Cationic Molecular Metal Chalcogenide Ligand‐Passivated Colloidal Quantum Dots and Their Application to Suppressed Dark‐Current Near‐Infrared Photodetectors

The surface of colloidal‐type quantum dots (QDs) is protected with surfactants to maintain their nanoscale size and dispersion in various solvents. Such protection is advantageous to the processability of the dots, but the surfactants also act as insulators, thereby adversely affecting the electrical properties of the resulting devices. Anion‐type molecular metal chalcogenide complexes (MCCs) have been developed as an alternative to these surfactants. However, anionic ligands limit the charges of the resulting QDs to negative values; thus, additional processes are required to compensate for these charges. Herein, this work prepares cationic‐type dimetal diselenium perchlorate MCCs (M2Se2(ClO4)2, M = Mn, Zn, and Sn) and applies them to stabilize colloidal QDs. The resulting M2Se2‐PbS QDs are then used to fabricate near‐infrared photodetectors (NIR‐PDs). The devices exhibit remarkably suppressed dark current densities (JD) of as low as 4.92 × 10−10 A cm−2 when compared with PDs based on 1,2 ethandithiol‐PbS (EDT‐PbS) (JD = 1.41 × 10−8 A cm−2). In addition, the devices exhibit a high responsivity of 0.07 A W−1 in response to 950 nm NIR light signals, as well as an excellent specific detectivity of 5.66 × 1012 Jones at 950 nm. Finally, this work fabricates hybrid‐type QD films using cationic and anionic MCC‐PbS QDs and obtains a high external quantum efficiency (EQE) of 13.1%. This work reports the synthesis of M2Se22+ cationic metalchalcogenide ligands through exchange of metal cations such as Mn, Zn, and Sn on Na2Se2 ligands, and proceeds with ligand exchange to various quantum dots (QDs). Using them, this work reports the fabrication of near‐infrared (NIR; 950 nm) photodetector devices using Mn2Se2‐PbS QDs, and confirms that the Mn2Se2‐PbS has the characteristic of suppressing dark current compared with the conventional 1,2 ethandithiol‐PbS.