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(Top left: 2a) X‐ray photoelectron spectroscopy (XPS) measurements of unmodified, Zr‐containing and Sn‐containing molybdenum oxide layers. The MoOx region label indicates a region in which Mo(V) and Mo(IV) can occur simultaneously as impurities in the MoO3 matrix; (Bottom left: 2b) XPS fits of the relevant present Mo species, demonstrating the occurrence of the MoO3‐x sub‐oxide, MoO3 being the dominant species and charging or molybdenum vacancies; XPS (top right: 2c) and UPS (bottom right: 2d) determination of the valence band edge of unmodified and Zr‐ and Sn‐containing MoOx. Figure 2b only contains a single XPS plot, as both the unmodified and additive‐containing XPS measurements overlapped perfectly.
Source publication
The identification, fine‐tuning, and process optimization of appropriate hole transporting layers (HTLs) for organic solar cells is indispensable for the production of efficient and sustainable functional devices. In this study, the optimization of a solution‐processed molybdenum oxide (MoOx) layer fabricated from a combustion precursor is carried...
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... investigate the influence of the presence of zirconium and tin inside MoOx HTLs in organic photovoltaics, Zr- and Sn-containing molybdenum oxide films were compared to unmodified MoOx films via complementary analysis techniques. Thermogravimetric analysis (TGA) results obtained on dried fine powders (grain size <63 μm) show a very similar decomposition process for all three precursor systems ( Figure S2). Hence, all spin coated layers received an identical thermal treatment. ...
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... affects the electronic structure of molybdenum oxide, and thereby the hole extraction efficiency, charge recombination at Mo(V) gap states, the series resistance [44], and the shunt resistance (in OPV) [26]. However, this work ( Figure 2a) demonstrates a strong resemblance between the unmodified and Zr- or Sn-incorporated MoOx layers. In all cases, the molybdenum 3d5/2 core level is situated at the expected position for Mo(VI), being 232.7 eV, indicating the formation of mainly MoO3. ...
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... all cases, the molybdenum 3d5/2 core level is situated at the expected position for Mo(VI), being 232.7 eV, indicating the formation of mainly MoO3. Especially in the sub-stoichiometric MoO3-x region (towards lower binding energies, in which Mo occurs in the (V) or even (IV) oxidation state), the similarity between the Zr-containing, Sn-containing, and unmodified MoOx layer is remarkable (Figure 2b). Therefore, an eventual difference in device performance cannot be attributed to changes in the molybdenum oxidation state. ...
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... investigate possible modifications in the electronic structure induced by Zr and Sn additives, measurements of the valence band structure exploiting x-ray photoelectron spectroscopy (XPS, Figure 2c) and ultraviolet photoelectron spectroscopy (UPS, Figure 2d) were conducted. From these figures, the position of the valence band maximum with respect to the Fermi energy (the latter corresponding to zero binding energy) can be extracted, resulting in values of 3.15 eV (XPS) and 3.05 eV (UPS), both agreeing fairly well with literature results reported for undoped MoO3 [46]. ...
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... investigate possible modifications in the electronic structure induced by Zr and Sn additives, measurements of the valence band structure exploiting x-ray photoelectron spectroscopy (XPS, Figure 2c) and ultraviolet photoelectron spectroscopy (UPS, Figure 2d) were conducted. From these figures, the position of the valence band maximum with respect to the Fermi energy (the latter corresponding to zero binding energy) can be extracted, resulting in values of 3.15 eV (XPS) and 3.05 eV (UPS), both agreeing fairly well with literature results reported for undoped MoO3 [46]. ...
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... the XPS measurement ( Figure 2c) indicates a similar valence band maximum for the 35 nm-thick and the 220 nm-thick layers, providing supplementary proof that no indium diffusion takes place. Although slight changes in band structure can be noted if the UPS measurements (Figure 2d) for the different layers are carefully compared, the most plausible cause is surface contamination, as the UPS sampling depth is only 1 nm, and the samples were prepared ex-situ. ...
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... the XPS measurement ( Figure 2c) indicates a similar valence band maximum for the 35 nm-thick and the 220 nm-thick layers, providing supplementary proof that no indium diffusion takes place. Although slight changes in band structure can be noted if the UPS measurements (Figure 2d) for the different layers are carefully compared, the most plausible cause is surface contamination, as the UPS sampling depth is only 1 nm, and the samples were prepared ex-situ. As such, it can be confirmed that Sn and Zr will act as additives, rather than as dopants. ...
