Highly sensitive solution-processed organic photodetectors (OPDs) with a broadband response ranging from visible to near infrared (NIR) and excellent overall device performance are demonstrated. The OPDs were fabricated from a blend consisting of a wide-band gap polymer donor and a newly developed fused octacylic small-molecule electron acceptor with an acceptor-donor-acceptor structure, which shows relatively high and balanced hole/electron mobility and allows for a thicker photo-active layer (∼300 nm). In conjunction with the use of an optimized inverted device structure, the dark current density of the OPDs was suppressed to an ultralow level of (8.3 ± 5.5) × 10-10A cm-2 at a bias of -1 V and the capability to direct weak light intensity is down to 0.24 pW cm-2; both are among the lowest reported values for OPDs. Owing to the low shot noise enabled by the inverted structure and the low thermal noise due to the high shunt resistance of the device, the obtained OPDs show a spectrally flat photoresponse in the range of 350-950 nm (UV-vis-NIR) and a maximal specific detectivity (D*) of (2.1 ± 0.1) × 1013 Jones at 800-900 nm, which are among the best results of NIR OPDs reported to date and represents a highly sensitive photodetector for weak optical signal detection. Besides, the OPDs show a wide bandwidth of 30 kHz, a fast temporal response time around 12 us ∼14 us, and a large linear dynamic range of 106 dB.
Keywords: dark current density; non-fullerene acceptors; organic photodetectors; specific detectivity; weak optical signal detection.