Optical Absorption Efficiency Research Articles

Bias‐Selectable Si Nanowires/PbS Nanocrystalline Film n–n Heterojunction for NIR/SWIR Dual‐Band Photodetection

AbstractIn this study, a solution method derived dual‐band photodetector (PD) based on silicon nanowires /PbS nanocrystalline film n–n heterojunction, which exhibits typical bias‐selectable spectral response in both near‐infrared (NIR) and short‐wave infrared (SWIR) bands, is presented. It is found that by adjusting the polarity of the bias voltage, the photoresponse of the device can be switched between three operation modes. The device exhibits high responsivities of 2100 mA W−1 at −0.15 V and 31 mA W−1 at 0 V, respectively, in the NIR region. Remarkably, the maximum responsivity and detectivity under 2000 nm illumination are determined as 290 mA W−1 and 2.4 × 1010 Jones, comparable to or even better than some PbS commercial PDs. The enhanced performance comes from the improved optical absorption and higher efficiency of charge separation and collection owing to the heterojunction geometry. It's also revealed that the bias‐controllable spectral response is attributed to the selectively transportation of photocarriers across the junction barrier. The study demonstrates the capability of detecting two distinct IR regions with the same pixel, which has great potential in future optoelectronic systems for IR imaging applications.

Metal-organic framework single crystal infrared photodetector

Metal–organic frameworks (MOFs) are an emerging class of functional materials possessing the coupled optical and electrical responses necessary for the operation of modern optoelectronic devices. Yet, the realization of near infrared MOF-based photodetector is still a challenge. Here, we report on the MOF single crystal photodetector with 600–1000 nm spectral range, overlapping with the efficient optical absorption of the MOF (HKUST-1), converting the light energy to electric one. We detect that 0.1 s response rate of the detector turned out to be higher than the previously announced MOF-based photodetectors, that is due to the fairly fast and reversible process of desorption of coordinated water molecules underlying the mechanism of charge carrier generation. We also confirm the 1 mJ cm−2 fluence for the threshold photodetection due to a photostimulated change in the optical properties of the MOF, rather than its degradation, which paves the way to fast and multiple detection of a low-intensity infrared laser light on the MOF single crystal.

Lead halide perovskite sensitized WSe2 photodiodes with ultrahigh open circuit voltages

Two-dimensional semiconductors (2DSCs) have attracted considerable interests for optoelectronic devices, but are often plagued by the difficulties in tailoring the charge doping type and poor optical absorption due to their atomically thin geometry. Herein, we report a methylammonium lead iodide perovskite (CH3NH3PbI3)/2DSC heterojunction device, in which the electric-field controllable ion migration in the perovskite layer is exploited to induce reversible electron- and hole-doping effects in the underlying monolayer tungsten diselenide (WSe2) to form a programmable p–n photodiode. At the same time, the CH3NH3PbI3 layer functions as a highly efficient sensitization layer to greatly boost the optical absorption and external quantum efficiency (EQE) of the resulting photodiode. By asymmetrically poling the perovskite layer, gold-contacted CH3NH3PbI3/WSe2 devices show a switchable open circuit voltage up to 0.78 V, along with a high EQE of 84.3%. The integration of tunable graphene-contacts further improves the photodiode performance to achieve a highest open circuit voltage of 1.08 V and a maximum EQE of 91.3%, greatly exceeding those achieved previously in 2DSC lateral diodes. Our studies establish a non-invasive approach to switch optoelectronic functions and open up a new avenue toward high-performance reconfigurable optoelectronic devices from 2DSCs.

