performance has gradually improved reaching a photoconversion efficiency of over 18%, [6] photo-active materials typically contain the toxic element Pb as in PbS or CsPbI 3 CQDs. [6][7][8][9][10] There have been endeavors to find suitable candidates having a band gap for efficient solar photoconversion replacing the current Pb-containing materials. [11][12][13][14][15][16] Based on the high absorptivity in the solar spectral range and high dielectric constant, AgBiS 2 CQD materials show great potential for nextgeneration thin-film photovoltaics. [11,[17][18] So far, the solar cells using AgBiS 2 CQDs present the highest power conversion efficiency (PCE) of 9.2%, while the PCEs using other lead-free CQD materials are still less than 5%. [19] Nevertheless, there is still room for further improvement in terms of efficiency and stability which will make it competitive.In particular, the conventional AgBiS 2 CQD solar cells have a problem in that their charge extraction is poor despite their excellent light absorption. For example, the carrier transport problem becomes more severe in a higher charge carrier density under light illumination. [11,20] Typical deviations from the ideal current density result from the low mobility of carriers or charge imbalance in the structure due to interfacial recombination. [21,22] Until recently, most efforts have focused on improving the structural or size homogeneity of AgBiS 2 CQDs during their synthesis, [19,23] or controlling the surface trapping of the synthesized CQDs by developing surface modification processes. [20,24] The increase in material property has led to an increase in the PCE to some extent, but the problem of recombination at the interface has not been investigated so far.Here, we introduce a hybrid mixture of a charge acceptor and donor at the interface to promote carrier extraction in AgBiS 2 CQD solar cells. [25][26][27] Specifically, we use a quantum dot polymer bulk heterojunction (QPB) film composed of a blend of AgBiS 2 CQD and PTB7 (Poly [[4,8-bis[(2-ethylhexyl)oxy] benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl) carbonyl]thieno[3,4-b]thiophenediyl]]) polymers at the hole collecting interface and present an efficient, robust AgBiS 2 CQD solar cells. The PCE of the QPB-AgBiS 2 solar cell is increased by up to 6.78% compared to cells without QPB Remarkable progress over the past decade in photovoltaics using solutionprocessed nanomaterials as light absorbers has placed colloidal quantum dot (CQD)-based devices on the map. As such, AgBiS 2 CQDs have garnered significant attention as materials exhibiting a high absorptivity with environmentally benign alternatives to Pb-chalcogenide or Pb halide perovskite-CQDs. Yet, AgBiS 2 CQD-based solar cells have gravely underperformed compared to Pb-containing devices, particularly in the metrics of charge carrier extraction from the AgBiS 2 absorber, hence its relative mediocrity. To specifically address the extraction efficiency, a bulk heterostructure (QPB) interlayer at the CQD/polymer interface i...

Various material properties change considerably when material is thinned down to nanometer thicknesses. Accordingly, researchers have been trying to obtain homogeneous thin films with nanometer thickness but depositing homogeneous few nanometers thick gold film is challenging as it tends to form islands rather than homogenous film. Recently, studies have revealed that treating the substrate with an organic buffer, (3-mercaptopropyl) trimethoxysilane (MPTMS) enables deposition of ultra-thin gold film having thickness as low as 5 nm. Different aspects of MPTMS treatment for ultra-thin gold films like its effect on the structure and optical properties at visible wavelengths have been investigated. However, the effect of the MPTMS treatment on electrical conductivity of ultra-thin gold film at terahertz frequency remains unexplored. Here, we measure the complex conductivity of nanometer-thick gold films deposited onto an MPTMS-coated silicon substrate using terahertz time-domain spectroscopy. Following the MPTMS treatment of the substrate, the conductivity of the films was found to increase compared to those deposited onto uncoated substrate for gold films having the thickness less than 11 nm. We observed 5-fold enhancement in the conductivity for a 7 nm-thick gold film. We also demonstrate the fabrication of nanoslot-antenna arrays in 8.2-nm-thick gold films. The nanoslot-antenna with MPTMS coating has resonance at around 0.5 THz with an electric field enhancement of 44, whereas the nanoslot-antenna without MPTMS coating does not show resonant properties. Our results demonstrate that gold films deposited onto MPTMS-coated silicon substrates are promising advanced materials for fabricating ultra-thin terahertz plasmonic devices.

We report on a prototypical study of the detection of microplastic embedded in table salts by using terahertz time-domain spectroscopy. In the experiment, high-density polyethylene (HDPE) of sizes from 150 to 400 μm are used as a representative microplastic and mixed with table salts. Analyzing terahertz transmittance with an effective medium model, we extract various optical properties such as refractive index, absorption coefficient, and real/imaginary parts of the dielectric constant of the mixture. Consequently, the optical properties exhibit volume-ratio-dependence in 0.1–0.5 THz regimes. Especially, the refractive index and the real part of the dielectric constant possess monotonic frequency dependence, meaning that the quantities can be relevant indicators for the detection of the microplastic in terms of practical applications. Our work proves that terahertz time-domain spectroscopy can pave a way to recognize microplastic mixed with salts and be expanded for detecting various micro-sized particles.