Tailoring a Back‐Contact Barrier for a Self‐Powered Broadband Kesterite Photodetector With Ultralow Dark Current Enabling Ultra‐Weak‐Light Detection

ABSTRACT Visible and near‐infrared photodetectors are widely used in intelligent driving, health monitoring, and other fields. However, the application of photodetectors in the near‐infrared region is significantly impacted by high dark current, which can greatly reduce their performance and sensitivity, thereby limiting their effectiveness in certain applications. In this work, the introduction of a C₆₀ back interface layer successfully mitigated back interface reactions to decrease the thickness of the Mo(S,Se)₂ layer, tailoring the back‐contact barrier and preventing reverse charge injection, resulting in a kesterite photodetector with an ultralow dark current density of 5.2 × 10⁻⁹ mA/cm² and ultra‐weak‐light detection at levels as low as 25 pW/cm². Besides, under a self‐powered operation, it demonstrates outstanding performance, achieving a peak responsivity of 0.68 A/W, a wide response range spanning from 300 to 1600 nm, and an impressive detectivity of 5.27 × 10¹⁴ Jones. In addition, it offers exceptionally rapid response times, with rise and decay times of 70 and 650 ns, respectively. This research offers important insights for developing high‐performance self‐powered near‐infrared photodetectors that have high responsivity, rapid response times, and ultralow dark current.