Computational analysis of optical absorption efficiency and photothermal effect of Fe3O4/Au and Fe3O4/Ag core/shell spherical nanoparticles for thermoplasmonics applications

We present a detailed theoretical analysis of the temperature rise in the vicinity of an illuminated magnetite/gold and magnetite/silver core/shell nanospheres submerged in water. The computation is performed under the Lorenz theory and the electrostatic-thermal transfer analogy approach to derive the steady-state temperature distribution in the vicinity of the nanoparticle. Localized surface plasmon resonances are found to be the most efficient in photothermal effect, as expected. The gold and silver nanospheres allow a significant, almost uniform temperature rise at their vicinities, but with spectrally localized stimulating light, around 389 and 535 nm, respectively. An equally important photothermal effect can be obtained by magnetite/gold and magnetite/silver core/shell nanospheres. The most interesting is the tunability of the frequency of stimulating light from ultraviolet to near infrared by a simple adjustment of the global diameter of the nanosphere and the relative thickness of its shell. The distribution of the temperature rise over the plasmonic shell-water interface deviates from a uniform distribution for an increasingly small relative shell thickness.

Topological insulator-based nonlinear optical effects and functional devices

Topological insulators (TIs) are a new type of electronic material with the insulating bulk state and topologically protected conducting surface/edge state. TI materials exhibiting outstanding optical properties containing high carrier mobility, ultrahigh refractive index, wide operating spectral range, and dynamic tunability play an important role in optical functional devices. Especially, the TI materials with special topological energy bands possess high nonlinear optical coefficient, superior to conventional semiconductor and two-dimensional materials. The nonlinear optical characters of TIs are expected to realize highly efficient nonlinear optical conversion, nonlinear absorption, and all-optical switching, terahertz emission. TIs will provide a new platform for the interaction between light and matter as well as the development of nonlinear optics. In this review, we conclude current advances about some research on TI-based nonlinear optical effects and related devices, and give a prospect of potential applications for TIs in nonlinear optics.

Realization of photocatalytic hydrogen production by optimizing energy band structure and promoting charges separation over the S-doped CoFe2O4 microrods

As a green, renewable, and clean energy acquisition technology, photocatalytic water splitting to produce hydrogen exhibits high potential in the efficient utilization of solar energy. Herein, S-doped CoFe2O4 microrods were prepared by a simple water bath sulphuration method. The characterization results show that with the increase of S-element doping, the optical absorption and charge separation efficiency of CoFe2O4 microrods are significantly improved. In addition, the upward shift of conduction band (CB) after sulphuration in S-doped CoFe2O4 promotes its optical reduction potential to increase, and then can achieve the photocatalytic water splitting to produce hydrogen without any cocatalyst. Density functional theory (DFT) calculations also confirm that the doping of S in CoFe2O4 can adjust the band structure, promote the upward shift of CB, and accelerate the carrier separation efficiency. These findings suggest the infinite potential of S-doped CoFe2O4 photocatalyst and solar energy for water splitting.

Excellent surface plasmon and hot carrier properties of transition metal nitride at different temperatures

Plasmonic materials that exhibit excellent plasmonic behavior at high temperatures would greatly expand existing applications, but the search for such materials is ongoing. Transition metal nitrides with good conductivity and high-temperature stability are promising candidates for temperature-dependent plasmonic applications. Here, we systematically investigate the temperature-dependent surface plasmon and hot carrier properties of TiN and VN. Significantly, high temperatures significantly affect the phonon-assisted intraband transition processes. Meanwhile, TiN and VN exhibit efficient optical absorption and low surface plasmon loss at different temperatures, which are comparable to or even higher than Ag. In particular, the surface plasmon response of TiN extends to visible light, making it an excellent candidate for low-loss and broadband plasmonic applications at high temperatures. In contrast, VN exhibits a much narrower plasmonic window, which is mainly suitable for infrared low-loss plasmonic devices. For hot carriers, the energy and probability distributions of hot holes in TiN and hot electrons in VN exhibit robustness to temperature. Meanwhile, transport properties indicate that the temperature effect on hot holes is significantly higher than that on hot electrons in TiN and VN. Therefore, we expect that the reported results will provide theoretical guidance for the design of next-generation high-temperature plasmonic devices.

