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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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Performance analysis of c-Si heterojunction solar cell with passivated transition metal oxides carrier-selective contacts
摘要： Transition metal oxides (TMOs) as passivating carrier-selective contact layers are investigated for silicon heterojunction solar cells. MoOx as hole-selective layer and TiOx as an electron-selective layer are explored in detail to design a high-efficiency silicon heterojunction solar cell without any specified surface passivation layer. The thickness and optical transparency of the MoOx hole-selective layer have been evaluated through optical simulation. The impact of TMOs’ work function and their passivation quality has been examined in detail to extract the maximum conversion efficiency from silicon heterojunction solar cells. To increase the optical absorption in c-Si, the micro–nanopillar structure has also been implemented. It has been found that the barrier height at the TMO/silicon heterocontact plays a significant role in the overall performance improvement of the solar cell. The optimized cell design without doping and separate passivating layer can achieve a power conversion efficiency of ~ 22%. Our findings open the potential pathways and opportunities to obtain simplified heterojunction solar cells at lower temperatures and without impurity doping.
关键词： Surface recombination velocity,Carrier-selective contact layers,Transition metal oxides,c-Si heterojunction solar cells
更新于2025-09-23 15:21:01
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Nanoscale spatial mapping of charge carrier dynamics in perovskite solar cells
摘要： Charge carrier dynamics and behaviors are key parameters and need to be mapped at the nanoscale in order to search for correct materials for high-performance solar cells. Unfortunately, currently, there are no existing tools or capabilities that can simultaneously map charge carrier dynamics at nanometer range in solar cells. Here we use a Transient Photo-response AFM (TP-AFM) to map for the first time apparent carrier recombination lifetime (τr), transport time (τt) and diffusion length (LD) in hybrid perovskites solar cells. These spatially resolved parameters reveal substantial variations at grain boundaries (GBs) τr, τt and LD at GBs broaden the performance of these state-of-the-art mixed cation perovskites. Detail analysis of these parameters allow us to conclude that reduced density of trap states and recombination in mixed cation perovskites at GBs and its surrounding locations (extending to several nanometers into the grain interior) implies less ion migration. This first of its kind experimental realization of nanoscale mapping of charge carrier dynamics in photovoltaic materials can be used for applications in other optoelectronic devices.
关键词： Perovskites,Nanoscale mapping and ion migration,Grain boundary,Charge carrier dynamics
更新于2025-09-23 15:21:01
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Tweaking the physics of interfaces between monolayers of buckled cadmium sulfide for a superhigh piezoelectricity, excitonic solar cell efficiency and thermoelectricity
摘要： Interfaces of heterostructures are routinely studied for different applications. Interestingly, monolayers of the same material when interfaced in an unconventional manner can bring about novel properties. For instance, CdS monolayers, stacked in a particular order, are found to show unprecedented potential in the conversion of nanomechanical energy, solar energy and waste heat into electricity, which has been systematically investigated in this work, using DFT based approaches. Moreover, stable ultrathin structures showing strong capabilities for all kinds of energy conversion are scarce. The emergence of a very high out-of-plane piezoelectricity, |d33| ~ 56 pm/V, induced by the inversion symmetry broken in the buckled structure helps to supersede the previously reported bulk wurzite GaN, AlN and Janus multilayer structures of Mo and W based dichalcogenides. The piezoelectric coefficients have been found to be largely dependent on the relative stacking between the two layers. CdS bilayer is a direct band gap semiconductor with its band edges straddling the water redox potential, thereby making it thermodynamically favorable for photocatalytic applications. Strain engineering facilitates its transition from type-I to type-II semiconductor in CdS bilayer stacked over monolayer boron phosphide, and the theoretically calculated power conversion efficiency (PCE) in the 2D excitonic solar cell exceeds 27% for a fill factor of 0.8, which is much higher than that in ZnO/CdS/CuInGaSe solar cell (20% efficiency). Thermoelectric properties have been investigated using semi classical Boltzmann transport equations for electrons and phonons within the constant relaxation time approximation coupled to deformation potential theory, which reveal ultralow thermal conductivity (~ 0.78 Wm-1K-1) at room temperature due to the presence of heavy element Cd, strong anharmonicity (high mode Gruneisen parameter at long wavelength, phonon lifetime < 5 ps), low phonon group velocity (4 km/s) and low Debye temperature (260 K). Such a low thermal conductivity is lower than that of dumbbell silicene (2.86 Wm-1K-1), SnS2 (6.41 Wm-1K-1) and SnSe2 (3.82 Wm-1K-1), SnP3 (4.97 Wm-1K-1). CdS bilayer shows a thermoelectric figure of merit (ZT) ~ 0.8 for p-type and ~ 0.7 for n-type doping at room temperature. Its ultrahigh carrier mobility (μe ~2270 cm2V-1s-1) is higher than that of single layer MoS2 and comparable to that in InSe. The versatile properties of CdS bilayer together with its all-round stability supported by ab initio molecular dynamics simulation, phonon dispersion and satisfaction of Born-Huang stability criteria highlight its outstanding potential for applications in device fabrication and applications in next generation nanoelectronics and energy harvesting.