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... nm (discussed further), the roughness reduces drastically upon the addition of zirconium and tin into the combustion precursor, down to below 3 nm. However, in this case, the presence of additives does not dramatically affect the outgassing during the precursor decomposition pathway (as illustrated by TGA, Figure S2). Both zirconium and tin are introduced in a very limited amount (0.5%) using similar acetylacetonate compounds, and no catalytic decomposition effect can be observed in the TGA profiles. ...
Citations
... Orthorhombic MoO 3 is an n-type semiconductor with a wide band gap (about 3.2 eV) and a high relative permittivity [4]. Therefore, MoO 3 can be used, among others, in batteries, resistive random-access memories, sensors, and organic light-emitting diodes [4][5][6][7][8][9][10][11][12]. An additional important aspect of MoO 3 is its layered structure, i.e., its adjacent two-dimensional (2D) crystalline layers are bound by weak van der Waals interactions [2,13]. ...
Molybdenum trioxide shows many attractive properties, such as a wide electronic band gap and a high relative permittivity. Monolayers of this material are particularly important, as they offer new avenues in optoelectronic devices, e.g., to alter the properties of graphene electrodes. Nanoscale electrical characterization is essential for potential applications of monolayer molybdenum trioxide. We present a conductive atomic force microscopy study of an epitaxially grown 2D molybdenum oxide layer on a graphene-like substrate, such as highly oriented pyrolytic graphite (HOPG). Monolayers were also investigated using X-ray photoelectron spectroscopy, atomic force microscopy (semi-contact and contact mode), Kelvin probe force microscopy, and lateral force microscopy. We demonstrate mobility of the unpinned island under slight mechanical stress as well as shaping and detachment of the material with applied electrical stimulation. Non-stoichiometric MoO3-x monolayers show heterogeneous behavior in terms of electrical conductivity, which can be related to the crystalline domains and defects in the structure. Different regions show various I–V characteristics, which are correlated with their susceptibility to electrodegradation. In this work, we cover the existing gap regarding nanomanipulation and electrical nanocharacterization of the MoO3 monolayer.
... When studying the effects of blending charge-transporting materials and QDs, QLEDs with a conventional CdSe/ZnS QD EML and an HQD EML were separately fabricated. Two types of HTL materials were used to verify the combined effects of an HQD EML and an HTL; one type was MoOx [48,49], while the other was TAPC HTL. ...
Despite the importance of charge carrier injection balance for achieving high performance with quantum dot light-emitting diodes (QLEDs), there have been comparatively few relevant studies. Thus, we extensively analyzed charge carrier behaviors of QLEDs using an impedance spectroscopy (IS) method and a QLED-equivalent circuit. This yielded both the capacitive and resistive values of each of the emission layer (EML) and the charge transport layer (CTL), revealing the relationships between these values and device performance. Using this analysis method, we examined the effects of the combination of hybrid quantum dot (QD) EMLs and CTLs on QLED performance. The CdSe/ZnS QD and di-[4-(N,N-di-p-tolyl-amino)-phenyl]cyclohexane blended hybrid QD EML, in combination with the di-[4-(N,N-di-p-tolyl-amino)-phenyl]cyclohexane hole transport layer, produced electron–hole balance in EMLs and resulted in a remarkable improvement in device performance. The maximum current efficiency of a green QLED using this combination was 43.7 cd/A, which was approximately two-fold greater than the maximum current efficiency of a QLED with a conventional CdSe/ZnS QD EML and much better than previously reported values for green QLEDs with CdSe/ZnS-based EMLs. In summary, we have greatly improved QLED performance via charge balance optimization. Herein, we present the methods for this improvement, along with an analysis of carrier behavior.
... The smallest band offset (1.13 eV) between the valence band edge of V 0.05 MoO x and P3HT HOMO level favored the hole transport due to having the lowest resistance among all V-MoO x films [111]. Marchal et al. reported a decrease of 3 nm in the surface roughness of MoO x HTL by adding 0.5 mol% of Zr and Sn via a combustion chemical deposition method at low temperatures [112]. The Zr and Sn atoms also covered the surface defects of MoO x , forming a uniform and well-covered HTL film on the ITO electrode (see Figure 4a). ...
... (a) AFM and SEM images of unmodified and modified MoOx HTL. Adapted with permission from[112]. (b) Energy levels of pristine and doped MoO 3 with a NiOx layer. ...
