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Decoupling Effects of Surface Recombination and Barrier Height on p-Si(111) Photovoltage in Semiconductor|Liquid Junctions via Molecular Dipoles and Metal Oxides
摘要： This work provides insight into carrier dynamics in a model photoelectrochemical system comprised of a semiconductor, metal oxide, and metal. To isolate carrier dynamics from catalysis, a common catalytic metal (Pt) is used in concert with an outer-sphere redox couple. Silicon (111) substrates were surface-functionalized with electronegative aryl moieties (p-nitrophenyl and m-dinitrophenyl). A mixed monolayer using p-nitrophenyl/methyl exhibited high surface quality as determined by X-ray photoelectron spectroscopy (low surface SiOx content) and low surface recombination velocity. This substrate also exhibited the expected positive surface dipole, as evidenced by rectifying J?V behavior on p-type substrates, and by positive photovoltage measured by surface photovoltage spectroscopy. Its close molecular relative m-dinitrophenyl exhibited poor electronic surface quality as indicated by high SiOx coverage and high surface recombination velocities (S > 3000 cm s?1). Photoelectrochemical J?V measurements of p-type Si-functionalized surfaces in contact with a high concentration (50 mM) of methyl viologen (MV2+) in aqueous media revealed VOC values that are correlated with the measured barrier heights. In contrast, low-concentration (1.5 mM) MV2+ experiments revealed significant contributions from surface recombination. Next, the electronic and (photo)electrochemical properties were studied as a function of ALD metal oxide deposition (TiO2, Al2O3) and Pt deposition. For the m-dinitrophenyl substrate, ALD deposition of both TiO2 and Al2O3 (150 °C, amorphous) decreased the surface recombination velocity. Surprisingly, this TiO2 deposition resulted in negative shifts in VOC for all surfaces (possibly ALD-TiO2 defect band effects). However, Pt deposition recovered the efficiencies beyond those lost in TiO2 deposition, affording the most positive VOC values for each substrate. Overall, this work demonstrates that (1) when carrier collection is kinetically fast, p-Si(111)?R devices are limited by thermal emission of carriers over the barrier, rather than by surface recombination. And (2) although TiO2 |Pt improves the PEC performance of all substrates, the beneficial effects of the underlying (positive) surface dipole are still realized. Lastly (3) Pt deposition is demonstrated to provide beneficial charge separation effects beyond enhancing catalytic rates.
关键词： solar fuels,interfacial dipole,atomic layer deposition (ALD),surface functionalization,band-edge modulation,photoelectrochemistry
更新于2025-09-23 15:22:29
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Influence of Film Thickness on the Electronic Band Structure and Optical Properties of Pa??Ia??N CH <sub/>3</sub> NH <sub/>3</sub> PbI <sub/>3a??x</sub> Cl <sub/>x</sub> Perovskite Solar Cells
摘要： The phenomenal optoelectronic properties of lead halide perovskites have spurred a remarkable worldwide effort to develop them as photovoltaic materials. The morphology and crystal structure of the films have a profound effect on the characteristics and performance of devices; however, the influence of underlying hole transport layers (HTLs) or electron transport layers (ETLs) and film thickness on the film morphology and electronic characteristics remains unclear. In this work, we have studied the characteristics of perovskite films with variable thickness, including the morphological, crystal, optical properties and electronic band structure of these films using scanning electron microscopy (SEM), X-ray diffraction (XRD) and ultraviolet-visible (UV-vis) absorption spectra. The corresponding performance of perovskite solar cells (PSCs) devices was correlated with the different thicknesses of perovskite films. Additionally, ultraviolet photoelectron spectroscopy (UPS) results show that for the optimized perovskite thickness (310 nm) the interfacial dipole (?) formed at the interface with the substrate reaches its highest value of 0.23 eV. Hence, this strong dipole compared to other thicknesses allows the carriers to be swept out efficiently.
