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

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 (DDC3F), which easily generates strong g-band emission (green index (I-green/I-blue) of approximate to 5 under ultraviolet exposure for 3 h) in amorphous state, shows an excellent spectra stability of deep-blue emission with a green index of approximate to 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 H2O 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.