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Graduate Student Seminar - 04/14/2017

"Open-Circuit Voltage Mapping of Next-Generation Solar Cells"

by Beth Tennyson

Friday, April 14, 2017 -- 12:00 p.m.
Large Conference Room, 1207 Energy Research Facility

Advisor: Asst. Prof. Marina Leite

The best low-cost, high-efficiency photovoltaics (PV) are composed of polycrystalline grains that can locally limit device performance, specifically, the open-circuit voltage (Voc­). Thus, it is imperative to understand where the deficiencies occur in order to control and suppress their activity. Here, we present a functional nano-imaging method to correlate structural defects with electric response. We realize illuminated-Kelvin probe force microscopy (KPFM) as a tool to directly measure Voc with spatial resolution < 50 nm, five orders of magnitude better than previous reports, Fig 1b. We image the local Voc in the different grains composing both CdTe and CIGS solar cells and find certain boundaries act as a non-radiative recombination center. We expand the KPFM method to map the dynamics of the local voltage response in perovskite solar cells with fast-KPFM (16 s/scan), enabling us to map local Voc in real-time and at the nanoscale. Our novel functional microscopy platform can be implemented to diagnose emerging PV materials such as lead-free hybrid organic-inorganics and dye-sensitized solar cells. Thus, it will critically impact high-efficiency, low-cost PV by identifying the relation between a material’s structural properties and its electrical response at the nanoscale.

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