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Enhanced carrier mobility and power conversion efficiency of organic solar cells by adding 2D Bi<sub>2</sub>OS<sub>2</sub>
摘要： Although polymer solar cells (PSCs) have many advantages, they have obtained great progress in the two decades, the low charge carrier mobility still restricts performance progress of PSCs. Two-dimensional (2D) Bi-based semiconductor nanomaterial (Bi2OS2) can be a potential material for improving the charge carrier mobility in the active layer of PSCs, because it exhibits a high carrier mobility, suitable band gap, wide absorption range, and good stability. In this work, we synthesize the 2D Bi2OS2 nanomaterial and incorporate it into active layer of PSCs as a third component for the first time. By introduction 1 wt% 2D Bi2OS2 nanomaterial into the PSCs, the power conversion efficiency (PCE) of PSCs can be obviously improved by more than 17% comparison with binary PSCs (from 10.51% to 12.31%). The enhancement of PCE is mainly due to the improving of charge transport, surface morphology, and crystallization of active layer. It is worth noting that the 2D Bi2OS2 play the role of the heterogeneous nucleation in the active layer, resulting in the enhanced crystallization of PBDB-T and ITIC. These results not only provide a way to improve the performance of PSCs, but also show that the 2D Bi2OS2 nanomaterial has great potential application in the PSCs.
关键词： crystallinity,2D Bi2OS2 nanomaterial,Polymer solar cells,charge carrier transport
更新于2025-09-16 10:30:52
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Impact of PbI <sub/>2</sub> Passivation and Grain Size Engineering in CH <sub/>3</sub> NH <sub/>3</sub> PbI <sub/>3</sub> Solar Absorbers as Revealed by Carrier‐Resolved Photo‐Hall Technique
摘要： With power conversion efficiencies now exceeding 25%, hybrid perovskite solar cells require deeper understanding of defects and processing to further approach the Shockley-Queisser limit. One approach for processing enhancement and defect reduction involves additive engineering—, e.g., addition of MASCN (MA = methylammonium) and excess PbI2 have been shown to modify film grain structure and improve performance. However, the underlying impact of these additives on transport and recombination properties remains to be fully elucidated. In this study, a newly developed carrier-resolved photo-Hall (CRPH) characterization technique is used that gives access to both majority and minority carrier properties within the same sample and over a wide range of illumination conditions. CRPH measurements on n-type MAPbI3 films reveal an order of magnitude increase in carrier recombination lifetime and electron density for 5% excess PbI2 added to the precursor solution, with little change noted in electron and hole mobility values. Grain size variation (120–2100 nm) and MASCN addition induce no significant change in carrier-related parameters considered, highlighting the benign nature of the grain boundaries and that excess PbI2 must predominantly passivate bulk defects rather than defects situated at grain boundaries. This study offers a unique picture of additive impact on MAPbI3 optoelectronic properties as elucidated by the new CRPH approach.
关键词： photo-Hall characterization,defect passivation,charge carrier transport,perovskites,charge recombination
更新于2025-09-12 10:27:22
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Enhanced Charge Carrier Transport in 2D Perovskites by Incorporating Single-Walled Carbon Nanotubes or Graphene
摘要： Two-dimensional (2D) organic-inorganic (hybrid) perovskites are considered promising candidates to replace conventional three-dimensional (3D) perovskites for solar cell applications as they have good resistance against moisture and UV light. However, the use of 2D perovskite is associated with a significant decrease in power efficiency resulting from their low photogenerated charge carrier density and poor charge transport. To improve power efficiency in 2D perovskites, highly crystalline films (near-single-crystal quality) of 2D perovskite needs to be synthesized where the alignment of the inorganic perovskite components is controlled to have vertical alignment with respect to the contacts to improve charge transport. In this work, we explored strategies to overcome this limitation, by integrating 2D perovskite with single-walled carbon nanotubes or graphene to enable more efficient extraction of charge carriers toward electric contacts. Longer carrier lifetimes were achieved after the incorporation of the carbon nanostructures in the films and at cell level, power efficiency increased by two-fold.
