Organosilane Monolayer Research Articles

Detecting nuclear spins in an organosilane monolayer using nitrogen-vacancy centers for analysis of precursor self-assembly on diamond surface

We demonstrated the correlation spectroscopy of organosilane monolayers using an ensemble of shallow nitrogen-vacancy centers as the quantum sensor. Several types of organosilane monolayers were grown directly on the diamond surface by exposing the surface to a silane precursor vapor. The feasibility of detecting 1H and 19F in the monolayer was examined by correlation spectroscopy measurements. The effect of the magnetic dipole–dipole interaction on the peak width was also discussed by comparing the spectrum of the monolayer with that of surface-attached 1H and that of immersion oil. The results highlight the feasibility of nitrogen-vacancy centers as the spin probe for physicochemical analyses of monolayers grown on the diamond surface.

Time-of-Flight Secondary Ion Mass Spectrometry Analyses of Self-Assembled Monolayers of Octadecyltrimethoxysilane on SiO2 Substrate

The self-assembled monolayers (SAMs) of organosilanes formed on an oxide substrate are thought to have a polymerized –Si–O–Si– network due to the homocondensation of silanols of hydrolyzed silane headgroups, which is the most significant difference in the SAMs of organosilanes in comparison with those of alkanethoils and organophsosphonic acids. In order to explore the interface chemistry of organosilane SAMs, surface-sensitive time-of-flight secondary ion mass spectrometry (ToF-SIMS) was used to compare ion fragmentation differences between the SAMs of octadecyltrimethoxysilane (OTMS) formed on a SiO2 substrate and free OTMS molecules, as well as oxide substrate. The ability of ToF-SIMS to verify the hydrolysis of the methoxy groups of OTMS molecules and to assess the polymerized –Si–O–Si– network in their SAMs was demonstrated, which shows that ToF-SIMS provides unique information to help us understand the interface chemistry of OTMS SAMs formed on oxides.

Controllable organosilane monolayer density of surface bonding using silatranes for thiol functionalization of silica particles for liquid chromatography and validation of microanalytical method for elemental composition determination

The present work systematically investigates a new strategy for the functionalization of silica gel using alkyl silatrane chemistry instead of alkylsilanes for synthesis of chromatographic stationary phases. In this work, silica was chemically modified for further functionalization by a thiol-ene click reaction. Thus, 3-mercaptopropylsilatrane (MPS) was used which is capable to form self-assembled monolayers (SAM) on top of silanol surfaces in a controlled manner as previously shown for silicon wafers. The utility of this chemistry for stationary phase synthesis in liquid chromatography was not evaluated yet. Hence, silica surface modifications using MPS were studied in comparison to established 3-mercaptopropyltrimethoxysilane (MPTMS) chemistry. First, the employed elemental analysis method was validated and it showed excellent intra-day and inter-day precisions (typically less than 5% RSD). It could be shown that the reaction kinetics of MPS was roughly 35-times faster than with MPTMS. After 30 min reaction time with MPS, the thiol content reached 74% of the maximal coverage. Due to controlled chemistry with MPS, which does not lead to oligomeric siloxane network at the silica surface, the ligand coverage was lower. However, multiple silanization cycles with MPS led to a dense surface coverage (around 4 µmol m−2). 29Si cross polarization/magic angle spinning (CP/MAS) solid-state NMR revealed distinct T1/T2/T3 ratios for MPS and MPTMS materials with up to 80% T3 (indicative for trifunctional siloxane linkage) for MPS and around 20% T3 for MPTMS. This indicates a more homogeneous, thinner monolayer film of MPS on the silica surface, as compared to an irregular thick oligomeric siloxane network with MPTMS. Bonding of quinine carbamate as chiral selector afforded an efficient chiral stationary phase (CSP) for chromatographic enantiomer separation. Separation factors were comparable to MPTMS-bonded CSP, however, chromatographic efficiency was much better for the MPS-bonded CSP. H/u curves indicated a reduced mass transfer resistance by roughly factor 3 for MPS- compared to MPTMS-bonded CSP. This confirms better chromatographic performance of surfaces with homogeneous monolayer compared to network structures on the silica surface which suffer from poor stationary phase mass transfer.