关键词： Power conversion efficiency,Excitonic solar cell,Piezoelectricity,Photocatalysis,Solar energy,Semiconductor,Thermoelectricity,Carrier mobility
更新于2025-09-23 15:21:01
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Non-fullerene small molecule acceptors with three-dimensional thiophene/selenophene-annulated perylene diimides for efficient organic solar cells
摘要： Three-dimensional non-fullerene acceptors with a spiro core linked with S/Se fused perylene diimides possess appropriate energy levels, twisted molecular configuration and high carrier mobility, leading to a power conversion efficiency of 6.95% for the organic solar cells.
关键词： perylene diimides,organic solar cells,carrier mobility,non-fullerene acceptors,spiro core
更新于2025-09-23 15:21:01
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Improvement of Cu(In,Ga)Se <sub/>2</sub> solar cell performance by thiourea treatment
摘要： We investigated the effects of a thiourea treatment performed to the absorber of Cu(In,Ga)Se2 (CIGS) solar cells. The thiourea treatment successfully improved the open-circuit voltage, fill factor, and conversion efficiency of the solar cells. Reduced ideality factor and reverse saturation current density demonstrated that the suppression of carrier recombination contributed to the improvement in solar cell performance. Increased intensity in cross-sectional electron-beam-induced current measurements confirmed the improved film quality with the thiourea treatment. Additionally, an enhanced carrier density observed with the treatment suggests the passivation of donor-type defects. These results indicate that the thiourea treatment is promising to improve the absorber quality and enhance the performance of CIGS solar cells.
关键词： thiourea treatment,solar cell,Cu(In,Ga)Se2,carrier recombination,film quality
更新于2025-09-23 15:21:01
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Effect of indium alloying on the charge carrier dynamics of thick-shell InP/ZnSe quantum dots
摘要： Thick-shell InP/ZnSe III–V/II–VI quantum dots (QDs) were synthesized with two distinct interfaces between the InP core and ZnSe shell: alloy and core/shell. Despite sharing similar optical properties in the spectral domain, these two QD systems have differing amounts of indium incorporation in the shell as determined by high-resolution energy-dispersive x-ray spectroscopy scanning transmission electron microscopy. Ultrafast fluorescence upconversion spectroscopy was used to probe the charge carrier dynamics of these two systems and shows substantial charge carrier trapping in both systems that prevents radiative recombination and reduces the photoluminescence quantum yield. The alloy and core/shell QDs show slight differences in the extent of charge carrier localization with more extensive trapping observed in the alloy nanocrystals. Despite the ability to grow a thick shell, structural defects caused by III–V/II–VI charge carrier imbalances still need to be mitigated to further improve InP QDs.
关键词： indium alloying,InP/ZnSe,charge carrier dynamics,photoluminescence quantum yield,quantum dots
更新于2025-09-23 15:21:01
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New Unsymmetrical Bisacridine Derivatives Noncovalently Attached to Quaternary Quantum Dots Improve Cancer Therapy by Enhancing Cytotoxicity toward Cancer Cells and Protecting Normal Cells
摘要： The use of nanoparticles for the controlled drug delivery to cells has emerged as a good alternative to traditional systemic delivery. Quantum dots (QDs) offer potentially invaluable societal benefits such as drug targeting and in vivo biomedical imaging. In contrast, QDs may also pose risks to human health and the environment under certain conditions. Here, we demonstrated that a unique combination of nanocrystals core components (Ag-In-Zn-S) would eliminate the toxicity problem and increase their biomedical applications. The alloyed quaternary nanocrystals Ag-In-Zn-S (QDgreen, Ag1.0In1.2Zn5.6S9.4; QDred, Ag1.0In1.0Zn1.0S3.5) were used to transport new unsymmetrical bisacridine derivatives (UAs, C-2028 and C-2045) into lung H460 and colon HCT116 cancer cells for improving the cytotoxic and antitumor action of these compounds. UAs were coupled with QD through physical adsorption. The obtained results clearly indicate that the synthesized nanoconjugates exhibited higher cytotoxic activity than unbound compounds, especially toward lung H460 cancer cells. Importantly, unsymmetrical bisacridines noncovalently attached to QD strongly protect normal cells from the drug action. It is worth pointing out that QDgreen or QDred without UAs did not influence the growth of cancer and normal cells, which is consistent with in vivo results. In noncellular systems, at pH 5.5 and 4.0, which relates to the conditions of endosomes and lysosomes, the UAs were released from QD-UAs nanoconjugates. An increase of total lysosomes content was observed in H460 cells treated with QDs-UAs which can affect the release of the UAs from the conjugates. Moreover, confocal laser scanning microscopy analyses revealed that QD-UAs nanoconjugates enter H460 cells more efficiently than to HCT116 and normal cells, which may be the reason for their higher cytotoxicity against lung cancer. Summarizing, the noncovalent attachment of UAs to QDs increases the therapeutic efficiency of UAs by improving cytotoxicity toward lung H460 cancer cells and having protecting effects on normal cells.
