High‐Efficiency Tin Halide Perovskite Solar Cells: The Chemistry of Tin (II) Compounds and Their Interaction with Lewis Base Additives during Perovskite Film Formation

Abstract

Mixed halide perovskite compounds with the formula AMX 3 (A þ ¼ CH 3 NH 3 (MA)/HC(NH 2) 2 (FA)/Cs/Rb; M 2þ ¼ Pb, Sn; X À ¼ Cl, Br, I) have emerged as a potential material for fabrication of next-generation solar cells with high photovoltaic performance. [1] A recent study has shown that perovskite solar cells (PSCs) can be fabricated with a high power conversion efficiency (PCE) of 25.5% with Pb as the divalent metal in the compound. [2] Unfortunately, the presence of toxic Pb remains questionable for largescale production. Fortunately, Sn, which is located above Pb in group IV of the periodic table of elements, is a promising candidate for harmless photovoltaic applications. Compared to Pb, Sn is less toxic and can form perovskite compounds with various cations. Sn-based perovskite compounds possess fascinating properties for solar cell applications, such as a narrower bandgap, a lower exciton binding energy, a high charge carrier mobility, and a slightly smaller radius than Pb 2þ , which allows for the replacement of Pb by Sn while retaining the perovskite structure. Notably, the Sn-perovskite materials possess an optimal bandgap for solar cell applications between 1.1 and 1.4 eV and can be decomposed to nontoxic materials such as Sn II oxide (SnO 2). [3] However, fabricating high-quality Sn-based perovskite films is still unmanageable due to the lack of a basic understanding of the Sn II compounds. Such lacking hinders the potential realization of the corresponding film properties, such as surface morphology, pinhole-free layer formation, and low crystallinity. Until now, the most successful of the Sn-PSCs have been fabricated with FASnI 3 as the absorber layer.

Stable tin perovskite solar cells developed via additive engineering

“…SnF 2 additives have been previously shown to contribute to the formation of heterogeneous nucleation sites by prenucleation to produce dense tin perovskite films [49,51]. In our study, the experimental solubility of the Sn(Ac) 2 dissolved in DMSO was about 0.018 mol L −1 at 25°C, which is far less than that of SnF 2 (0.22 mol L −1 ).…”

Stability Improvement of Tin‐Based Halide Perovskite by Precursor‐Solution Regulation with Dual‐Functional Reagents

“…[11] In this case, Sn 2+ cations at the surfaces and grain boundaries (GBs) are easily oxidized to Sn 4+ , which further leads to defect formation. [24][25][26][27] Two factors may affect the optoelectronic properties of Sn-based perovskite films: the stability of precursors [28] and the nucleation-crystallization process of the perovskite film. [29,30] They take effect at different stages within the conventional solution-based film formation process, namely before and during the perovskite formation, respectively.…”

Review of Interface Passivation of Perovskite Layer

“…In addition, HC(NH 2 ) 2 (FA) and Cs can be used to replace MA owing to their wider absorption range; consequently, a bandgap corresponding to the entire wavelength range of visible light can be achieved, thereby resulting in a higher energy conversion rate [ 14 , 15 ]. Tin-based PSCs exhibit electronic structures and semiconductor properties that are similar to those of perovskites, including a high absorption coefficient, high carrier mobility, and an ideal bandgap [ 16 , 17 , 18 ]. This is ideal for the manufacture of environmentally friendly PSCs.…”