4:30 PM - EN05.08.12
Material Stability Assessment of Low Band Gap Pb-Sn Perovskites
Christina Kamaraki1,2,Matthew Klug1,Laura Miranda1
Oxford Photovoltaics Ltd1,University of Bath2
Show Abstract
Mixed lead-tin (Pb-Sn) perovskites have excelled as leading candidates for low band gap absorber materials demonstrating efficiencies up to 21% for single junctions1,2and 24.8% for all-perovskite tandem solar cells3. Although various ionic species and ratios can be combined to form low band gap perovskites, the propensity of Sn2+ to oxidize comprises the Achilles’ heel of all of these compositions resulting in undesirable p-type doping of the material and poor optoelectronic quality4–7. A deep understanding of the intrinsic degradation mechanisms is imperative in order to successfully integrate these materials into perovskite multi-junctions and even though the deleterious effects of Sn oxidation have been widely explored, the composition’s influence on degradation mechanisms has captured less attention.
Herein, the impact of the intrinsic stability of various low band gap compositions is investigated by monitoring changes in their structural and optoelectronic properties during either thermal or humidity stressing over time. As expected, the vulnerability of the material under humidity exposure scales with increased Sn content, while the degradation is governed by the A-cation choice under thermal stressing and absence of oxygen, with the compositions including volatile species proving to be more susceptible. Interestingly, even under humidity exposure different degradation response was observed for compositions with the same Sn content and different A-cation combination, indicating that ambient stability depends not only in Sn content but on A-site as well. Moreover, practical characterization methods which best capture this degradation at the time scales meaningful for device operation are identified. Our side-by-side degradation assessment highlights how materials composition can alter the degradation footprint and particularly how ion choice influences the speed and the mechanism of degradation, which can inform compositional selection for the practical development of all-perovskite tandems.
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