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- 2019
- FSO Communication System
- Subcarrier Intensity Modulation
- Atmospheric Turbulence
- Bit Error Rate
- Average Irradiance
- Optoelectronic Information Science and Engineering
- Galgotias College of Engineering and Technology
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A focus on charge carrier recombination and energy conversion efficiency in nanohybrid photovoltaics
摘要： We investigated the effect of multiwall carbon nanotubes grafted with poly(3-dodecylthiophene) (CNT-graft-PDDT) on the performance of poly(3-hexylthiophene) (P3HT):phenyl-C61-butyric acid methyl ester photovoltaic cells. It is demonstrated that the presence of small amounts of these modified CNTs improves the structural organization of the films as evidenced by the grazing incidence wide-angle X-ray scattering studies. The ultraviolet–visible (UV–Vis) spectroscopy revealed that the incorporation of CNT-graft-PDDT changes the absorption intensity and induces a redshift to characteristic peaks. CNT hybrid features have appeared on the surface morphology as verified by atomic force microscopic images. The concentration of additive was optimized at 0.5 wt% to obtain the highest efficiency. Doping with this concentration of CNT-graft-PDDT led to 380% power conversion efficiency improvement by enhancement of short-circuit current density (Jsc) from 5.12 to 11.98 mA/cm2, open-circuit voltage (Voc) from 0.6 to 0.66 V, and fill factor from 0.41 to 0.62 in comparison with a reference cell. The photophysics of hybrid systems were also studied by means of the electrochemical impedance spectroscopy as well as Voc and Jsc dependent on the light intensity.
关键词： Organic photovoltaic cells,Charge carrier recombination,Energy conversion,CNT-graft-PDDT
更新于2025-09-23 15:21:01
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How the Mixed Cations (Guanidium, Formamidinium, and Phenylethylamine) in Tin Iodide Perovskites Affect Their Charge Carrier Dynamics and Solar Cell Characteristics
摘要： Despite recent interest in lead-free Sn iodide perovskite (ASnI3) solar cells, the role of mixed A-site cations is yet to be fully understood. Here, we report the effect of the ternary mixing of organic A-site cations (guanidium, GA; formamidinium, FA; and phenylethylamine, PEA) on the solar cell performance and charge carrier dynamics that are evaluated using time-resolved microwave conductivity (TRMC). (GAxFA1?x)0.9PEA0.1SnI3 exhibits the maximum power conversion efficiency (PCE) of 7.90% at x = 0.15 and a drastic decrease with increasing GA content. Notably, our TRMC measurements of ASnI3 with/without a hole transport layer reveal the same trend with the devices. From the analyses, we suggest that a variation of electron mobility affected by the location of the GA cation in the grains significantly impacts the PCE. Our work sheds light on the role of mixed A-site cations and directs a route toward the further development of Sn perovskite solar cells.
关键词： time-resolved microwave conductivity,mixed A-site cations,solar cell performance,Sn iodide perovskite,charge carrier dynamics,lead-free
更新于2025-09-23 15:21:01
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Effects of Size and Localized States in Charge Carrier Dynamics and Performance of Solution Processed Graphene Quantum Dots/Silicon Heterojunction near-UV Photodetectors
摘要： Influence of size and localized defect states on photogenerated carrier recombination dynamics, which affects the performance of graphene quantum dots (GQDs) based Si-compatible near-UV heterojunction photodetectors, is reported. GQDs of varying size from ~3.0 to ~8.0 nm have been prepared by a top down method of oxidative cutting of graphene oxide followed by hydrothermal reduction and gradient centrifugation at different speeds. Structural, compositional, photophysical characteristics and photocarrier dynamics of different sized samples have been studied. Spectroscopic features and carrier dynamics of GQDs are effectively controlled by their size and localized surface states, which also determine the average recombination lifetime of photo-generated carriers. Two-terminal vertical heterojunction photodetector devices fabricated using solution processed quantum dots exhibit superior performance over a broad spectrum with a peak response in the near UV (380 nm) region. The device fabricated using ~6.0 nm diameter GQDs displayed highest peak responsivity of 3.5 A/W showing an interesting correlation with carrier dynamics. To our best knowledge, this is the only report in graphene quantum dots or carbon nanostructure genre, showing the direct correlation between size of the quantum dots and localized surface states on photocarrier dynamics and consequential performance of photodetector devices.