Recent Development of Carbon-Nanotube-Based Solar Heat Absorption Devices and Their Application.

Population growth and the current global weather patterns have heightened the need to optimize solar energy harvesting. Solar-powered water filtration, electricity generation, and water heating have gradually multiplied as viable sources of fresh water and power generation, especially for isolated places without access to water and energy. The unique thermal and optical characteristics of carbon nanotubes (CNTs) enable their use as efficient solar absorbers with enhanced overall photothermal conversion efficiency under varying solar light intensities. Due to their exceptional optical absorption efficiency, low cost, environmental friendliness, and natural carbon availability, CNTs have attracted intense scientific interest in the production of solar thermal systems. In this review study, we evaluated CNT-based water purification, thermoelectric generation, and water heating systems under varying solar levels of illumination, ranging from domestic applications to industrial usage. The use of CNT composites or multilayered structures is also reviewed in relation to solar heat absorber applications. An aerogel containing CNTs was able to ameliorate water filtering performance at low solar intensities. CNTs with a Fresnel lens improved thermoelectric output power at high solar intensity. Solar water heating devices utilizing a nanofluid composed of CNTs proved to be the most effective. In this review, we also aimed to identify the most relevant challenges and promising opportunities in relation to CNT-based solar thermal devices.

Strongly reduced optical absorption efficiency of soot with addition of potassium chloride in sooting premixed flames

Optical properties of soot have been investigated with and without potassium chloride (KCl) salt added to the soot formation process in a premixed ethylene/air flame. A strong decrease in optical absorption efficiency of the soot was observed with increasing amounts of KCl added to the fuel based on the method of fluence curve analysis using laser-induced incandescence (LII). To understand the reason for this major change in absorption efficiency, probe sampling and subsequent structural analysis were performed using Raman spectroscopy and high-resolution transmission electron microscopy (HRTEM). Raman spectra indicated no significant difference between the nanostructure of soot from the two main cases; a reference case without addition of salt, and a case with addition of ∼600 ppm K. In the case of K addition, HRTEM showed slightly less compact nanostructure signified by somewhat shorter interlayer spacing, and significantly different polar ordering of carbon lamellae indicating smaller primary particles, thereby supporting previous TEM studies on soot sampled from the same flames showing smaller soot particle sizes with KCl addition. The impact on soot absorption properties from the observed differences is discussed. It is speculated that the main cause for the lower absorption with K addition is a quantum confinement effect due to reduction in soot particle size.

Optoelectronic properties and ion diffusion mechanism in 2D perovskites Cs3BX5 (B = Ge, Sn, and Pb; X = Cl, Br, and I): A first–principles investigation

Mitigating ion migration is a big challenge for optoelectronic perovskite materials. In this work, we investigate a novel family of layered halide perovskites Cs3BX5 (B = Ge, Sn, and Pb; X = Cl, Br, and I) by first–principles calculations. These compounds exhibit direct bandgap and small effective masses of electrons and holes. The optical absorption and spectroscopic limited maximum efficiency suggest the promising potential for these materials in solar energy conversion. The suppressed ionic conductivity has also been demonstrated by the higher energy barriers of halide ions migrations, which would be conducive to mitigate the hysteresis in perovskite solar cells.

Bandgap engineering in BP/PtO2 van der Waals (vdW) hetero-bilayer using first-principles study

