Novel Dark Current Reduction Strategy via Deep Bulk Traps for High-Performance Solution-Processed Organic Photodetectors.

The performance improvement of the organic photodetectors (OPDs) focuses on suppressing the dark current density ( J d ) to improve the specific detectivity. In this work, a dark current reduction strategy relying on constructing limited deep traps in the active layer to suppress charge injection rate was newly proposed. And an optimization method has been successfully demonstrated on the solution-processed OPDs accordingly. Compared with the J d expressed by the OPD with the shallow trap system, the device with deep bulk traps exhibits a dramatically reduced dark current while ensuring high responsivity. At a bias of -2 V, the optimized photodiode with a J d down to 1.4 × 10 -5 mA cm -2 and a maximum responsivity of 0.42 A W -1 @620 nm was realized, leading to a maximum detectivity calculated from shot noise of 6.23 × 10 12 Jones. This value is 49-fold higher than that of the original OPD with the same structure. The effects of deep traps inside the semiconductor film on injected carriers and photogenerated carriers are well explained by the relative positions of the initial hopping levels. A better understanding of charge transport regimes in OPD helps to open new approaches for constructing high-performance OPD toward practical applications.