关键词： Graphene quantum dots,carrier dynamics,heterojunction,Si-compatible,near-UV photodetectors
更新于2025-09-23 15:21:01
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Bis(4-methylthio)phenyl)amine-based hole transport materials for highly-efficient perovskite solar cells: insight into the carrier ultrafast dynamics and interfacial transport
摘要： Hole transport layers (HTLs) play a significant role in the performance of perovskite solar cells. A new class of linear small-molecules based on bis(4-methylthio)phenyl)amine as an end group, carbon, oxygen and sulfur as the center atoms for the center unit (denoted as MT-based small-molecule), respectively, have been applied as HTL, and two of them presented the efficiency over 20% in the planar inverted perovskite solar cells (PSCs), which demonstrated a significant improvement in comparison with the widely used HTL, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (known as PEDOT:PSS), in the planar inverted architecture. The ultrafast carrier dynamics show that the excited hot carrier cooling process of MT-based small-molecule HTL samples is faster than that of PEDOT:PSS samples. The kinetic analysis of photo-bleaching peaks of femtosecond transient absorption spectra reveals that the traps at the interface between MT-based small-molecule HTLs and MAPbI3 can be filled much quicker than that at PEDOT/MAPbI3 interfaces. Moreover, the hole injection time from MAPbI3 to MT-based small-molecule HTLs is around 10 times quicker than that to PEDOT:PSS. Such quick trap filling and hole extraction bring a significant enhancement in photovoltaic performances. These findings uncover the carrier transport mechanisms and illuminate a promising approach for the design of new HTLs for highly-efficient perovskite solar cells.
关键词： hole transport layer,perovskite solar cell,ultrafast carrier dynamics
更新于2025-09-23 15:21:01
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Potential and limitations of CsBi3I10 as photovoltaic material
摘要： Herein we demonstrate the dry synthesis of CsBi3I10 both as free-standing material as well as in the form of homogeneous thin films, deposited by thermal vacuum deposition. Chemical and optical characterization shows high thermal stability, phase purity, and photoluminescence centered at 700 nm, corresponding to a bandgap of 1.77 eV. These characteristics make CsBi3I10 a promising low-toxicity material for wide bandgap photovoltaics. Nevertheless, the performance of this material as a semiconductor in solar cells remains rather limited, which can be at least partially ascribed to a low charge carrier mobility, as determined from pulsed-radiolysis, time-resolved microwave conductivity. Further developments should focus on understanding and overcoming the current limitations in charge mobility, possibly by compositional tuning through doping and/or alloying, as well as optimizing thin film morphology which may be another limiting factor.
