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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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Photogenerated-Carrier Separation and Transfer in Two-Dimensional Janus Transition Metal Dichalcogenides and Graphene van der Waals Sandwich Heterojunction Photovoltaic Cells
摘要： Two-dimensional (2D) Janus transition metal dichalcogenides (JTMDs) show direct band gaps and strong visible-light absorption with promising applications in photovoltaic (PV) cells. Here, we investigate the electronic structures and dynamics of photogenerated carriers in 2D JTMDs and graphene van der Waals sandwich heterojunction (G/JTMDs/G) photovoltaic cells by using first-principles calculations. We find that the intrinsic built-in electric field in JTMDs results in an asymmetry potential, which can be used to effectively enhance the separation and transfer of photogenerated carriers from JTMDs to different graphene layers with a preferred direction within hundreds of femtoseconds in the G/JTMDs/G heterostructures. Furthermore, the photogenerated electrons (holes) can transfer from monolayer MoSSe (MoSeTe) to the graphene sheets by the Se side with lower (higher) potential, while the transfer of the photogenerated holes (electrons) is prohibited due to the large separation between donor and acceptor states.
关键词： First-principles calculations,van der Waals heterostructures,Janus transition metal dichalcogenides,Photogenerated carriers,Two-dimensional materials,Graphene,Charge transfer,Photovoltaic cells
更新于2025-09-23 15:21:01
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Ultrafast Electron Cooling and Decay in Monolayer WS <sub/>2</sub> Revealed by Time- and Energy-Resolved Photoemission Electron Microscopy
摘要： A comprehensive understanding of the ultrafast electron dynamics in two-dimensional transition metal dichalcogenides (TMDs) is necessary for their applications in optoelectronic devices. In this work, we contribute a study of ultrafast electron cooling and decay dynamics in the supported and suspended monolayer WS2 by time- and energy-resolved photoemission electron microscopy (PEEM). Electron cooling in the Q valley of the conduction band is clearly resolved in energy and time, on a timescale of 0.3 ps. Electron decay is mainly via defect trapping process on a timescale of several picoseconds. We observed that the trap states can be produced and increased by laser illumination under ultra-high vacuum, and the higher local optical-field intensity led to the faster increase of trap states. The enhanced defect trapping could significantly modify the carrier dynamics and should be paid attention to in photoemission experiments for two-dimensional materials.
关键词： transition metal dichalcogenides,defect trapping,ultrafast dynamics,energy-resolved,electron cooling,photoemission electron microscopy
更新于2025-09-23 15:21:01
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Stark Spectroscopic Evidence that a Spin Change Accompanies Light Absorption in Transition Metal Polypyridyl Complexes
摘要： The “Franck?Condon” (FC) excited state is the ?rst state created when a molecule absorbs a visible photon. Here we report Stark and visible absorption spectroscopies that interrogate the FC state of rigorously diamagnetic [M(bpy)3]2+ complexes, where bpy is 2,2′-bipyridine and M = Fe, Ru, and Os. Direct singlet-to-triplet metal-to-ligand charge transfer (MLCT) transitions are evident in the 550?750 nm region of the absorbance spectrum of [Os(bpy)3]2+, yet are poorly resolved or absent for [Ru(bpy)3]2+ and [Fe(bpy)3]2+. In the presence of a strong 0.4?0.8 MV/cm electric ?eld, well-resolved transitions are observed for all the complexes in this same spectral region. In particular, an electroabsorption feature at 633 nm (15 800 cm?1) provides compelling evidence for the direct population of a high spin [Fe(bpy)3]2+* MLCT excited state. Group theoretical considerations and Liptay analysis of the Stark spectra revealed dramatic light-induced dipole moment changes in the range μΔ = 3?9 D with the triplet transitions consistently showing shorter charge transfer distances. The ?nding that the spin of the initially populated FC excited state di?ers from that of the ground state, even with a relatively light ?rst row transition metal, is relevant to emerging applications in energy up-conversion, dye sensitization, spintronics, photoredox catalysis, and organic light emitting diodes (OLEDs).
