Investigation of Film Morphology and Device Performance Based on Size-Controlled Bulk-Heterojunction Nanoparticles in Organic Photodetector

Abstract

Bulk-heterojunction systems, which are based on donor and acceptor, have been studied as active layers of organic electronic devices owing to their various advantages including simple fabrication, broadband absorption, and efficient charge generation. Recently, to expand the utilization scope of bulk heterojunction systems into industrial applications, various research on bulk-heterojunction nanoparticles (BHJ-NPs)-based electronic devices have attracted attention due to the possibility of environmentally friendly processes. Moreover, BHJ-NPs exhibit novel properties at the nanoscale arising from their high surface area-to-volume ratio, providing potential as new organic optoelectronic materials. To successfully introduce the colloidal nanoparticle dispersion to organic electronic devices, the morphology control of BHJ-NPs films is significant. Herein, I synthesized the size-controlled PM6:Y6-based BHJ-NPs for organic photodetector and explored their size-dependent properties together with thermal-dependent phenomena, which are closely related to film morphology. Small-sized nanoparticles with a high temperature annealing of 200 °C accomplished high device performance with the enhancement of photocurrent, achieving a photosensitivity of 2.16, a photoresponsivity of 38.4 mA/W, and a specific detectivity of 2.28x10^9 Jones as critical organic phototransistor parameters. Compared to large-sized BHJ-NPs over 100 nm in diameter, high quality and fine film formation with low RMS roughness can be obtained from the small and medium-sized BHJ-NPs, showing enhanced Y6 molecular aggregation states. Furthermore, the high temperature thermal annealing (200 °C) can induce the coalescences between BHJ-NPs and increase intermolecular interactions effectively while enhancing the aggregation of donor and acceptor. Optimizing the size of BHJ-NPs and film annealing temperature improves optical and electrical properties with fine film morphology for environmentally friendly-processed nanoparticle-based organic photodetectors.