Understanding the correlation between energy-state mismatching and open-circuit voltage loss in bulk heterojunction solar cells

Photoinduced intermolecular charge transfer(PICT)determines the voltage loss in bulk heterojunction(BHJ)organic photovoltaics(OPVs),and this voltage loss can be minimized by inducing efficient PICT,which requires energy-state matching between the donor and acceptor at the BHJ interfaces.Thus,both geometrically and energetically accessible delocalized state matching at the hot energy level is crucial for achieving efficient PICT.In this study,an effective method for quantifying the hot state matching of OPVs was developed.The degree of energy-state matching between the electron donor and acceptor at BHJ interfaces was quantified using a mismatching factor(MF)calculated from the modified optical density of the BHJ.Furthermore,the correlation between the open-circuit voltage(Voc)of the OPV device and energy-state matching at the BHJ interface was investigated using the calculated MF.The OPVs with small absolute MF values exhibited high Voc values.This result clearly indicates that the energy-state matching between the donor and acceptor is crucial for achieving a high Voc in OPVs.Because the MF indicates the degree of energy-state matching,which is a critical factor for suppressing energy loss,it can be used to estimate the Voc loss in OPVs.

Surface repair of wide-bandgap perovskites for high-performance all-perovskite tandem solar cells

Wide-bandgap(WBG)perovskite solar cells(PSCs)play a fundamental role in perovskite-based tandem solar cells.However,the efficiency of WBG PSCs is limited by significant open-circuit voltage losses,which are primarily caused by surface defects.In this study,we present a novel method for modifying surfaces using the multifunctional S-ethylisothiourea hydrobromide(SEBr),which can passivate both Pb^(-1)and FA^(-1)terminated surfaces,Moreover,the SEBr upshifted the Fermi level at the perovskite interface,thereby promoting carrier collection.This proposed method was effective for both 1.67 and 1.77 eV WBG PSCs,achieving power conversion efficiencies(PCEs)of 22.47%and 19.90%,respectively,with V_(OC)values of 1.28 and 1.33 V,along with improved film and device stability.With this advancement,we were able to fabricate monolithic all-perovskite tandem solar cells with a champion PCE of 27.10%,This research offers valuable insights for passivating the surface trap states of WBG perovskite through rational multifunctional molecular engineering.

Broadband all-fiber optical phase modulator based on photo-thermal effect in a gas-filled hollow-core fiber

We report broadband all-fiber optical phase modulation based on the photo-thermal effect in a gas-filled hollow-core fiber.The phase modulation dynamics are studied by multi-physics simulation.A phase modulator is fabricated using a 5.6-cm-long anti-resonant hollow-core fiber with pure acetylene filling.It has a half-wave optical power of 289 mW at 100 kHz and an average insertion loss 0.6 dB over a broad wavelength range from 1450 to 1650 nm.The rise and fall time constants are 3.5 and 3.7μs,respectively,2–3 orders of magnitude better than the previously reported microfiber-based photo-thermal phase modulators.The gas-filled hollow-core waveguide configuration is promising for optical phase modulation from ultraviolet to mid-infrared which is challenging to achieve with solid optical fibers.

Enhanced charge separation by interchain hole delocalization in nonfullerene acceptor-based bulk heterojunction materials

Bulk heterojunction(BHJ)composites show improved power conversion efficiencies when optimized in terms of morphology using various film processing methods.A reduced carrier recombination loss in an optimized BHJ was characterized previously.However,the driving force that leads to this reduction was not clearly understood.In this study,we focus on the decreased carrier recombination loss and its driving force in optimized nonfullerene acceptor-based PTB7-Th:IEICO-4F BHJ composites.We demonstrate that the optimized BHJ shows deactivation in the sub-nanosecond nongeminate carrier recombination process.The driving force for this deactivation was determined to be the improved interchain hole delocalization between the polymers.An enhanced interchain hole delocalization was observed using steady-state photoinduced absorption(PIA)spectroscopy.In particular,increased splitting between the polaron PIA bands was noted.Moreover,improved interchain hole delocalization was observed for other state-of-the-art BHJ materials,including D18:Y6 with optimized morphologies.

