9 research outputs found
Scanning Angle Raman Spectroscopy of Poly(3-hexylthiophene)-Based Films on Indium Tin Oxide, Gold, and Sapphire Surfaces
Interest in realizing conjugated polymer-based films with controlled morphology for efficient electronic devices, including photovoltaics, requires a parallel effort to characterize these films. Scanning angle (SA) Raman spectroscopy is applied to measure poly(3-hexylthiophene) (P3HT):phenylâC61âbutyric acid methyl ester (PCBM)-blend morphology on sapphire, gold, and indium tin oxide interfaces, including functional organic photovoltaic devices. Nonresonant SA Raman spectra are collected in seconds with signal-to-noise ratios that exceed 80, which is possible due to the reproducible SA signal enhancement. Raman spectra are collected as the incident angle of the 785 nm excitation laser is precisely varied upon a prism/sample interface from approximately 35 to 70°. The width of the âŒ1447 cmâ1 thiophene CâC stretch is sensitive to P3HT order, and polymer order varied depending on the underlying substrate. This demonstrates the importance of performing the spectroscopic measurements on substrates and configurations used in the functioning devices, which is not a common practice. The experimental measurements are modeled with calculations of the interfacial mean square electric field to determine the distance dependence of the SA Raman signal. SA Raman spectroscopy is a versatile method applicable whenever the chemical composition, structure, and thickness of interfacial polymer layers need to be simultaneously measured
Subdiffraction, Luminescence-Depletion Imaging of Isolated, Giant, CdSe/CdS Nanocrystal Quantum Dots
Subdiffraction spatial resolution luminescence depletion imaging was performed with giant CdSe/14CdS nanocrystal quantum dots (g-NQDs) dispersed on a glass slide. Luminescence depletion imaging used a Gaussian shaped excitation laser pulse overlapped with a depletion pulse, shaped into a doughnut profile, with zero intensity in the center. Luminescence from a subdiffraction volume is collected from the central portion of the excitation spot, where no depletion takes place. Up to 92% depletion of the luminescence signal was achieved. An average full width at half-maximum of 40 ± 10 nm was measured in the lateral direction for isolated g-NQDs at an air interface using luminescence depletion imaging, whereas the average full width at half-maximum was 450 ± 90 nm using diffraction-limited, confocal luminescence imaging. Time-gating of the luminescence depletion data was required to achieve the stated spatial resolution. No observable photobleaching of the g-NQDs was present in the measurements, which allowed imaging with a dwell time of 250 ms per pixel to obtain images with a high signal-to-noise ratio. The mechanism for luminescence depletion is likely stimulated emission, stimulated absorption, or a combination of the two. The g-NQDs fulfill a need for versatile, photostable tags for subdiffraction imaging schemes where high laser powers or long exposure times are used
Quantitative Comparison of Organic Photovoltaic Bulk Heterojunction Photostability Under Laser Illumination
Quantitative Comparison of Organic Photovoltaic Bulk Heterojunction Photostability Under Laser Illumination
The
photostability of bulk heterojunction organic photovoltaic films containing
a polymer donor and a fullerene-derivative acceptor was examined using
resonance Raman spectroscopy and controlled laser power densities.
The polymer donors were polyÂ(3-hexylthiophene-2,5-diyl) (P3HT), polyÂ[[9-(1-octylnonyl)-9H-carbazole-2,7-diyl]-2,5-thiophenediyl-2,1,3-benzothiadiazole-4,7-diyl-2,5-thiophenediyl]
(PCDTBT), or polyÂ({4,8-bisÂ[(2-ethylhexyl)Âoxy]ÂbenzoÂ[1,2-b:4,5-bâČ]Âdithiophene-2,6-diyl}Â{3-fluoro-2-[(2-ethylhexyl)Âcarbonyl]ÂthienoÂ[3,4-<i>b</i>]Âthiophenediyl}) (PTB7). Four sample preparation methods
were studied: (i) thin or (ii) thick films with fast solvent evaporation
under nitrogen, (iii) thick films with slow solvent evaporation under
nitrogen, and (iv) thin films dried under nitrogen followed by thermal
annealing. Polymer order was assessed by monitoring a Raman peakâs
full width at half-maximum and location as a function of illumination
time and laser power densities from 2.5 Ă 10<sup>3</sup> to 2.5
Ă 10<sup>5</sup> W cm<sup>â2</sup>. Resonance Raman spectroscopy
measurements show that before prolonged illumination, PCDTBT and PTB7
have the same initial order for all preparation conditions, while
P3HT order improves with slow solvent drying or thermal annealing.
All films exhibited changes to bulk heterojunction structure with
2.5 Ă 10<sup>5</sup> Wcm<sup>â2</sup> laser illumination
as measured by resonance Raman spectroscopy, and atomic force microscopy
images show evidence of sample heating that affects the polymer over
an area greater than the illumination profile. Photostability data
are important for proper characterization by techniques involving
illumination and the development of devices suitable for real-world
applications
Scanning Angle Raman Spectroscopy of Poly(3-hexylthiophene)-Based Films on Indium Tin Oxide, Gold, and Sapphire Surfaces
Interest in realizing conjugated
polymer-based films with controlled morphology for efficient electronic
devices, including photovoltaics, requires a parallel effort to characterize
these films. Scanning angle (SA) Raman spectroscopy is applied to
measure polyÂ(3-hexylthiophene) (P3HT):phenylâC61âbutyric
acid methyl ester (PCBM)-blend morphology on sapphire, gold, and indium
tin oxide interfaces, including functional organic photovoltaic devices.
Nonresonant SA Raman spectra are collected in seconds with signal-to-noise
ratios that exceed 80, which is possible due to the reproducible SA
signal enhancement. Raman spectra are collected as the incident angle
of the 785 nm excitation laser is precisely varied upon a prism/sample
interface from approximately 35 to 70°. The width of the âŒ1447
cm<sup>â1</sup> thiophene Cî»C stretch is sensitive to
P3HT order, and polymer order varied depending on the underlying substrate.
This demonstrates the importance of performing the spectroscopic measurements
on substrates and configurations used in the functioning devices,
which is not a common practice. The experimental measurements are
modeled with calculations of the interfacial mean square electric
field to determine the distance dependence of the SA Raman signal.
SA Raman spectroscopy is a versatile method applicable whenever the
chemical composition, structure, and thickness of interfacial polymer
layers need to be simultaneously measured