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Origin of the High Donor-Acceptor Composition Tolerance in Device Performance and Mechanical Robustness of All-Polymer Solar Cells
摘要： High tolerance regarding photovoltaic performance in terms of donor:acceptor (D:A) composition ratio is reported for all-polymer solar cells (all-PSCs), which is a crucial advantage in producing large-scale devices with high reproducibility. To understand the origin of high D:A ratio tolerance in all-PSCs, we investigate the molecular weight (MW) effects of the P(NDI2OD-T2) polymer acceptor (PA) on photovoltaic and mechanical robustness of PBDB-T:P(NDI2OD-T2) all-PSCs. Also, we compare the all-PSCs with other types of PSCs consisting of the same polymer donor but using small molecule acceptors (SMAs) including ITIC and PC71BM. It is observed that the D:A ratio tolerances of both the photovoltaic and mechanical properties are highly dependent on the PA MW and the acceptor material types. For example, at a high D:A ratio of 15:1, all-PSCs using high MW PA (number-average molecular weight (Mn)= 97 kg mol-1) exhibit 13 times higher normalized power conversion efficiency (PCE) than all-PSCs using low MW PA (Mn= 11 kg mol-1), and 20 times higher than ITIC-based PSCs. In addition, the electron mobilities in all-PSCs based on high MW PA are well maintained even at very high D:A ratio, whereas the electron mobilities in low MW PA all-PSCs and SMA-based PSCs decrease by 3- and 4-orders of magnitude, respectively, when the D:A ratio increases from 1:1 to 15:1. Thus, we suggest that the formation of tie molecules and chain entanglements by long polymer chains bridging adjacent crystalline domains is the main origin of excellent D:A tolerance in both mechanical robustness and photovoltaic performance. This work provides an important material design guideline for the reproducible production of flexible and stretchable all-PSCs.
关键词： molecular weight effects,mechanical robustness,donor-acceptor composition tolerance,photovoltaic performance,all-polymer solar cells
更新于2025-09-12 10:27:22
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Performance evaluation of composition graded layer of aSi1-xGex: H in n+aSi:H/i-aSi:H/p+aSi1-xGex:H graded band gap single junction solar cells
摘要： The work investigates the role of composition grading of amorphous silicon germanium alloy on single junction graded band gap amorphous silicon solar cells, for the first time. The fabrication and optical characterization of composition graded aSi1-xGex: H alloy by varying the gas flow rate of germane (GeH4) are presented. We propose the composition graded p+aSi1-xGex: H layer to be considered as one of the active layers in amorphous silicon based solar cells. The principle of operation of the solar cell is illustrated with the energy band diagram of proposed n+aSi:H/i-aSi:H/p+aSi1-xGex:H solar cell structure. Further, the behavior of the structure is evaluated through simulation in terms of proposed layer thickness variation and temperature variation. It is observed that the proposed structure is capable of delivering an open circuit voltage (V oc), short circuit current density (Jsc), Fill Factor (FF) and conversion efficiency (g) of 1.1 V, 15.56 mA/cm2, 0.885 and 15.19% respectively, which is at par with any other single junction amorphous silicon solar cells. The cell performance parameters were compared with related state of the art as well as our previous works. The performance parameters of proposed structure show that it is better to use a single composition graded layer instead of using a number of non-graded composition layers in photovoltaic structures, which reduces complexity and cost of fabrication.
关键词： Internal Quantum Efficiency,Optical band gap,Germane flow rate,Conversion efficiency,Composition grading,PECVD
更新于2025-09-12 10:27:22
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Tuning methylammonium iodide amount in organolead halide perovskite materials by post-treatment for high-efficiency solar cells
摘要： In this study, the composition of organic-inorganic perovskite materials is tuned by methylammonium iodide (MAI) post-treatment for high photovoltaic performance. By spin-coating MAI solutions of different concentrations, the amounts of PbI2 and MAI in perovskite layers are tuned. In perovskites, the removal of PbI2 through a reaction with MAI decreases the hysteresis in photocurrent density-voltage curves. Further, by treating perovskites with a high-concentration MAI solution, the excess MAI is incorporated into the perovskites. These perovskites with excess MAI show better power conversion efficiencies (of up to 20.7%) than perovskites with excess PbI2, because of the decrease in trap density. Since the present post-treatment can control perovskite composition without affecting the morphology and crystallinity of the perovskite crystals, this technique would be a useful tool to improve the photovoltaic performance of perovskite solar cells.
