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Triple cation Cs/methylammonium (MA)/formamidinium (FA) and double halide Br/I lead perovskites improved the stability and efficiency of perovskite solar cells (PVSCs). However, their effects on alloyed Pb–Sn perovskites are unexplored. In this work, perovskite thin films with the composition Cs x (MA 0.17 FA 0.83 ) 1−x Pb 1−y Sn y (I 0.83 Br 0.17 ) 3 are synthesized utilizing a one-step solution process plus an anti-solvent wash technique and deployed in PVSCs with an inverted architecture. All films show a cubic crystal structure, demonstrating that compositional tuning of both the tolerance factor and crystallization rate allows for dense, single phase formation. The band gaps, affected by both lattice constriction and octahedral tilting, show opposite trends in Pb-rich or Sn-rich perovskites with the increase of Cs for fixed Sn compositions. The Cs 0.05 (MA 0.17 FA 0.83 ) 0.95 Pb 0.25 Sn 0.75 (I 0.83 Br 0.17 ) 3 PVSCs achieve a power conversion efficiency (PCE) of 11.05%, a record for any PVSC containing 75% Sn perovskites, and the Cs 0.10 (MA 0.17 FA 0.83 ) 0.90 Pb 0.75 Sn 0.25 (I 0.83 Br 0.17 ) 3 PVSCs reach a record PCE of 15.78%. Moreover, the triple cation and double halide alloyed Pb–Sn perovskites exhibit improved device stability under inert and ambient conditions. This study, which illustrates the impact of cation and halide tuning on alloyed Pb–Sn perovskites, can be used to further eliminate Pb and improve device performance of high Sn PVSCs and other optoelectronic devices.
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This content will become publicly available on December 23, 2026
Polymorphism and Phase Control in Dion–Jacobson 2D 3-(Aminomethyl)piperidinium-Based Metal Iodide Perovskites
Two-dimensional halide perovskites exhibit rich structural diversity and tunable optoelectronic properties, making them promising materials for energy, sensing, and photonic applications. We report the structural mapping of four distinct polymorphs, γ (P21/c), β (P4/mbm), α (P4/mmm), and δ (Cmcm) in the two-dimensional iodoplumbate, iodostannate, and iodogermanate perovskite so-called Dion–Jacobson series (3AMP)MI4 (M = Sn, Pb, Ge), where 3AMP is 3-(aminomethyl)piperidinium. The phases exhibit systematic evolution in octahedral distortion, lattice symmetry, and metal–halide geometry, enabling structural control over optoelectronic properties. Notably, the α-phase of (3AMP)SnI4 represents a rare, ambient-stable, high-symmetry structure for Sn-based perovskites, without a phase transition down to 100 K. Variable-temperature single-crystal diffraction, powder X-ray diffraction (PXRD), and calorimetry reveal metal- and temperature-dependent polymorph interconversions, including the emergence of long-range supercell reflections in Pb-rich compositions at low temperature. Optical spectroscopy and photoelectron yield spectroscopy confirm band gap tunability and band alignment trends, highlighting symmetry-dependent shifts and anomalous band gap bowing in mixed-metal systems, verified by electronic structure calculations. Calculations additionally indicate that the higher symmetry phases have reduced electron and hole effective masses compared to the lower symmetry phases.
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- Award ID(s):
- 2404059
- PAR ID:
- 10686313
- Publisher / Repository:
- American Chemical Society
- Date Published:
- Journal Name:
- Chemistry of Materials
- Volume:
- 37
- Issue:
- 24
- ISSN:
- 0897-4756
- Page Range / eLocation ID:
- 9869 to 9885
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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