Wet Chemical Cleaning of Organosilane Monolayers

Thin organic self-assembled monolayer films are used to promote adhesion and seal the pores of metal oxides as well as direct the deposition of layers on patterned surfaces. Defects occur as the self-assembled monolayer forms, and the number and type of defects depend on surface preparation, deposition solvent, temperature, time and other parameters. Particles commonly deposit during organosilane self-assembly on metal oxide surfaces. The particles are defects because they are prone to react in subsequent processing, which may not be desirable if the organosilane serves as a pore sealant or passivation layer. Cleaning the organosilane by solvent extraction to remove non-polar agglomerates followed by an aqueous mixture of ammonium hydroxide and hydrogen peroxide, which is Standard Clean 1, a common particle removal step for silicon surfaces, produced monolayers with few agglomerates based on atomic force microscopy without etching the layer. The combined cleaning sequence contained fewer particles than separate cleaning steps, showing that the cleans removed particles with different compositions. The thickness and contact angle of cleaned monolayers was comparable to those made using a costlier solvent.

Modified Organosilane Monolayers With Enhanced Radiation Stability.

Organosilane monolayers containing long carbon chains are susceptible to damage when exposed to X-rays and other radiation during characterization or processing. The origin of the damage has been attributed to both energetic photons and photoelectrons. These particles can break bonds in the molecules comprising the layer altering its composition and structure and can create silanol groups at the interface between the monolayer and the silicon dioxide surface. A common practice to minimize damage is to keep the X-ray beam time as short as possible. In this study, we report a method to deposit an organosilane monolayer on silicon dioxide that withstands X-ray beam damage to the interface. Adding the small monofunctional trimethylchlorosilane to a layer composed of the long-chain trifunctional octadecyltrichlorosilane prevented X-ray beam damage for at least 4 h. Interfacial damage was monitored by titrating silanol groups with TiCl4 and water atomic layer deposition and measuring the TiO2 deposited by X-ray photoelectron spectroscopy (XPS). The small monofunctional silane reacted with residual silanol groups capping the siloxane (-Si-O-Si-O-) chains at the interface. The low silanol group concentration minimized X-ray beam damage and prevented TiO2 from depositing to the detection limit of XPS. Using a small molecule to terminate reactive groups could improve the stability of monolayers not only during characterization and processing, but also when the monolayer is a component in an electrical device by reducing sources of interfacial charge traps.

Detecting and Removing Defects in Organosilane Self-Assembled Monolayers.

Defects occur as self-assembled monolayers form, and the number and type of defects depend on the surface preparation and deposition solvent, among other parameters. Indirect measures to detect defects using a layer property, such as the thickness or bond vibrational frequency, are used routinely for process development but often lack sensitivity. Direct measures using an atomic probe offer a glimpse of defect structures but over a small fraction of the layer. Direct detection after reacting defects by etching or deposition is more common, and this approach has advanced our understanding of how monolayers form and has led to improved monolayers for a variety of applications. Here we show that a series of TiCl4 gas pulses reacts with defects in organosilane layers on SiO2 depositing TiO, which was measured by X-ray photoelectron spectroscopy. The defects were silanol groups and siloxane bridge bonds at the interface between the layer and the SiO2 surface and on agglomerates physisorbed to the layer. As the TiO saturation coverage or the total number of defects decreased, the incubation period in which no TiO was detected became longer. Cleaning the layer by solvent extraction to remove nonpolar agglomerates followed by an aqueous mixture of ammonium hydroxide and hydrogen peroxide, which is Standard Clean 1, a common particle removal step for silicon surfaces, produced an organosilane monolayer without agglomerates based on atomic force microscopy. After a second organosilane immersion, the monolayer density rose to 3.8 molecules/nm2. This monolayer inhibited the deposition of TiO on the SiO2 surface for 250 pulses of TiCl4 and 200 complete TiO2 atomic layer deposition cycles using TiCl4 and water vapor, and it failed at 300 complete cycles. The Standard Clean 1 solution not only removed defects left by solvent extraction but also led to the reorganization of the organosilane layer.

Dense Organosilane Monolayer Resist That Directs Highly Selective Atomic Layer Deposition

Organosilane monolayers are part of many process flows in nanoelectronics and biotechnology because of their versatility. Monolayers that inhibit reactions on silicon/silicon oxide surfaces are nee...

