Optically Induced Long-Lived Chirality Memory in the Color-Tunable Chiral Lead-Free Semiconductor (R)/(S)‑CHEA4Bi2BrxI10−x (x = 0−10)

Hybrid organic-inorganic perovskites are optoelectronic materials with tunable chemical and electronic structures. Incorporating chiral organic molecules into perovskite networks has attracted great attention due to their potential in lighting applications and optical communication. Here, we introduce chiral organic molecules (R)/(S)-1-cyclohexylethylamine (R/S-CHEA) into bismuth-based materials with a perovskite-related motif, to synthesize chiral lead-free (R)/(S)-CHEA4Bi2BrxI10-x crystals and thin films. We perform single-crystal XRD measurements and density-functional theory (DFT) calculations to identify their crystal and electronic band structures. We investigate their optical properties, and find circular dichroism, which we tune over a wide wavelength range from 300 - 500 nm by changing the bromide-to-iodide ratio. Further, we employ transient absorption and time-resolved PL spectroscopy to investigate charge carrier dynamics, which show long-lived excitations with optically-induced chirality memory up to microsecond timescales. Our demonstration of color-tunable and chiral lead-free perovskites opens a new avenue for the discovery of high performance lead-free spintronic materials with optical functionalities.