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Instruments / Technical Area	Publication Details	Published
I07-Surface & interface diffraction	Efficiency enhancement of small molecule organic solar cells using hexapropyltruxene as an interface layer Hanyang Ye , Sameer Vajjala Kesava , Josue Martinez Hardigree , Roisin E. Brown , Giulio Mazzotta , Ross Warren , Peter J. Skabara , Moritz Riede Journal Of Materials Chemistry C 8, 4909 - 4918 DOI: 10.1039/C9TC06845G Diamond Proposal Number(s): [18016] Show Abstract ▼ Abstract: The quenching of excitons in organic solar cells can play a significant role in limiting their power conversion efficiency (PCE). In this article, we investigate the effect of a thin layer of hexapropyltruxene inserted at the interface between the electron donor boron subphthalocyanine chloride (SubPc) and its underlying hole contact in planar heterojunction solar cells. We find that a 3.8 nm hexapropyltruxene interlayer between the molybdenum oxide (MoOx) hole contact and SubPc is sufficient to improve PCE in SubPc/C60 fullerene solar cells from 2.6% to 3.0%, a ∼20% performance improvement. While the absorption stays roughly the same, the comparison of external and internal quantum efficiencies reveals a significant increase in SubPc's contribution to the current for light with wavelengths between 520 and 600 nm. Microstructure and surface morphology assessed with in situ Grazing-Incidence Wide-Angle X-Ray Scattering (GIWAXS) and Atomic Force Microscopy (AFM), are evaluated alongside in situ spectroscopic ellipsometry, and photoluminescence measurements. The microstructural investigations demonstrate changes to the surface and bulk of SubPc grown atop a hexapropyltruxene interlayer indicating that the latter acts as a template layer in a similar way as MoOx. However, the improvement in PCE is found to be mainly via reduced exciton quenching at the MoOx contact with the insertion of the hexapropyltruxene layer.	Apr 2020
E02-JEM ARM 300CF	Filamentary high-resolution electrical probes for nanoengineering Eugene J. H. Soh , Ghazi Syed , Giulio Mazzotta , Benjamin F. Porter , Moritz Riede , Robin Nicholas , Judy S. Kim , Harish Bhaskaran Nano Letters DOI: 10.1021/acs.nanolett.9b04302 Diamond Proposal Number(s): [22207] Show Abstract ▼ Abstract: Confining electric fields to a nanoscale region is challenging yet crucial for applications such as high resolution probing of electrical properties of materials and electric-field manipulation of nanoparticles. State-of-the-art techniques involving atomic force microscopy typically have a lateral resolution limit of tens of nanometers due to limitations in the probe geometry and stray electric fields that extend over space. Engineering the probes is the most direct approach to improving this resolution limit. However, current methods to fabricate high-resolution probes, which can effectively confine the electric fields laterally involve expensive and sophisticated probe manipulation, which has limited the use of this approach. Here, we demonstrate that nanoscale phase switching of configurable thin films on probes can result in high-resolution electrical probes. These configurable coatings can be both germanium-antimony-tellurium (GST) as well as amorphous-carbon, materials known to undergo electric field-induced non-volatile, yet reversible switching. By forming a localized conductive filament through phase transition, we demonstrate a spatial resolution of electrical field beyond the geometrical limitations of commercial platinum probes (i.e. an improvement of ~48%). We then utilize these confined electric fields to manipulate nanoparticles with single nanoparticle precision via dielectrophoresis. Our results advance the field of nanomanufacturing and metrology with direct applications for pick and place assembly at the nanoscale.	Jan 2020
I07-Surface & interface diffraction	In-situ observation of stacking fault evolution in vacuum-deposited C 60 J. F. M. Martinez Hardigree , I. R. Ramirez , G. Mazzotta , C. Nicklin , M. Riede Applied Physics Letters 111 DOI: 10.1063/1.4995571 Diamond Proposal Number(s): [15207] Open Access Show Abstract ▼ Abstract: We report an in-situ study of stacking fault evolution in C60 thin films using grazing-incidence x-ray scattering. A Williamson-Hall analysis of the main scattering features during growth of a 15 nm film on glass indicates lattice strain as high as 6% in the first 5 nm of the film, with a decrease to 2% beyond 8 nm thickness. Deformation stacking faults along the {220} plane are found to occur with 68% probability and closely linked to the formation of a nanocrystalline powder-like film. Our findings, which capture monolayer-resolution growth, are consistent with previous work on crystalline and powder C60 films, and provide a crystallographic context for the real-time study of organic semiconductor thin films.	Dec 2017
	Managing BHJ microstructural evolution for long-term photoconversion efficiency Josue Martinez Hardigree , Graham E. Morse , Priti Tiwana , Giulio Mazzotta , Ivan R. Ramirez , Christopher L. Nicklin , Owen R. Lozman , Moritz K. Riede Organic Photovoltaics XVII DOI: 10.1117/12.2238167 Show Abstract ▼ Abstract: In this presentation we evaluate the thermal and light-soaking stability of polymer:fullerene bulk heterojunctions (BHJs) based on a donor polymer recently developed by Merck Chemicals. Blade-coated thin films of pure polymer and BHJs incorporating either PC61BM or PC71BM were investigated using atomic force microscopy (AFM), grazing-incidence x-ray diffraction (GIXD), neutron reflectivity (NR), and UV-Visible spectroscopy. The addition of fullerene to the polymer at device-relevant concentrations (25-50% by weight) results in a 7-fold reduction in surface roughness relative to pure polymer films, attributed to a reduction in the pure polymer domain size with increasingly homogeneous polymer:fullerene mixing. Films subjected to accelerated stressing relevant to scalable OPV fabrication—thermal stressing at 120 °C for 1 hour or light-soaking under AM1.5 light for 8 hours—indicate robust stability to stressing, with thin films showing marginal but monotonic increases in roughness with increasing fullerene concentration. Wide-angle GIXD measurements indicate a contraction of 1-4% in features attributed to polymer crystalline domains upon annealing. Comparison of pre-and post-annealed films reveals increased correlation between polymer scattering features in the latter, consistent with improved ordering of the polymer backbone and sidechains. These findings, together with GIXD measurements of full device stacks and accelerated aging measurements of operational cells, support recent reports on the high photoconversion efficiency stability of this polymer BHJ system for highly scalable, long-lifetime OPVs.	Nov 2016

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