Organic photodetectors (OPDs) have attracted extensive attention due to their high flexibility, strong adaptability, lowcost, and compatibility with large-scale manufacturing technologies. However, achieving high specific detection (D*) and mechanical flexibility remains a challenge for flexible non-fullerene OPDs. A well-designed cathode interfacial layers (CILs) with good flexibility and stability is essential. Herein, a flexible CIL of tin ion-chelated polyethyleneimine ethoxylated (denoted as PEIE-Sn) is presented, which can effectively endow the devices with optimized cascade alignment and improved interface compatibility. The resulting flexible OPD exhibits an external quantum efficiency (EQE) of 59% and specific detectivity (D*) of 7.95*1012 Jones (720 nm, -0.5 V) with a slight change after 1500 bending cycles. OPD has been validated through heart rate monitoring using the photoplethysmography (PPG) method, demonstrating its potential application in wearable devices.
Reducing the dark current density (Jd) of organic photodetectors (OPD) is an effective way to improve some important figures of merits such as on-off ratio and specific detectivity (D*). Many studies have demonstrated that increasing the thickness of the active layer can effectively reduce the Jd of OPD, but at the same time it can cause a sharp decrease in responsivity and external quantum efficiency (EQE). In this work, a preheating spin coating method was used on the thick bulk-heterojunction (BHJ) active layer, which is composed of a polymer donor PBDB-T and a non-fullerene acceptor (NFA) Y6 with near-infrared (NIR) absorption. As a result, the thick BHJ OPD maintains a low Jd while the responsivity and EQE are greatly improved, therefore the optimized devices display a high D* over 1012 Jones at -0.5 V from 400 nm to 900 nm, indicating its application potential in visible-to-NIR detection. This work provides an effective strategy to enhance the performance of thick BHJ devices.
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