Reverse-distribution phase featured gradient heterojunction: A universal strategy to realize high-performance near-infrared organic photodetectors for real-time arterial monitoring

Near-infrared (NIR) organic photodetectors (OPDs) play significant roles in night vision, optical communication and bio-imaging for low cost, easy fabrication and flexibility. However, their development is facing a serious challenge that efforts on suppressing typically high dark current density (JD) generally encounter photoresponse loss because of accompanying with less exciton generation or poorer carrier extraction. Here, novel structure and mechanism are pioneered to overcome that challenge: forming a reverse-distribution phase featured gradient heterojunction (RP-GHJ) to build an effective charge transport channel. In such structure, increased barriers are established to prevent unfavorable charge injection for suppressing JD. Additionally, photogenerated carriers are wrapped by anti-recombination region in reverse phase for efficient charge extraction. Therefore, RP-GHJ suppresses JD of NIR-OPDs to 8.48 × 10−9 A cm−2 which is far superior to 1.81 × 10−6 A cm−2 of traditional BHJ one (bias of −1 V) and simultaneously keeps high photoresponse. Consequently, RP-GHJ makes NIR-OPD realize stable-high detectivity over 1013 Jones at bias region from 0 to − 0.5 V and when the bias increases from − 0.5 to − 1 V, decrease of specific detectivity is slight (under 830 nm). And more importantly, a very large linear dynamic range of nearly 160 dB is obtained under 0 V bias. The structure is proven to be universally effective in NIR-OPDs and a highly sensitive arterial pulse monitoring is developed. The novel structure and mechanism provide a universal strategy for realizing high-performance NIR-OPDs and their real applications.