Dark Current Suppression and Field‐Assisted Charge Extraction in Colloidal Quantum Dot Near‐Infrared Photodetectors Using Vertically Phase‐Separated Polymer Layers

Abstract Lead sulfide (PbS) colloidal quantum dots (CQDs) have emerged as promising materials for near‐infrared (NIR) and short wavelength infrared photodetection, owing to their cost‐effectiveness in production, and broadband absorption extending up to 1550 nm. This spectral range provides significant advantages for applications such as autonomous driving. However, the performance of PbS CQD‐based devices has been limited by their high leakage currents, especially under reverse bias, which limits detectivity and operational bandwidth. In this work, an innovative device architecture is proposed to substantially reduce dark current densities over a wide reverse bias voltage range. This approach integrates a multi‐barrier structure with interlayered polymer charge‐blocking layers within the CQD film, effectively suppressing leakage current and preventing breakdown under reverse bias. The CQD/polymer hybrid devices exhibit dark current densities as low as 2 × 10 −5 mA cm −2 under applied bias up to 5 V, and detectivity exceeding 6 × 10 12 Jones is consistently achieved between 3.5 and 6 V. This architecture also enables efficient field‐assisted charge extraction, leading to enhanced bandwidth reaching 660 kHz, far surpassing conventional CQD‐only devices. These results demonstrate a viable strategy to overcome the long‐standing trade‐off between detectivity and speed in NIR CQD photodetectors.