title: A Two-Step Absorber Deposition Approach To Overcome Shunt Losses in Thin-Film Solar Cells: Using Tin Sulfide as a Proof-of-Concept Material System.
abstract: As novel absorber materials are developed and screened for their photovoltaic (PV) properties, the challenge remains to reproducibly test promising candidates for high-performing PV devices. Many early-stage devices are prone to device shunting due to pinholes in the absorber layer, producing "false-negative" results. Here, we demonstrate a device engineering solution toward a robust device architecture, using a two-step absorber deposition approach. We use tin sulfide (SnS) as a test absorber material. The SnS bulk is processed at high temperature (400 °C) to stimulate grain growth, followed by a much thinner, low-temperature (200 °C) absorber deposition. At a lower process temperature, the thin absorber overlayer contains significantly smaller, densely packed grains, which are likely to provide a continuous coating and fill pinholes in the underlying absorber bulk. We compare this two-step approach to the more standard approach of using a semi-insulating buffer layer directly on top of the annealed absorber bulk, and we demonstrate a more than 3.5× superior shunt resistance Rsh with smaller standard error σRsh. Electron-beam-induced current (EBIC) measurements indicate a lower density of pinholes in the SnS absorber bulk when using the two-step absorber deposition approach. We correlate those findings to improvements in the device performance and device performance reproducibility.
authors: Department of Mechanical Engineering, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States.
authors: Vera
authors: V
authors: Steinmann
authors: Department of Mechanical Engineering, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States.
authors: Rupak
authors: R
authors: Chakraborty
authors: Department of Materials Science and Engineering, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States.
authors: Paul H
authors: PH
authors: Rekemeyer
authors: Department of Mechanical Engineering, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States.
authors: Katy
authors: K
authors: Hartman
authors: Department of Mechanical Engineering, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States.
authors: Riley E
authors: RE
authors: Brandt
authors: Department of Mechanical Engineering, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States.
authors: Alex
authors: A
authors: Polizzotti
authors: Department of Chemistry and Chemical Biology, Harvard University , Cambridge, Massachusetts 02138 United States.
authors: Chuanxi
authors: C
authors: Yang
authors: National Renewable Energy Laboratory , Golden, Colorado 80401, United States.
authors: Tom
authors: T
authors: Moriarty
authors: Department of Materials Science and Engineering, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States.
authors: Silvija
authors: S
authors: Gradečak
authors: Department of Chemistry and Chemical Biology, Harvard University , Cambridge, Massachusetts 02138 United States.
authors: Roy G
authors: RG
authors: Gordon
authors: Department of Mechanical Engineering, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States.
authors: Tonio
authors: T
authors: Buonassisi
keywords: device shunting; novel absorber materials; performance reliability; photovoltaics; thin-films; tin sulfide