A Micropatterning Strategy to Study Nuclear Mechanotransduction in Cells.

Micropatterning techniques have been widely used in biology, particularly in studies involving cell adhesion and proliferation on different substrates. Cell micropatterning approaches are also increasingly employed as in vitro tools to investigate intracellular mechanotransduction processes. In this report, we examined how modulating cellular shapes on two-dimensional rectangular fibronectin micropatterns of different widths influences nuclear mechanotransduction mediated by emerin, a nuclear envelope protein implicated in Emery–Dreifuss muscular dystrophy (EDMD). Fibronectin microcontact printing was tested onto glass coverslips functionalized with three different silane reagents (hexamethyldisilazane (HMDS), (3-Aminopropyl)triethoxysilane (APTES) and (3-Glycidyloxypropyl)trimethoxysilane (GPTMS)) using a vapor-phase deposition method. We observed that HMDS provides the most reliable printing surface for cell micropatterning, notably because it forms a hydrophobic organosilane monolayer that favors the retainment of surface antifouling agents on the coverslips. We showed that, under specific mechanical cues, emerin-null human skin fibroblasts display a significantly more deformed nucleus than skin fibroblasts expressing wild type emerin, indicating that emerin plays a crucial role in nuclear adaptability to mechanical stresses. We further showed that proper nuclear responses to forces involve a significant relocation of emerin from the inner nuclear envelope towards the outer nuclear envelope and the endoplasmic reticulum membrane network. Cell micropatterning by fibronectin microcontact printing directly on HMDS-treated glass represents a simple approach to apply steady-state biophysical cues to cells and study their specific mechanobiology responses in vitro.

Advanced Nanopatterning Using Scanning Probe Technology

Abstract This paper demonstrates two different lithographic techniques for micro/nanofabrication, viz. electrolithography technique driven by electromigration, and constructive lithography driven by anodic oxidation. The principle of electrolithography is based on electric field induced material transport which can be used for drawing patterns having dimensions from a few nanometres to a few hundred micrometres. Here, a thin Cr film is used as a masking layer and a polymer layer beneath it is used as a pattern transfer layer. A negatively biased scanning probe is used to perform electromigration on the metal film. The best resolution achieved with this technique is 9 nm. On the other hand, with the help of constructive lithography, micro/nano patterns are drawn on a highly ordered organosilane monolayer, self-assembled on silicon, using localized chemical reaction induced by an electrically biased tip or a focused e-beam.

Water adsorption and capillary bridge formation on silica micro-particle layers modified with perfluorinated organosilane monolayers

Monodisperse micron-sized silica particle monolayers deposited onto plasma-grown SiOx-ultra-thin films have been used as reference systems to investigate wetting, water adsorption and capillary bridge formation as a function of silica surface functionalization. 1H,1H, 2H,2H perfluorooctyltriethoxysil (FOTS) monolayers, have been deposited on the respective surfaces by means of chemical vapor deposition resulting in macroscopically low energy surfaces. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) reflection absorption spectroscopy confirmed the monolayer formation. Water adsorption isotherms were studied by a combination of in-situ FTIR reflection spectroscopy and quartz crystal microbalance (QCM) while macroscopic wetting was analysed by contact angle measurements. The comparative data evaluation indicates that the macroscopic wetting behaviour was changed as expected, however, that water nanodroplets formed both at intrinsic defects of the FOTS monolayer and at the FOTS/SiOx interface. Capillary bridges of liquid water are dominantly formed in the confined particle contact areas and between surface asperities on the particles. The comparison of wetting, adsorption and capillary bridge formation shows that the hydrophobization of porous materials by organosilane monolayers leads to the formation of morphology dependent nanoscopic defects that act as sites for preferential capillary bridge formation.

Interfacial Electron Beam Lithography: Chemical Monolayer Nanopatterning via Electron-Beam-Induced Interfacial Solid-Phase Oxidation.