关键词： photovoltaic material,thermal vacuum deposition,CsBi3I10,dry synthesis,charge carrier mobility
更新于2025-09-23 15:21:01
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Biocompatible superparamagnetic core-shell nanoparticles for potential use in hyperthermia-enabled drug release and as an enhanced contrast agent
摘要： Superparamagnetic iron oxide nanoparticles (SPIONs) and core-shell type nanoparticles, consisting of SPIONs coated with mesoporous silica and/or lipid, were synthesized and tested for their potential theranostic applications in drug delivery, magnetic hyperthermia and as a contrast agent. Transmission Electron Microscopy (TEM) confirmed the size of bare and coated SPIONs was in the range of 5-20 nm and 100-200 nm respectively. The superparamagnetic nature of all the prepared nanomaterials as indicated by Vibrating Sample Magnetometry (VSM) and their heating properties under an AC field confirm their potential for hyperthermia applications. Scanning Column Magnetometry (SCM) data showed that extrusion of bare-SPION (b-SPION) dispersions through a 100 nm polycarbonate membrane significantly improved the dispersion stability of the sample. No sedimentation was apparent after 18 hours compared to a pre-extrusion estimate of 43% settled at the bottom of the tube over the same time. Lipid coating also enhanced dispersion stability. Transversal relaxation time (T2) measurements for the nanoparticles, using a bench-top relaxometer, displayed a significantly lower value of 46 ms, with a narrow relaxation time distribution, for lipid silica coated SPIONs (Lip-SiSPIONs) as compared to that of 1316 ms for the b-SPIONs. Entrapment efficiency of the anticancer drug, Doxorubicin (DOX) for Lip-SPIONs was observed to be 35% which increased to 58% for Lip-SiSPIONs. Moreover, initial in-vitro cytotoxicity studies against human breast adenocarcinoma, MCF-7 cells showed that % cell viability increased from 57% for bSPIONs to 82% for Lip-SPIONs and to 87% for Lip-SiSPIONs. This suggests that silica and lipid coatings improve the biocompatibility of bSPIONs significantly and enhance the suitability of these particles as drug carriers. Hence, the magnetic nanomaterials prepared in this work have potential theranostic properties as a drug carrier for hyperthermia cancer therapy and also offer enhancement of contrast agent efficacy and a route to a significant increase in dispersion stability.
关键词： magnetoliposomes,drug carrier,cancer therapy,colloidal stability,hyperthermia,theranostic,Superparamagnetic iron oxide nanoparticles
更新于2025-09-23 15:21:01
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Ultrafast energy absorption and photoexcitation of bulk plasmon in crystalline silicon subjected to intense near-infrared ultrashort laser pulses
摘要： We investigate the non-linear response and energy absorption in bulk silicon irradiated by intense 12-fs near-infrared laser pulses. Depending on the laser intensity, we distinguish two regimes of non-linear absorption of the laser energy: for low intensities, energy deposition and photoionization involve perturbative three-photon transition through the direct bandgap of silicon. For laser intensities near and above 1014 W/cm2, corresponding to photocarrier density of order 1022 cm?3, we find that absorption at near-infrared wavelengths is greatly enhanced due to excitation of bulk plasmon resonance. In this regime, the energy transfer to electrons exceeds a few times the thermal melting threshold of Si. The optical reflectivity of the photoexcited solid is found in good qualitative agreement with existing experimental data. In particular, the model predicts that the main features of the reflectivity curve of photoexcited Si as a function of the laser fluence are determined by the competition between state and band filling associated with Pauli exclusion principle and Drude free-carrier response. The non-linear response of the photoexcited solid is also investigated for irradiation of silicon with a sequence of two strong and temporary non-overlapping pulses. The cumulative effect of the two pulses is non-additive in terms of deposited energy. Photoionization and energy absorption on the leading edge of the second pulse is greatly enhanced due to free carrier absorption.
关键词： bulk silicon,optical reflectivity,photoexcited solid,near-infrared laser pulses,Drude free-carrier response,non-linear response,energy absorption,plasmon resonance
更新于2025-09-23 15:21:01
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On-demand tuning of charge accumulation and carrier mobility in quantum dot solids for electron transport and energy storage devices
摘要： Assemblies of colloidal quantum dots (CQDs) are attractive for a broad range of applications because of the ability to exploit the quantum con?nement effect and the large surface-to-volume ratio due to their small dimensions. Each application requires different types of assemblies based on which properties are intended to be utilized. Greater control of assembly formation and optimization of the related carrier transport characteristics are vital to advance the utilization of these materials. Here, we demonstrate on-demand control of the assembly morphology and electrical properties of highly crosslinked CQD solids through the augmentation of various assembly methods. Employment of electric-double-layer (EDL) gating on these assembly structures (i.e., an amorphous assembly, a hierarchical porous assembly, and a compact superlattice assembly) reveals their intrinsic carrier transport and accumulation characteristics. Demonstrations of high electron mobility with a high current modulation ratio reaching 105 in compact QD ?lms and of a record-high areal capacitance of 400 μF/cm2 in an electric-double-layer supercapacitor with very thin (<100 nm) QD hierarchical porous assemblies signify the versatility of CQDs as building blocks for various modern electronic devices.
