Search

Extended shortwave infrared (eSWIR) photodetectors that employ solution‐processable semiconductors have attracted attention for use in applications such as ranging, night vision, and gas detection. Colloidal quantum dots (CQDs) are promising materials with facile bandgap tunability across the visible‐to‐mid‐infrared wavelengths. However, toxic elements, such as Hg and Pb, and the slow response time of CQD‐based IR photodetectors, limit their commercial viability. This article presents a novel eSWIR photodetector that is fabricated using silver telluride (Ag2Te) CQDs. Effective thiolate ligand exchange enables a lower trap density and improved carrier mobility in CQD solids. Furthermore, a vertical p‐n photodiode architecture with a favorable energy‐level landscape is utilized to facilitate charge extraction, resulting in a fast, room‐temperature‐operable, and toxic‐element‐free CQD photodetector. The best eSWIR Ag2Te CQD photodetector exhibits a fall time of 72 ns, representing the fastest response time among all prior CQD‐based eSWIR photodetectors, including those containing toxic elements, such as Pb and Hg. [ABSTRACT FROM AUTHOR]

Infrared (IR) optoelectronics have become important owing to their various applications, such as recognition, autonomous driving, and quantum communications. In particular, detection beyond 1400‐nm wavelength in the shortwave IR (SWIR) spectrum (i.e., 1550 nm) is important for eye safety, and long‐range communication. Recently, group III–V (InAs or InSb) colloidal quantum dots (CQDs) have attracted considerable interest due to their broadband optical tunability and toxic‐elements (Pb and Hg)‐free properties. Herein, a new approach is developed to synthesize highly monodispersed InSb CQD by employing the continuous injection method, which enables facile optical bandgap tuning at a SWIR wavelength of up to 0.9 eV. Furthermore, solution ligand exchange using halides and thiolates results in effective passivation of the InSb CQD surface and renders a stable p‐type CQD ink. Finally, bulk heterojunction (BHJ) structure is demonstrated using n‐type InAs:p‐type InSb CQDs, which exhibits broad absorption up to 1600 nm, and a sixfold higher responsivity compared with the pristine InSb CQD device due to the efficient charge transport in BHJ CQD solids. [ABSTRACT FROM AUTHOR]

Solution‐processed low‐bandgap semiconductors are crucial to next‐generation infrared (IR) detection for various applications, such as autonomous driving, virtual reality, recognitions, and quantum communications. In particular, III–V group colloidal quantum dots (CQDs) are interesting as nontoxic bandgap‐tunable materials and suitable for IR absorbers; however, the device performance is still lower than that of Pb‐based devices. Herein, a universal surface‐passivation method of InAs CQDs enabled by intermediate phase transfer (IPT), a preliminary process that exchanges native ligands with aromatic ligands on the CQD surface is presented. IPT yields highly stable CQD ink. In particular, desirable surface ligands with various reactivities can be obtained by dispersing them in green solvents. Furthermore, CQD near‐infrared (NIR) photodetectors are demonstrated using solution processes. Careful surface ligand control via IPT is revealed that enables the modulation of surface‐mediated photomultiplication, resulting in a notable gain control up to ≈10 with a fast rise/fall response time (≈12/36 ns). Considering the figure of merit (FOM), EQE versus response time (or −3 dB bandwidth), the optimal CQD photodiode yields one of the highest FOMs among all previously reported solution‐processed nontoxic semiconductors comprising organics, perovskites, and CQDs in the NIR wavelength range. [ABSTRACT FROM AUTHOR]

Solution‐processed ternary‐compound semiconductor AgBiS2 colloidal quantum dots (CQDs) are promising light‐absorbing materials owing to their nontoxicity and high absorption coefficient (>106 cm−1). However, rational strategies to passivate multi‐facet of ternary‐compound CQDs and manufacture stable CQD inks have not yet been proposed. In this paper, a ligand passivation strategy is proposed using a solution‐phase ligand exchange method. A quadruple‐ligand ensemble is employed to demonstrate multifaceted passivation on AgBiS2 CQDs and a highly stable CQD ink. Density functional theory studies reveal the secondary cation adsorption of silver halide passivation, indicating the synergistic passivation of the ligand ensemble. This yields a low trap density in CQD solids, improving the power conversion efficiency to 8.1% by 53% in CQD solar cells. Furthermore, the proposed device exhibits the fastest response time of 400 ns among all reported AgBiS2 devices, demonstrating its potential for efficient lead‐free optoelectronics. [ABSTRACT FROM AUTHOR]

The fabrication of heterostructures via solution process is one of the essential technologies for realizing efficient advanced-generation optoelectronics. Hybrid structures comprising colloidal quantum dots (CQD) and organic semiconducting molecules are garnering considerable research interest because of their complementing optical and electrical properties. However, blending both the materials and forming a stable electronic ink are a challenge owing to the solubility mismatch. Herein, a CQD:organic ternary-blended hybrid solar ink is devised, and efficient hybrid solar cells are demonstrated via single-step spin coating under ambient conditions. Specifically, the passivation of the benzoic acid ligand on the CQD surface enables the dissolution in low-polar solvent such as chlorobenzene, which yields a stable CQD:organic hybrid ink. The hybrid ink facilitates the formation of favorable thin-film morphologies and, consequently, improves the charge extraction efficiency of the solar cells. The resulting hybrid solar cells exhibit a power conversion efficiency of 15.24% that is the highest performance among all existing air-processed CQD:organic hybrid solar cells. [ABSTRACT FROM AUTHOR]