An ultra-low dark current AgBiS ₂ CQDs NIR photodetector using ZnO/MXenes bilayer electron transport layer for image sensor

AgBiS₂ colloidal quantum dots (CQDs) possess excellent optoelectronic properties, including high absorption coefficient, environmental friendliness, and facile solution processability. They are regarded as promising candidates to replace toxic Pb and Hg-based CQDs in the field of optoelectronics. However, the energy-levels mismatch between electron transport layer (ETL) and photoactive layer in AgBiS₂ CQDs photodetector affecting the performance of the device. To address this challenge, this study introduces ZnO/MXene bilayer ETL to optimize the interface energy-level alignment. A broad-spectrum, high-performance AgBiS₂CQDs photodetector has been realized, exhibiting an ultra-low dark current density of 6.1 × 10⁻⁸ A cm⁻², a broad detection spectrum ranges from 375 to 1120 nm, a specific detectivity (D*) of 7.8 × 10¹⁰ Jones at 980 nm, and a large linear dynamic range (LDR) of 80 dB. The device of bilayer ETL enhances the D* by 3.5 to 7 times compared to the control device by improving charge extraction and suppressing carrier recombination. Furthermore, integrating the photodetector with a thin-film transistor (TFT) array enables high-quality imaging under 850 nm near-infrared (NIR) illumination, demonstrating its significant potential for advanced image sensor applications.