title: Marked alkyl- vs alkenyl-substitutent effects on squaraine dye solid-state structure, carrier mobility, and bulk-heterojunction solar cell efficiency.
abstract: We report two new squaraine dyes substituted at the pyrrolic rings with n-hexyl (squaraine 1) or n-hexenyl (squaraine 2) chains. Although internal molecular structure variations are minimal, the presence of the terminal double bond results in a much more compact solid-state structure, dramatically affecting charge transport in the thin films; the hole mobility of 2 is approximately 5x that of 1, and the BHJ OPV power conversion efficiency (PCE) of 2 is approximately 2x that of 1. PCEs surpassing 2% for ambient solution-processed devices are demonstrated, the largest so far achieved for squaraine-based organic solar cells.
authors.affiliation: Department of Chemistry and the Argonne-Northwestern Solar Energy Research Center, Northwestern University, Evanston, Illinois 60208, USA.
authors.forename: Diego
authors.initials: D
authors.lastname: Bagnis
authors.forename: Luca
authors.initials: L
authors.lastname: Beverina
authors.forename: Hui
authors.initials: H
authors.lastname: Huang
authors.forename: Fabio
authors.initials: F
authors.lastname: Silvestri
authors.forename: Yan
authors.initials: Y
authors.lastname: Yao
authors.forename: Henry
authors.initials: H
authors.lastname: Yan
authors.forename: Giorgio A
authors.initials: GA
authors.lastname: Pagani
authors.forename: Tobin J
authors.initials: TJ
authors.lastname: Marks
authors.forename: Antonio
authors.initials: A
authors.lastname: Facchetti