Chemical nanopatterning-the deliberate nanoscale modification of the chemical nature of a solid surface-is conveniently realized using organic monolayer coatings to impart well-defined chemical functionalities to selected surface regions of the coated solid. Most monolayer patterning methods, however, exploit destructive processes that introduce topographic as well as other undesired structural and chemical transformations along with the desired surface chemical modification. In particular in electron beam lithography (EBL), organic monolayers have been used mainly as ultrathin resists capable of improving the resolution of patterning via local deposition or removal of material. On the basis of the recent discovery of a class of radiation-induced interfacial chemical transformations confined to the contact surface between two solids, we have advanced a direct, nondestructive EBL approach to chemical nanopatterning-interfacial electron beam lithography (IEBL)-demonstrated here by the e-beam-induced local oxidation of the -CH3 surface moieties of a highly ordered self-assembled n-alkylsilane monolayer to -COOH while fully preserving the monolayer structural integrity and molecular organization. In this conceptually different EBL process, the traditional resist is replaced by a thin film coating that acts as a site-activated reagent/catalyst in the chemical modification of the coated surface, here the top surface of the to-be-patterned monolayer. Structural and chemical transformations induced in the thin film coating and the underlying monolayer upon exposure to the electron beam were elucidated using a semiquantitative surface characterization methodology that combines multimode AFM imaging with postpatterning surface chemical modifications and quantitative micro-FTIR measurements. IEBL offers attractive opportunities in chemical nanopatterning, for example, by enabling the application of the advanced EBL technology to the straightforward nanoscale functionalization of the simplest commonly used organosilane monolayers.

Micropatterning of Au NPs on PEG Hydrogels Using Different Silanes To Control Cell Adhesion on the Nanocomposites.

Amino-silanization of silica-based substrates has proven to be effective in guiding the immobilization of citrate-stabilized Au NPs in a good, homogeneous fashion. This accomplishment has formed the basis of fabricating micropatterns of Au NPs on such substrates by patterning of oxidized silicon wafers with (3-aminopropyl)trimethoxysilane (amino-silane) using the microcontact printing (μCP) process. This micropattern of amino-silane is used to specifically adsorb Au NPs. To avoid unspecific adsorption to the nonsilanized areas on the silicon wafers, the nonstamped areas were backfilled with self-assembled monolayers of organosilanes, for example, with methyl- or perfluoro-end-groups. Finally, after having fabricated a micropattern of Au NPs on silicon wafers, the Au NP patterns were transferred onto poly(ethylene glycol) hydrogels by our newly developed procedures, and on these nanocomposite materials, controlled cell adhesion has been achieved. Furthermore, these materials are great candidates for plasmon-based biosensor applications and also for various medical applications, such as for drug delivery systems or photothermal therapies.

An omniphobic lubricant-infused coating produced by chemical vapor deposition of hydrophobic organosilanes attenuates clotting on catheter surfaces

AbstarctCatheter associated thrombosis is an ongoing problem. Omniphobic coatings based on tethering biocompatible liquid lubricants on self-assembled monolayers of hydrophobic organosilanes attenuate clotting on surfaces. Herein we report an efficient, non-invasive and robust process for coating catheters with an antithrombotic, omniphobic lubricant-infused coating produced using chemical vapor deposition (CVD) of hydrophobic fluorine-based organosilanes. Compared with uncoated catheters, CVD coated catheters significantly attenuated thrombosis via the contact pathway of coagulation. When compared with the commonly used technique of liquid phase deposition (LPD) of fluorine-based organosilanes, the CVD method was more efficient and reproducible, resulted in less disruption of the outer polymeric layer of the catheters and produced greater antithrombotic activity. Therefore, omniphobic coating of catheters using the CVD method is a simple, straightforward and non-invasive procedure. This method has the potential to not only prevent catheter thrombosis, but also to prevent thrombosis on other blood-contacting medical devices.

Cell-Shaping Micropatterns for Quantitative Super-Resolution Microscopy Imaging of Membrane Mechanosensing Proteins.

