Low‐Temperature Solution‐Processed Molybdenum Oxide Nanoparticle Hole Transport Layers for Organic Photovoltaic Devices

Lee, Yun Ju; Yi, Juan; Gao, Galen F.; Koerner, Hilmar; Park, Kyoungweon; Wang, Jian; Luo, Kaiyuan; Vaia, Richard A.; Hsu, Julia W. P.

doi:10.1002/aenm.201200229

Cited by 88 publications

(88 citation statements)

References 23 publications

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“…In comparison, a further increase in reaction time to 24 hr caused the nanoparticle size to increase back to 2 nm. The increase in size with longer reaction time is consistent with our previous observation that the average diameter of chemically oxidized npMoO x from SAXS had increased to 4 nm after ∼15 days of chemical oxidation [18] and indicates that Ostwald ripening for these nanoparticles only occurs with the addition of H 2 O 2 . Nevertheless, the nanoparticles are still small enough to form multilayer films with thickness of ∼10 nm.…”

Section: Resultssupporting

confidence: 78%

“…Even without added ligands, the suspension showed excellent stability and remained dispersed for more than 90 days. DLS of the assynthesized npMoO x suspension found a volume weighted mean diameter of 2.1 ± 0.9 nm (Figure 2(a), dashed line), in good agreement with the size determined using small-angle X-ray scattering (SAXS) [18]. Storage of the as-synthesized npMoO x in air for up to 120 hrs led to no change in size, as confirmed by DLS (data not shown).…”

Section: Resultssupporting

confidence: 68%

“…Nevertheless, the nanoparticles are still small enough to form multilayer films with thickness of ∼10 nm. Indeed, we previously showed using atomic force microscopy that a chemically oxidized MoO x suspension spin coated on top of P3HT:PCBM formed a pinholefree film that planarized the roughness of the underlying P3HT:PCBM layer [18]. Thus, while npMoO x size increases after chemical oxidation with increase Φ (Figure 2(b), purple).…”

Section: Resultsmentioning

confidence: 99%

“…In addition, the solvents currently used for the solution deposition of MoO x do not wet the organic layer to form a uniform thin film as required in an inverted OPV architecture, which shows superior stability in air compared to conventional devices [16,17]. Recently, our group developed a microwaveassisted synthesis of MoO x nanoparticles (npMoO x ) in nbutanol suspension, demonstrated formation of uniform thin films on poly(3-hexylthiophene): [6,6]-phenyl-C61-butyric acid methyl ester (P3HT : PCBM) blends using room temperature solution processing and examined performance of inverted OPV devices using npMoO x films as HTLs [18]. Here we focus on in situ chemical oxidation to optimize the npMoO x properties for HTL application.…”

Section: Introductionmentioning

confidence: 99%

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In SituChemical Oxidation of UltrasmallMoOxNanoparticles in Suspensions

Lee

Barrera

Luo

et al. 2012

Journal of Nanotechnology

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Nanoparticle suspensions represent a promising route toward low cost, large area solution deposition of functional thin films for applications in energy conversion, flexible electronics, and sensors. However, parameters such size, stoichiometry, and electronic properties must be controlled to achieve best results for the target application. In this report, we demonstrate that such control can be achieved via in situ chemical oxidation of MoO x nanoparticles in suspensions. Starting from a microwave-synthesized suspension of ultrasmall (d ∼ 2 nm) MoO x nanoparticles in n-butanol, we added H 2 O 2 at room temperature to chemically oxidize the nanoparticles. We systematically varied H 2 O 2 concentration and reaction time and found that they significantly affected oxidation state and work function of MoO x nanoparticle films. In particular, we achieved a continuous tuning of MoO x work function from 4.4 to 5.0 eV, corresponding to oxidation of as-synthesized MoO x nanoparticle (20% Mo 6+ ) to essentially pure MoO 3 . This was achieved without significantly modifying nanoparticle size or stability. Such precise control of MoO x stoichiometry and work function is critical for the optimization of MoO x nanoparticles for applications in organic optoelectronics. Moreover, the simplicity of the chemical oxidation procedure should be applicable for the development of other transition oxide nanomaterials with tunable composition and properties.

