Interfacial Charge Separation and Photogating-Induced Carrier Redistribution in Rose Bengal-Sensitized Oriented PBTTT-C14 Phototransistors Revealed by Time-Resolved Second Harmonic Generation
In this study, we demonstrate the direct visualization of photoinduced charge carrier redistribution by Time-Resolved Second Harmonic Generation (TRM-SHG) of enhanced photoresponse in organic phototransistors based on highly oriented PBTTT-C14 thin films fabricated via the unidirectional floating film transfer method (UFTM). The implementation of a bilayer structure, incorporating Rose Bengal (RB) dye spin-cast atop PBTTT-C14, dramatically improves device performance, with the photosensitivity enhanced up to ~106 orders of magnitude. The optimized devices exhibit high responsivity on the order of 7×102 A/W and extremely high specific detectivity on the order of 1016 Jones. Furthermore, enhanced photocarrier generation and dynamics in the bilayer device structure were directly visualized and investigated using time-resolved optical second-harmonic generation (TRM-SHG), providing additional insight into the charge transport mechanisms. The findings demonstrate an effective strategy to improve photoresponse in organic optoelectronic devices.