Processes Controlling the Distribution of Vertical Organic Composition in Organic Photodetectors by Ultrasonic-Assisted Solvent Vapor Annealing

Regulating the vertical composition distribution of an organic electronic donor and acceptor is an effective strategy for the fabrication of high-performance organic photodetectors (OPDs). In this study, after the one-step solution process to fabricate an active layer, an ultrasonic-assisted solvent vapor annealing method (UA-SVA) was proposed to modulate the vertical distribution of the PBDB-T:ITIC BHJ layer in an OPD device. Compared to the control device processed from SVA, the obtained OPD from UA-SVA exhibits both a decreased dark current and slightly enhanced photocurrent. As a result, the photodetectivity of the device treated by UA-SVA was more than one order of magnitude higher than that of the control counterpart in the detective spectrum ranging from 450 to 750 nm. Especially, a dramatically high photodetectivity of 2.17 × 1012 Jones at a wavelength of 688 nm has been achieved under a reverse bias of −0.5 V. To illuminate the reason for OPD performance improvement, ultraviolet–visible (UV–vis) absorption spectroscopy, space-charge-limited current (SCLC) method, atomic force microscopy (AFM), and water contact angle (WCA) measurement were performed, and the enhanced light-absorption intensity, improved charge carrier transport efficiency, and the modified interfacial contact and surface morphology of the BHJ active layer were observed.