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Earth-abundant Cu2BaSnS4-xSex (CBTSSe) represents a recent alter- native for Cu2ZnSn(S,Se)4 for solar energy conversion with a lower level of disorder and band tailing. We report the heterogeneous excited-state and trap-state pattern in different solution-processed CBTSSe films using ultrafast two-color pump-probe diffuse reflec- tance microscopic imaging. The spectroscopy/microscopy method can visualize and correlate the microscopic compositional and elec- tronic variations (i.e., trap states) in real space with time-resolved photophysics. Heterogeneity patterns in TAM images show that some grains exhibit a positive excited-state absorption (ESA) signal, while others show negative ground-state bleaching (GSB). Our re- sults visualize that film processing, such as air annealing and Na addition, has a clear influence on the heterogeneity of the excited- state pattern. Importantly, we report stable charge carrier over 100 ps. We applied the image principal component and histogram for quantitative analysis of TAM images to deconvolute and visu- alize the contribution and fingerprints of minority free carriers and sub-band-gap trapped carriers. 

1-Methylhexylammonium tin iodide yields the lowest reported melting temperature ( T m = 142 °C) to date among lead-free hybrid perovskite semiconductors. Molecular branching near the organic ammonium group coupled with tuning of metal/halogen character suppresses T m and facilitates effective melt-based deposition of films with 568 nm absorption onset. 

Introducing chirality into organic/inorganic hybrid materials can impart chiroptical properties such as circular dichroism. The ability to tune chiroptical properties in self‐assembled materials can have important implications for spintronic and optoelectronic applications. Here, a chiral organic cation, (R/S)‐4‐methoxy‐α‐methylbenzylammonium, is incorporated to synthesize the bismuth‐based hybrid organic–inorganic metal halide semiconductor, (R/S‐MeOMePMA)BiI₄. Thin films of this Bi‐based compound demonstrate large chiroptical responses, with circular dichroism anisotropy (g_CD) values up to ≈0.1, close to the highest value observed in another chiral metal‐halide semiconductor, (R‐MBA₂CuCl₄). Detailed investigation reveals that this large g_CDin (R/S‐MeOMePMA)BiI₄is caused by the apparent CD effect. Careful selection of deposition conditions and the concomitant thin‐film orientation enables the control of g_CD, with maximum value observed when its thin film has a well‐crystallized preferred (001) orientation parallel to the substrate. The results support a growing body of evidence that low symmetry plays an important role in achieving unusually large g_CDin these chiral metal–halide materials and provides design rules for achieving large chiroptical response via morphology control.

 

Trigonal Cu₂BaGe_1−xSn_xSe₄(CBGTSe) has recently gained interest as a potential photovoltaic absorber to target mitigation of antisite defect formation in Cu₂ZnSn(S,Se)₄. This study examines partial substitution of Cu by Ag as a potential approach to tune the properties of Ag‐incorporated CBGTSe in the following aspects: 1) phase stability and crystal structure as a function of Ag content; 2) film morphology and grain structure; 3) charge carrier properties; 4) band positions; and 5) charge carrier kinetics and recombination. Up to 20% of Cu can be substituted by Ag in CBGTSe, while above 20% a phase mixture appears. Increasing Ag content induces larger average grain size and reduced hole carrier densities. In contrast, photoelectron spectroscopy and photoluminescence measurements reveal negligible impact of Ag substitution on ionization potential (≈5.4 eV) and electron affinity (≈3.7 eV). Also, Ag content offers negligible impact on carrier lifetimes (few ns). Consistent with these fundamental properties, solar cells based on two different Ag/(Ag + Cu) ratios (≈0% and ≈20%) show comparable power conversion efficiencies (≈2.7–2.8%). These results indicate that CBGTSe films and solar cells may be less sensitive to Ag substitution compared to Cu₂ZnSn(S,Se)₄, at least at the current level of absorber and device optimization.

 

Two-dimensional (2D) hybrid metal halide perovskites have emerged as outstanding optoelectronic materials and are potential hosts of Rashba/Dresselhaus spin-splitting for spin-selective transport and spin-orbitronics. However, a quantitative microscopic understanding of what controls the spin-splitting magnitude is generally lacking. Through crystallographic and first-principles studies on a broad array of chiral and achiral 2D perovskites, we demonstrate that a specific bond angle disparity connected with asymmetric tilting distortions of the metal halide octahedra breaks local inversion symmetry and strongly correlates with computed spin-splitting. This distortion metric can serve as a crystallographic descriptor for rapid discovery of potential candidate materials with strong spin-splitting. Our work establishes that, rather than the global space group, local inorganic layer distortions induced via appropriate organic cations provide a key design objective to achieve strong spin-splitting in perovskites. New chiral perovskites reported here couple a sizeable spin-splitting with chiral degrees of freedom and offer a unique paradigm of potential interest for spintronics.