关键词： ion composition,performance enhancement,perovskite solar cells,trap density,surface treatment
更新于2025-09-12 10:27:22
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Impact of Donor–Acceptor Interaction and Solvent Additive on the Vertical Composition Distribution of Bulk-Heterojunction Polymer Solar Cells
摘要： The vertical composition distribution of bulk-heterojunction (BHJ) photoactive layer is known to have dramatic effects on photovoltaic performance in polymer solar cells. However, the vertical composition distribution evolution rules of BHJ films are still elusive. In this contribution, three BHJ film systems, composed of polymer donor PBDB-T and three different classes of acceptor –fullerene acceptor PCBM, small molecule acceptor ITIC, and polymer acceptor N2200 –are systematically investigated using neutron reflectometry to examine how donor–acceptor interaction and solvent additive impact the vertical composition distribution. Our results show that those three BHJ films possess homogeneous vertical composition distributions across the bulk of the film. While very different composition accumulations near the top and bottom surface were observed which could be attributed to different repulsion, miscibility, and phase separation between the donor and acceptor components as approved by the measurement of donor–acceptor Flory–Huggins interaction parameter χ. Moreover, the solvent additive 1,8-diiodooctane (DIO) can induce more distinct vertical composition distribution especially in non-fullerene acceptor based BHJ films. Thus, higher power conversion efficiencies were achieved in inverted solar cells because of facilitated charge transport in active layer, improved carrier collection at electrodes, suppressed charge recombination in BHJ solar cells.
关键词： Flory–Huggins Interaction Parameter χ,Bulk-Heterojunction,Neutron Reflectometry,Polymer Solar Cells,Vertical Composition Distribution
更新于2025-09-12 10:27:22
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Effect of helium-argon shielding gas in laser-metal inert-gas hybrid welded-brazed Al/steel dissimilar joint
摘要： Laser-metal inert-gas welding hybrid welding was applied to dissimilar butt joining of 304 stainless steel and 6063 aluminum alloy using three different shielding gas: 100% argon, 25% helium + 75% argon, and 50% helium + 50% argon. The influence of helium–argon shielding gas on the weld appearance and interfacial intermetallics layer of Al/stainless steel welding-brazing joint was discussed. The addition of helium can shrink arc, suppress laser plasma, and increase the stability of the droplet transfer process. Helium could not change the composition of the interface layer, which consists of θ-Fe(Al, Si)3 layer and τ5-Al7.2Fe1.8Si layer in the top, middle, and bottom regions of the joints. However, the interfacial intermetallics layer becomes thinner and the morphology was more uniform as the helium content changed from 0% to 50%. By analyzing the tensile fracture, it was found that the thicker θ-Fe(Al, Si)3 easily caused the fracture at the interface layer when using 100% argon. The highest tensile strength and the best ductility can be obtained by using 50% helium + 50% argon compared with that of joints obtained with 100% argon and 25% helium + 75% argon. Compared with joints welded in the pure argon atmosphere, the strength and ductility of joints increased by 18.4% and 191%, respectively.
关键词： laser-MIG hybrid welding-brazing,microstructure,composition of shielding gas,dissimilar materials
更新于2025-09-12 10:27:22
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Effect of Indium Composition on the Microstructural Properties and Performance of InGaN/GaN MQWs Solar Cells
摘要： In the present work, InGaN/GaN multiple quantum wells (MQWs) solar cells with different concentrations of indium have been investigated in-depth. It was demonstrated that applying a medium-high indium content (about 28%) does not facilitate solar cell photoelectric conversion efficiency due to the increase of edge dislocations. Moreover, the effects of different indium contents on InGaN/GaN MQWs solar cells were investigated and was revealed, that the short-circuit current density and photoelectric conversion efficiency are improved with the increase of indium contents. However, they show a noticeable reduction in the indium content of 28%. Furthermore, the optical properties and the behaviour of the microstructure defects were analysed. It was also demonstrated that the number of edge dislocations acted as non-radiation recombination centers increasing rapidly when the indium content reaches 28%, playing a key role in decreasing the active number of photon-generated carriers. As a result, the short-circuit current density and photoelectric conversion efficiency decrease obviously for an indium content of 28%. This work can provide insight into the origin of the degradation of these structures and the improvement of device design with medium-high indium contents.
关键词： solar cells.,InGaN/GaN multiple quantum wells (MQWs),microstructure and performance,Indium composition
更新于2025-09-12 10:27:22
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Fabrication of chemical composition controlled YbFe <sub/>2</sub> O <sub/>4</sub> epitaxial thin films
摘要： The crystal growth of YbFe2O4 requires oxidant-poor conditions, thus YbFe2O4 usually contains a large number of iron deficiencies even in the bulk single crystal. The use of an ArF laser for laser ablation is effective to reduce the amount of active oxygen species and a wide process window to form the YbFe2O4 epitaxial films becomes available. By using the widened process window and an iron-rich target, the chemical composition of the YbFe2O4 epitaxial thin films is successfully controlled. The effect of the iron composition on the charge ordering transition can be discussed using the nonlinear I–V behavior. The threshold electric field changes depending on the iron composition owing to the broadening of the 3-dimensional (3D) charge order region, which affects the robustness of the 3D charge order against an electric field in YbFe2O4 thin films.
