Dark Current Prevention and Fast Response of Efficient Injection Barrier Formation in Organic Photodetectors

Complementary metal-oxide semiconductors (CMOS) image sensors include of photodetectors in pixel units. Organic photodetectors have in-built advantages in terms of chemically tailorable optical bandgap energy, lightweight components, solution and room temperature processable process via a specific molecular design. Specially, since the organic sensitive layers show excellent mechanical properties, curved and flexible design of photodetector is implemented. Despite many advantages of organic photodetectors, the dark current and noise current can induce degradation of detector performance. However, the source of dark current is unclear which of various contributions, such as electron flow through the junction, shunt leakage, thermionic emission, and tunnelling, are dominant.<br/>In this research, we investigated source of dark current in organic photodetector structure consisting of photosensitive layers, interlayers, and electrodes. First, we introduce a non-fullerene acceptor to photodetector structure by comparing with a fullerene acceptor. The non-fullerene acceptor, eh-IDTBR leads to a high detectivity (1.61×10¹³ cm Hz^1/2/W) and a faster response time (2.7 μs) than those of fullerene acceptor (PC₇₁BM)-based photodetector. The eh-IDTBR can form higher injection barrier related with the excellent dark current suppression. In addition, the photodetector with eh-IDTBR shows excellent stability than the device with fullerene under continuous reverse bias and thermal stress.[1,2] Second, we apply carbon nanotubes as transparent anodic electrode. The carbon nanotubes reveal notable mechanical, optical, and electronic properties, which can realize curved and flexible organic photodetector structure with nearly 100% omnidirectional detection. The carbon nanotube electrode leads to a high detectivity of 2.07×10¹⁴ cm Hz^1/2/W, which is 100 times higher than that of device with the indium–tin oxide. The carbon nanotube electrode suppresses dark current to 9.62×10^-13 A/cm² owing to its deep work function and high electron injection barrier. The flexible organic photodetectors are fabricated with the carbon nanotube electrode and operate stably after a bending test of 500 cycles.[2] Consequently, it is demonstrated the implementation of curved and flexible design by introducing the non-fullerene acceptor and the carbon nanotubes. This work sets a milestone in investigation of dark current and photo response for high-performance organic photodetectors.<br/><br/>W. Jang, S. Rasool, B. G. Kim, J. Kim, J. Yoon, S. Manzhos, H. K. Lee, I. Jeon, D. H. Wang, Adv. Funct. Mater., 2020, 30(45), 2001402<br/>W. Jang, T.-Q. Nguyen, D. H. Wang, Adv. Funct. Mater., 2022, in press.<br/>W. Jang, B. G. Kim, A. Shawky, S. Seo, M. S. Kim, K. Kim, Q. Zhang, E. I. Kauppinen, S. Maruyama, I. Jeon, D. H. Wang, Nano Today, 2021, 37, 101081