Disorder-Enabled Sub-bandgap Absorption in Ag2S Amorphous Nanodots for Dual-Band Infrared Photodetection

High-performance infrared photodetection is essential for emerging applications such as optical communication and night vision; however, extending the spectral response range beyond intrinsic bandgap limits remains a significant challenge for traditional crystalline materials. Herein, a facile synthesis of silver sulfide (Ag 2 S) crystalline nanodots (CNDs) and Ag 2 S amorphous nanodots (ANDs) to extend the responsive wavelength beyond the bandgap limits of conventional Ag 2 S colloidal quantum dots (CQDs) is reported. As compared to Ag 2 S-CNDs as the active layer, our dual-band infrared photodetector ITO/ZnO/PbS/Ag 2 S-ANDs/MXene/Au, in which the active layer of Ag 2 S-ANDs is in amorphous nanodots, exhibited dramatically superior performance of 100-fold higher photocurrent under 15.6 mW/cm 2 1550 nm illumination. As a result, a high specific detectivity of 2.32 × 10 13 Jones with a responsivity of 1.05 A/W is obtained from the photodetector ITO/ZnO/PbS/Ag 2 S-ANDs/MXene/Au under 0.2 μW/cm 2 980 nm illumination at 0 V, as well as a high specific detectivity of 4.47 × 10 11 Jones with a responsivity of 0.01 A/W under 8.5 μW/cm 2 1550 nm illumination, showing its higher performance among the top PbS CQD-based photodetectors. Therefore, this work demonstrates that amorphous inorganic nanomaterials offer a highly promising strategy for broadening the detection wavelength range for high-performance photodetectors.