Highly Uniform Pyrene-Based Host–Guest-Doped Organic Thin Films with Ultralow ASE Threshold and High Stability

Organic semiconductor thin-film lasers hold broad application prospects. High-quality organic films can effectively reduce optical losses in the gain medium, thereby enhancing the operational efficiency and stability of the devices. However, due to the occurrence of postgrowth evolution, organic thin films may undergo morphological and structural degradation over time, resulting in additional optical loss. Here, we propose a strategy to suppress thin-film failure through the control of postgrowth evolution from phase transition and crystallization. We synthesize two pyrene-based derivatives, which are employed as host and guest materials to construct a host–guest luminescent system. This system is systematically compared with a conventional system using CBP as the host material. Experimental results show that both doped systems achieve high photoluminescence quantum yields and ultralow ASE thresholds (less than 1 μJ cm –2 ) in thin films. We analyze the temporal evolution of the morphological and optical gain properties of the two film systems. It is found that the CBP-based films undergo severe morphological degradation in a short period due to crystallization and phase separation, completely losing their optical gain capability. In contrast, the pyrene-based host–guest film maintains high morphological integrity after more than 20 days of storage, exhibiting only localized microcrystallization, while the ASE threshold remains consistently lower than 10 μJ cm –2, demonstrating significantly enhanced material durability and application potential.