Patterning cells on microcontact-printed substrates is a powerful approach to control cell morphology and introduce specific mechanical cues on a cell's molecular organization. Although global changes in cellular architectures caused by micropatterns can easily be probed with diffraction-limited optical microscopy, studying molecular reorganizations at the nanoscale demands micropatterned substrates that accommodate the optical requirements of single molecule microscopy techniques. Here, we developed a simple micropatterning strategy that provides control of cellular architectures and is optimized for nanometer accuracy single molecule tracking and three-dimensional super-resolution imaging of plasma and nuclear membrane proteins in cells. This approach, based on fibronectin microcontact printing on hydrophobic organosilane monolayers, allows evanescent wave and light-sheet microscopy of cells whilst fulfilling the stringent optical demands of point reconstruction optical microscopy. By imposing steady-state mechanical cues on cells grown in these micropatterns, we reveal nanoscale remodeling in the dynamics and the structural organizations of the nuclear envelope mechanotransducing protein emerin and of the plasma membrane mechanosensing protein caveolin-1 using single particle tracking photoactivated localization microscopy and direct stochastic optical reconstruction microscopy imaging. In addition to allowing quantitative biophysical studies of mechanoresponsive membrane proteins, this approach provides an easy means to probe mechanical regulations in cellular membranes with high optical resolution and nanometer precision.

Multifold Electrical Conductance Enhancements at Metal-Bismuth Telluride Interfaces Modified Using an Organosilane Monolayer.

Controlling electrical transport across metal-thermoelectric interfaces is key to realizing high efficiency devices for solid state refrigeration and waste-heat harvesting. We obtain up to 17-fold increases in electrical contact conductivity Σc by inserting a mercaptan-terminated organosilane monolayer at Cu-Bi2Te3 and Ni-Bi2Te3 interfaces, yielding similar Σc for both metals by offsetting an otherwise 7-fold difference. The Σc improvements are underpinned by silane-moiety-induced inhibition of Cu diffusion, promotion of high-conductivity interfacial nickel telluride formation, and mercaptan-induced reduction of Bi2Te3 surface oxides. Our findings should enable incorporating nanomolecular layers with appropriately chosen terminal moieties in thermoelectric device metallization schemes without metal diffusion barriers.

Optimization and upscaling of spin coating with organosilane monolayers for low-k pore sealing

For porous low-k film to be integrated into the next generation of interconnects, the pores need to be sealed against metal ions and barrier precursors. Self-assembled monolayers (SAMs) from organosilane precursor are spin coated onto 300mmk=2.2 low-k wafers. Two solvents, propylene glycol monomethyl ether acetate (PGMEA) and methanol with different dielectric constant of 8.3 and 20.1, are evaluated in terms of SAMs layer quality and sealing efficiency at coupon level. SAMs deposited from PGMEA show better sealing than SAMs deposited from methanol and therefore are selected for upscaling. Full wafer spin coating results show that a concentration of 0.05mM or below results in a partial coverage and a tilt angle as high as 70° from the backbone to the normal. Aggregation is observed for all tested concentrations and is worse for higher concentrations, which is possibly induced by the non-negligible presence of water in PGMEA solvents. In order to test the sealing efficiency of the SAMs layer against metal barrier precursors, MnN films by chemical vapor deposition (CVD) and TaNx/Ta (TNT) films by physical vapor deposition (PVD) are deposited on SAM coated low-k wafers. HfO2 is also deposited by Atomic layer deposition (ALD), which is not considered as a barrier but to test the sealing against ALD precursors. Depth profiling Rutherford Backscattering Spectrometry (RBS) measurements indicate an effective sealing of SAMs against CVD and ALD precursors but not against PVD barrier.

Plasma-Enhanced Chemical Vapor Deposition (PE-CVD) yields better Hydrolytical Stability of Biocompatible SiOx Thin Films on Implant Alumina Ceramics compared to Rapid Thermal Evaporation Physical Vapor Deposition (PVD).

Densely sintered aluminum oxide (α-Al2O3) is chemically and biologically inert. To improve the interaction with biomolecules and cells, its surface has to be modified prior to use in biomedical applications. In this study, we compared two deposition techniques for adhesion promoting SiOx films to facilitate the coupling of stable organosilane monolayers on monolithic α-alumina; physical vapor deposition (PVD) by thermal evaporation and plasma enhanced chemical vapor deposition (PE-CVD). We also investigated the influence of etching on the formation of silanol surface groups using hydrogen peroxide and sulfuric acid solutions. The film characteristics, that is, surface morphology and surface chemistry, as well as the film stability and its adhesion properties under accelerated aging conditions were characterized by means of X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), inductively coupled plasma-optical emission spectroscopy (ICP-OES), and tensile strength tests. Differences in surface functionalization were investigated via two model organosilanes as well as the cell-cytotoxicity and viability on murine fibroblasts and human mesenchymal stromal cells (hMSC). We found that both SiOx interfaces did not affect the cell viability of both cell types. No significant differences between both films with regard to their interfacial tensile strength were detected, although failure mode analyses revealed a higher interfacial stability of the PE-CVD films compared to the PVD films. Twenty-eight day exposure to simulated body fluid (SBF) at 37 °C revealed a partial delamination of the thermally deposited PVD films whereas the PE-CVD films stayed largely intact. SiOx layers deposited by both PVD and PE-CVD may thus serve as viable adhesion-promoters for subsequent organosilane coupling agent binding to α-alumina. However, PE-CVD appears to be favorable for long-term direct film exposure to aqueous solutions.