关键词： transition metal polypyridyl complexes,MLCT transitions,light absorption,spin change,Stark spectroscopy
更新于2025-09-23 15:21:01
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High-Performance p-BP/n-PdSe2 Near-Infrared Photodiode with Fast and Gate-Tunable Photoresponse
摘要： Van der Waals heterostructures composed of transition metal dichalcogenide (TMDs) materials have become a remarkable compact system that could offer an innovative architecture for advanced engineering in high-performance energy-harvesting and optoelectronic devices. Here, we report a novel van der Waals (vdW) TMDs heterojunction photo-diode composed of black phosphorus (p-BP) and palladium diselenide (n-PdSe2) which establish a high and tunable rectification and photoresponsivity. A high rectification up to ≈ 7.1 × 105 is achieved which is successfully tuned by employing the back gate voltage to the heterostructure devices. Besides, the device significantly shows the high and gate-controlled photoresponsivity of ?? = 9.6 × 105 ?? ?? ―1, 4.53 × 105 ???? ―1 and 1.63 × 105 ???? ―1 under the influence of light of different wavelengths (?? = 532, 1064 and 1310 nm) in visible and near-infrared regions respectively due to interlayer optical transition and low Schottky. The device also demonstrates extraordinary values of detectivity (?? = 5.8 × 1013 Jones) and external quantum efficiency (?????? ≈ 9.4 × 106), which are an order of magnitude higher than the currently reported values. The effective enhancement of photovoltaic characteristics in visible and infrared regions of this TMDs heterostructure based system has a huge potential in the field of optoelectronics to realize high-performance infrared photodetectors.
关键词： rectification,palladium diselenide,detectivity,photoresponsivity,transition metal dichalcogenide materials,near-infrared
更新于2025-09-23 15:21:01
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Strongly Coupled Coherent Phonons in Single-Layer MoS <sub/>2</sub>
摘要： We present a transient absorption setup combining broadband detection over the visible-UV range with high temporal resolution (～20fs) which is ideally suited to trigger and detect vibrational coherences in different classes of materials. We generate and detect coherent phonons (CPs) in single layer (1L) MoS2, as a representative semiconducting 1L-Transition Metal Dichalcogenide (TMD), where the confined dynamical interaction between excitons and phonons is unexplored. The coherent oscillatory motion of the out-of-plane A'1 phonons, triggered by the ultrashort laser pulses, dynamically modulates the excitonic resonances on a timescale of few tens fs. We observe an enhancement by almost two orders of magnitude of the CP amplitude when detected in resonance with the C exciton peak, combined with a resonant enhancement of CP generation efficiency. Ab Initio calculations of the change in 1L-MoS2 band structure induced by the A'1 phonon displacement confirm a strong coupling with the C exciton. The resonant behavior of the CP amplitude follows the same spectral profile of the calculated Raman susceptibility tensor. These results explain the CP generation process in 1L-TMDs and demonstrates that CP excitation in 1L-MoS2 can be described as a Raman-like scattering process.
关键词： exciton-phonon interaction,Coherent phonons,transient absorption spectroscopy,transition metal dichalcogenides,ab-initio calculation
更新于2025-09-23 15:21:01
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Ultrafast dynamics in van der Waals heterostructures
摘要： Van der Waals heterostructures are synthetic quantum materials composed of stacks of atomically thin two-dimensional (2D) layers. Because the electrons in the atomically thin 2D layers are exposed to layer-to-layer coupling, the properties of van der Waals heterostructures are defined not only by the constituent monolayers, but also by the interactions between the layers. Many fascinating electrical, optical and magnetic properties have recently been reported in different types of van der Waals heterostructures. In this Review, we focus on unique excited-state dynamics in transition metal dichalcogenide (TMDC) heterostructures. TMDC monolayers are the most widely studied 2D semiconductors, featuring prominent exciton states and accessibility to the valley degree of freedom. Many TMDC heterostructures are characterized by a staggered band alignment. This band alignment has profound effects on the evolution of the excited states in heterostructures, including ultrafast charge transfer between the layers, the formation of interlayer excitons, and the existence of long-lived spin and valley polarization in resident carriers. Here we review recent experimental and theoretical efforts to elucidate electron dynamics in TMDC heterostructures, extending from timescales of femtoseconds to microseconds, and comment on the relevance of these effects for potential applications in optoelectronic, valleytronic and spintronic devices.