关键词： Film thickness,Perovskite,Solar cell,Interfacial dipole
更新于2025-09-23 15:19:57
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The effect of introducing antibiotics into organic light-emitting diodes
摘要： The quest to improve the performance of organic light-emitting diodes (OLEDs) has led to the exploration of new materials with properties like interfacial dipole, excitons generation, and bandgap alignment. Here, we exploit these strategies by investigating the interaction of the antibiotic ampicillin with a widely used optoelectronic material, to fabricate state-of-the-art OLEDs. The charge distribution on the ampicillin molecule facilitates the generation of an interfacial dipole with a large magnitude. The optimum fusion of the two materials provides an enhanced bandgap alignment, charge balance and J/H-aggregated excitons. Values of current efficiency (120 cdA?1), external quantum efficiency (~35%) and power efficiency (70 lmW?1) are demonstrated. The cross-evaluation of performance with penicillin devices indicates the significance of ampicillin’s specific molecular structure in improving performance. The detailed investigations demonstrate that ampicillin has superior optoelectronic properties with high potential to contribute extensively in OLEDs and photovoltaics.
关键词： OLEDs,interfacial dipole,bandgap alignment,exciton generation,ampicillin
更新于2025-09-16 10:30:52
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Modulating Charge Separation Efficiency of Water Oxidation Photoanodes with Polyelectrolyte‐Assembled Interfacial Dipole Layers
摘要： The charge separation efficiency of water oxidation photoanodes is modulated by depositing polyelectrolyte multilayers on their surface using layer-by-layer (LbL) assembly. The deposition of the polyelectrolyte multilayers of cationic poly(diallyldimethylammonium chloride) and anionic poly(styrene sulfonate) induces the formation of interfacial dipole layers on the surface of Fe2O3 and TiO2 photoanodes. The charge separation efficiency is modulated by tuning their magnitude and direction, which in turn can be achieved by controlling the number of bilayers and type of terminal polyelectrolytes, respectively. Specifically, the multilayers terminated with anionic poly(styrene sulfonate) exhibit a higher charge separation efficiency than those with cationic counterparts. Furthermore, the deposition of water oxidation molecular catalysts on top of interfacial dipole layers enables more efficient photoelectrochemical water oxidation. The approach exploiting the polyelectrolyte multilayers for improving the charge separation efficiency is effective regardless of pH and types of photoelectrodes. Considering the versatility of the LbL assembly, it is anticipated that this study will provide insights for the design and fabrication of efficient photoelectrodes.
关键词： interfacial dipole,polyelectrolyte multilayers,charge separation,photoelectrodes
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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Suppressing Interfacial Dipoles to Minimize Open‐Circuit Voltage Loss in Quantum Dot Photovoltaics
摘要： Quantum-dot (QD) photovoltaics (PVs) offer promise as energy-conversion devices; however, their open-circuit-voltage (VOC) deficit is excessively large. Previous work has identified factors related to the QD active layer that contribute to VOC loss, including sub-bandgap trap states and polydispersity in QD films. This work focuses instead on layer interfaces, and reveals a critical source of VOC loss: electron leakage at the QD/hole-transport layer (HTL) interface. Although large-bandgap organic materials in HTL are potentially suited to minimizing leakage current, dipoles that form at an organic/metal interface impede control over optimal band alignments. To overcome the challenge, a bilayer HTL configuration, which consists of semiconducting alpha-sexithiophene (α-6T) and metallic poly(3,4-ethylenedioxythiphene) polystyrene sulfonate (PEDOT:PSS), is introduced. The introduction of the PEDOT:PSS layer between α-6T and Au electrode suppresses the formation of undesired interfacial dipoles and a Schottky barrier for holes, and the bilayer HTL provides a high electron barrier of 1.35 eV. Using bilayer HTLs enhances the VOC by 74 mV without compromising the JSC compared to conventional MoO3 control devices, leading to a best power conversion efficiency of 9.2% (>40% improvement relative to relevant controls). Wider applicability of the bilayer strategy is demonstrated by a similar structure based on shallow lowest-unoccupied-molecular-orbital (LUMO) levels.
关键词： band engineering,quantum dot solar cells,interfacial dipole,hole transport layers
更新于2025-09-11 14:15:04