Abstract
Interface effects between metal electrodes and organic films are crucial for the overall performance of organic electronics devices. We investigate effects from gold electrodes deposited on spin-coated films of poly(p-phenylene vinylene) (PPV). While a thin Au layer (16 nm) did not affect the absorption and emission spectra of PPV, a 64 nm thick Au layer induced blue shifts in both spectra owing to the reduction in the effective conjugation degree of PPV segments. Upon combining photoluminescence and Raman scattering spectroscopies, we noted that the Au clusters interact preferentially with the phenyl rings of the polymer chain, leading to shifts in the vibrational modes at 1100 and 555 cm-1 and a significant change in the electron-phonon coupling inferred from the Huang-Rhys parameters. These results are consistent with theoretical predictions in ab initiocalculations, which imply that the final properties of polymeric devices may be tuned with adequate conditions for electrode deposition.
Highlights
Conjugated polymers can be used in emissive layers in polymer light emitting diodes (PLEDs), solar cells, and sensors.[1]
The thick Au layer caused a blue shift - owing to a decrease in the effective PPV conjugation degree - and broadening of the absorbance spectrum in comparison with the PPV layer
We have shown that the deposition of gold electrodes on PPV films may affect the polymer properties depending on the electrode thickness
Summary
Conjugated polymers can be used in emissive layers in polymer light emitting diodes (PLEDs), solar cells, and sensors.[1]. The possible applications of poly(p-phenylene vinylene) (PPV) and its derivatives in flat colored displays triggered a number of fundamental studies on the physical processes in emissive devices,[1-3] most of which comprise a polymer layer between two metal films. The latter may serve either as electrodes for charge injection in electroluminescent devices or mirrors in cavities to manipulate the radiative properties of the emissive species in the polymer. To facilitate analyzing the spectral effects, only one-half of the PPV film was covered with the Au film evaporated at a pressure of 10-1 mbar, and with the same sample we could analyze the spectra with and without the Au layer. The scattering signal was collected in the backscattering configuration under a microscope using the excitation laser line at 514.5 nm with a spectral resolution of 4 cm-1
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