title: Metastable defect formation at microvoids identified as a source of light-induced degradation in a-Si:H.
abstract: Light-induced degradation of hydrogenated amorphous silicon (a-Si:H), known as the Staebler-Wronski effect, has been studied by time-domain pulsed electron-paramagnetic resonance. Electron-spin echo relaxation measurements in the annealed and light-soaked state revealed two types of defects (termed type I and II), which can be discerned by their electron-spin echo relaxation. Type I exhibits a monoexponential decay related to indirect flip-flop processes between dipolar coupled electron spins in defect clusters, while the phase relaxation of type II is dominated by 1H nuclear spin dynamics and is indicative for isolated spins. We propose that defects are either located at internal surfaces of microvoids (type I) or are isolated and uniformly distributed in the bulk (type II). The concentration of both defect type I and II is significantly higher in the light-soaked state compared to the annealed state. Our results indicate that in addition to isolated defects, defects on internal surfaces of microvoids play a role in light-induced degradation of device-quality a-Si:H.
authors.affiliation: Helmholtz-Zentrum Berlin für Materialien und Energie, Institut für Silizium-Photovoltaik, Kekuléstr. 5, 12489 Berlin, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Fehr
authors.affiliation: Helmholtz-Zentrum Berlin für Materialien und Energie, Institut für Silizium-Photovoltaik, Kekuléstr. 5, 12489 Berlin, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Schnegg
authors.affiliation: Helmholtz-Zentrum Berlin für Materialien und Energie, Institut für Silizium-Photovoltaik, Kekuléstr. 5, 12489 Berlin, Germany.
authors.forename: B
authors.initials: B
authors.lastname: Rech
authors.affiliation: Forschungszentrum Jülich, Institut für Energie- und Klimaforschung, Photovoltaik, 52425 Jülich, Germany.
authors.forename: O
authors.initials: O
authors.lastname: Astakhov
authors.affiliation: Forschungszentrum Jülich, Institut für Energie- und Klimaforschung, Photovoltaik, 52425 Jülich, Germany.
authors.forename: F
authors.initials: F
authors.lastname: Finger
authors.affiliation: Freie Universität Berlin, Fachbereich Physik, Arnimallee 14, 14195 Berlin, Germany.
authors.forename: R
authors.initials: R
authors.lastname: Bittl
authors.affiliation: Freie Universität Berlin, Fachbereich Physik, Arnimallee 14, 14195 Berlin, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Teutloff
authors.affiliation: Helmholtz-Zentrum Berlin für Materialien und Energie, Institut für Silizium-Photovoltaik, Kekuléstr. 5, 12489 Berlin, Germany.
authors.forename: K
authors.initials: K
authors.lastname: Lips