Based on the motivation of the recent advancement of the van der Waals heterostructure (vdW HBL), we have studied the tunable optoelectronic properties of the two-dimensional (2D) boron phosphide–platinum di-oxide (BP/PtO2) heterostructure using dispersion corrected density functional theory (DFT). Six different stackings are considered to stack the 2D BP upon 2D PtO2 and are tested through DFT. Phonon spectra and binding energy calculation validate the dynamical and chemical stability of the constructed heterostructures. It is found that HBL1, HBL3, and HBL4 have type-II indirect band gaps of 0.001, 0.027, and 0.021 eV, respectively whereas the other HBLs 2, 4, and 5 show a semiconductor–metal transition. The variation in the interlayer distances, cross-plane electric field, and biaxial strain can effectively tune the bandgap, although type-II band alignment remains unaffected in all cases. A large built-in electric field, of ∼15 eV in electrostatic potential between the 2D structures and type-II band alignment of the HBL, suggests efficient separation of charges in all the HBLs. The bandgaps are highly responsive to the interlayer distances, electric field, and biaxial strain in the HBL. It is found that the bandgap increases under the application of compressive strain and an external electric field along the negative z-direction up to −0.4 V/Å. Interestingly, a semiconductor–metal transition occurs for tensile strain and the external electric field along the positive z-direction. All HBLs have efficient optical absorption in the visible and UV portions of the solar spectra, which is highly anticipated for optoelectronics applications. These unrivaled properties of the vdW BP/PtO2 HBL that we have explored make them a promising candidate for nano-electronic devices and infrared detector applications.

Efficient interfacial charge transfer of BiOCl-In2O3 step-scheme heterojunction for boosted photocatalytic degradation of ciprofloxacin

• Step-scheme In 2 O 3 -BiOCl heterojunctions were synthesized by molten salt method. • Molten-salt method without organic solvent for the BiOCl-In 2 O 3 composites could endow clean surface, which is beneficial to the adsorption of reactants in the photocatalytic degradation process. • In 2 O 3 -BiOCl heterojunctions exhibited excellent photocatalytic degradation of ciprofloxacin. • Boosting photocatalytic performance is due to the formation of step-scheme heterojunction. • • O 2− and H + played critical roles in photocatalytic degradation process of ciprofloxacin. BiOCl as a representative layered bismuth-based photocatalyst with Sillén-structure has aroused wide public concern on photocatalytic degradation. However, the photocatalytic efficiency of pristine BiOCl is currently restricted by its low optical absorption and charge separation efficiency. Herein, step-scheme (S-scheme) heterojunctions of In 2 O 3 nanoparticle and BiOCl micron-sheet were constructed by a convenient molten salt method by using a LiNO 3 -KNO 3 system. The In 2 O 3 -BiOCl heterojunctions exhibit higher optical absorption performance from 380 nm to 700 nm than the pristine BiOCl and enhanced photocatalytic property toward ciprofloxacin (CIP) degradation under Xenon lamp illumination. The sample 20%In 2 O 3 -BiOCl showed the highest photodegradation efficiency, attaining 91% removal of CIP within 35 min, which was 39.6 times and 3.2 times higher than that of pristine In 2 O 3 and BiOCl, respectively. The improved photodegradation property mainly resulted from the novel S-scheme mechanism, which boosted highly efficient separation of the photo-induced carriers. The photoluminescence spectrometric test and transient photocurrent response results demonstrated that In 2 O 3 -BiOCl composite exhibited efficient separation of photo-generated charge carriers. This work would provide new insights into the design of novel S-scheme photocatalytic systems with applicability in photocatalytic water treatment.

Improving Photoelectric Conversion with Broadband Perovskite Metasurface.

The miniaturization and integration of optoelectronic devices require progressive size reduction of active layers, resulting in less optical absorption and lower quantum efficiency. In this work, we demonstrate that introducing a metasurface made of hybrid organic-inorganic perovskite (HOIP) can significantly enhance broadband absorption and improve photon-to-electron conversion, which roots from exciting Mie resonances together with suppressing optical transmission. On the basis of the HOIP metasurface, a broadband photodetector has been fabricated where photocurrent boosts more than 10 times in the frequency ranging from ultraviolet to visible. The device response time is less than 5.1 μs at wavelengths 380, 532, and 710 nm, and the relevant 3 dB bandwidth is over 0.26 MHz. Moreover, this photodetector has been applied as a signal receiver for transmitting 2D color images in broadband optical communication. These results accentuate the practical applications of HOIP metasurfaces in novel optoelectronic devices for broadband optical communication.

