Ultrafast dynamics of a highly-emissive zero-dimensional organic tin bromide perovskite

Photoluminescence and Stability of Dion-Jacobson Tin-Based Halide Perovskites with Different Spacer Cation Chain Length

Two-dimensional tin halide perovskites are of significant interest for light emitting applications. Here, we investigate the effect of organic cation A on the stability of different Dion-Jacobson tin-based halide perovskites. The ASnBr4 materials using diammonium cation A with shorter alkyl chains are found to exhibit improved stability, exhibiting dramatic stability difference between the most stable HDASnBr4, where HDA denotes 1,6-hexanediammonium, and two materials with 8- and 10-carbon alkyl chain ammonium cations. The HDASnBr4 powders were thermally stable at 100 °C in an argon environment but exhibited decreasing photoluminescence with time in ambient air at 100 °C. The sample degradation at 100 °C is accelerated compared to room temperature, but it proceeds along similar pathways, namely phase transformation followed by perovskite decomposition. Light emission from HDASnBr4 thin films could be further enhanced by methanol vapor treatment, and warm white emission with Commission Internationale de l'Eclairage (CIE) coordinates (0.37, 0.34) could be obtained by combining HDASnBr4 with a blue-emitting polymer film, while direct mixing of blue phosphor and HDASnBr4 powder yields white emission with CIE coordinates of (0.34, 0.32).

Cubic Halide Double Perovskite Nanocrystals with Anisotropic Free Excitons and Self-Trapped Exciton Photoluminescence

In this work, we first developed Cs₂KBiCl₆ cubic double perovskite nanocrystals and a series of morphologically isotropic double perovskite nanocrystals. Different contributions of different elements to self-trapped states were revealed by density functional theory. Meanwhile, these double perovskite nanocrystals exhibit the coexistence of free and self-trapped exciton dual-color photoluminescence. Femtosecond transient absorption spectroscopy can confirm that the double perovskite nanocrystals produce a relatively obvious structural deformation in the excited state. We infer that this can lead to a large deviation of the excitation and emission transition dipoles, thus causing large photoluminescence anisotropy. Most importantly, we observe for the first time that both free exciton emission and self-trapped exciton emission are highly anisotropic, which are comparable to or even better than that of lead halide perovskites. This research paves the way for exploring more possibilities and practical applications.

Self-healing 2D/3D perovskite for efficient and stable p-i-n perovskite solar cells

Beyond the p-i-n perovskite solar cell's high-power conversion efficiency (PCE), its moisture instability is the most challenging factor in its commercialization. Recently, the innovative use of three and two-dimensional multi-structures, by creating a barrier against the penetration of moisture and oxygen, has played a very influential role in improving the PSC's long-term stability. Here, a new strategy, the anti-solvent quenching method, is used to construct multi-structure perovskite by involving cetyltrimethylammonium bromide (CTAB) as an active agent. The solar cell efficiency is significantly improved during the perovskite formation on the substrate by creating a multidimensional (2D/3D) heterojunction perovskite. The synergistic role of using 2D/3D heterojunction perovskite structures led to the 29.2% improvement (14.58-18.84) in the PCE. The attractive ability of the 2D/3D active layer in self-healing has increased the perovskite's long-term stability under harsh environmental conditions.

Electron-Phonon Coupling Mediated Self-Trapped-Exciton Emission and Internal Quantum Confinement in Highly Luminescent Zero-Dimensional (Guanidinium)6Mn3X12 (X = Cl and Br)

We report a large Stokes shift and broad emission band in a Mn-based organic-inorganic hybrid halide, (guanidinium)₆Mn₃Br₁₂ [GuMBr], consisting of trimeric units of distorted MnBr₆ octahedra representing a zero-dimensional compound with a liquid like crystalline lattice. Analysis of the photoluminescence (PL) line width and Raman spectra reveals the effects of electron-phonon coupling, suggestive of the formation of Frenkel-like bound excitons. These bound excitons, regarded as the self-trapped excitons (STEs), account for the large Stokes shift and broad emission band. The excited-state dynamics was studied using femtosecond transient absorption spectroscopy, which confirms the STE emission. Further, this compound is highly emissive with a PL quantum yield of ∼50%. With chloride ion incorporation, we observe enhancement of the emissive properties and attribute it to the effects of intrinsic quantum confinement. Localized electronic states in flat bands lining the gap and their strong coupling with phonons are confirmed with first-principles calculations.

Efficient Photoluminescence of Manganese-Doped Two-Dimensional Chiral Alloyed Perovskites

In this work, we introduced chiral cations into the achiral two-position layered perovskite system for the first time to form an alloyed system that still retains a clear layered structure. In addition, in order to explore the potential photoelectric properties of the alloyed system, manganese ions were doped into the alloyed system. The XRD pattern shows that the steady-state absorption and emission spectra of the alloyed system have a large structural distance, while the doped manganese system exhibits a two-color photoluminescence phenomenon. In addition, combined with time-resolved fluorescence and testing, the photoluminescence characteristics and ultralong lifetime of Mn-doped samples were further characterized. The exciton band structure of the lead halide perovskite framework can be adjusted through this design strategy. Mn²⁺ ions can form characteristic energy levels in the host system and then energy transfer of excitons occurs, which is of great significance for the development of new functional and high-efficiency photoluminescent materials.