In situ PM‐IRRAS studies of organothiols and organosilane monolayers–ZnO interfaces at high water activities

In situ photoelastic‐modulated Fourier transform infrared reflection absorption spectroscopy has been applied for the investigation of interfacial stability of organothiol and organosilane monolayer films on nanocrystalline zinc oxide thin films. It has been shown that for octadecyltriethoxysilane films, exposure to high water activities results in physisorption of water in the cross‐linked film. This high water activity at the interface leads to a reversible wet de‐adhesion of the interfacial silanol groups from the ZnO surface. However, the organothiol seems to form a denser monolayer and a stable by S–Zn bond that is resistant to the competition with adsorbed water. The reversible attachment for cross‐linked organosilanol films has been demonstrated for the first time by means of an in situ spectroscopic method on model ZnO surfaces. Copyright © 2016 John Wiley & Sons, Ltd.

Quantitative comparison of cancer and normal cell adhesion using organosilane monolayer templates: an experimental study on the anti-adhesion effect of green-tea catechins.

The main constituent of green tea, (-)-Epigallocatechin-3-O-gallate (EGCG), is known to have cancer-specific chemopreventive effects. In the present work, we investigated how EGCG suppresses cell adhesion by comparing the adhesion of human pancreatic cancer cells (AsPC-1 and BxPC-3) and their counterpart, normal human embryonic pancreas-derived cells (1C3D3), in catechin-containing media using organosilane monolayer templates (OMTs). The purpose of this work is (1) to evaluate the quantitativeness in the measurement of cell adhesion with the OMT and (2) to show how green-tea catechins suppress cell adhesion in a cancer-specific manner. For the first purpose, the adhesion of cancer and normal cells was compared using the OMT. The cell adhesion in different type of catechins such as EGCG, (-)-Epicatechin-3-O-gallate (ECG) and (-)-Epicatechin (EC) was also evaluated. The measurements revealed that the anti-adhesion effect of green-tea catechins is cancer-specific, and the order is EGCG≫ECG>EC. The results agree well with the data reported to date, showing the quantitativeness of the new method. For the second purpose, the contact area of cells on the OMT was measured by reflection interference contrast microscopy. The cell-OMT contact area of cancer cells decreases with increasing EGCG concentration, whereas that of normal cells remains constant. The results reveal a twofold action of EGCG on cancer cell adhesion-suppressing cell attachment to a candidate adhesion site and decreasing the contact area of the cells-and validates the use of OMT as a tool for screening cancer cell adhesion.

An organosilane self-assembled monolayer incorporated into polymer solar cells enabling interfacial coherence to improve charge transport

The reproducible silylation of titanium oxide (TiO2) with small molecular (dichloromethyl) dimethylchlorosilane (DCS) as the cathode buffer layer was developed to improve electron extraction. Through incorporating the DCS capping layer into polymer solar cells (PSCs), the interfacial coherence of devices could be enhanced, leading to a shift in nanocrystallite size and a smaller internal charge transport resistance. Furthermore, a TiO2/DCS combined interfacial layer could serve as both an exciton dissociation center and a charge transfer channel, which results in a reduction in the energy barrier and electron loss, improving hole-blocking and surface-state passivation in the TiO2 interfacial layer. The Kelvin probe measurements demonstrate that the employment of the DCS nanolayer decreases conduction band energy of TiO2via forming a dipole layer at the interface of TiO2 and the DCS nanolayer, which tunes the work-function of the device and ulteriorly enhances charge carrier transfer between the electrode and the active layer. As a result, the photocurrent and the fill factor of the PSCs are both increased, resulting in an increased power conversion efficiency (PCE) of 6.959%.