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Ultra-thin films of barium fluoride with low work function for thermionic-thermophotovoltaic applications
摘要： The deposition of barium fluoride thin and ultra-thin films on gallium arsenide substrates was performed by electron beam evaporation for analyzing the influence of film thickness and chemical composition on the work function of the resulting heterostructure. X-ray photoemission spectroscopy combined with ultraviolet photoemission spectroscopy measurements reveals that films of 2 nm nominal thickness and Ba/F ? 1.0 stoichiometry ratio induce the achievement of a significantly low work function of 2.1 eV to the BaFx/GaAs heterostructure. The significant reduction of the work function at least down to 3.0 eV is confirmed by a test thermionic converter operating at a cathode temperature of 1385 C, where the heterostructure was applied as anode. The low work function, together with a negligible optical absorption, makes feasible the practical application of barium fluoride coatings on GaAs within hybrid thermionic-thermophotovoltaic devices.
关键词： Ultraviolet photoemission spectroscopy,Work function,Barium fluoride,Thermionic-thermophotovoltaic energy conversion
更新于2025-09-19 17:13:59
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Self-Assembled Monolayers with Embedded Dipole Moments for Work Function Engineering of Oxide Substrates
摘要： Self-assembled monolayers (SAMs) are frequently used for work function (WF) engineering of different materials. For this, typically dipolar groups are attached to the molecule terminus at the SAM?ambient interface, which also influences its chemistry. WF engineering and interface chemistry can, however, be decoupled from one another using embedded dipolar groups, as has been demonstrated before for thiolate SAMs on metals. Herein, we extend this concept to oxide substrates. For this, a series of biphenyl-based molecules with a phosphonic acid (PA) anchoring group was synthesized, with one of the nonpolar phenyl units exchanged for a polar pyrimidine moiety, the dipole moment of which is oriented either toward (“down”) or away (“up”) to/from the PA group and, consequently, to/from the substrate. SAMs of these molecules formed on indium tin oxide (ITO), a frequently used and application-relevant oxide substrate, feature a uniform molecular configuration, dense molecular packing, and an upright molecular orientation. These SAMs exhibit pronounced electrostatic effects associated with the embedded dipolar groups, viz. shifts of the characteristic peaks in the C 1s X-ray photoelectron spectra and WF variations. The latter values were found to be 3.9, 4.85, and 4.4 eV for the up, down, and nonpolar reference SAM-engineered ITO, respectively. Consequently, these SAMs can serve as a powerful tool to monitor WF engineering effects in a variety of device assembles, decoupling these effects from the interface chemistry. The comparably low WF value for the up SAM is particularly important since it extends a rather limited variety of SAMs capable of lowering the WF of ITO.
关键词： Phosphonic acid,Self-assembled monolayers,Work function engineering,Embedded dipolar groups,Indium tin oxide,Oxide substrates
更新于2025-09-19 17:13:59
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Numerical Simulation on Effects of TCO Work Function on Performance of a-Si:H Solar Cells
摘要： In this paper, we have investigated the effect of the work function of transparent conducting oxides (TCO) on the performance of a-Si:H p-i-n solar cells, including open circuit voltage (VOC), short circuit current (JSC), fill factor (FF) and conversion efficiency, using AFORS-HET software. The simulation has focused on two layers: front contact work function (ΦTCO-front) and back contact work function (ΦTCO-back) with various band energy gap from 4.7 eV to 5.3 eV and 4.2 eV to 4.9 eV respectively. From the simulation results, we know that the work function of TCO greatly affects the performance of solar cells such as Voc, Jsc, FF and conversion efficiency. By optimization, we arrive at results of Voc, Jsc, FF and conversion efficiencies of 0.88 V, 8.95 mA / cm2, 65% and 5.1% respectively, by using ΦTCO-front of 5.2 eV. When ΦTCO-front > 5.2 eV, the values of VOC, FF and conversion efficiency have been saturated, while the value of the J sc actually begins to decrease. Furthermore, when the ΦTCO - back is 4.3 eV, we get the best results for VOC, Jsc, FF and conversion Efficiency of 0.9 V, 8.96 mA / cm2, 73 % and 5.9 % respectively. When ΦTCO-back > 4.3 eV, the values of VOC, FF and conversion efficiency begin to decrease, while the value of the Jsc does not change significantly. These optimizations may help for producing low cost high efficiency p-i-n solar cells experimentally.
