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 (Ag2S) crystalline nanodots (CNDs) and Ag2S amorphous nanodots (ANDs) to extend the responsive wavelength beyond the bandgap limits of conventional Ag2S colloidal quantum dots (CQDs) is reported. As compared to Ag2S-CNDs as the active layer, our dual-band infrared photodetector ITO/ZnO/PbS/Ag2S-ANDs/MXene/Au, in which the active layer of Ag2S-ANDs is in amorphous nanodots, exhibited dramatically superior performance of 100-fold higher photocurrent under 15.6 mW/cm2 1550 nm illumination. As a result, a high specific detectivity of 2.32 × 1013 Jones with a responsivity of 1.05 A/W is obtained from the photodetector ITO/ZnO/PbS/Ag2S-ANDs/MXene/Au under 0.2 μW/cm2 980 nm illumination at 0 V, as well as a high specific detectivity of 4.47 × 1011 Jones with a responsivity of 0.01 A/W under 8.5 μW/cm2 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.