High-order harmonic generation in a microfluidic device for the investigation of ultrafast dynamics in organic perovskites

Extreme UltraViolet (XUV) sources based on High Harmonic Generation (HHG) in noble gases enable ultrafast spectroscopy with extreme temporal resolutions and site and chemical selectivity, with transient absorption in the XUV allowing access to purely electronic dynamics in molecules and solids. To reduce the complexity of efficient harmonic generation, we designed a HHG scheme in a microfluidic device [1] achieving a high photon-flux and broadband phase matching up to 200 eV. This source is coupled with a beamline for transient absorption, with an XUV spectrometer and a polarimeter recently developed at CNR-IFN. Such a setup allows to study light-matter interaction in solids with an unprecedented temporal and spatial resolution, while enabling an element-selective and oxidation-state specific spectroscopy [2], as photon absorption in the XUV occurs at the atomic cores, locally probing both the electronic and the structural environment of specific atoms.

Metal Halide Perovskites (MHPs) are a class of direct bandgap semiconductors with properties that can be tuned by changing their chemical composition ABX 3 , particularly the metal B (Pb, Sn), and halogen X (I, Br). While their optoelectronic properties, such as long carrier lifetimes and diffusion length and small Stokes shift, are well suited for photovoltaics and light emitting applications [3], the physics of these materials is still not completely understood, e.g. concerning defects from lattice distortions, ionic mobility, the polaronic character of excited free carriers and excitons [5] and the nonradiative losses related to Auger recombination [6]. Typically, MHPs conduction band is composed of orbital states of metal and halogen atoms, making them an interesting system for a transient XUV set up which can access the absorption edges of I and Br. Here we report on developing a beamline for site-sensitive ultrafast XUV spectroscopy to explore nonradiative charge recombination and charge transfer at the femtosecond time-scale in MPHs.