title: Effect of Molecule-Surface Reaction Mechanism on the Electronic Characteristics and Photovoltaic Performance of Molecularly Modified Si.
abstract: We report on the passivation properties of molecularly modified, oxide-free Si(111) surfaces. The reaction of 1-alcohol with the H-passivated Si(111) surface can follow two possible paths, nucleophilic substitution (SN) and radical chain reaction (RCR), depending on adsorption conditions. Moderate heating leads to the SNreaction, whereas with UV irradiation RCR dominates, with SNas a secondary path. We show that the site-sensitive SNreaction leads to better electrical passivation, as indicated by smaller surface band bending and a longer lifetime of minority carriers. However, the surface-insensitive RCR reaction leads to more dense monolayers and, therefore, to much better chemical stability, with lasting protection of the Si surface against oxidation. Thus, our study reveals an inherent dissonance between electrical and chemical passivation. Alkoxy monolayers, formed under UV irradiation, benefit, though, from both chemical and electronic passivation because under these conditions both SNand RCR occur. This is reflected in longer minority carrier lifetimes, lower reverse currents in the dark, and improved photovoltaic performance, over what is obtained if only one of the mechanisms operates.These results show how chemical kinetics and reaction paths impact electronic properties at the device level. It further suggests an approach for effective passivation of other semiconductors.
authors.affiliation: Department of Materials & Interfaces, Weizmann Institute of Science , Rehovoth 76100, Israel.
authors.forename: Omer
authors.initials: O
authors.lastname: Yaffe
authors.forename: Tal
authors.initials: T
authors.lastname: Ely
authors.forename: Rotem
authors.initials: R
authors.lastname: Har-Lavan
authors.forename: David A
authors.initials: DA
authors.lastname: Egger
authors.forename: Steve
authors.initials: S
authors.lastname: Johnston
authors.forename: Hagai
authors.initials: H
authors.lastname: Cohen
authors.forename: Leeor
authors.initials: L
authors.lastname: Kronik
authors.forename: Ayelet
authors.initials: A
authors.lastname: Vilan
authors.forename: David
authors.initials: D
authors.lastname: Cahen