Significance of Ambient Temperature Control for Highly Reproducible Layered Perovskite Light-Emitting Diodes

Achieving high reproducibility in materials properties of perovskites is critical to the reliable development of optoelectronic device applications such as photovoltaics and light-emitting diodes. However, it can be difficult to obtain reproducible and optimized performance from these materials, particularly for reduced-dimensional perovskites, because different 2D/quasi-2D perovskite layer numbers have similar formation energies. Here, we report that variations in the exact ambient temperature during solution processing, even in the small range of 21–31 °C, as may occur during the day or across seasons, influence the formation and crystallographic orientation of Ruddlesden–Popper phase perovskites with a formula of PEA2MAn–1PbnBr3n+1. We find that growth at a lower ambient temperature (∼21 °C) predominantly favors low-n phases of the perovskite, especially n = 1 with an orientation parallel to the substrate. Conversely, higher ambient temperatures (∼26 and 31 °C) yield a larger fraction of high-n phases with a vertical orientation and suppressed the formation of the low-n phases. We show that the coexistence of parallel and perpendicular orientations leads to improvements in the electrical and photophysical properties, and consequently improved light-emitting device performance. Furthermore, higher ambient temperatures affect the surface morphology through the formation of cubic grains. Consequently, the precise ambient temperature yields a relative standard deviation of 9.9% for maximum luminance, while uncontrolled temperature causes a high relative standard deviation of 71.4%. These findings highlight the importance of ambient temperature control during processing of layered perovskites. We anticipate that this study should help the field of optoelectronic device research improve the reproducibility in the fabrication of low-dimensional perovskite-based devices.