Global energy demand is increasing; thus, emerging renewable energy sources, such as organic solar cells (OSCs), are fundamental to mitigate the negative effects of fuel consumption. Within OSC’s advancements, the development of efficient and stable interface materials is essential to achieve high performance, long-term stability, low costs, and broader applicability. Inorganic and nanocarbon-based materials show a suitable work function, tunable optical/electronic properties, stability to the presence of moisture, and facile solution processing, while organic conducting polymers and small molecules have some advantages such as fast and low-cost production, solution process, low energy payback time, light weight, and less adverse environmental impact, making them attractive as hole transporting layers (HTLs) for OSCs. This review looked at the recent progress in metal oxides, metal sulfides, nanocarbon materials, conducting polymers, and small organic molecules as HTLs in OSCs over the past five years. The endeavors in research and technology have optimized the preparation and deposition methods of HTLs. Strategies of doping, composite/hybrid formation, and modifications have also tuned the optical/electrical properties of these materials as HTLs to obtain efficient and stable OSCs. We highlighted the impact of structure, composition, and processing conditions of inorganic and organic materials as HTLs in conventional and inverted OSCs.
... [33] werea blet op roduce indium tin oxide TCO films with low electrical resistivity (4.2 10 À4 W cm) with an SCS procedure based on acetylacetonea nd metal nitrates. Bai et al. [34] achieved PEDOT:PSS-competitive NiO x hole transporting layers at temperatures as low as 175 8Cu sing SCS, just as Marchal et al. [28,35] employed SCS to obtain MoO x interface layers,r educing the temperature compared to conventional synthesis routes. [36] Wang et al. [37] obtained p-typeT CO films at 180 8Cm ixing metal nitrates with glycine in methoxyethanol. ...
Solution‐based (multi)metal oxide synthesis has been carried out employing a large diversity of precursor routes. The selection of an appropriate synthesis strategy is frequently dictated by the resulting material properties, although this choice should also be based on green chemistry principles, atom economy considerations and energy efficiency. In order to limit the required energy budget to convert the chemical precursor to the target oxide material, various approaches were recently reported. This Review summarizes some frequently encountered low‐temperature routes, critically assessing their application window and advantages. More specifically, auto‐combustion synthesis, UV‐assisted decomposition routes, sol–gel network adjustments and precursor complex design concepts are discussed. It is expected that this toolbox of low‐temperature strategies may assist further progress in the field, stimulating novel applications, such as flexible electronics or organic–oxide hybrid materials, which are very sensitive to the temperature requirements.
The development of efficient and stable interface materials is an important part of the research in organic photovoltaics (OPVs), which aims to realize higher efficiency, longer lifetime, lower cost, easier fabrication, and wider applicability. MoO3 exhibits suitable work function, adjustable electronic structure, favorable ohmic contact with organic materials, remarkable stability in the presence of water and oxygen, and excellent solution processing properties, making it an ideal anode buffer layer (ABL) for OPVs. This review analyzes the photoelectric characteristics of MoO3 based on the crystalline structure and its fundamentals as ABL in OPVs. To simplify the fabrication procedure, AHM, MoO2(acac)2, and MoO3 powder are used as precursors for solution processing MoO3 buffer layer, the attempts are still ongoing. Strategies of composite/hybrid, modification and doping are utilized to optimize the MoO3 ABL to obtain more efficient and stable OPVs. Combining the optical and electronic properties of MoO3, diverse applications are introduced in inverted, semi-transparent devices and tandem architectures, show the wide applicability of MoO3 in OPVs. This review draws the outline of the relationships between the composition, structure and processing method of MoO3 and device performance, and further studies for fully understand it from a deeper level are extremely needed, which is beneficial to improve the performance of OPVs and the research for solar cells with similar structure, such as perovskite solar cells.
As one of the most promising technologies for next-generation lighting and displays, white organic light-emitting diodes (WOLEDs) have received enormous worldwide interest due to their outstanding properties, including high efficiency, bright luminance, wide viewing angle, fast switching, lower power consumption, ultralight and ultrathin characteristics, and flexibility. In this invited review, the main parameters which are used to characterize the performance of WOLEDs are introduced. Subsequently, the state-of-the-art strategies to achieve high-performance WOLEDs in recent years are summarized. Specifically, the manipulation of charges and excitons distribution in the four types of WOLEDs (fluorescent WOLEDs, phosphorescent WOLEDs, thermally activated delayed fluorescent WOLEDs, and fluorescent/phosphorescent hybrid WOLEDs) are comprehensively highlighted. Moreover, doping-free WOLEDs are described. Finally, issues and ways to further enhance the performance of WOLEDs are briefly clarified.
