High‐Throughput Development of Humidity‐Stable Quasi‐2D Perovskites with a Low Amplified Spontaneous Emission Threshold

ABSTRACT Quasi‐2D perovskites are promising laser gain media owing to their outstanding optoelectronic properties, and their humidity stability is strongly influenced by the organic ligand cations. However, most existing studies focus on a limited number of cations at fixed doping levels or on single‐crystal systems because manual exploration of large quasi‐2D compositional spaces is challenging. Here, we employ a high‐throughput experimental platform to systematically compare the stability of aliphatic Ruddlesden–Popper and Dion–Jacobson quasi‐2D lead bromide perovskite films under simulated fog‐ and dew‐like conditions. We propose that film humidity tolerance is governed by a competition between surface hydrophobicity and grain‐boundary density. Moreover, the poor wettability of precursor solutions containing Ruddlesden–Popper long‐chain cations deteriorates film formation. Guided by morphological characterization, we introduce organic cations, including nonylammonium and 1,12‐diammonium, into the precursor solutions and obtain films that exhibit an exceptionally low amplified spontaneous emission (ASE) threshold of 7.5 µJ·cm − 2 together with outstanding stability under extreme humidity. Notably, the ASE threshold remains nearly unchanged after nine months in ambient air. This work elucidates the key factors governing extreme‐humidity stability in quasi‐2D perovskites and provides a high‐throughput route to laser gain media that combine long‐term air stability with an ultra‐low ASE threshold.