Low-dimensional metal-halide perovskites have recently emerged as a promising platform for exploring spin-dependent photophysical phenomena owing to their structural flexibility, strong spin–orbit coupling, and tunable electronic structures. In particular, the incorporation of chiral organic cations into low-dimensional (1D or 2D) inorganic frameworks enables the formation of intrinsically chiral semiconductors exhibiting remarkable chiroptical responses and spin-selective carrier transport. Simultaneously, molecular design offers opportunities to introduce macroscopic polarity, opening new pathways toward unconventional photoelectric conversion mechanisms.

Our research focuses on molecular engineering of chirality and polarity in low-dimensional hybrid perovskites. By employing chiral aromatic ammonium molecules as structure-directing cations, we have developed 1D helical lead-halide perovskites composed of face-sharing [PbI₆]^4- octahedral chains. These materials exhibit giant circular dichroism and strong spin-split band structures arising from the combination of structural chirality and strong spin–orbit coupling. As a result, highly efficient circularly polarized light (CPL) photodetection has been achieved without external optical filters, demonstrating direct conversion of optical helicity into electrical signals [1].

Beyond chiral photodetection, we recently demonstrated that molecular substituent engineering could transform nonpolar helical perovskites into chiral–polar semiconductors. Structural analyses revealed that subtle modifications of organic molecular symmetry significantly alter crystal packing and macroscopic polarization. The resulting polar materials exhibit pronounced photovoltaic responses under zero-bias conditions, indicating the emergence of bulk photovoltaic effects (BPVEs). The polarity direction can be reversed by switching molecular handedness, leading to opposite photocurrent polarities in enantiomeric crystals [2,3].

These findings establish a direct relationship between molecular symmetry, crystal polarity, and spin-dependent photoresponses. The coexistence of chirality and polarity provides a unique opportunity to couple optical selection rules, spin polarization, and non-centrosymmetric carrier generation within a single material platform.

Furthermore, recent spectroscopic and electrical investigations suggest the presence of spin-polarized carrier generation and transport processes extending beyond conventional molecular CISS mechanisms. The one-dimensional helical inorganic framework serves not only as a chiral template but also as an electronically active pathway supporting long-range spin transport. Such characteristics are expected to provide new routes toward spin-optoelectronic functionalities including current-induced magnetization, nonreciprocal transport, and spin-dependent photovoltaic conversion.

In this presentation, recent advances in molecularly engineered low-dimensional perovskites will be discussed, with particular emphasis on the interplay between chirality, polarity, and spin-dependent photofunctions. Future prospects for chiral spin photonics and spin-optoelectronic devices based on low-dimensional semiconductors will also be highlighted.