Tin halide perovskite (Sn-HPs) photovoltaics could potentially equal or exceed the performance of their more toxic Pb-based analogues if defect state densities, particularly originating from the presence of Sn4+, can be significantly decreased. Numerous additives are incorporated into Sn-HPs to minimize the amount of Sn4+, including SnF2, reducing agents such as hydrazine derivatives, and various antioxidants. Despite the frequent use of additives to reduce Sn4+ content, there is limited understanding of how they function and consequently limited guidance for the development of new additives. Herein, we use cyclic voltammetry to probe the redox behavior of SnI2, SnI4, Sn-HP precursor solutions, and 18 different additives. Through 119Sn NMR measurements we show that hydrochloride containing additives undergo halide exchange with SnI4 to form SnIxCly, which results in decreased Sn4+ concentrations and less p-type character in the Sn-HP films. We find that the most effective additive at lowering the Sn4+ content in FASnI3 is not capable of reducing SnI4 or forming SnIxCly, but rather it acts as a sacrificial and coordinating antioxidant. In general, when selecting additives for Sn-HPs it is important to account for the redox potential, coordination with Sn species, ability to react with oxygen, and the potential for halide exchange.
|Number of pages||8|
|Journal||Journal of Materials Chemistry A|
|State||Published - Jun 6 2022|
Bibliographical noteFunding Information:
S. J., K. R. G., and A. J. H. acknowledge support from the National Science Foundation under cooperative agreement No. 1849213. H. R. A., and K. R. G. acknowledge the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award Number DE-SC0018208 for supporting the XPS and UPS measurements. H. P. and K. R. G. acknowledge support from the National Science Foundation, DMR 2102257, for supporting part of the XPS measurements. A. J. H. acknowledges the University of Kentucky for providing start-up funding. A. F. M. acknowledges the U.S. Department of Energy, Established Program to Support Competitive Research, DE-SC0021283, and the National Science Foundation CHE 2108134 for supporting the NMR measurements.
© 2022 The Royal Society of Chemistry
ASJC Scopus subject areas
- Chemistry (all)
- Renewable Energy, Sustainability and the Environment
- Materials Science (all)