Manganese doped eco-friendly CuInSe2 colloidal quantum dots for boosting near-infrared photodetection performance

CuInSe2 (CISe) colloidal quantum dots (QDs) display promising applications in photodetection especially within near-infrared (NIR) regions due to their high extinction coefficient and environmental-friendly. However, the high trap density and poor crystal quality introduced by the ternary structure result in low photodetection of CISe QDs devices. Herein, we dope transition metal manganese ions (Mn2+) into CISe QDs to tackle the above problems. Structural characterization results demonstrate the crystal quality of CISe QDs is improved by doping Mn2+ during the synthesis of QDs. The transient absorption (TA) spectroscopic study together with the space-charge-limited current (SCLC) measurements show the charge carrier lifetime of Mn-CISe QDs is much longer than that of the CISe QDs, due to the Mn2+ doping state serve as hole capturer forming a charge-compensated pair with the Cu2+ defect that makes the long-lived Cu2+ radiative recombination dominate. Furthermore, Mn2+ doping concurrently modifies the conduction band minimum and valence band maximum level of the QDs verified by the ultraviolet photoelectron spectroscopy (UPS), which determines the driving force for charge carrier transfer to acceptors. The optimal Mn2+ doping level (0.01 Mn:Cu feed ratio) balanced the above two factors in the QDs. The detector based on such Mn-CISe QDs exhibits responsivity of 30 mA/W and specific detectivity of 4.2 × 1012 Jones at near-infrared wavelength, the response speed of 0.76 µs, and suppressed dark current density of 1.6 × 10−10 A cm−2.