Fabrication of Efficient Formamidinium Tin Iodide Perovskite Solar Cells through SnF₂–Pyrazine Complex

Abstract

To fabricate efficient formamidinium tin iodide (FASnI3) perovskite solar cells (PSCs), it is essential to deposit uniform and dense perovskite layers and reduce Sn(4+) content. Here we used solvent-engineering and nonsolvent dripping process with SnF2 as an inhibitor of Sn(4+). However, excess SnF2 induces phase separation on the surface of the perovskite film. In this work, we report the homogeneous dispersion of SnF2 via the formation of the SnF2-pyrazine complex. Consequently, we fabricated FASnI3 PSCs with high reproducibility, achieving a high power conversion efficiency of 4.8%. Furthermore, the encapsulated device showed a stable performance for over 100 days, maintaining 98% of its initial efficiency.

Mixed‐Organic‐Cation Tin Iodide for Lead‐Free Perovskite Solar Cells with an Efficiency of 8.12%

“…When the content of FA was enhanced, the grain boundaries gradually became more evident, and the FASnI 3 film shows crystal grains with sharp edges and clear boundaries. At lower FA contents ( x = 0.00, 0.25, and 0.50), some white grains are found in the films, which may be ascribed to the phase separation induced by SnF 2 19, 27. These films also exhibit incomplete coverage with a few pinholes, which may explain the low FF and the slightly lower average J sc of their corresponding devices.…”

“…The use of dimethyl sulfoxide (DMSO) as the precursor solvent has proven to be crucial in acquiring homogeneous films, as it forms a SnI 2 ·3DMSO intermediate phase that retards the rapid crystallization of Sn‐based perovskites 18. Seo and co‐workers employed a SnF 2 ‐pyrazine complex to improve the morphology of FASnI 3 films and obtained a PCE of 4.8% 19. There are also reports on adopting more suitable device structures for Sn‐based PSCs.…”

Lead‐Free Hybrid Perovskite Absorbers for Viable Application: Can We Eat the Cake and Have It too?

“…The author has concluded that the SnF 2 cannot only improve interfacial energy alignment but also increase stability to electron beam damage. Nowadays, most Sn‐based perovskites films prepared by solution deposition need additional SnF 2 to get good performance,47, 48, 57, 58, 73 including the recent (FA) 0.75 (MA) 0.25 SnI 3 based PSCs with the highest PCE of 8.12% 56. Additionally, Ma et al134 claimed that SnF 2 as the inhibitor of Sn 2+ oxidation in the MASnI 3 film could increase the fluorescence lifetime up to 10 times and give longer carrier diffusion lengths >500 nm, compared with pristine MASnI 3 films.…”

“…In the case of tin perovskite, the popularly used SnF 2 additive for the elimination of the Sn vacancy could result in poor film morphology and bad device performance due to the phase separation of SnF 2 within the perovskite film 6, 135. In this regard, Lee et al58 introduced pyrazine into FASnI 3 perovskite precursors in conjunction with SnF 2 in the form of the SnF 2 ‐pyrazine complex ( Figure 10 a,b). The complex is believed to assist a uniform distribution SnF 2 in the perovskite film, thereby substantially improving the morphology of FASnI 3 perovskite.…”

“…The heterojunction depleted hole‐transporting layer‐free solar cells based on mesoporous TiO 2 showed a high photocurrent up to 21 mA cm −2 and a PCE of 3.15%. Furthermore, Lee et al58 used mixed solvents of N,N ‐dimethylformamide (DMF) and DMSO in FASnI 3 precursor solution followed by toluene drop‐casting, which led to uniform and dense FASnI 3 perovskite layers. The role of DMSO was to retard the crystallization of FAI and SnI 2 during spin‐coating process ( Figure 11 a–d).…”