关键词： lung and colon cancer cells,unsymmetrical bisacridine derivatives,drug-carrier degradation pathway,pH-dependent release,cellular uptake,in vivo antitumor efficacy,Ag-In-Zn-S nanocrystals,cytotoxic activity
更新于2025-09-23 15:21:01
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Suggestions on Efficiency Droop of GaN-based LEDs
摘要： InGaN/GaN-based light-emitting diodes (LEDs) are widely used in modern society and industry among different areas. However, InGaN/GaN LEDs suffer from an efficiency droop issue: The internal efficiency decreases during high current injection. The efficiency droop significantly affects the development of GaN-based LEDs devices in efficiency and light-output areas. Therefore, the improvement of the droop phenomenon has become a significant topic. This paper introduces several possible mechanisms of droop phenomenon based on different hypotheses including Auger Recombination, Carrier Delocalization and Electron Leakage. Furthermore, some proposals to mitigate efficiency droop, including semipolar LEDs, electron blocking layer(EBL), quaternary alloy and chip design will be discussed and analyzed. Also, it will provide some suggestions for the further optimization of droop phenomenon in each proposal.
关键词： electron blocking layer,semipolar LEDs,GaN-based LEDs,Auger Recombination,chip design,quaternary alloy,Carrier Delocalization,Electron Leakage,efficiency droop
更新于2025-09-23 15:21:01
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An Experimental and Theoretical Study into Interface Structure and Band Alignment of the Cu2Zn1-xCdxSnS4 Heterointerface for Photovoltaic Applications
摘要： To improve the constraints of kesterite Cu2ZnSnS4 (CZTS) solar cell, such as undesirable band alignment at p?n interfaces, bandgap tuning, and fast carrier recombination, cadmium (Cd) is introduced into CZTS nanocrystals forming Cu2Zn1-xCdxSnS4 through cost-effective solution-based method without post-annealing or sulfurization treatments. A synergetic experimental-theoretical approach was employed to characterize and assess the optoelectronic properties of Cu2Zn1-xCdxSnS4 materials. Tunable direct band gap energy ranging from 1.51 eV to 1.03 eV with high absorption coefficient was demonstrated for the Cu2Zn1-xCdxSnS4 nanocrystals with changing Zn/Cd ratio. Such bandgap engineering in Cu2Zn1-xCdxSnS4 helps in effective carrier separation at interface. Ultrafast spectroscopy reveals a longer lifetime and efficient separation photo-excited charge carriers in Cu2CdSnS4 (CCTS) nanocrystals compared to that of CZTS. We found that there exists a type-II staggered band alignment at the CZTS (CCTS)/CdS interface, from cyclic voltammetric (CV) measurements, corroborated by first-principles density functional theory (DFT) calculations, predicting smaller conduction band offset (CBO) at the CCTS/CdS interface as compared to the CZTS/CdS interface. These results point towards efficient separation of photoexcited carriers across the p?n junction in the ultrafast time scale and highlight a route to improve device performances.
关键词： grain boundary,photovoltaic,cation substitution,Earth-abundant material,interfacial engineering,band offset,ultrafast carrier dynamics
更新于2025-09-23 15:21:01
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[IEEE 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Chicago, IL, USA (2019.6.16-2019.6.21)] 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Hot-Carrier Extraction in InAs/GaAs Quantum Dot Superlattice Solar Cells
摘要： We demonstrated hot-carrier (HC) extraction in GaAs solar cells containing InAs/GaAs quantum dot superlattices (QDSLs) functioning as a light absorber at 15 K. The short-circuit current density and the open-circuit voltage in the QDSL solar cells show step-wise changes as a function of the excitation photon density because of state filling under below-bandgap excitation. Furthermore, the short-circuit current density and the open-circuit voltage originated from the HC extraction were enhanced by increasing the period of the QDSL due to the improved absorptivity.
关键词： InAs quantum dots,GaAs,quantum dot superlattices,energy-selective barrier,hot-carrier solar cells
更新于2025-09-23 15:21:01