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Section: Resultssupporting

confidence: 78%

Section: Resultssupporting

confidence: 68%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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In SituChemical Oxidation of UltrasmallMoOxNanoparticles in Suspensions

Lee

Barrera

Luo

et al. 2012

Journal of Nanotechnology

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“…9 Among TMOs, molybdenum oxide (MoO 3 ) is a promising candidate because of its transparency, air stability, and high work function (WF). [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] In the early stages of OSC research, vacuumdeposition was conducted for the fabrication of MoO 3 thin-lms. However, as a large-area and low-cost roll-to-roll (R2R) fabrication has attracted attention for practical applications, a number of attempts have been conducted to obtain solution-processed MoO 3 as a HTL in OSCs.…”

Section: Introductionmentioning

confidence: 99%

Ultrafast laser-assisted synthesis of hydrogenated molybdenum oxides for flexible organic solar cells

et al. 2016

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A novel method to synthesize a hydrogenated molybdenum oxide (H y MoO 3Àx ) thin film by irradiation of photons using a KrF laser (l ¼ 248 nm) on an ammonium heptamolybdate ((NH 4 ) 6 Mo 7 O 24 $4H 2 O) precursor layer is demonstrated. The laser-assisted synthesis is simple, and can be conducted in an ambient atmosphere without damaging the underlying bottom electrode and plastic substrate. The exposure time (30 ns) is extremely short compared to thermal annealing (>3 min). Because the highenergy photons are absorbed by the MoO 3 layer and provide the activation energy for the reaction, the hydrogen atoms that dissociate from the ammonium molecules bond to the MoO 3 ; this process yields a H y MoO 3Àx thin-film. By controlling the laser energy, the stoichiometry of the H y MoO 3Àx layer can be manipulated to simultaneously obtain advantageous electrical properties of both high work function (5.6 eV) and electrical conductivity (9.9 mS cm À1). The H y MoO 3Àx hole transport layer (HTL) is successfully demonstrated on flexible top-illuminated PTB7:PCBM organic solar cells (OSCs). This OSC has good mechanical flexibility, and 75% higher short-circuit current than the device with a PEDOT:PSS HTL.Finite-domain time-difference simulations were conducted to verify the enhancement of the photocurrent. The thin layer of H y MoO 3Àx was proven to be suitable for the microcavity condition which allows a resonant wavelength match to the PTB7:PCBM active layer.

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Self‐Assembled Quasi‐3D Nanocomposite: A Novel p‐Type Hole Transport Layer for High Performance Inverted Organic Solar Cells

Cheng

Zhang

Zhao

et al. 2018

Adv Funct Materials

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Hole transport layer (HTL) plays a critical role for achieving high performance solution-processed optoelectronics including organic electronics. For organic solar cells (OSCs), the inverted structure has been widely adopted to achieve prolonged stability. However, there are limited studies of p-type effective HTL on top of the organic active layer (hereafter named as top HTL) for inverted OSCs. Currently, p-type top HTLs are mainly 2D materials, which have an intrinsic vertical conduction limitation and are too thin to function as practical HTL for large area optoelectronic applications. In the present study, a novel self-assembled quasi-3D nanocomposite is demonstrated as a p-type top HTL. Remarkably, the novel HTL achieves ≈15 times enhanced conductivity and ≈16 times extended thickness compared to the 2D counterpart. By applying this novel HTL in inverted OSCs covering fullerene and non-fullerene systems, device performance is significantly improved. The champion power conversion efficiency reaches 12.13%, which is the highest reported performance of solution processed HTL based inverted OSCs. Furthermore, the stability of OSCs is dramatically enhanced compared with conventional devices. The work contributes to not only evolving the highly stable and large scale OSCs for practical applications but also diversifying the strategies to improve device performance.

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Low‐Temperature Solution‐Processed Molybdenum Oxide Nanoparticle Hole Transport Layers for Organic Photovoltaic Devices

Cited by 88 publications

References 23 publications

In SituChemical Oxidation of UltrasmallMoOxNanoparticles in Suspensions

In SituChemical Oxidation of UltrasmallMoOxNanoparticles in Suspensions

Ultrafast laser-assisted synthesis of hydrogenated molybdenum oxides for flexible organic solar cells

Self‐Assembled Quasi‐3D Nanocomposite: A Novel p‐Type Hole Transport Layer for High Performance Inverted Organic Solar Cells

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