Self-assembled tri-, tetra- and penta-ethylene glycols as easy, expedited and universal interfacial cathode-modifiers for inverted polymer solar cells

Cao, Fong Yi; Lai, Yinchieh; Chen, Yung Lung; Cheng, Yen‐Ju

doi:10.1039/c6ta01983h

Cited by 15 publications

(16 citation statements)

References 57 publications

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“…For example, the amino‐rich PEIE tuned the interfacial dipole and resulted in a decrease in WF for the corresponding electrodes. Cheng and co‐workers used nonconjugated OH‐rich poly(ethylene oxide) as an IF material and observed a decrease in WF for the ITO electrode, due to IF dipoles arising from oxygen coordination . It has been demonstrated previously that modification of ZnO with PCBM (a conjugated carbon structure) led to a decrease in WF .…”

Section: Resultsmentioning

confidence: 98%

Carbonized Bamboo‐Derived Carbon Nanodots as Efficient Cathode Interfacial Layers in High‐Performance Organic Photovoltaics

Juang

Kao

Wang

et al. 2018

Adv Materials Inter

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have been demonstrated as efficient IFmodified layer for OPV applications, [2] including self-organized molecules, [3] conjugated materials, [2b] ionic compounds (e.g., electrolytes), [4] metal oxides, [1g,5] and nonconjugated organic materials. [6] Typically, the mechanism through which the PCE is improved relies on (i) passivation of interfaces to suppress carrier recombination, [7] (ii) enhanced carrier extraction, [8] (iii) enhancing interfacial dipoles and modifying the work function (built-in dipole) of the electrode to ensure better energy levels alignment, [9] (iv) smoothing the surface of the substrate, [10] and (v) optimizing the blend film morphology. [11] Carbon nanodots (CNDs) are interesting carbon nanomaterials for optoelectronic applications because of their strong luminescence emissions, good water solubility, tunable optical and electronic properties, and photochemical stability. [12] CNDs typically comprise sp 2 -hybridized carbon atoms and present oxygen-containing functional groups (e.g., epoxy, ether, carbonyl, hydroxyl, carboxylic acid) on their surfaces. These oxygen-rich functionalities impart the CNDs with high water dispersibility and make them ready for modification with organic, inorganic, or biological materials. [13] CNDs exhibit interesting photoluminescence (PL) properties because of their sizes, edge shapes, and surface functional groups, and have demonstrated potential applicability in sensing, catalysis, biolabeling, photovoltaic devices, optoelectronic devices, and energy storage. [13d,e,14] CNDs have been employed as active layers, electrolytes, dopants, hole transporting layers, and interfacialmodified layers (IFLs) for dye-sensitized organic and perovskite solar cells. [12] Chen and co-workers first demonstrated the use of amino-based CNDs as efficient zinc oxide (ZnO) or Al-doped ZnO IFLs for OPVs and observed improvements in PCE of up to 10.24%. [13c] Yang et al. used CNDs as a cathode [indium tin oxide (ITO)]-modifying layer that enhanced the interfacial dipole, thereby decreasing the work function (WF) of the electrode and increasing the performance of derived OPV devices from 4.14% to 8.13% when using a poly [4,8bis(5-(2-ethylhexyl)thien-2-yl)benzo [1,2-b:4,5-b′-dithiopheneco-3-fluorothieno[3,4-b] thiophene-2-carboxylate](PTB7-Th)/ phenyl-C 71 -butyric acid methyl ester (PC 71 BM) blend film as the active layer. [15] These previous studies highlight the potential emerging applications of CNDs as IFLs. CNDs can be prepared

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Section: Resultsmentioning

confidence: 98%

Carbonized Bamboo‐Derived Carbon Nanodots as Efficient Cathode Interfacial Layers in High‐Performance Organic Photovoltaics

Juang

Kao

Wang

et al. 2018

Adv Materials Inter

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“…For example, in base treatment, bases bind with the acidic sites on the ITO surface and the remaining cations assembled on top of ITO substrate, thus forming an interface dipole and decreasing the ITO WF. Based on this principle, many basic organic materials with amino groups were reported for use as CIMs in OSCs . Deng and co‐workers reported environmentally friendly biomaterial glycylglycine (Gly–Gly, Scheme ) as a CIM in inverted OSCs .…”

Section: Small Molecule Cathode Interlayermentioning

confidence: 99%

Small Molecule Interlayers in Organic Solar Cells

Zhang

Usman

2018

Advanced Energy Materials

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This review provides an up‐to‐date review about the small molecule interlayers (SMIs) in organic solar cells (OSCs). Compared to polymer interlayers, SMIs exhibit intrinsic advantages such as easy synthesis and purification, monodispersity, well‐defined chemical structure, and high batch‐to‐batch reproducibility. Recently, various SMIs have been reported with landmark efficiencies of over 10% in both conventional and inverted OSCs, exhibiting promising potential in commercial application. In this review, the authors summarize the progress of SMIs from a device fabrication point of view, paying particular attention to the material categories, molecular design, preparation process, and applicable device structure. In addition, the working mechanisms of different SMIs are also discussed, including the structure–property relationships and the corresponding impact on device performance. Finally, a brief outlook is provided that includes opportunities and challenges in this emerging area.

