title: Crystallinity and morphology effects on a solvent-processed solar cell using a triarylamine-substituted squaraine.
abstract: 2,4-Bis[4'-(N,N-di(4″-hydroxyphenyl)amino)-2',6'-dihydroxyphenyl]squaraine (Sq-TAA-OH, optical bandgap 1.4 eV, HOMO level -5.3 eV by ultraviolet photoelectron spectroscopy) is used as an active layer material in solution processed, bulk-heterojunction organic photovoltaic cells with configuration ITO/PEDOT:PSS/Sq-TAA-OH:PC71BM/LiF/Al. Power conversion efficiencies (PCEs) up to 4.8% are obtained by a well-reproducible procedure using a mixture of good and poor Sq-TAA-OH solubilizing organic solvents, with diiodooctane (DIO) additive to make a bulk heterojunction layer, followed by thermal annealing, to give optimized V(OC) = 0.84-0.86 V, J(SC) = 10 mA cm(-2), and FF = 0.53. X-ray diffraction and scattering studies of pristine, pure Sq-TAA-OH solution-cast films show d-spacing features similar to single-crystal packing and spacing. The DIO additive in a good solvent/poor solvent mixture apparently broadens the size distribution of Sq-TAA-OH crystallites in pristine films, but thermal annealing provides a narrower size distribution. Direct X-ray diffraction and scattering morphological studies of "as-fabricated" active layers show improved Sq-TAA-OH/PC71BM phase separation and formation of crystallites, ∼48 nm in size, under conditions that give the best PCE.
authors.affiliation: Department of Chemistry and ‡Department of Polymer Science and Engineering, University of Massachusetts , Amherst, Massachusetts 01003, United States.
authors.forename: Supravat
authors.initials: S
authors.lastname: Karak
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Homnick
authors.forename: Andrea M
authors.initials: AM
authors.lastname: Della Pelle
authors.forename: Youngju
authors.initials: Y
authors.lastname: Bae
authors.forename: Volodimyr V
authors.initials: VV
authors.lastname: Duzhko
authors.forename: Feng
authors.initials: F
authors.lastname: Liu
authors.forename: Thomas P
authors.initials: TP
authors.lastname: Russell
authors.forename: Paul M
authors.initials: PM
authors.lastname: Lahti
authors.forename: S
authors.initials: S
authors.lastname: Thayumanavan