Sulfur-Donor Additives Preferentially Coordinate Pb²⁺ in Perovskite Precursor Solutions

Conference · Fri Dec 06 04:00:00 EST 2019

DOI:https://doi.org/10.2172/1659408· OSTI ID:1659408

Hamill, Joseph ^[1]; Romiluyi, Oluwaseun; Thomas, Sara; Zhang, Fengyu; Zhao, Xiaoming; Toney, Michael; Schwartz, Jeffrey; Kahn, Antoine; Clancy, Paulette; Loo, Lynn

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1. Princeton University

Lewis base solvents, such as dimethylsulfoxide (DMSO), that strongly coordinate with Pb²⁺ are commonly added to hybrid organic-inorganic perovskite (HOIP) precursor solutions to improve thin-film morphology and subsequent photovoltaic (PV) performance. Although nearly all previous studies of precursor solution chemistry have focused on oxygen-donor solvents as Lewis base additives, we expect “softer,” sulfur-donor solvents to coordinate more strongly with Pb²⁺, a borderline-soft Lewis acid. To confirm this hypothesis, we performed extended X-ray absorption fine structure (EXAFS) spectroscopy at the Pb LIII absorption edge to probe the coordination environment of Pb²⁺ in solutions comprising mixtures of S- and O-donor solvents. Of the S- and O-donor solvent pairs examined, the S-donor solvent consistently outcompetes its O-donor structural analog for coordination sites around Pb²⁺. In the specific comparison between N-methyl-2-pyrrolidone thione (NMPT) and N-methylpyrrolidone (NMP), density-functional theory calculations indicate that NMPT coordination with Pb²⁺ is favored by 10 kcal/mol relative to NMP coordination with Pb²⁺. Similar to the addition of DMSO to precursor solutions, the incorporation of NMPT in fractional quantities provides morphological control of the perovskite film. Unlike DMSO, however, we found NMPT to be stable against undesired transmethylation or disproportionation reactions with methylammonium [1]. Consequentially, films processed with NMPT exhibit no sub-gap electronic states near the valence band edge, in contrast with films prepared using DMSO. We thus believe NMPT merits serious consideration as a solution additive for producing stable HOIP precursor solutions and high-quality HOIP thin films.

[1] Hamill, J. C.; Sorli, J. C.; Pelczer, I.; Schwartz, J. and Loo, Y. -L. Acid-catalyzed reactions activate DMSO as a reagent in perovskite precursor inks. Chemistry of Materials 2019, 31, 2114-2120.

• Research Organization: Princeton University
• Sponsoring Organization: USDOE Office of Energy Efficiency and Renewable Energy (EERE), Renewable Power Office. Solar Energy Technologies Office
• DOE Contract Number: EE0008560
• OSTI ID: 1659408
• Country of Publication: United States
• Language: English