title: Conformal fabrication of colloidal quantum dot solids for optically enhanced photovoltaics.
abstract: Colloidal quantum dots (CQD) are an attractive thin-film material for photovoltaic applications due to low material costs, ease of fabrication, and size-tunable band gap. Unfortunately, today they suffer from a compromise between light absorption and photocarrier extraction, a fact that currently prevents the complete harvest of incoming above-band-gap solar photons. We have investigated the use of structured substrates and/or electrodes to increase the effective light path through the active material and found that these designs require highly conformal application of the light-absorbing films to achieve the greatest enhancement. This conformality requirement derives from the need for maximal absorption enhancement combined with shortest-distance charge transport. Here we report on a means of processing highly conformal layer-by-layer deposited CQD absorber films onto microstructured, light-recycling electrodes. Specifically, we engineer surface hydrophilicity to achieve conformal deposition of upper layers atop underlying ones. We show that only with the application of conformal coating can we achieve optimal quantum efficiency and enhanced power conversion efficiency in structured-electrode CQD cells.
authors.affiliation: †Department of Electrical and Computer Engineering, University of Toronto, 10 King's College Road, Toronto, Ontario M5S 3G4, Canada.
authors.forename: André J
authors.initials: AJ
authors.lastname: Labelle
authors.affiliation: †Department of Electrical and Computer Engineering, University of Toronto, 10 King's College Road, Toronto, Ontario M5S 3G4, Canada.|‡Department of Electrical and Computer Engineering, Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, United States.
authors.forename: Susanna M
authors.initials: SM
authors.lastname: Thon
authors.affiliation: †Department of Electrical and Computer Engineering, University of Toronto, 10 King's College Road, Toronto, Ontario M5S 3G4, Canada.|§Fuel Cell Research Center, Korea Institute of Science and Technology (KIST), Seoul 136-791, South Korea.
authors.forename: Jin Young
authors.initials: JY
authors.lastname: Kim
authors.affiliation: †Department of Electrical and Computer Engineering, University of Toronto, 10 King's College Road, Toronto, Ontario M5S 3G4, Canada.|⊥School of Materials Science and Engineering, Hefei University of Technology, 193 Tunxi Road, Hefei, Anhui Province 230009, People's Republic of China.
authors.forename: Xinzheng
authors.initials: X
authors.lastname: Lan
authors.affiliation: †Department of Electrical and Computer Engineering, University of Toronto, 10 King's College Road, Toronto, Ontario M5S 3G4, Canada.
authors.forename: David
authors.initials: D
authors.lastname: Zhitomirsky
authors.affiliation: †Department of Electrical and Computer Engineering, University of Toronto, 10 King's College Road, Toronto, Ontario M5S 3G4, Canada.
authors.forename: Kyle W
authors.initials: KW
authors.lastname: Kemp
authors.affiliation: †Department of Electrical and Computer Engineering, University of Toronto, 10 King's College Road, Toronto, Ontario M5S 3G4, Canada.
authors.forename: Edward H
authors.initials: EH
authors.lastname: Sargent
keywords: colloidal quantum dots; conformal thin film; optically enhanced solar cells; photovoltaics; solution-processed thin film; structured electrodes