Inhibition of Sn2+ Oxidation in FASnI3 Perovskite Precursor Solution and Enhanced Stability of Perovskite Solar Cells by Reductive Additive

Md Abdul Karim; Kiyoto Matsuishi; Md Emrul Kayesh; Yulu He; Ashraful Islam

doi:10.1021/acsami.3c07903

Inhibition of Sn²⁺ Oxidation in FASnI₃ Perovskite Precursor Solution and Enhanced Stability of Perovskite Solar Cells by Reductive Additive

ACS Appl Mater Interfaces. 2023 Oct 4;15(39):45823-45833. doi: 10.1021/acsami.3c07903. Epub 2023 Sep 22.

Authors

Md Abdul Karim^{1

2}, Kiyoto Matsuishi³, Md Emrul Kayesh¹, Yulu He^{1

2}, Ashraful Islam¹

Affiliations

¹ Photovoltaic Materials Group, Center for Green Research on Energy and Environmental Materials, National Institute for Materials Science (NIMS), 1-2-1 Sengen, Tsukuba 305-0047, Ibaraki, Japan.
² Graduate School of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba 305-8573, Ibaraki, Japan.
³ Faculty of Pure and Applied Sciences, University of Tsukuba, Tsukuba 305-8573, Ibaraki, Japan.

PMID: 37738477
DOI: 10.1021/acsami.3c07903

Abstract

Tin-based halide perovskite solar cells (Sn-PSCs) have attracted a progressive amount of attention as a potential alternative to lead-based PSCs (Pb-PSCs). Sn-perovskite films are fabricated by a solution process spin-coating technique. However, the efficiency of these devices varies significantly with the different batches of precursor solution due to the poor chemical stability of SnI₂-DMSO and the oxidation of Sn²⁺ to Sn⁴⁺. This study investigated the origin of Sn²⁺ oxidation before film formation, and it was identified that the ionization of SnI₂ in dimethyl sulfoxide (DMSO) causes the oxidation of free Sn²⁺ and I^- ions. To address these issues, this study introduces the reductive additive 4-fluorophenylhydrazine hydrochloride (4F-PHCl) in the FASnI₃ perovskite precursor solution. The hydrazine functional (-NH-NH₂) group converted detrimental Sn⁴⁺ and I₂ defects back to Sn²⁺ and I^- in precursor solution while retaining the properties of the perovskite solution. Furthermore, the addition of 4F-PHCl in the precursor solution effectively slows the crystallization process, enhancing the crystallinity of FASnI₃ perovskite films and guaranteeing the Sn²⁺/I^- stoichiometric ratio, ultimately leading to a power conversion efficiency (PCE) of 10.86%. The hydrophobic fluorinated benzene ring in 4F-PHCl ensures moisture stability in perovskite films, allowing unencapsulated PSCs to retain over 92% of their initial PCE in an N₂-filled glovebox for 130 days. Moreover, the 4F-PHCl-modified encapsulated PSCs showed superior operational stability for 420 h and maintained 95% of their initial PCE for 300 h under maximum power point tracking at 1 sun continuous illumination. This study's findings provide a promising pathway to create a controlled Sn-based perovskite precursor solution for highly reproducible and stable Pb-free Sn-PSCs.

Keywords: bulk defect; inhibition of oxidation; moisture stability; precursor solution; solution properties.