关键词： electron transport,electric-double-layer gating,energy storage devices,carrier mobility,colloidal quantum dots
更新于2025-09-23 15:21:01
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Further Development of Near-Infrared Mediated Quantum Dots and Paclitaxel Co-loaded Nanostructured Lipid Carrier System for Cancer Theragnostic
摘要： Of colloidal systems, ceteris paribus, nanostructured lipid carriers are second to none in offering a single-unit platform for multifunctional benefits. Quantum dots are known to possess unique properties that make them ideal for imaging purpose and that they may be used for cancer detection. For several decades, paclitaxel has been the most effective drug against a wide range of solid tumours. Theragnostic nanomedicine provides a platform to monitor, evaluate, and individualize treatment in real time. Evaluation of cancer treatment outcome at an early stage therapy is key to increase survival prospects of a patient. Previously, a novel co-loaded nanostructured lipid carriers’ theragnostic system for parenteral administration was developed. The aim of this study was to further investigate the co-loaded nanostructured lipid carriers in order to provide interpretation necessary for preclinical elucidation of the formulation, in part. The co-loaded nanostructured lipid carriers were prepared by oil/water emulsification-solvent evaporation technique. In this study, stability and co-loaded nanostructured lipid carriers’ internalization by MCF 7 and HepG2 cells were investigated. The co-loaded nanostructured lipid carriers was stable at 4(cid:2)C for 1 month. The formulation was successfully internalized by MCF-7 and HepG2 cells. Nevertheless, the co-loaded nanostructured lipid carrier was more apt for MCF-7 cells. This finding affirms the formulation to be the most appropriate for breast cancer treatment. In addition, if taken correctly by a patient for a month, the formulation would give true reflection of the contents’ amounts, the factor paramount to appropriate changes in treatment protocol. It can therefore safely be concluded that the co-loaded nanostructured lipid carrier formulation may be potentially an effective theragnostic translational system.
关键词： translational system,cellular uptake,theragnostic,stability study,co-loaded nanostructured lipid carrier
更新于2025-09-23 15:21:01
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Strategically Modulating Carriers and Excitons for Efficient and Stable Ultrapurea??Green Fluorescent OLEDs with a Sterically Hindered BODIPY Dopant
摘要： Ultrapure colors are vital for displays to obtain the highly desired wide color-gamut. Till now, only boron-dipyrromethene derivatives (BODIPYs) have demonstrated ultrapure full-colors but suffer from low excitons utilization efficiency as dopants in organic light-emitting diodes. It is proposed here that with a thermally activated delayed fluorophore to sensitize BODIPYs, all excitons can be recycled, which, still, is challenged by exciton loss through Dexter energy transfer (DET) from sensitizer to dopant and direct charge trapping on BODIPYs. Hence, a sterically hindered BODIPY-type dopant with a bulk substituent on the meso-position is developed to suppress DET, exhibiting a high photo-luminance quantum yield of 98% and a small full width at half maximum of 28 nm. Moreover, the device structure is elaborately designed, successfully modulating carriers and excitons to avoid charge trapping on dopant and also trigger multiple-sensitizing processes to reduce exciton loss. Consequently, a state-of-the-art maximum external quantum efficiency/power efficiency of 19.0%/85.7 lm W?1 are realized together with an ultrapure-green emission of Commission Internationale de l’Eclairage coordinates of (0.26, 0.67) and a long half-lifetime of 2947 h at an initial luminance of 1000 cd m?2.
关键词： carrier modulation,ultrapure green emission,exciton modulation,high-efficiency devices,fluorescent organic light-emitting diodes,long-lifetime devices
更新于2025-09-23 15:21:01