关键词： YbFe2O4,laser ablation,epitaxial thin films,chemical composition control,charge ordering
更新于2025-09-11 14:15:04
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Ni/4H-SiC interaction and silicide formation under excimer laser annealing for ohmic contact
摘要： Nickel Silicidation reactions were activated on 4H-SiC using laser annealing at wavelength of 308 nm to study interaction and re-action of the involved atomic species. With this intent, the deposited nickel layer thickness was scaled from 100 nm to 10 nm and the laser fluence was spanned from 2.2 to 4.2 J/cm2. A combination of structural characterization by X-ray diffraction, Energy-Dispersive X-ray spectroscopy, Raman Spectroscopy, Transmission Electron Microscopy and morphological investigations through Scanning Electron Microscopy with theoretical predictions as a function of the applied laser fluence, have unveiled that the starting nickel thickness plays a main role, especially above the threshold for nickel melting (2.8J/cm2). As a general paradigm, sufficient silicon release from the substrate occurs above this threshold that is available for silicidation, with amount increasing with the laser fluence. This addresses stoichiometry and morphology of the silicided contact that indeed depend on the available Nickel atoms (i.e. the Ni layer thickness) and on the thermal profile, as tested at a fixed fluence of 3.8J/cm2. In addition, a layer-by-layer variable stoichiometry is established in each sample through the contact, with the deepest silicide being relatively more Si-rich. All those findings have impact on the electrical parameters of testing diodes. Based on data cross-linking, NiSi2 contacting layers and C-free interfaces provide a convenience in reducing resistance contributions.
关键词： simulation,silicon carbide,power device,UV-laser,silicidation reaction,chemical composition
更新于2025-09-11 14:15:04
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Pulsed laser deposition with rapid beam deflection by a galvanometer mirror scanner
摘要： A pulsed laser deposition system with rapid beam deflection (RBD-PLD) by a galvanometer mirror scanner has been developed for alternating ablation of multiple targets with a single laser instrument. In this system, the alternating deposition of different target materials is carried out by scanning the laser beam between the positionally fixed targets with a galvanometer mirror instead of mechanically switching the target positions on a fixed optical path of the laser beam as is done in conventional pulsed laser deposition (PLD) systems. Thus, the “wait” time required for switching target materials to be deposited, which typically takes several seconds in a conventional system, can be made as short as a few milliseconds. We demonstrate some of the advantages of this PLD system in several technologically important aspects of thin film synthesis: (1) fast fabrication of binary alloy films, (2) preparation of natural composition spread libraries, (3) effect of the target switching time on the deposition of volatile compounds, (4) control of the degree of mixing of two different materials in a film, and (5) efficient growth of compositionally graded thin films.
关键词： galvanometer mirror scanner,rapid beam deflection,composition spread libraries,volatile compounds,pulsed laser deposition,thin film synthesis,compositionally graded thin films,binary alloy films
更新于2025-09-11 14:15:04
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Effect of powder characteristics on production of oxide dispersion strengthened Fe 14Cr steel by laser powder bed fusion
摘要： In order to assess the potentialities of additive manufacturing in nuclear industry, Oxide Dispersion Strengthened (ODS) Fe\14Cr steels are produced by laser powder bed fusion (L-PBF). Such materials are currently manufactured by milling a Fe\14Cr atomized powder with Y2O3 and TiH2 powders. The resulting powder has a non-spherical shape being coarser than powders typically used in L-PBF equipment. The influence of powder characteristics on the processability of ODS Fe\14Cr by L-PBF are studied in details. Four different powders are used. These powders differ from size, morphology and chemical composition. Finer is the powder; wider is the process range to obtain dense samples. This phenomenon could be mitigated by transferring an amount of energy superior to 110 J.mm?3. The presence of yttrium and titanium gives columnar microstructure for ODS samples, whereas Fe\14Cr samples have stirred microstructure. Titanium and yttrium form oxides, which enlarge the melt pool and induce columnar growth.
关键词： Additive manufacturing,Powder flowability,Metal Matrix Composites (MMCs),Chemical composition,Laser Powder Bed Fusion (L-PBF),Particle size distribution
更新于2025-09-11 14:15:04