Spatial and spectral measurement of laser-driven protons through radioactivation

The simultaneous measurement of the spatial profile and spectrum of laser-accelerated protons is important for further optimization of the beam qualities and applications.We report a detailed study regarding the underlying physics and regular procedure of such a measurement through the radioactivation of a stack composed of aluminum,copper,and CR-39 plates as well as radiochromic films(RCFs).After being radioactivated,the copper plates are placed on imaging plates(IPs)to detect the positrons emitted by the reaction products through contact imaging.The spectrum and energy-dependent spatial profile of the protons are then obtained from the IPs and confirmed by the measured ones from the RCFs and CR-39 plates.We also discuss the detection range,influence of electrons,radiation safety,and spatial resolution of this measurement.Finally,insights regarding the extension of the current method to online measurements and dynamic proton imaging are also provided.

A conformal titanyl phosphate amorphous overlayer for enhancing photoelectrochemical hydrogen peroxide production

Photoelectrochemical(PEC)H_(2)O_(2)production through water oxidation reaction(WOR)is a promising strategy,however,designing highly efficient and selective photoanode materials remains challenging due to competitive reaction pathways.Here,for highly enhanced PEC H_(2)O_(2)production,we present a conformal amorphous titanyl phosphate(a-TP)overlayer on nanoparticulate TiO_(2)surfaces,achieved via lysozyme-molded in-situ surface reforming.The a-TP overlayer modulates surface adsorption energies for reaction intermediates,favoring WOR for H_(2)O_(2)production over the competing O_(2)evolution reaction.Our density functional theory calculations reveal that a-TP/TiO_(2)exhibits a substantial energy uphill for the O·*formation pathway,which disfavors O_(2)evolution but promotes H_(2)O_(2)production.Additionally,the a-TP overlayer strengthens the built-in electric field,resulting in favorable kinetics.Consequently,a-TP/TiO_(2)exhibits 3.7-fold higher Faraday efficiency(FE)of 63%at 1.76 V vs.reversible hydrogen electrode(RHE)under 1 sun illumination,compared to bare TiO_(2)(17%),representing the highest FE among TiO_(2)-based WOR H_(2)O_(2)production systems.Employing the a-TP overlayer constitutes a promising strategy for controlling reaction pathways and achieving efficient solar-to-chemical energy conversion.

INTRACELLULAR MANIPULATION BY FEMTOSECOND LASERS:REVIEW

Multiphoton absorption of femtosecond laser pulses focused through an objective with high numerical aperture(NA)can be used to image and manipulate cellular and intracellular objects.This review highlights recent advances in intracellular manipulation,including nanosurgery and labeling in living cells with femtosecond lasers.

Graded doped structure fabricated by vacuum spray method to improve the luminance of polymer light-emitting diodes

An increase in luminance of a polymer light-emitting diode(PLED) was obtained by fabricating a graded doping structure using a vacuum spray method. The small electron transport molecule, Tris(8-hydroxyquinolinato) aluminum(III)(Alq3), was graded dispersed along the film in the direction of growth in the hole transport polymer poly(3-hexylthiophene-2,5-diyl)(P3HT, regiorandom) layer of the PLED, despite being dissolved in the same organic solvent as the polymer. The PLED reported here, which is composed of a graded structure, emitted brighter light than PLEDs composed of pure polymer or of a blend of active layers prepared by spin coating and/or vacuum spray methods.

Investigation of the factors affecting the limit of detection of laser-induced breakdown spectroscopy for surface inspection

Laser-induced breakdown spectroscopy(LIBS) was examined to detect a trace substance adhered onto Al alloys for the surface inspection of materials to be adhesively bonded. As an example of Si contamination, silicone oil was employed and sprayed onto substrates with a controlled surface concentration. LIBS measurements employing nanosecond UV pulses(λ?=?266 nm) and an off-axis emission collection system with different detecting heights were performed. Because surface contaminants are involved in the plasma formed by laser ablation of the substrates, the relative contribution of the surface contaminants and the substrates to the plasma emission could be changed depending on the conditions for plasma formation. The limit of detection(LOD) was evaluated under several detecting conditions for investigating the factors that affected the LOD. A significant factor was the standard deviation values of signal intensities obtained for the clean substrates. This value varied depending on the measurement conditions.For the Al alloy(A6061), the smallest LOD obtained was 0.529 μg?·?cm^(-2). Furthermore, an improved LOD(0.299 μg?·?cm^(-2)) was obtained for the Al alloy with a lower Si content.

