Stability against oxygen is an important factor affecting the performance of organic semiconductor devices. Improving photooxidation stability can prolong the service life of the device and maintain the mechanical and photoelectric properties of the device. Generally, various encapsulation methods from molecular structure to macroscopic device level are used to improve photooxidation stability. Here, we adopted a crystallization strategy to allow 14H-spiro[dibenzo[c,h]a-cridine-7,9′-uorene] (SFDBA) to pack tightly to resist fluo-rescence decay caused by oxidation. In this case, the inert group of SFDBA acts as a “steric armor”, protecting the photosensitive group from being attacked by oxygen. Therefore, compared with the fluorescence quenching of SFDBA powder under two hours of sunlight, SFDBA crystal can maintain its fluorescence emission for more than eight hours under the same conditions. Furthermore, the photolu-minescence quantum yields (PLQYs) of the crystalline film is 327.37 % higher than that of the amorphous film. It shows that the crystal-lization strategy is an effective method to resist oxidation.