Schematic (left) and transmission electron micrograph (right) of a cross section of a tandem organic photovoltaic cell. The enhancement distance (shaded region) and diffusion lengths and of the donor (D) layer and acceptor (A) layer of each device (PV 1 and PV 2) are labeled. clusters are visible in the micrograph and are shown (filled circles) in the schematic. The schematic shows a representation of current generation in the tandem cell, where dissociation of excitons at the DA interface leads to a hole in PV 1 and electron in PV 2 which contribute to photocurrent. The excess electron in PV 1 and hole in PV 2 recombine at the cluster layer to prevent cell charging.
(a) Real and (b) imaginary dielectric functions for as functions of photon energy. Bulk is shown as a solid line and (dashed line) and - (dotted line) diameter clusters are also shown.
(a) Simulated surface-plasmon polariton (SPP) resonance wavelength for a circular particle as a function of the relative permittivity of the embedding medium. (b) Simulated SPP resonance wavelength vs axial ratio for a particle in vacuum. Dashed lines indicate resonance wavelengths for a particle with an axial ratio of . Inset shows the geometry of the simulation.
Real, (upper panel), and imaginary, (lower panel), indices of refraction of thin films of (solid line) and PTCBI (dashed line) as functions of wavelength, measured via ellipsometry.
Measured absorbance spectra for (dotted curve), (dashed curve), and film on (solid curve). All films are deposited on quartz substrates.
Contour map of the calculated intensity enhhancement of a chain of particles with diameter and center-to-center spacing at . The particles lie on a quartz substrate and are embedded in a dielectric medium . Contour labels represent the intensity enhancement and are spaced by 0.5. The polarization vector is indicated by the arrow and propagation is in the direction. Inset: schematic of the simulated geometry containing a film on a cluster covered quartz substrate.
Average calculated intensity enhancement on the surface of a diameter particle as a function of wavelength for different embedding media.
Absorption (dotted lines) and average intensity enhancement (solid lines) simulated on the surface of a diameter circular and elliptical particle (axial ratio of 0.5). Both particles have the same area and are embedded in a dielectric with .
(a) Maximum calculated intensity enhancement at the midpoint between two clusters of a lD chain of particles vs the surface-to-surface spacing, , of a chain of diameter circular (solid lines) and elliptical particles (dashed lines). (b) Simulated surface-plasmon polariton (SPP) peak wavelength as a function of . The particles in (a) and (b) are embedded in a dielectric with .
Intensity enhancement calculated at the axis of a chain of particles embedded in a medium vs wavelength. Solid lines indicate an array of -diameter clusters while dotted lines indicate elliptical particles of axial ratio 0.5 with the same area. Surface-to-surface spacings of (open squares), (filled circles), and (open triangles) are shown.
Measured absorbance of varying thicknesses of on quartz at a wavelength of with (triangles) and without (squares) a cluster layer. Solid curves show fits to the data. Inset: the difference of the absorbance of the films with and without a layer vs thickness . Solid curve provides a guide to the eye.
The effective enhancement length calculated for a 1D chain of diameter circular (solid lines) and elliptical (axial ratio ) particles (dashed lines) embedded in a dielectric with as a function of the surface-to-surface spacing of particles in the chain.
Calculated external quantum efficiency spectra for a tandem PV cell (a) with and (b) without the presence of clusters. The structure of the device is . Open circles show for the front cell (PV I, see Fig. 1) while filled squares show for the back cell (PV 2). The contributions to from the and PTCBI layers for PV 1 (solid curves) and PV 2 (dashed curves) are also shown.
Parameters of various cells under 1 sun simulated illumination.
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