Ultra-small PbSe Quantum Dots Synthesis by Chemical Nucleation Controlling

Ultra-small PbSe quantum dots (QDs) were synthesized using conventional hot-injection method.A small amount of Sn was used as a nucleation promotion agent to control nucleation and growth during the QDs synthesis process.The average diameter of the QDs is about 1.6 nm,of which absorption peak centers at 550 nm and photoluminescence peak centers at 750 nm under 350 nm laser excitation with power as low as 500 μW.Transmission electron microscopy images confirm that the QDs size well matches with the calculated diameter from Brus equation.This match and electron energy loss spectroscopy analysis proves that Sn is not involved into the final structure of the ultra-small PbSe QDs.An ion-exchange process was proposed for the nucleation control and ultra-small QDs synthesis.The prepared ultra-small QDs could be a promising candidate for luminescence,solar cell devices,and others.

Fabrication of iron disilicide from multilayer by helicon plasma sputtering

Helicon plasma sputtering of Fe/Si multilayer followed by thermal annealing in Ar atmosphere was used to fabricate β-FeSi2 films. [Fe 0.5nm/Si 1.6nm] 120 multilayer was deposited on Si（100） substrate and then the samples were annealed at 900℃ for 2h or at 9001000℃ for 10s. Annealed samples were characterized by X-ray diffractometry（XRD）, Rutherford backscattering spectroscopy, scanning electron microscopy and optical absorption measurement. （202）/（220） oriented β-FeSi2 films are fabricated from the multilayer according to XRD patterns. It is found that there is a very small redistribution of Fe and Si components in the films during the thermal annealing, so that a good stoichiometry of FeSi2 can be obtained. It is also revealed by scanning electron microscopy that multilayer technology can result in a smooth surface for β-FeSi2 films. Optical absorption spectra demonstrate that the films have a direct band gap of 0.9eV at room temperature.

Versatile control of concentration gradients in non-fullerene acceptor-based bulk heterojunction films using solvent rinse treatments

Solvent rinse treatments using polar methanol(Me OH)and nonpolar n-hexane have been developed for controlling material concentration gradients along the longitudinal direction of non-fullerene acceptor-based bulk heterojunction(BHJ)films comprised of electron donor polymer,PBDB-T and acceptor,ITIC-m.Before the used solvents(chlorobenzene with 1 vol%DIO)were completely evaporated,ITIC-m rich domains were formed at the top surface of the BHJ films after they were rinsed with Me OH,as evidenced by water contact angle,atomic force microscopy,time-of-flight secondary ion mass spectroscopy,which led to enhanced electron transport in the conventional structure of organic solar cells(OSCs).In contrast,after rinsing with n-hexane,ITIC-m rich domains were formed at the bottom surface of the films,which improved electron transport in the inverted structure OSCs.The enhanced carrier transports increased the PCEs(11.80%and 11.15%)in both conventional and inverted OSCs by 10.29%and 10.35%compared with control devices.The versatile control of material concentration gradients is determined to be feasible owing to the chemical interaction of the used substrates(glass,PEDOT:PSS,and Zn O)and rinsing solvents.

Detection of Influenza Viruses Attached to an Optical Disk

Detection of polystyrene beads with a diameter of 100 nm was conducted using an optical disk drive tester equipped with a laser of 405 nm wavelength and an objective lens with a numerical aperture of 0.65. The polystyrene beads were used to mimic the influenza virus. A grooved disk with a (ZnS)85(SiO2)15/SiO2 layered surface structure was used for the detection. The detection of influenza viruses (A/Udorn/307/1972) with Au nanoparticles was also demonstrated using the optical disk drive tester. In this case, a grooved disk with an indium tin oxide (ITO) film was used. The ITO film functioned both to tune the reflectance of the disk and as an electrically conductive layer for scanning electron microscopy. In both cases, the target substances were successfully recognized in a single scan with a high scanning speed of 4.9 m/s. The results indicate that this optical disk system can be used to detect 100 nm scale substances like influenza viruses, which are smaller than the diffraction limit of the system.

