Efficient Bulk Defect Suppression Strategy in FASnI₃ Perovskite for Photovoltaic Performance Enhancement

Abstract

Despite Sn‐based perovskite solar cells (PSCs) prevailing over lead‐free candidates, the Sn vacancies (VSn) and Sn4+ defects seriously deteriorate device photovoltaic performance. The presently reported methods can only effectively achieve surface defect passivation, and it is of great challenge and fundamental importance to develop efficient strategy to deal with the intrinsic defects located inside the lattice. Herein, a novel bulk defect suppression strategy is proposed, introducing large organic piperazine cations (PZ2+) into the lattice of 3D FASnI3 perovskite to restrain the generation of bulk defects. The incorporation of PZ2+ results in forming a FA1−2yPZ2ySn1−yI3 (0 ≤ y ≤ 0.25) structure with no reduction in dimensionality, which guarantees the continuity of [SnI6] octahedral structures with unobstructed carrier transport and reduced charged defects. The potent interactions between PZ2+ and [SnI6] structures enhance VSn formation energy and effectively suppress bulk defect formation. As a result, the FASnI3+1%PZ films exhibit optimized crystalline quality, decreased background carrier density, lower p‐type self‐doping, and reduced trap state density. Benefiting from the above advantages, the FASnI3+1%PZ device achieves an optimal PCE of 9.15% and unencapsulated device maintains over 95% of initial PCE after aging for 1000 h in N2 golvebox. The bulk defect suppression strategy provides fire‐new building bricks toward high‐performance Sn‐based PSCs.

Dimensional Tailoring Endows Tin Halide Perovskite Solar Cells with High Efficiency and Stability

“…4 The molecular structures of bulky organic cations used in low-dimensional tin halide perovskites. [15,26,32,40,50,53,57,59,61,62,64,65,67,68,[70][71][72][73][74] with SnX 6 4− octahedrons tailoring with different n value. Dimensionality regulation not only enhances device stability and efficiency but also alleviates self-doping behavior and ion migration.…”

“…Large organic spacer layers such as PEA + , BA + , or GA + cut the 3D tin perovskites into low-dimensional layered structures along specific planes, further improving air stability and achieving high efficiency. [70,73] Fig. 6 (a) The chemical structure of (FSA) 2 SnI 4 and (FSA) 2 MASn 2 I 7 tin perovskites.…”

“…Other bulky ammonium cations, such as DEA + (diethylammonium), BA + , GA + , and DPPA + (3,3-diphenylpropylammonium) could also replace FAI in 3D FASnI 3 . [54,66,70,72] Kayesh et al used hydrophobic long carbon chain organic cation 5-AVA + to passivate grain boundaries, thus improving efficiency from 3.4% to 7.0% in p-i-n devices. [59] Hayase et al partial substitution of FA + by DEA + and obtained better charge transport.…”

“…A novel sequential deposition strategy upon 3D tin perovskites was attempted by a suitable solvent hexafluoro-2-propanol (HFP). [70] They dissolved BA + , ALA + , 2F-PEA + , 2F-AN + (anilinium), PEA + , and HA + (hexylammonium) in HFP as a second step to modify GA 0.2 FA 0.8 SnI 3 -1% EDAI 2 perovskite, which helped to grow a stable 2D-3D bilayer to resistance to water and oxygen intrusion after when exposure in the air (Fig. 8b).…”

“…Copyright 2020, Royal Society of Chemistry. (b) Schematic diagram of sequential deposition by surface treatment of 2D organic cations [70]. Copyright 2021, American Chemical Society.…”