关键词： work function,AFORS-HET,numerical simulation,a-Si:H,p-i-n solar cell
更新于2025-09-16 10:30:52
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The green poly-lysine enantiomers as electron-extraction layers for high performance organic photovoltaics
摘要： In this study, we first revealed green materials – poly-lysines (poly-L-lysine and poly-L-lysine blend poly-D-lysine) – as electron-extraction layers (EELs) in organic photovoltaics (OPVs). The distinct configurations of poly-lysine enantiomers were verified by conducting zeta potential analysis, and their work function (WF)-tuning capabilities for indium tin oxide (ITO) were affirmed by ultraviolet photoelectron spectroscopy (UPS). These two poly-lysine groups, with different arrangements of the amino groups that built up different surface dipoles on the ITO substrate, altered the surface energy and WF of ITO. Poly-L-lysine optimized the WF of ITO for efficient carrier transport in the OPV device, in the electron transporting layer-free OPV devices, and we observed a high power conversion efficiency (PCE) of 10.01% in the device configuration of ITO/interlayer/BHJ/MoO3/Ag. As the first examination of poly-lysine enantiomers for OPVs, we provided the WF-tuning functions – increasing polarity as an interfacial dipole is formed at the corresponding interface, and discovered a promising interfacial material possessing high efficiency and benefitting from a long-term stability to perform in a stable PCE with about 80% of its original PCE remaining after continuous heat and light treatment for 400 hours.
关键词： interfacial dipole,organic photovoltaics,electron-extraction layers,poly-lysine,work function tuning
更新于2025-09-16 10:30:52
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Effect on the reduction of the barrier height in rear-emitter silicon heterojunction solar cells using Ar plasma-treated ITO film
摘要： In this study, we investigated the effect of plasma treatment on an indium tin oxide (ITO) film under an ambient Ar atmosphere. The sheet resistance of the plasma-treated ITO film at 250 W (37.6 ?/sq) was higher than that of the as-deposited ITO film (34 ?/sq). Plasma treatment was found to decrease the ITO grain size to 21.81 nm, in comparison with the as-deposited ITO (25.49 nm), which resulted in a decrease in the Hall mobility. The work function of the Ar-plasma-treated ITO (WFITO = 4.17 eV) was lower than that of the as-deposited ITO film (WFITO = 5.13 eV). This lower work function was attributed to vacancies that formed in the indium and oxygen vacancies in the bonding structure. Rear-emitter silicon heterojunction (SHJ) solar cells fabricated using the plasma-treated ITO film exhibited an open circuit voltage (VOC) of 734 mV, compared to SHJ cells fabricated using the as-deposited ITO film, which showed a VOC of 704 mV. The increase in VOC could be explained by the decrease in the work function, which is related to the reduction in the barrier height between the ITO and a-Si:H (n) of the rear-emitter SHJ solar cells. Furthermore, the performance of the plasma-treated ITO film was verified, with the front surface field layers, using an AFORS-HET simulation. The current density (JSC) and VOC increased to 39.44 mA/cm2 and 736.8 mV, respectively, while maintaining a WFITO of 3.8 eV. Meanwhile, the efficiency was 22.9% at VOC = 721.5 mV and JSC = 38.55 mA/cm2 for WFITO = 4.4 eV. However, an overall enhancement of 23.75% in the cell efficiency was achieved owing to the low work function value of the ITO film. Ar plasma treatment can be used in transparent conducting oxide applications to improve cell efficiency by controlling the barrier height.
