Oriented Naphthalene-<i>O</i>-propylammonium-Based (NOP)<sub>4</sub>Au<i>B</i><sup>III</sup>I<sub>8</sub> (<i>B</i> = Au, Bi, Sb) Ruddlesden-Popper Two-Dimensional Gold Double Perovskite Thin Films Featuring High Charge-Carrier Mobility.
Journal of the American Chemical Society (2025)
Abstract:
Two-dimensional perovskites show intriguing optoelectronic properties due to their anisotropic structure and multiple quantum well structure. Here, we report the first three gold-based Ruddlesden-Popper type two-dimensional double perovskites with a general formula (NOP)4AuIBIIII8 (B = Au, Bi, Sb) employing naphthalene-O-propylammonium (NOP) as an organic cation. They were found to form highly crystalline thin films on various substrates, predominantly oriented in the [001] direction featuring continuous, crack-free film areas on the μm2 scale. The thin films show strong optical absorption in the visible region, with band gap energies between 1.48 and 2.32 eV. Density functional theory calculations support the experimentally obtained band gap energies and predict high charge-carrier mobilities and effective charge separation. A comprehensive study with time-resolved microwave conductivity (TRMC) and optical-pump-THz-probe (OPTP) spectroscopy revealed high charge-carrier mobilities for lead-free two-dimensional perovskites of 4.0 ± 0.2 cm2(V s)-1 and charge-carrier lifetimes in the range of μs. Photoconductivity measurements under 1 sun illumination demonstrated the material's application as a photodetector, showing a 2-fold increase in conductivity when exposed to light.Aerosol-Assisted Crystallization Lowers Intrinsic Quantum Confinement and Improves Optoelectronic Performance in FAPbI<sub>3</sub> Films.
The journal of physical chemistry letters American Chemical Society (ACS) 16:9 (2025) 2212-2222
Abstract:
FAPbI<sub>3</sub> has emerged as a promising semiconductor for photovoltaic applications offering a suitable bandgap for single-junction cells and high chemical stability. However, device efficiency is negatively affected by intrinsic quantum confinement (QC) effects that manifest as additional peaks in the absorption spectra. Here, we show that aerosol-assisted crystallization is an effective method to improve crystallinity and suppresses regions exhibiting QC in FAPbI<sub>3</sub>. We demonstrate that films with minimized QC effects exhibit markedly enhanced optoelectronic properties, such as higher charge-carrier mobilities and recombination lifetimes. Films crystallized under an aerosol solvent flow of either a mixture of <i>N</i>,<i>N</i>-dimethylformamide and dimethyl sulfoxide or methylammonium thiocyanate vapor displayed reduced charge-carrier recombination losses and improved diffusion lengths compared to those of thermally annealed control films. Our study indicates clear correlations between suppression of QC features in absorption spectra with optimization of crystallinity and mitigation of internal strain, highlighting pathways toward high-performance solar cells.Inter‐Layer Diffusion of Excitations in 2D Perovskites Revealed by Photoluminescence Reabsorption
Advanced Functional Materials Wiley (2025)
Abstract:
<jats:title>Abstract</jats:title><jats:p>2D lead halide perovskites (2DPs) offer chemical compatibility with 3D perovskites and enhanced stability, which are attractive for applications in photovoltaic and light‐emitting devices. However, such lowered structural dimensionality causes increased excitonic effects and highly anisotropic charge‐carrier transport. Determining the diffusivity of excitations, in particular for out‐of‐plane or inter‐layer transport, is therefore crucial, yet challenging to achieve. Here, an effective method is demonstrated for monitoring inter‐layer diffusion of photoexcitations in (PEA)<jats:sub>2</jats:sub>PbI<jats:sub>4</jats:sub> thin films by tracking time‐dependent changes in photoluminescence spectra induced by photon reabsorption effects. Selective photoexcitation from either substrate‐ or air‐side of the films reveals differences in diffusion dynamics encountered through the film profile. Time‐dependent diffusion coefficients are extracted from spectral dynamics through a 1D diffusion model coupled with an interference correction for refractive index variations arising from the strong excitonic resonance of 2DPs. Such analysis, together with structural probes, shows that minute misalignment of 2DPs planes occurs at distances far from the substrate, where efficient in‐plane transport consequently overshadows the less efficient out‐of‐plane transport in the direction perpendicular to the substrate. Through detailed analysis, a low out‐of‐plane excitation diffusion coefficient of (0.26 ± 0.03) ×10<jats:sup>−4</jats:sup> cm<jats:sup>2</jats:sup> s<jats:sup>−1</jats:sup> is determined, consistent with a diffusion anisotropy of ≈4 orders of magnitude.</jats:p>Room-temperature epitaxy of α-CH3NH3PbI3 halide perovskite by pulsed laser deposition
Nature Synthesis (2025) 1-12
Spatiotemporal Spectroscopy of Fast Excited-State Diffusion in 2D Covalent Organic Framework Thin Films.
Journal of the American Chemical Society American Chemical Society (ACS) 147:2 (2025) 1758-1766