Cationic Liganding is at the Origin of Quantum Well Orientation and Population Distribution in Reduced Dimensional Perovskites

Layered hybrid perovskite (LHP) films exhibit highly anisotropic properties including charge and energy transport along quantum wells (QWs), as well as energy and charge transfer between QWs of different sizes. The control of QW orientation and population distribution within LHP films is therefore critically important to various applications ranging from solar cells to LEDs, lasers, and field-effect transistors. It is not surprise, then the hybrid perovskites community has deemed it a scientific and technological imperative to understand the origins of QW orientation and population distribution in LHP films. Despite tremendous recent efforts to understand the mechanism of crystallization in these materials, significant questions remain about the origins of crystalline texture, QW orientation and distribution in LHPs. Here we elucidate the precise solution-to-solid conversion of the sol into the LHP thin film by the aid of using multimodal in-situ characterization techniques such as grazing-incidence wide-angle X-ray scattering (GIWAXS), UV-vis absorption, and photoluminescence (PL). We identify, for the first time, the presence of oriented colloidal templating nanostructures (CTNs) during spin coating at the sol-air interface, that are highly emissive but do not diffract, well before the onset of crystallization of the QWs or 3D phases. According to our in-situ observations along with quantitative analysis, we propose a growth model for CTNs that can explain the underlying reason behind tremendous texture in these thin-films. Furthermore, we test our hypothesis by engineering CTNs during antisolvent drip to manipulate the texture as well as QWs distribution in LHP thin films.