关键词： Work function,Silicon heterojunction solar cell,Transparent conducting oxide,AFORS-HET,Plasma treatment,Indium Tin Oxide
更新于2025-09-16 10:30:52
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Optimizing Lignosulfonic Acid-Grafted Polyaniline as a Hole-Transport Layer for Inverted CH <sub/>3</sub> NH <sub/>3</sub> PbI <sub/>3</sub> Perovskite Solar Cells
摘要： A conducting polymer of lignosulfonic acid-grafted, polyaniline-doped camphorsulfonic acid (LS-PANI-CSA), created via a low-temperature solution process, has been explored as an efficient hole-transport layer (HTL) for inverted single cation?anion CH3NH3PbI3 perovskite solar cells. The performance of the solar cell was optimized in this study by tuning the morphology and work function of LS-PANI-CSA films using dimethylsulfoxide (DMSO) as a solvent in treatment. Results showed that DMSO washing enhanced the electronic properties of the LS-PANI-CSA film and increased its hydrophobicity, which is very important for perovskite growth. The perovskite active layer deposited onto the DMSO-treated LS-PANI-CSA layer had higher crystallinity with large grain sizes (>5 μm), more uniform and complete surface coverage, and very low pinhole density and PbI2 residues compared to untreated LS-PANI-CSA. These enhancements result in higher device performance and stability. Using DMSO-treated LS-PANI-CSA as an HTL at 15 nm of thickness, a maximum 10.8% power conversion efficiency was obtained in ITO/LS-PANI-CSA/MAPbI3/PCBM/BCP/Ag inverted-device configurations. This was a significant improvement compared to 5.18% for devices based on untreated LS-PANI-CSA and a slight improvement over PEDOT:PSS-based devices with 9.48%. Furthermore, the perovskite based on treated LS-PANI-CSA showed the higher stability compared to both untreated LS-PANI-CSA and PEDOT:PSS HTL-based devices.
关键词： stability,hole-transport layer,hydrophobicity,perovskite solar cells,device performance,work function,lignosulfonic acid-grafted polyaniline,DMSO treatment,conducting polymer
更新于2025-09-16 10:30:52
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Energy Level Modification with Carbon Dot Interlayers Enables Efficient Perovskite Solar Cells and Quantum Dot Based Lighta??Emitting Diodes
摘要： Controlling the transport and minimizing charge carrier trapping at interfaces is crucial for the performance of various optoelectronic devices. Here, how electronic properties of stable, abundant, and easy-to-synthesized carbon dots (CDs) are controlled via the surface chemistry through a chosen ratio of their precursors citric acid and ethylenediamine are demonstrated. This allows to adjust the work function of indium tin oxide (ITO) films over the broad range of 1.57 eV, through deposition of thin CD layers. CD modifiers with abundant amine groups reduce the ITO work function from 4.64 to 3.42 eV, while those with abundant carboxyl groups increase it to 4.99 eV. Using CDs to modify interfaces between metal oxide (SnO2 and ZnO) films and active layers of solar cells and light-emitting diodes (LEDs) allows to significantly improve their performance. Power conversion efficiency of CH3NH3PbI3 perovskite solar cells increases from 17.3% to 19.5%; the external quantum efficiency of CsPbI3 perovskite quantum dot LEDs increases from 4.8% to 10.3%; and that of CdSe/ZnS quantum dot LEDs increases from 8.1% to 21.9%. As CD films are easily fabricated in air by solution processing, the approach paves the way to a simplified manufacturing of large-area and low-cost optoelectronic devices.
