Highly Photosensitive, Near Infrared Bulk‐Heterojunction Organic Photodiodes With Mg‐ and Li‐Doped ZnO Electron Transport Layer

ABSTRACT Near‐infrared (NIR) organic photodiodes (OPDs) are of increasing demand in applications such as security cameras, autonomous vehicles, and artificial vision systems. However, due to the inherently low bandgap of organic semiconductors used for NIR light absorption, high dark current remains a critical challenge. In this work, we propose a magnesium‐ and lithium‐doped ZnO (MLZO) as an electron transport layer (ETL) and hole‐blocking layer (HBL) to suppress dark currents in bulk‐heterojunction (BHJ) formed by the polymer donor of poly(benzothiadiazole) (PD2001) and non‐fullerene acceptor of dithienocyclopentathieno thiophene indone (PA940). The BHJ employing an MLZO ETL exhibits a very low dark current of 9.21 × 10 −10 A cm −2 and a high external quantum efficiency (EQE) of 58% and detectivity of 2.75 × 10 13 Jones at 950 nm. Note that the OPD with ZnO ETL exhibits the dark current of 1.23 × 10 −8 A/cm 2 . The device demonstrates fast response with rise and fall times of 42 and 72 µs, respectively. The photoabsorber consists of a BHJ with polymer PD2001 and PA940, which have bandgaps of 1.7 and 1.17 eV, respectively, and has broad light absorption over 400–1100 nm. Under 950 nm illumination at −2 V, the PD2001:PA940 BHJ exhibits a high sensitivity of 5.73 × 10 5 . With the BHJ OPD, a 5 × 5 image sensor array is demonstrated. These results support the application of MLZO ETL for NIR image sensors.