title: Phototransport in networks of tetrapod-shaped colloidal semiconductor nanocrystals.
abstract: Tetrapod-shaped CdSe(core)/CdTe(arms) colloidal nanocrystals, capped with alkylphosphonic acids or pyridine, were reacted with various small molecules (acetic acid, hydrazine and chlorosilane) which induced their tip-to-tip assembly into soluble networks. These networks were subsequently processed into films by drop casting and their photoconductive properties were studied. We observed that films prepared from tetrapods coated with phosphonic acids were not photoconductive, but tip-to-tip networks of the same tetrapods exhibited appreciable photocurrents. On the other hand, films prepared from tetrapods coated with pyridine instead of phosphonic acids were already highly photoconductive even if the nanocrystals were not joined tip-to-tip. Based on the current-voltage behavior under light we infer that the tunneling between tetrapods is the dominant charge transport mechanism. In all the samples, chemically-induced assembly into networks tended to reduce the average tunneling barrier. Additionally, pyridine-coated tetrapods and the tip-to-tip networks made out of them were tested as active materials in hybrid photovoltaic devices. Overall, we introduce an approach to chemically-induced tip-to-tip assembly of tetrapods into solution processable networks and demonstrate the enhancement of electronic coupling of tetrapods by various ligand exchange procedures.
authors.affiliation: Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genova, Italy.
authors.forename: Isabella R
authors.initials: IR
authors.lastname: Franchini
authors.forename: Adriano
authors.initials: A
authors.lastname: Cola
authors.forename: Aurora
authors.initials: A
authors.lastname: Rizzo
authors.forename: Rosanna
authors.initials: R
authors.lastname: Mastria
authors.forename: Anna
authors.initials: A
authors.lastname: Persano
authors.forename: Roman
authors.initials: R
authors.lastname: Krahne
authors.forename: Alessandro
authors.initials: A
authors.lastname: Genovese
authors.forename: Andrea
authors.initials: A
authors.lastname: Falqui
authors.forename: Dmitry
authors.initials: D
authors.lastname: Baranov
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Gigli
authors.forename: Liberato
authors.initials: L
authors.lastname: Manna
mesh_terms: D019187:Cadmium Compounds / Q000737:chemistry; D003102:Colloids / Q000737:chemistry*; D008024:Ligands; D008422:Materials Testing; D046529:Microscopy, Electron, Transmission / Q000379:methods; D053758:Nanoparticles / Q000737:chemistry*; D036103:Nanotechnology / Q000379:methods; D063065:Organophosphonates / Q000737:chemistry; D010777:Photochemistry / Q000379:methods*; D011725:Pyridines / Q000737:chemistry; D018036:Selenium Compounds / Q000737:chemistry; D012666:Semiconductors; D013691:Tellurium / Q000737:chemistry
chemical_list: D019187:Cadmium Compounds; D003102:Colloids; D008024:Ligands; D063065:Organophosphonates; D011725:Pyridines; D018036:Selenium Compounds; C058667:cadmium selenide; C023666:pyridine; D013691:Tellurium; C028337:cadmium telluride