关键词： 2D perovskites,charge-carrier transport,solar cells,single-walled carbon nanotubes,graphene
更新于2025-09-11 14:15:04
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Enhanced carrier transport and bandgap reduction in sulfur-modified BiVO <sub/>4</sub> photoanodes
摘要： Recent progress on bismuth vanadate (BiVO4) has shown it to be among the highest performing metal oxide photoanode materials. However, further improvement, especially in the form of thin film photoelectrodes, is hampered by its poor charge carrier transport and its relatively wide bandgap. Here, sulfur incorporation is used to address these limitations. A maximum bandgap decrease of ~0.3 eV is obtained, which increases the theoretical maximum solar-to-hydrogen efficiency from 9 to 12%. Hard X-ray photoelectron spectroscopy (HAXPES) measurements as well as density functional theory (DFT) calculations show that the main reason for the bandgap decrease is an upward shift of the valence band maximum. Time-resolved microwave conductivity measurements reveal an ~3 times higher charge carrier mobility compared to unmodified BiVO4, resulting in a ~70% increase in the carrier diffusion length. This work demonstrates that sulfur doping can be a promising and practical method to improve the performance of wide-bandgap metal oxide photoelectrodes.
关键词： bismuth vanadate,photoelectrochemical performance,charge carrier transport,BiVO4,sulfur incorporation,bandgap reduction
更新于2025-09-11 14:15:04
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Radially resolved electronic structure and charge carrier transport in silicon nanowires
摘要： The electronic structure of silicon nanowires is studied using density functional theory. A radially resolved density of states is discussed for different nanowire diameters and crystal orientations. This approach allows the investigation of spatially varying electronic properties in the radial direction and extends previous studies, which are usually driven by a one-dimensional band structure analysis. We demonstrate strong differences in the electronic structure between the surface and the center of the nanowire, indicating that the carrier transport will mainly take place in the center. For increasing diameters, the density of states in the center approaches the bulk density of states. We find that bulk properties, such as the indirect nature of the band gap, become significant at a nanowire diameter of approximately 5 nm and beyond. Finally, the spatial characteristic of the current is visualized in terms of transmission pathways on the atomic scale. Electron transport is found to be more localized in the nanowire center than the hole transport. It also depends on the crystal orientation of the wire. For the growing demand of silicon nanowires, for example in the field of sensors or field-effect transistors, multiple conclusions can be drawn from the present work, which we discuss towards the end of the publication.
关键词： charge carrier transport,radially resolved density of states,silicon nanowires,density functional theory,electronic structure
更新于2025-09-09 09:28:46
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Crystal facet engineering induced anisotropic transport of charge carriers in a perovskite
摘要： Precise control of crystal orientations and macroscopic morphology of a perovskite crystal is crucial for various optoelectronic applications relying on charge carrier transport tuning along exposed crystal facets. Here, taking methylammonium lead bromide (CH3NH3PbBr3) as an example, and employing a novel crystal facet engineering method, we successfully construct two kinds of perovskite crystals with exposed {001} and {110} facets. We find that the free carriers’ photoluminescence lifetime on the {001} facets can be 3 times longer than that on {110} facets. The related mechanisms are investigated via fluorescence lifetime imaging microscopy and in situ transmission electron microscopy. These indicate that the different trap state density of exposed facets and crystal structure changing of CH3NH3PbBr3 under light and electron beam irradiation lead to the differences in carrier transport along different facets. By distinguishing the charge carrier transport on different CH3NH3PbBr3 exposed facets, micro-photodetectors have been constructed. A device fabricated with the {001} exposed facets exhibited two orders of magnitude higher photocurrent and half as much dark current as a {110} facet-based device. Thus, the crystal facet engineering of perovskites can be widely adopted for understanding physical/chemical properties of perovskite crystals and provides great potential for novel perovskite optoelectronic device applications.
关键词： crystal facet engineering,charge carrier transport,optoelectronic applications,photodetectors,perovskite
更新于2025-09-09 09:28:46