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Gijun Seo1 Vishal Yeddu1 Do Young Kim1

1, Oklahoma State University, Tulsa, Oklahoma, United States

Organic infrared (IR) photodetectors are especially promising due to their strong absorption in the near-infrared (IR) regions, color selectivity, and compatibility with low-cost roll-to-roll processing. In this work, Tin(IV) 2,3-naphthalocyanine dichloride (SnNcCl2) was used as the IR absorbing small molecule donor for fabricating IR photodetectors as well as IR sensitive organic light-emitting diode (IR-OLED). The SnNcCl2 devices show strong IR response beyond 1100 nm which commercially available Si-based devices cannot offer. SnNcCl2 as a donor needs to have an acceptor with a proper energy band alignment to efficiently dissociate photo-generated excitons because of the nature of the excitonic material with strong binding energy. C60 and Phenyl-C61-butyric acid methyl ester (PC60BM) were used as the acceptors with different lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) levels. Using a C60 acceptor, the SnNcCl2 IR photodetectors showed very high dark currents (~ 3 × 10-5 A/cm2 at -1 V). It is because the HOMO level of a SnNcCl2 is too close to the LUMO level of C60 acceptor, thus resulting in the charge generation effect between the HOMO level of a SnNcCl2 donor and the LUMO level of a C60 acceptor. Using a PC60BM acceptor with high-lying LUMO level, in contrast with C60, the dark current of the SnNcCl2 photodetectors was significantly reduced to ~ 4 × 10-8 A/cm2 at -1 V. It means that the high-lying LUMO level of the PC60BM acceptor sufficiently suppresses the charge generation effect. The acceptors with different LUMO levels also significantly affected the IR sensitive OLED with the SnNcCl2 IR absorbing donor. Upon IR irradiation, both devices with PCBM and C60 acceptors turned on at ~4.5 V. In dark, however, while the PC60BM device showed higher turn-on voltage (10 V), the C60 device has no significant different turn-on voltage with IR irradiation. Upon IR irradiation, both devices with PC60BM and C60 acceptors turned on at ~4.5 V. In dark, however, while the PC60BM device showed high turn-on voltage (10 V), the C60 device showed low turn-on voltage (5V), which is similar to that under IR irradiation condition. It means that the SnNcCl2/C60 layer as the charge generation layer can efficiently supply the hole current to light-emitting layer even without IR irradiation. A systematic study of these devices and the underlying device physics will be presented.

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