10 research outputs found
Quantitative Comparison of Organic Photovoltaic Bulk Heterojunction Photostability Under Laser Illumination
Junction Riemann problem for one-dimensional shallow water equations with bottom discontinuities and channels width variations
Fourier Transform-Plasmon Waveguide Spectroscopy: A Nondestructive Multifrequency Method for Simultaneously Determining Polymer Thickness and Apparent Index of Refraction
Fourier transform (FT)-plasmon waveguide
resonance (PWR) spectroscopy
measures light reflectivity at a waveguide interface as the incident
frequency and angle are scanned. Under conditions of total internal
reflection, the reflected light intensity is attenuated when the incident
frequency and angle satisfy conditions for exciting surface plasmon
modes in the metal as well as guided modes within the waveguide. Expanding
upon the concept of two-frequency surface plasmon resonance developed
by Peterlinz and Georgiadis [Opt. Commun. 1996, 130, 260], the apparent index of refraction and the
thickness of a waveguide
can be measured precisely and simultaneously by FT-PWR with an average
percent relative error of 0.4%. Measuring reflectivity for a range
of frequencies extends the analysis to a wide variety of sample compositions
and thicknesses since frequencies with the maximum attenuation can
be selected to optimize the analysis. Additionally, the ability to
measure reflectivity curves with both p- and s-polarized light provides
anisotropic indices of refraction. FT-PWR is demonstrated using polystyrene
waveguides of varying thickness, and the validity of FT-PWR measurements
are verified by comparing the results to data from profilometry and
atomic force microscopy (AFM)
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-b′]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 peak’s
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
× 10<sup>5</sup> W cm<sup>–2</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 × 10<sup>5</sup> Wcm<sup>–2</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