materials have shown particular versatility and promise among these compounds. These semiconductors take advantage of a diverse bonding scheme and chemical differences among cations to target a degree of antisite defect resistance. Within this set of compounds, the materials containing both Ag and Sr have not been experimentally studied and leave a gap in the full understanding of the family. Here, we have synthesized powders and single crystals of two Ag-and Sr-containing compounds, Ag 2 SrSiS 4 and Ag 2 SrGeS 4 , each found to form in the tetragonal I4̅ 2m structure of Ag 2 BaGeS 4 . During the synthesis targeting the title compounds, two additional materials, Ag 2 Sr 3 Si 2 S 8 and Ag 2 Sr 3 Ge 2 S 8 , have also been identified. These cubic compounds represent impurity phases during the synthesis of Ag 2 SrSiS 4 and Ag 2 SrGeS 4 . We show through hybrid density functional theory calculations that Ag 2 SrSiS 4 and Ag 2 SrGeS 4 have highly dispersive band-edge states and indirect band gaps, experimentally measured as 2.08(1) and 1.73(2) eV, respectively. Second-harmonic generation measurements on Ag 2 SrSiS 4 and Ag 2 SrGeS 4 powders show frequencydoubling capabilities in the near-infrared range.

The spatial heterogeneity of carrier dynamics in polycrystalline metal halide perovskite (MHP) thin films has a strong influence on photovoltaic device performance; however, the underlying cause has not yet been clearly understood. Here we report the sub-micrometer scale mapping of charge carrier dynamics in CH 3 NH 3 PbI 3 thin films using time-resolved nonlinear optical microscopy, specifically transient absorption microscopy (TAM) with sub-picosecond (ps) and time-resolved photoluminescence (PL) microscopy with nanosecond temporal resolution. To study the influence of physical morphology on charge carrier dynamics, MHP thin films having granular-and fibrous structures were investigated. On both types of films, spatial regions with short-lived transient gain signals (fast non-radiative relaxation within ~ 1 ps) typically show slower charge recombination via radiative relaxation, which we attribute to the presence of additional energy states near the band edge. In addition, fibrous films show longer PL lifetimes. Interestingly, the functional contrast shown Received: ((will be filled in by the editorial staff)) Revised: ((will be filled in by the editorial staff))