Electron Correlation in High Temperature Cuprates

Electron correlation plays a key role in high-temperature cuprate superconductors. Material-parameter dependence of cuprates is important to clarify the mechanism of high temperature superconductivity. In this study, we examine the ground state of the three-band Hubbard model (d-p model) that explicitly includes oxygen p orbitals. We consider the half-filled case with the large on-site Coulomb repulsion Ud by using the variational Monte Carlo method. The ground state is insulating when Ud is large at half-filling. The ground state undergoes a transition from a metal to a Mott insulator when the level difference εp-εd is increased.

Long distance all-optical logic operations through a single multimode fiber empowered by wavefront shaping

Multimode fibers(MMFs)are a promising solution for high-throughput signal transmission in the time domain.However,crosstalk among different optical modes within the MMF scrambles input information and creates seemingly random speckle patterns at the output.To characterize this process,a transmission matrix(TM)can be used to relate input and output fields.Recent innovations use TMs to manipulate the output field by shaping the input wavefront for exciting advances in deep-brain imaging,neuron stimulation,quantum networks,and analog operators.However,these approaches consider input/output segments as independent,limiting their use for separate signal processing,such as logic operations.Our proposed method,which makes input/output segments as interdependent,adjusts the phase of corresponding output fields using phase bias maps superimposed on input segments.Coherent superposition enables signal logic operations through a 15-m-long MMF.In experiments,a single optical logic gate containing three basic logic functions and cascading multiple logic gates to handle binary operands is demonstrated.Bitwise operations are performed for multi-bit logic operations,and multiple optical logic gates are reconstructed simultaneously in a single logic gate with polarization multiplexing.The proposed method may open new avenues for long-range logic signal processing and transmission via MMFs.

Mixed-dimensional stacked nanocomposite structures for a specific wavelength-selectable ambipolar photoresponse

Mixed-dimensional composite structures using zero-dimensional(0D)quantum dots(QDs)and two-dimensional(2D)transition metal dichalcogenides(TMDs)materials are expected to attract great interest in optoelectronics due to the potential to generate new optical properties.Here,we report on the unique optical characteristics of a devices with mixed dimensional vertically stacked structures based on tungsten diselenide(WSe_(2))/CdSeS QDs monolayer/molybdenum disulfide(MoS_(2))(2D/0D/2D).Specifically,it exhibits an ambipolar photoresponse characteristic,with a negative photoresponse observed in the 400-600 nm wavelength range and a positive photoresponse appeared at 700 nm wavelength.It resulted in the high negative responsivity of up to 52.22 mA·W^(−1)under 400 nm,which is 163 times higher than that of the photodetector without CdSeS QDs.We also demonstrated the negative photoresponse,which could be due to increased carrier collision probability and non-radiative recombination.Device modeling and simulation reveal that Auger recombination among the types of non-radiative recombination is the main cause of negative photocurrent generation.Consequently,we discovered ambipolar photoresponse near a specific wavelength corresponding to the energy of quantum dots.Our study revealed interesting phenomenon in the mixed low-dimensional stacked structure and paved the way to exploit it for the development of innovative photodetection materials as well as for optoelectronic applications.

High-throughput compositional mapping of triple-cation tin-lead perovskites for high-efficiency solar cells

Mixed tin-ead perovskites suffer from structural instability and rapid tin oxidation;thus,the investigation of their optimal composition ranges is important to address these inherent weaknesses.The critical role of triple cations in mixed Sn–Pb iodides is studied by performing a wide range of compositional screenings over mechanochemically synthesized bulk and solution-processed thin films.A ternary phase map of FA(Sn_(0.6)Pb_(0.4))I_(3),MA(Sn_(0.6)Pb_(0.4))I_(3),and Cs(Sn_(0.6)Pb_(0.4))I_(3)is formed,and a promising composition window of(FA_(0.6-x)MA_(0.4)Cs_(x))Sn_(0.6)Pb_(0.4)I_(3)(0≤x≤0.1)is demonstrated through phase,photoluminescence,and stability evaluations.Solar cell performance and chemical stability across the targeted compositional space are investigated,and FA_(0.55)MA_(0.4)Cs_(0.05)Sn_(0.6)Pb_(0.4)I_(3)with strain-relaxed lattices,reduced defect densities,and improved oxidation stability is demonstrated.The inverted perovskite solar cells with the optimal composition demonstrate a power conversion efficiency of over 22%with an open-circuit voltage of 0.867 V,which corresponds to voltage loss of 0.363 V,promising for the development of narrow-bandgap perovskite solar cells.

