How additives for tin halide perovskites influence the Sn4+ concentration. Issue 25 (14th June 2022)

• Record Type: Journal Article
• Authors: Joy, Syed; Atapattu, Harindi R.; Sorensen, Stephanie; Pruett, Henry; Olivelli, Alexander B.; Huckaba, Aron J.; Miller, Anne-Frances; Graham, Kenneth R.
• Is Part Of: Journal of materials chemistry. Volume 10:Issue 25(2022)
• Page Start: 13278
• Page End: 13285
• Publication Date: 2022-06-14
• Subjects: Materials -- Research -- Periodicals; Chemistry, Analytic -- Periodicals; Environmental sciences -- Research -- Periodicals; 543.0284
• DOI: 10.1039/d2ta01429g
• Languages: English
• ISSNs: 2050-7488

Abstract

Abstract : Additives for tin halide perovskites are investigated and several mechanisms, including halide exchange, coordination with Sn halides, and sacrificial antioxidant behavior are observed to decrease Sn 4+ content in the perovskites. Abstract : 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 Sn 4+, can be significantly decreased. Numerous additives are incorporated into Sn-HPs to minimize the amount of Sn 4+, including SnF2, reducing agents such as hydrazine derivatives, and various antioxidants. Despite the frequent use of additives to reduce Sn 4+ 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 119 Sn NMR measurements we show that hydrochloride containing additives undergo halide exchange with SnI4 to form SnI x Cl y, which results in decreased Sn 4+ concentrations and less p-type character in the Sn-HP films. We find that the most effective additive at lowering the Sn 4+ content in FASnI3 is not capable of reducing SnI4 or forming SnI x Cl y, 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.