Two-dimensional perovskites, in which inorganic layers are stabilized by organic spacer molecules, are attracting increasing attention as a more robust analogue to the conventional three-dimensional metal-halide perovskites. However, reducing the perovskite dimensionality alters their optoelectronic properties dramatically, yielding excited states that are dominated by bound electron-hole pairs known as excitons, rather than by free charge carriers common to their bulk counterparts. Despite the growing interest in two-dimensional perovskites for both light harvesting and light emitting applications, the full impact of the excitonic nature on their optoelectronic properties remains unclear, particularly regarding the spatial dynamics of the excitons within the two-dimensional (2D) plane.Here, we present direct measurements of in-plane exciton transport in single-crystalline layered perovskites. Using time-resolved fluorescence microscopy, we show that excitons undergo an initial fast, intrinsic normal diffusion through the crystalline plane, followed by a transition to a slower subdiffusive regime as excitons get trapped. Interestingly, the early intrinsic exciton diffusivity depends sensitively on the choice of organic spacer. We find a clear correlation between the stiffness of the lattice and the diffusivity, suggesting exciton-phonon interactions to be dominant in determining the spatial dynamics of the excitons in these materials. Our findings provide a clear design strategy to optimize exciton transport in these systems. lead, tin), X is a halide anion (chloride, bromide, iodide), L is a long organic spacer molecule, and n is the number of octahedra that make up the thickness of the inorganic layer. The separation into fewatom thick inorganic layers yields strong quantum and dielectric confinement effects. 38 As a result, the exciton binding energies in 2D perovskites can be as high as several hundreds of meVs, which is around an order of magnitude larger than those found in bulk perovskites. [39][40][41] The excitonic character of the excited state is accompanied by an effective widening of the bandgap, an increase in the oscillator strength, and a narrowing of the emission spectrum. [40][41][42] The strongest confinement effects are observed for n = 1, where the excited state is confined to a single B-X-octahedral layer (see Figure 1a).Light harvesting using 2D perovskites relies on the efficient transport of excitons and their subsequent separation into free charges. 43 This stands in contrast to bulk perovskites in which free charges are generated instantaneously thanks to the small exciton binding energy. 39 Particularly, with excitons being neutral quasi-particles, the charge extraction becomes significantly more challenging as they cannot be guided to the electrodes through an external electric field. 44 Excitons need to diffuse to an interface before the electron and hole can be efficiently separated into free charges. 45 On the other hand, for light emitting applications the spatial displacement is ...

Two-dimensional layered perovskites are attracting increasing attention as more robust analogues to the conventional three-dimensional metal-halide perovskites for both light harvesting and light emitting applications. However, the impact of the reduced dimensionality on the optoelectronic properties remains unclear, particularly regarding the spatial dynamics of the excitonic excited state within the two-dimensional plane. Here, we present direct measurements of exciton transport in single-crystalline layered perovskites. Using transient photoluminescence microscopy, we show that excitons undergo an initial fast diffusion through the crystalline plane, followed by a slower subdiffusive regime as excitons get trapped. Interestingly, the early intrinsic diffusivity depends sensitively on the choice of organic spacer. A clear correlation between lattice stiffness and diffusivity is found, suggesting exciton-phonon interactions to be dominant in the spatial dynamics of the excitons in perovskites, consistent with the formation of exciton-polarons. Our findings provide a clear design strategy to optimize exciton transport in these systems.

Two-dimensional (2D) metal-halide perovskites are attractive for use in light harvesting and light emitting devices, presenting improved stability as compared to the more conventional three-dimensional perovskite phases. Significant attention has...

Halide mixing is one of the most powerful techniques to tune the optical bandgap of metal-halide perovskites. However, halide mixing has commonly been observed to result in phase segregation, which reduces excited-state transport and limits device performance. While the current emphasis lies on the development of strategies to prevent phase segregation, it remains unclear how halide mixing may affect excited-state transport even if phase purity is maintained. Here, we study exciton transport in phase pure mixed-halide 2D perovskites of (PEA) 2 Pb(I 1– x Br x ) 4 . Using transient photoluminescence microscopy, we show that, despite phase purity, halide mixing inhibits exciton transport. We find a significant reduction even for relatively low alloying concentrations. By performing Brownian dynamics simulations, we are able to reproduce our experimental results and attribute the decrease in diffusivity to the energetically disordered potential landscape that arises due to the intrinsic random distribution of alloying sites.

The development of nanoscience has allowed to propose new ways of clinical treatment and diagnosis. Specifically, there has been a development of nano-optical devices based on plasmonic effects in metal nanoparticles. Plasmons in nanostructures are highly environmentally sensitive due to localized electric field enhancements, which have been employed, among other devices, in chemical sensors and biosensors. Nanostructured metals have overpassed the sensitivity performance of traditional surface plasmon resonance systems (surface plasmon polaritons travelling on continuous metallic films) (Haes & Van Duyne, 2004; Mauriz, Garcia-Fernandez, & Lechuga, 2016). The sensitivity of the localized surface plasmon approach was emergently exploited with triangular silver nanoparticles in a generic biotin-streptavidin immobilization system (Haes & Van Duyne, 2002). The principle was then transferred to technological substrates (such as optical fibres; Chau, Lin, Cheng, & Lin, 2006) using different metals (mainly gold; Hiep et al., 2007) and nanoscale geometries (such as disks; Hanarp, Kall, & Sutherland, 2003) to solid substrates incorporating more complex immobilization strategies (such as the peptide nucleic acid-DNA binding; Endo, Kerman, Nagatani, Takamura, & Tamiya, 2005). Among the diversity of metallic nanoparticles, gallium nanoparticles (GaNPs) have the advantage that they can be deposited in a fast, simple and cheap way on a wide variety of substrates, that is by applying Joule-effect thermal evaporation. As result of their

Paper offers a low-cost and widely available substrate for electronics. It posses alternative characteristics to silicon, as it shows low density and high-flexibility, together with biodegradability. Solution processable materials, such...

We present transient microscopy measurements of interlayer energy transport in (PEA)₂PbI₄ perovskite. We find efficient interlayer exciton transport (0.06 cm²/s), which translates into a diffusion length that exceeds 100 nm and a sub-ps timescale for energy transfer. While still slower than in-plane exciton transport (0.2 cm²/s), our results show that excitonic energy transport is considerably less anisotropic than charge-carrier transport for 2D perovskites.

The use of inexpensive benchtop plotters in combination with refillable writing pens and markers as a powerful route to print nanomaterial‐based inks on paper substrates is studied. It is proved that this approach is very robust, it can be used to print inks of many different solution‐processable nanomaterials, and is very precise, allowing pattern features with pitch separation as narrow as 80 μm. The general character of this printing platform by printing van der Waals materials, organic semiconductors, hybrid perovskites and colloidal nanoparticles with a broad range of properties (from insulators to superconductors) is illustrated. The system is used to easily create several example applications such as an all‐printed, paper‐supported photodetector. This printing platform can be very helpful for research groups with a wealth of expertise in synthesis of solution‐processable nanomaterials but that lack the infrastructure, resources, and expertise to perform traditional inkjet printing for fast device prototyping.