compounds / Q000737:chemistry*; D012666:Semiconductors; D055672:Static Electricity; D013691:Tellurium / Q000737:chemistry*
chemical_list: D019187:Cadmium Compounds; D018036:Selenium Compounds; C058667:cadmium selenide; D013691:Tellurium; C028337:cadmium telluride