Micro- and nanocrystalline methylammonium lead iodide (MAPI)-based thin-film solar cells today reach power conversion efficiencies of over 20%. We investigate the impact of grain boundaries on charge carrier transport in large crystal MAPI thin films using time-resolved photoluminescence (PL) microscopy and numerical model calculations. Crystal sizes in the range of several tens of micrometers allow for the spatially and time resolved study of boundary effects. Whereas long-ranged diffusive charge carrier transport is observed within single crystals, no detectable diffusive transport occurs across grain boundaries. The observed PL transients are found to crucially depend on the microscopic geometry of the crystal and the point of observation. In particular, spatially restricted diffusion of charge carriers leads to slower PL decay near crystal edges as compared to the crystal center. In contrast to many reports in the literature, our experimental results show no quenching or additional loss channels due to grain boundaries for the studied material, which thus do not negatively affect the performance of the derived thin-film devices.

We investigated the angular radiation patterns, a key characteristic of an emitting system, from individual silver nanowires decorated with rare earth ion-doped nanocrystals. Back focal plane radiation patterns of the nanocrystal photoluminescence after local two-photon excitation can be described by two emission channels: Excitation of propagating surface plasmons in the nanowire followed by leakage radiation and direct dipolar emission observed also in the absence of the nanowire. Theoretical modeling reproduces the observed radiation patterns which strongly depend on the position of excitation along the nanowire. Our analysis allows to estimate the branching ratio into both emission channels and to determine the diameter dependent surface plasmon quasimomentum, important parameters of emitter-plasmon structures. KeywordsPlasmonics; metallic nanowires; rare earth ions; back focal plane imaging; up-conversion Propagating surface plasmon polaritons (SPPs) are electromagnetic waves bound to a metaldielectric interface. They offer the distinguished possibility to concentrate light to subwavelength scales and transport this energy over a length several magnitudes larger. [1][2][3][4] These properties provide the basis for plasmonics, a very active research area aiming at optical device miniaturization and the integration of optics and electronics on a single chip. 5,6 Metallic nanowires (NWs) have drawn particular attention as plasmonic building blocks due to their successful implementation as waveguides, 7-9 routers and logic gates. 10-12 SPPs on metallic NWs have been investigated by direct visualization, 13 using a scanning aperture probe, 14 by electrical detection 15 as well as by calculations. 16 A key step in plasmonic applications of NWs is the coupling of the initial energy source to the NW and the contributing energy relaxation pathways. 17,18 Importantly, subwave-length light confinement by the SPPs can be used to enhance the interaction between objects and light. 19 This coupling and the excitation and propagation of SPPs have been experimentally visualized by leakage radiation microscopy 20-22 combined with imaging of the back focal plane (BFP) for a variety of plasmonic structures and devices. [23][24][25] In this manuscript we studied the coupling of the emission from rare earth doped nanocrystals to SPP modes in silver NWs on glass. We use the ability of these nanocrystals to exhibit stable, non-bleaching upconverted photoluminescence (PL) on the anti-Stokes side * To whom correspondence should be addressed achim.hartschuh@cup.uni-muenchen.de. Europe PMC Funders Group Europe PMC Funders Author ManuscriptsEurope PMC Funders Author Manuscripts of the laser energy 26 to avoid temporal intensity fluctuations and to exclude any background contribution from laser scattering, metal luminescence or the sample substrate. Importantly, since two-photon excitation requires high excitation densities it will only be efficient at the position of the laser focus. Two-photon excitation of NCs located outsid...

Perovskite-based thin-film solar cells today reach power conversion efficiencies of more than 22%. Methylammonium lead iodide (MAPI) is prototypical for this material class of hybrid halide perovskite semiconductors and at the focal point of interest for a growing community in research and engineering. Here, a detailed understanding of the charge carrier transport and its limitations by underlying scattering mechanisms is of great interest to the material’s optimization and development. In this article, we present an all-optical study of the charge carrier diffusion properties in large-crystal MAPI thin films in the tetragonal crystal phase from 170 K to room temperature. We probe the local material properties of individual crystal grains within a MAPI thin film and find a steady decrease of the charge carrier diffusion constant with increasing temperature. From the resulting charge carrier mobility, we find a power law dependence of μ ∝ T m with m = −(1.8 ± 0.1). We further study the temperature-dependent mobility of the orthorhombic crystal phase from 50 to 140 K and observe a distinctly different exponent of m = −(1.2 ± 0.1).