Exciton Chirality Transfer Empowers Self‐Triggered Spin‐Polarized Amplified Spontaneous Emission from 1D‐Anchoring‐3D Perovskites

Spin‐polarized lasers, arising from stimulated emission of imbalanced spin populations, play a vital role in spin‐optoelectronics. It is usually tackled by external spin injection, inevitably suffering from additional losses across the barriers from injection sources to gain materials. Herein, spin‐polarized coherent light emission is self‐triggered from the 1D‐anchoring‐3D perovskites, where the imbalanced populations in achiral 3D perovskites are endowed with the spin selectivity of exciton chirality (EC) underpinned by chiral 1D perovskites. Efficient transfer of EC is enabled by rapid energy transfer, thereby creating an imbalance of the spin population of excited states. Stimulated emission of such populations brings self‐triggered spin‐polarized amplified spontaneous emission in the composite perovskites, yielding a higher degree of polarization (DOP) than that based on optical spin injection into bare achiral 3D perovskites. Chemical diversity of composite perovskites not only enables to adjust band gap for broadband output of spin‐polarized light signals but also promises to manipulate radiative decay and spin relaxation toward remarkably increased DOP. These results highlight the importance of EC transfer mechanism for spin‐polarized lasing and represent a crucial step toward the development of chiral‐spintronics. Self‐triggered spin‐polarized coherent light emission is achieved through stimulated emission of imbalanced spin population in the 3D@1D perovskites. The population is produced by exciton chirality transfer from chiral 1D perovskites to achiral 3D perovskites without external spin injection. The compositions of 3D@1D perovskites are tailored for broadband output of spin‐polarized amplified spontaneous emission with distinct degree of polarization.