Crystallization‐Enhanced Stability by Effectively Suppressing Photooxidation Defect for Optoelectronic Devices

Abstract Effective protection against photooxidation of organic wide‐bandgap semiconductors is a potential method to afford high efficient deep‐blue emission for full color displays. Herein, the crystallization effect of fluorene‐based blue emitter on suppressing the formation of long‐wavelength green band ( g ‐band) defect is demonstrated through the model of self‐assembled organic micro/nanocrystals. The selected molecule 2,2'‐bi(9,9‐dipropyl)fluorene (DDC 3 F), which easily generates strong g ‐band emission (green index ( I green / I blue ) of ≈5 under ultraviolet exposure for 3 h) in amorphous state, shows an excellent spectra stability of deep‐blue emission with a green index of ≈0 and an unchangeable CIE coordination of (0.18, 0.09) in crystalline nanorod morphologies. Such effect of crystallization‐induced stability enhancement can be further extended into other solution‐processing methods such as brushing. Molecular dynamic simulation reveals that crystalline nanorods with compact molecular packing enable to effectively block the diffusion of O 2 and H 2 O molecules, which is crucial to suppress the occurrence of photooxidation reactions. Along with high quantum yield of 87% from crystallization‐induced luminescence enhancement effect, such ultrastable deep‐blue emission on crystalline film can also be maintained in solution‐processing organic light‐emitting diode devices. The supramolecular self‐assembled micro/nanocrystals strategy provides a potential platform to maintain ultrastable color purity in organic optoelectronic devices.