关键词： ITO work function,solar cells,interface engineering,light-emitting diodes,carbon dots
更新于2025-09-16 10:30:52
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Synergistic Interface Energy Band Alignment Optimization and Defect Passivation toward Efficient and Simplea??Structured Perovskite Solar Cell
摘要： Efficient electron transport layer–free perovskite solar cells (ETL-free PSCs) with cost-effective and simplified design can greatly promote the large area flexible application of PSCs. However, the absence of ETL usually leads to the mismatched indium tin oxide (ITO)/perovskite interface energy levels, which limits charge transfer and collection, and results in severe energy loss and poor device performance. To address this, a polar nonconjugated small-molecule modifier is introduced to lower the work function of ITO and optimize interface energy level alignment by virtue of an inherent dipole, as verified by photoemission spectroscopy and Kelvin probe force microscopy measurements. The resultant barrier-free ITO/perovskite contact favors efficient charge transfer and suppresses nonradiative recombination, endowing the device with enhanced open circuit voltage, short circuit current density, and fill factor, simultaneously. Accordingly, power conversion efficiency increases greatly from 12.81% to a record breaking 20.55%, comparable to state-of-the-art PSCs with a sophisticated ETL. Also, the stability is enhanced with decreased hysteresis effect due to interface defect passivation and inhibited interface charge accumulation. This work facilitates the further development of highly efficient, flexible, and recyclable ETL-free PSCs with simplified design and low cost by interface electronic structure engineering through facile electrode modification.
关键词： perovskite solar cells,energy level alignment,work function,nonconjugated small molecules,electron transport layers
更新于2025-09-16 10:30:52
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Selfa??Assembled Ionic Liquid for Highly Efficient Electron Transport Layer Free Perovskite Solar Cells
摘要： The electron-transport-layer (ETL) free perovskite solar cells (PSCs) are attractive because of fewer layers and hence lower cost, but the lower photovoltaic performance, as compared to the ETL-contained PSCs, largely restricts their practical applications. Herein, we design and synthesize hydroxylethyl functionalized imidazolium iodide, whose single crystal structure is determined, and propose self-assembled ionic liquid on the conductive substrate for ETL-free PSCs. It is found that the self-assembly of the ionic liquid on the conductive substrate can lower the work function of the conductive substrate, enhance the interfacial electron extraction, and meanwhile retard interfacial charge recombination. As a consequence, the power conversion efficiency is remarkably improved from 9.01% to 17.31% upon the self-assembly of ionic liquid on the conductive substrate. This finding provides a new way to achieve highly efficient ETL free PSCs.
关键词： electron transport layer free,perovskite solar cell,self-assembly,Ionic liquid,work function
更新于2025-09-16 10:30:52
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Controlled Growth of Silver Nanoparticles on Indium Tin Oxide Substrates by Plasma-Assisted Hot-Filament Evaporation: Physical Properties, Composition, and Electronic Structure
摘要： High-density silver (Ag) nanoparticles of controllable size and uniformity were used to enhance conductivity and luminance efficiency in an organic light emitting diode device. As part of this experiment, Ag nanoparticles were deposited on indium tin oxide (ITO) substrates by using plasma-assisted hot-filament evaporation. These nanoparticles mainly exhibited spherical grain morphology, with average diameters ranging between 7.5 and 45.7 nm depending on substrate temperature; the size of Ag nanoparticles are known to increase with rises in substrate temperatures up to 250°C, a phenomenon attributable to thermally induced surface diffusion. With regards to the optical spectra, the characteristics of the localised surface plasmon resonance were directly affected by changes in the physical properties of the Ag nanoparticles, such as diameter and interparticle distance. The X-ray photoemission spectroscopy results revealed the formation of a shell layer of silver oxide on the Ag nanoparticles. This resulted in a significant effect on the optical and electrical properties of the Ag nanoparticles/ITO. The highest density of Ag nanoparticles deposited at 80°C were associated with the lowest sheet resistance and work function at 7.45 Ohm/square and 3.97 eV, respectively, while increases in the oxide formation significantly increased the sheet resistance and work function up to 200°C. The effects of substrate temperature on the morphology, structure, as well as optical and electrical properties of the deposited Ag nanoparticles on ITO are discussed in further detail in this report.
关键词： Substrate temperature,Silver,Surface plasmon resonance,Work function,Silver oxide,Nanoparticles,Plasma-assisted hot-filament evaporation
更新于2025-09-12 10:27:22