Search

Simultaneous realization of high quality factor (Q), sensitivity, and figure of merit (FOM) play a pivotal role in building the THz sensor. For such purpose, we propose an all-polymeric Bloch surface wave (BSW) structure that supports a bright BSW mode and a dark surface Fano state that is embedded in the continuum, both of which coupled to the same radiation channels. The existence of the sharp dip with a maximum depth of Fano line could be interpreted with the physics of Friedrich–Wintgen bound states in the continuum (FW-BICs), because of the destructive interference between bright BSW and dark surface Fano modes. A strong angular- and frequency-dependent Q was found. Related influential factors to Q value may also include an asymmetric arrangement of top and grating layers, together with the weak coupling provided by photonic crystals. One numerically optimized design shows a quality factor Q of the Fano mode as 23,670, which is almost two orders higher than that in conventional metallic-metamaterial-based designs. The optimized sensitivity can numerically reach 4.34 THz/RIU in the frequency domain, which is one order higher than that reported in all-dielectric metasurfaces. We infer the high sensitivity is related to the phase-matching condition provided by near-subwavelength gratings. The associated FOM can reach 8857/RIU. Besides, the proposed design also numerically demonstrates high sensitivity in the angular domain ∼125.5°/RIU. Considering it poses no specific requirement for materials that own high contrast of permittivity in the THz regime, large interfacing area, the mechanical and chemical robustness offered by polymers and low cost in fabrication, such all-polymeric BSW structure that supports novel Fano resonance in THz window may give access to rich applications in hazardous gas detection and label-free bio-sensing.

Terahertz metamaterial sensing (TMS) is a new interdisciplinary technology. A TMS system employs terahertz waves as the pumping source, these then interact with the sample and carry the substance information, e.g., refractive index, absorption spectra. These properties are relevant to the molecular rotation and vibration states produced by a surface‐plasmon‐polariton‐like effect. TMS technology is usually characterized by large penetration depth and high sensitivity. Owing to these advantages, TMS may be used for ultratrace detection and consequently has a wide range of practical applications in biomedicine, food safety, environmental monitoring, industry and agriculture, material characterization, and safety inspection. Furthermore, TMS performance is determined not only by the structural topology of metamaterials, but also by their compositions and substrates. This paper reviews the essential fundamentals, relevant applications, and recent advances in TMS technology with a focus on the influence of material selection on TMS performance. This review is envisaged to be used as a key reference for developing TMS‐based functional devices with enhanced characteristics. [ABSTRACT FROM AUTHOR]

Two solution-processableacceptor–donor–acceptor(A-D-A) structured organic molecules with bithienyl-substituted benzodithiophene(BDTT) as central and donor unit, indenedione (ID) as acceptor unitand end groups, and thiophene (T) or bithiophene (bT) as π-bridges,D1 and D2, are designed and synthesized for the application as donormaterials in organic solar cells (OSCs). Two corresponding moleculeswith alkoxy side chains on BDT, DO1, and DO2 are also synthesizedfor comparison. The four compounds possess broad absorption coveringthe wavelength range 450–740 nm and relatively lower HOMO energylevels from −5.16 to about −5.19 eV. D2 and DO2 withbithiophene π-bridges demonstrate stronger absorbance and higherhole mobilities than the compounds with thiophene π-bridges.The power conversion efficiency (PCE) values of the OSCs based onthe organic compounds/PC70BM (1.5:1, w/w) are 6.75% forD2, 5.67% for D1, 5.11% for DO2, and 4.15% for DO1. The results indicatethat the molecules with thienyl conjugated side chains and bithiopheneπ-bridges show better photovoltaic performance. The PCE of theD2-based OSC are among the highest values in the OSCs based on thesolution-processed organic small molecules. [ABSTRACT FROM AUTHOR]

Hybrid nanostructured silicon–organic solar cells have been pursued as a low‐cost solution for silicon photovoltaic devices. However, it is difficult for the organic semiconductor, typically poly(3,4‐ethylenedioxythiophene):polystyrene (PEDOT:PSS), to fully cover the nanostructured silicon surface due to the high surface tension of the polymer solution and the small size of the cavities in nanostructured silicon. As a result, the performance of the hybrid solar cells is limited by the defect‐induced surface recombination and poor hole extraction. In this work, an inorganic hole‐transporting layer, copper(I) thiocyanate (CuSCN), is introduced between silicon nanowire (SiNW) and PEDOT:PSS to improve the junction quality. The effect of CuSCN on as‐fabricated SiNW and tetramethylammonium hydroxide (TMAH)‐treated SiNW structures is examined, and it is shown that in both cases CuSCN can well cover the SiNW surface due to the easy penetration of its solution into the silicon nanostructure. As a result, the power conversion efficiency of the solar cells has been dramatically improved from 7.68% to 10.5% for as‐fabricated SiNW‐based‐hybrid cells, and from 10.75% to 12.24% for TMAH‐passivated SiNW‐based‐hybrid cells, suggesting that the double hole‐transporting layer approach can effectively improve the junction quality in hybrid organic‐nanostructured silicon‐based devices. An inorganic hole‐transporting layer, copper(I) thiocyanate (CuSCN), is introduced between silicon nanowire (SiNW) and poly(3,4‐ethylenedioxythiophene):polystyrene (PEDOT:PSS) to improve the junction quality. The power conversion efficiency of the solar cells has been dramatically improved 10.75–12.24%, suggesting that the double hole‐transporting layer approach can effectively improve the junction quality in hybrid organic‐nanostructured silicon based devices. [ABSTRACT FROM AUTHOR]