Five-layer planar hot-electron photodetectors at telecommunication wavelength of 1550 nm.

Cost-effective and high-responsivity photodetectors at a telecommunication wavelength of 1550 nm are highly desired in optical communication systems. Differing from conventional semiconductor-based photodetectors, several planar hot-electron photodetectors (HE PDs) that operate at 1550 nm have been reported. However, these devices were often comprised of many planar layers and exhibited relatively low responsivities. Herein, we propose a design of high-performance planar HE PDs consisting of five layers. Utilizing Fabry-Pérot (FP) resonance, the nearly perfect absorption of the proposed device can be achieved at the targeted wavelength of 1550 nm. Simulation results show that FP resonance orders are crucial for the optical absorption efficiencies, and then electrical responses. Analytical electrical calculations reveal that, benefiting from the strong absorption (>0.6) in the ultrathin Au layer with a thickness of 5 nm and the low Schottky barrier (0.5 eV) of Au-MoS2 contact, predicted responsivity of proposed HE PD at zero-order FP resonance is up to ∼10 mA/W. Our design provides a new approach to realize low-cost and efficient photodetection for optical communication technology.

Investigation of Quantum Size Effects on the Optical Absorption in Ultrathin Single Quantum Well Solar Cell Embedded as a Nanophotonic Resonator

Subwavelength optical nanocavity using semiconductor nanostructures is a key nanophotonic approach for various optoelectronic devices. In such low-dimensional systems, size-dependent changes can arise due to quantum confinement (QC). In this article, the implications of quantum-size effects on the light harvesting in ultrathin single quantum well solar cell (SQWSC) are analyzed. This device is based on silicon (barrier)/germanium (QW) nanostructures integrated as a deep-subwavelength nanophotonic resonator. Compared with the state-of-the-art, the novelty of this article consists of the investigation of the synergy between photonic and electronic confinements at both functional materials and device levels. It is shown that QC effects enhance the optical absorption efficiency in both low-dimensional germanium single layers and QW structures. However, this is affected by the barrier heights and the interface states. In the SQWSC devices, the changes of the photocurrent output, the resonance condition and the absorption edge as a function of QW thickness are explained based on the optical field and the local absorption distributions. Shorter nanocavity lengths with thinner QW nanoabsorbers result in blue-shifted resonance wavelength, suitable maximum optical field intensity in the visible wavelengths range as well as promoted photonic confinement. This enables an enhancement of the optical absorption efficiency relative to thick counterparts. The nonlinearity in the thickness-related photocurrent implies a drastic reduction in QW thickness while preserving a high photocurrent level. The presented considerations in SQWC could be extended as design rules for the optimization of the photocurrent in derived multiple quantum well systems and for relevant color-neutral semitransparent devices.

Perovskite solar cell with light trappers fabricated by double metal cladding waveguide technology

Local surface plasmon resonance (LSPR) based on metal nanostructures was widely used in enhanced light capture and light absorption. In addition, LSPR can also facilitate processes such as exciton dissociation and charge transfer (CT) in solar cells. We developed perovskite solar cells (PSCs) by coating chips with hexagon-like nanostructures on the backside of Indium tin oxide (ITO) conductive glass using the double metal cladding waveguide (DMCW) technology. The optical absorption and photoelectric conversion efficiency (PCE) of the PSCs with different morphologies of chips were analyzed. The LSPR of the chips corresponded with the absorption capacity of perovskite. LSPR enhanced the scattering, gathering, and capture of light energy. Because the strong absorption rates at the long wavelengths after 600 nm in the ultraviolet visible (UV–Vis) spectrum, the properties of PSCs with the chips are improved. The PCE and short circuit current density (Jsc) increased by 27.21%, and 6.78%, respectively, attributed to the increase in the optical path of incident light and the light absorption capacity of the active layer.

