title: PbSe nanocrystal excitonic solar cells.
abstract: We report the design, fabrication, and characterization of colloidal PbSe nanocrystal (NC)-based photovoltaic test structures that exhibit an excitonic solar cell mechanism. Charge extraction from the NC active layer is driven by a photoinduced chemical potential energy gradient at the nanostructured heterojunction. By minimizing perturbation to PbSe NC energy levels and thereby gaining insight into the "intrinsic" photovoltaic properties and charge transfer mechanism of PbSe NC, we show a direct correlation between interfacial energy level offsets and photovoltaic device performance. Size dependent PbSe NC energy levels were determined by cyclic voltammetry and optical spectroscopy and correlated to photovoltaic measurements. Photovoltaic test structures were fabricated from PbSe NC films sandwiched between layers of ZnO nanoparticles and PEDOT:PSS as electron and hole transporting elements, respectively. The device current-voltage characteristics suggest a charge separation mechanism that is distinct from previously reported Schottky devices and consistent with signatures of excitonic solar cells. Remarkably, despite the limitation of planar junction structure, and without film thickness optimization, the best performing device shows a 1-sun power conversion efficiency of 3.4%, ranking among the highest performing NC-based solar cells reported to date.
authors.affiliation: School of Chemical and Biomolecular Engineering, School of Applied and Engineering Physics, Department of Chemistry and Chemical Biology, Department of Materials Science and Engineering, Cornell University, Ithaca, New York 14853, USA.
authors.forename: Joshua J
authors.initials: JJ
authors.lastname: Choi
authors.forename: Yee-Fun
authors.initials: YF
authors.lastname: Lim
authors.forename: Mitk'el B
authors.initials: MB
authors.lastname: Santiago-Berrios
authors.forename: Matthew
authors.initials: M
authors.lastname: Oh
authors.forename: Byung-Ryool
authors.initials: BR
authors.lastname: Hyun
authors.forename: Liangfeng
authors.initials: L
authors.lastname: Sun
authors.forename: Adam C
authors.initials: AC
authors.lastname: Bartnik
authors.forename: Augusta
authors.initials: A
authors.lastname: Goedhart
authors.forename: George G
authors.initials: GG
authors.lastname: Malliaras
authors.forename: Héctor D
authors.initials: HD
authors.lastname: Abruña
authors.forename: Frank W
authors.initials: FW
authors.lastname: Wise
authors.forename: Tobias
authors.initials: T
authors.lastname: Hanrath