关键词： spin and valley polarization,charge transfer,valleytronic,transition metal dichalcogenide,Van der Waals heterostructures,excited-state dynamics,spintronic devices,interlayer excitons,optoelectronic
更新于2025-09-23 15:21:01
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2D Material Optoelectronics for Information Functional Device Applications: Status and Challenges
摘要： Graphene and the following derivative 2D materials have been demonstrated to exhibit rich distinct optoelectronic properties, such as broadband optical response, strong and tunable light–mater interactions, and fast relaxations in the flexible nanoscale. Combining with optical platforms like fibers, waveguides, grating, and resonators, these materials has spurred a variety of active and passive applications recently. Herein, the optical and electrical properties of graphene, transition metal dichalcogenides, black phosphorus, MXene, and their derivative van der Waals heterostructures are comprehensively reviewed, followed by the design and fabrication of these 2D material-based optical structures in implementation. Next, distinct devices, ranging from lasers to light emitters, frequency convertors, modulators, detectors, plasmonic generators, and sensors, are introduced. Finally, the state-of-art investigation progress of 2D material-based optoelectronics offers a promising way to realize new conceptual and high-performance applications for information science and nanotechnology. The outlook on the development trends and important research directions are also put forward.
关键词： transition metal dichalcogenides,optoelectronics,MXene,van der Waals heterostructures,information devices,graphene,black phosphorus,2D materials
更新于2025-09-23 15:21:01
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A hydrothermally synthesized MoS <sub/>2(1a??x)</sub> Se <sub/>2x</sub> alloy with deep-shallow level conversion for enhanced performance of photodetectors
摘要： Photoelectric detectors based on binary transition metal chalcogenides have attracted widespread attention in recent years. However, due to the high-temperature synthesis of binary TMD, high-density deep-level defect states may be generated, leading to poor responsiveness or a long response time. Besides, the addition of an alloy will change the DLDSs from deep to shallow energy levels caused by S vacancies. In this paper, MoS2(1?x)Se2x nanostructures were synthesized by a hydrothermal method, and a novel type of photodetector was fabricated by using the synthesized material as a light sensitive material. The MoSSe-based photodetector not only has a high photocurrent, but also exhibits a wide spectral response in the range of 405 nm to 808 nm. At the same time, it can achieve a responsivity of 1.753 mA W?1 under 660 nm laser irradiation of 1.75 mW mm?2. Therefore, this work can be considered as a method of constructing a new type of photodetector with a simple process and low cost.
关键词： MoS2(1?x)Se2x,photoelectric detectors,photodetector,transition metal chalcogenides,hydrothermal synthesis
更新于2025-09-23 15:21:01
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Toward Valleya??Coupled Spin Qubits
摘要： The bid for scalable physical qubits has attracted many possible candidate platforms. In particular, spin-based qubits in solid-state form factors are attractive as they could potentially benefit from processes similar to those used for conventional semiconductor processing. However, material control is a significant challenge for solid-state spin qubits as residual spins from substrate, dielectric, electrodes, or contaminants from processing contribute to spin decoherence. In the recent decade, valleytronics has seen a revival due to the discovery of valley-coupled spins in monolayer transition metal dichalcogenides. Such valley-coupled spins are protected by inversion asymmetry and time reversal symmetry and are promising candidates for robust qubits. In this report, the progress toward building such qubits is presented. Following an introduction to the key attractions in fabricating such qubits, an up-to-date brief is provided for the status of each key step, highlighting advancements made and/or outstanding work to be done. This report concludes with a perspective on future development highlighting major remaining milestones toward scalable spin-valley qubits.
关键词： valleytronics,qubits,quantum information,transition metal dichalcogenides,quantum dots
更新于2025-09-23 15:21:01