Cationic ligation guides quantum-well formation in layered hybrid perovskites

Layered hybrid perovskites (LHPs) have emerged as promising reduced-dimensional semiconductors for next-generation photonic and energy applications, wherein controlling the size, orientation, and distribution of quantum wells (QWs) is of paramount importance. Here, we reveal that bulky molecular spacers act as crystal-terminating ligands to form colloidal nanoplatelets (NPLs) during early stages of LHP formation. NPLs template the crystallization of LHPs. Using multi-modal diagnostics, we prove that NPLs ripen and grow, playing a decisive role in the time evolution of QW size, population distribution, and orientation. We demonstrate antisolvent drip interrupts NPL ripening and thereby controls QW orientation, population, and energy cascades within LHP films. Using this approach, we achieve low-threshold amplified emission (AE) with remarkable reproducibility. We further introduce synthesized NPLs in the antisolvent step of 3D perovskites to control facet orientation and achieve enhanced efficiency and stability in wide-bandgap solar-cell devices compared to untextured controls.