Plasmonic bound states in the continuum for unpolarized weak spatially coherent light

Plasmonic resonances empowered by bound states in the continuum(BICs) offer unprecedented opportunities to tailor light–matter interaction. However, excitation of high quality-factor(Q-factor) quasi-BICs is often limited to collimated light at specific polarization and incident directions, rendering challenges for unpolarized focused light. The major hurdle is the lack of robustness against weak spatial coherence and poor polarization of incident light. Here, addressing this limitation, we demonstrate sharp resonances in symmetric plasmonic metasurfaces by exploiting BICs in the parameter space, offering ultraweak angular dispersion effect and polarization-independent performance. Specifically, a high-Q(≈71) resonance with near-perfect absorption(>90%) is obtained for the input of unpolarized focused light covering wide incident angles(from 0° to 30°). Also, giant electric and magnetic field enhancement simultaneously occurs in quasi-BICs. These results provide a way to achieve efficient near-field enhancement using focused light produced by high numerical aperture objectives.

Multi-millijoule terahertz emission from laser- wakefield-accelerated electrons

High-power terahertz radiation was observed to be emitted from a gas jet irradiated by 100-terawatt-class laser pulses in the laser-wakefield acceleration of electrons.The emitted terahertz radiation was characterized in terms of its spectrum,polarization,and energy dependence on the accompanying electron bunch energy and charge under various gas target conditions.With a nitrogen target,more than 4 mJ of energy Was produced at<10 THz with a laser-to-terahertz conversion efficiency of~0.15%.Such strong terahertz radiation is hypothesized to be produced from plasma electrons accelerated by the ponderomotive force of the laser and the plasma wakefelds on the time scale of the laser pulse duration and plasma period.This model is examined with analytic calculations and particle-in-cell simulations to better understand the generation mechanism of high-energy terahertz radiation in laser-wakefield acceleration.

Learning-based super-resolution interpolation for sub-Nyquist sampled laser speckles

Information retrieval from visually random optical speckle patterns is desired in many scenarios yet considered challenging.It requires accurate understanding or mapping of the multiple scattering process,or reliable capability to reverse or compensate for the scattering-induced phase distortions.In whatever situation,effective resolving and digitization of speckle patterns are necessary.Nevertheless,on some occasions,to increase the acquisition speed and/or signal-to-noise ratio(SNR),speckles captured by cameras are inevitably sampled in the sub-Nyquist domain via pixel binning(one camera pixel contains multiple speckle grains)due to finite size or limited bandwidth of photosensors.Such a down-sampling process is irreversible;it undermines the fine structures of speckle grains and hence the encoded information,preventing successful information extraction.To retrace the lost information,super-resolution interpolation for such sub-Nyquist sampled speckles is needed.In this work,a deep neural network,namely SpkSRNet,is proposed to effectively up sample speckles that are sampled below 1/10 of the Nyquist criterion to well-resolved ones that not only resemble the comprehensive morphology of original speckles(decompose multiple speckle grains from one camera pixel)but also recover the lost complex information(human face in this study)with high fidelity under normal-and low-light conditions,which is impossible with classic interpolation methods.These successful speckle super-resolution interpolation demonstrations are essentially enabled by the strong implicit correlation among speckle grains,which is non-quantifiable but could be discovered by the well-trained network.With further engineering,the proposed learning platform may benefit many scenarios that are physically inaccessible,enabling fast acquisition of speckles with sufficient SNR and opening up new avenues for seeing big and seeing clearly simultaneously in complex scenarios.