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“…The reduced effective anode work function results in injection barrier for holes at the anode, which is also evident from the increased R S (see Table and Figure S2). Indeed, Cao et al utilized PEG as cathodic interlayer at the ITO/organic interface in inverted cells . We will demonstrate spontaneous PEG interlayers formation in inverted cells and address this hypothesis further in the text.…”

Section: Resultsmentioning

confidence: 70%

“…For devices that are annealed prior to the Al, PEG is nearly absent from the interface (Figure b, blue line), while the V oc decreases significantly with increasing PEG concentration (blue circles in Figure ). The reduction of V oc suggests that during annealing PEG molecules not only segregate closer to the bottom substrate, as realized by DSIMS depth profiles (Figure ), but probably adsorb to the ITO/PEDOT:PSS electrode to form an aligned dipole layer which reduces the effective work function of the anode. − …”

Section: Resultsmentioning

confidence: 96%

“…Interestingly, this performance value is lower than that obtained for devices that were annealed only after the Al deposition, even with PEG concentrations under the approximated saturation value (0.55 mg/mL). We assign the reduced J sc and V oc to nonreversible PEG adsorption at the bottom organic/anode interface during the first thermal treatment. − …”

Section: Resultsmentioning

confidence: 99%

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Dynamics of Additive Migration to Form Cathodic Interlayers in Organic Solar Cells

Vinokur

Obuchovsky

Deckman

et al. 2017

ACS Appl. Mater. Interfaces

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Migration of additives to organic/metal interfaces can be used to self-generate interlayers in organic electronic devices. To generalize this approach for various additives, metals, and organic electronic devices it is first necessary to study the dynamics of additive migration from the bulk to the top organic/metal interface. In this study, we focus on a known cathode interlayer material, polyethylene glycol (PEG), as additive in P3HT:PCBM blends and study its migration to the blend/Al interface during metal deposition and its effect on organic solar cell (OSC) performance. Using dynamic secondary ion mass spectroscopy (DSIMS) depth profiles and X-ray photoelectron spectroscopy surface analysis (XPS), we quantitatively correlate the initial concentration of PEG in the blend and sequence of thermal annealing/metal deposition processes with the organic/Al interfacial composition. We find that PEG is initially distributed within the film according to the kinetics of the spin coating process, i.e., the majority of PEG accumulates at the bottom substrate, while the minority resides in the film. During electrode evaporation, PEG molecules kinetically "trapped" near the film surface migrate to the organic/Al interface to reduce the interfacial energy. This diffusion-limited process is enhanced with the initial concentration of PEG in the solution and with thermal annealing after metal deposition. In contrast, annealing the film before metal deposition stalls PEG migration. This mechanism is supported by corresponding OSC devices showing that V increases with PEG content at the interface, up to a saturation value associated with the formation of a continuous PEG interlayer. Presence of a continuous interlayer excludes the driving force for further migration of PEG to the interface. Revealing this mechanism provides practical insight for judicious selection of additives and processing conditions for interfacial engineering of spontaneously generated interlayers.

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Self-assembled tri-, tetra- and penta-ethylene glycols as easy, expedited and universal interfacial cathode-modifiers for inverted polymer solar cells

Abstract: Non-conjugated triethylene glycol (3-EG), tetraethylene glycol (4-EG) and pentaethylene glycol (5-EG) are presented as new cathode modification materials to achieve high-performance inverted-PCSs.

Cited by 15 publications

References 57 publications

Carbonized Bamboo‐Derived Carbon Nanodots as Efficient Cathode Interfacial Layers in High‐Performance Organic Photovoltaics

Carbonized Bamboo‐Derived Carbon Nanodots as Efficient Cathode Interfacial Layers in High‐Performance Organic Photovoltaics

Small Molecule Interlayers in Organic Solar Cells

Dynamics of Additive Migration to Form Cathodic Interlayers in Organic Solar Cells

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