Two-dimensional (2D) Sn-based perovskites are a kind of non-toxic environment-friendly luminescent material. However, the research on the luminescence mechanism of this type of perovskite is still very controversial, which greatly limits the further improvement and application of the luminescence performance. At present, the focus of controversy is defects and phonon scattering rates. In this work, we combine the organic cation control engineering with temperature-dependent transient absorption spectroscopy to systematically study the interband exciton relaxation pathways in layered A₂SnI₄ (A = PEA⁺, BA⁺, HA⁺, and OA⁺) structures. It is revealed that exciton-phonon scattering and exciton-defect scattering have different effects on exciton relaxation. Our study further confirms that the deformation potential scattering by charged defects, not by the non-polar optical phonons, dominates the excitons interband relaxation, which is largely different from the Pb-based perovskites. These results enhance the understanding of the origin of the non-radiative pathway in Sn-based perovskite materials.

In order to conquer the challenges in the current technology to couple a dye-sensitized solar cell (DSSC) with a photonic crystal (PC), we propose a novel design of PC-based photoanode, composed of a thick TiO₂ nanoparticle absorption layer and a thin TiO₂ nanotube photonic crystal (TiO₂ NT PC) membrane. In this architecture, the bandgap of TiO₂ NT PC can be precisely tailored by modulating the anodization parameters using the current-pulse anodization process. Owing to the selective reflectivity of TiO₂ NT PC, the power conversion efficiency (PCE) of the electrodes reveals a strong wavelength dependence. Strategies to enhance the efficiency of the newly designed DSSC and its relation to the selective reflection of the photoanode are discussed and evaluated by experimental and simulated results. Meanwhile, the functionality of TiO₂ NT PC, offering both PC and light-scattering effects, has also been clarified. The combined effects of PC and light-scattering yield the maximum enhancement in PCE (39.5%) when the tailored TiO₂ NT PC, with the best matching of its reflectance maximum to the dye absorption maximum, is integrated into a DSSC. The work presented here provides new insights into the design and tailoring of a photonic crystal to enhance the PCE of DSSCs for practical applications.

Achieving perovskite-based high–color purity blue-emitting light-emitting diodes (LEDs) is still challenging. Here, we report successful synthesis of a series of blue-emissive two-dimensional Ruddlesden-Popper phase single crystals and their high–color purity blue-emitting LED demonstrations. Although this approach successfully achieves a series of bandgap emissions based on the different layer thicknesses, it still suffers from a conventional temperature-induced device degradation mechanism during high-voltage operations. To understand the underlying mechanism, we further elucidate temperature-induced device degradation by investigating the crystal structural and spectral evolution dynamics via in situ temperature-dependent single-crystal x-ray diffraction, photoluminescence (PL) characterization, and density functional theory calculation. The PL peak becomes asymmetrically broadened with a marked intensity decay, as temperature increases owing to [PbBr₆]⁴⁻ octahedra tilting and the organic chain disordering, which results in bandgap decrease. This study indicates that careful heat management under LED operation is a key factor to maintain the sharp and intense emission.

Recently, all-inorganic halide perovskites have received enormous attention because of their excellent optoelectronic properties. Among them, the power conversion efficiency (PCE) of all-inorganic halide perovskite solar cells has made rapid progress in the last few years. However, understanding the intrinsic physical nature of halide perovskites, especially the dynamic process of photo-generated carriers, is a key for improving the PCE. In this review, we introduced and summarized the photoluminescence (PL) technique used to explore the carrier dynamic process in all-inorganic halide perovskites. Several physical models were proposed to investigate the dynamic parameters, i.e., recombination lifetime and diffusion length, by analyzing the steady-state PL as well as the time-resolved PL spectra. We also discussed the distinction of PL spectral behavior between bulk halide perovskite samples and those grown with transport layers due to the participation of different dominant dynamic paths. Finally, we briefly described some other optical techniques reported to study the relevant physical properties of all-inorganic halide perovskites.