Design and analysis of III-V two-dimensional van der Waals heterostructures for ultra-thin solar cells

Van der Waals (vdW) heterostructures consist of six group III-V monolayers MX (M = Ga, In, X = P, As, Sb) have been systematically investigated via hybrid functional HSE06 based on DFT calculations in order to evaluate their utilities in potential solar cell materials. 24 different stacking configurations for the 15 heterostructures each, with a total of 360 different structure models, are designed and discussed. These vdW heterostructures are found to be energetically favorable with formation energies, calculated using DFT-D3 method, vary from −1.5 eV to 0.5 eV. The energetic and electronic properties of these heterostructures are examined. Our results show that the stacking model BB-3 for most heterostructures holds suitable type-II bandgaps around 1.1 eV, which guarantee the potential for solar cell applications. Furthermore, the power conversion efficiencies (PCEs) for GaSb/InSb and GaAs/InAs are found to reach 22.88% and 20.65% respectively. The optimal bandgap size, efficient optical absorption with ultrahigh photoresponsivity enable these materials to be promising candidates in optoelectronic devices.

Moisture Stability of Perovskite Solar Cells Processed in Supercritical Carbon Dioxide.

Performance degradation under environmental conditions currently limits the practical utility of perovskite-based solar cells. The moisture stability of CH3NH3PbI3 perovskite films and solar cells was measured during exposure to three different levels of relative humidity. The films were crystallized at two different temperatures with and without simultaneous exposure to supercritical carbon dioxide. The film crystallinity, optical absorption, and device photoconversion efficiency was measured over time for three relative humidity levels and both crystallization methods. It was determined that film crystallization in supercritical CO2 resulted in significant improvement in moisture stability for films processed at 50 °C, but negligible improvement in stability for films processed at 100 °C.

Improvement of Laser Shock Peening Depth Through Regulation of Surface Optical Absorption

AbstractLaser shock peening is conducted to enhance the mechanical properties of metals. Efficient optical absorption of metal surface is desirable to increase the laser shock peening depth. In this work, a method is proposed to regulate the absorption behavior by surface colorizing to increase the affected depth and magnitude of nanosecond laser shock peening (NLSP). Colorized samples are fabricated with high absorption of 400–1500 nm, which is 89% higher than that of un‐colorized samples. This regulated optical response is attributed to the multi‐reflection/absorption behavior within nano‐to‐micro‐scale structures. Nano‐to‐micro‐scale structure‐based approaches offer controllable concurrent tailoring of a higher residual stress depth and greater magnitude. Black samples exhibit higher affected depth (64.71%) and magnitude (17.87%) values for the compressive residual stress than un‐colorized samples with unit peak power density after NLSP. Experimental results show that coarse grains are refined on surfaces, and the depths of grain refinement and dislocation propagation increase for colorized samples, which exhibit a regulated surface optical behavior. Therefore, this study presents a promising approach that the regulation of surface optical absorption of metals can be incorporated into the improvement of laser shock peening depth.

High-Entropy-Alloy Nanoparticles with Enhanced Interband Transitions for Efficient Photothermal Conversion.

Photothermal materials with broadband optical absorption and high conversion efficiency are intensively pursued to date. Here, proposing by the d-d interband transitions, we report an unprecedented high-entropy alloy FeCoNiTiVCrCu nanoparticles that the energy regions below and above the Fermi level (±4 eV) have been fully filled by the 3d transition metals, which realizes an average absorbance greater than 96 % in the entire solar spectrum (wavelength of 250 to 2500 nm). Furthermore, we also calculated the photothermal conversion efficiency and the evaporation rate towards the steam generation. Due to its pronounced full light capture and ultrafast local heating, our high-entropy-alloy nanoparticle-based solar steam generator has over 98 % efficiency under one sun irradiation, meanwhile enabling a high evaporation rate of 2.26 kg m-2 h-1 .