An n-Type All-Fused-Ring Molecule with Photoresponse to 1000 nm for Highly Sensitive Near-Infrared Photodetector

Organic photodetectors (OPDs) have attracted extensive attention due to their advantages of solution processability, flexibility, and easy integration with pixel circuit. These merits make OPDs promising for many applications, such as bioimaging, optical communication, wearable biological monitoring, etc. A critical parameter determining the device performance of OPDs is dark current. To suppress dark current and enhance the detectivity of OPDs, the general strategies are to increase the film thickness of active layers and or to optimize the phase separation morphology. However, the suppression of dark current by molecular design of active layer materials is rarely reported.

Recently, Jun Liu's research team of Changchun Institute of Applied Chemistry published an article in Advanced Materials. In this work, they report an n-type all-fused-ring molecule FM2 with bandgap of as small as 1.2 eV and onset absorption wavelength of exceeding 1000 nm. It consists of 14 π-conjugated rings with ADA’DA molecular configuration. Most importantly, due to the fixed conformation and consequently low conformation disorder, FM2 exhibits a low trap density. As a result, organic photodetector (OPD) based on FM2 exhibits a remarkably low dark current density (J_d) of 2.01 × 10^？10 A cm^？2 at 0 V. The device shows a shot-noise-limited specific detectivity (D_sh*) of exceeding 10¹³ Jones at 400–1000 nm wavelength region with a peak specific detectivity of 4.65 × 10¹³ Jones at 880 nm, which is among the best reported for self-powered NIR OPDs. This work not only discloses a unique advantage of all-fused-ring molecules with low trap intensity in solid state, but also suggests a new kind of high-performance n-type semiconductors for NIR OPDs.

Y. Z. Zhang, Y. J. Yu, X. Y. Liu, J. H. Miao*, Y. C. Han, J. Liu*, L. X. Wang, Adv. Mater., 2023, 35, 2211714.

Small molecule acceptor FM2 with all-fused-ring configuration achieves highly sensitive photodetection in near-infrared region.