Efficient lasing in size-tunable self-assembled organic microcavities

Blue-emitting organic semiconductor microcavities are attractive candidates for low-threshold, narrow-linewidth microlasers, but the controllable fabrication of high-quality cavities remains challenging. As a readily accessible organic gain material, 1,4-bis(4-methylstyryl)benzene (p-MSB) can spontaneously form single-crystalline microcavities through solution self-assembly and exhibits favorable amplified spontaneous emission (ASE) characteristics. However, self-assembled p-MSB microcavities typically adopt elongated hexagonal geometries with unequal side lengths, leading to increased optical mode leakage, weakened optical confinement, and limited lasing performance. Here, by regulating the solution atmosphere during self-assembled crystal growth, we obtained high-quality p-MSB hexagonal microcavities. The regular p-MSB hexagonal microcavities (regular-PHMs) with nearly identical side lengths were obtained by further adjusting the p-MSB concentration. As the cavity geometry approaches an ideal regular hexagon, optical mode leakage is effectively suppressed, leading to efficient lasing with a low optical pumping threshold of ∼4.12 µJ cm^-2, a narrow linewidth of 0.2 nm, and a high-quality factor of ∼2283. In addition, single-mode lasing was realized by reducing the size of the regular-PHMs. These excellent lasing properties are closely associated with the cavity geometry and size, both of which can be precisely controlled through the crystal preparation process. This work demonstrates that size-tunable organic microcavities provide a promising platform for optical circuits and next-generation miniaturized optoelectronic devices.