Publications
High-resolution spectroscopic mapping of the chemical contrast from nanometer domains in P3HT:PCBM organic blend films for solar cell applications
Wang, X., Zhang, D.*, Braun, K., Egelhaaf, H.-J., Brabec, C. J., Meixner, A. J.*
Advanced Functional Materials 20 (2010) 492
Confocal and near-field spectroscopic mapping techniques are used to investigate the interplay between morphology, molecular distribution and photoluminescence (PL) quenching efficiencies in P3HT:PCBM blend films which have been annealed at 140 °C for different time. The relevant photophysical information from the blend solar cell films with 10 nm spatial resolution is achieved.
Nanoscale spectroscopic imaging of organic semiconductor films by plasmon-polariton coupling
Zhang, D.*, Heinemeyer, U., Stanciu, C., Sackrow, M., Braun, K., Hennemann, L. E., Wang, X., Scholz, R., Schreiber, F., Meixner, A. J.*
Physical Review Letters 104 (2010) 056601
Tip-enhanced near-field optical images and correlated topographic images of an organic semiconductor
film (diindenoperylene,DIP) on Si have been recorded with high optical contrast and high spatial
resolution (17nm) using a parabolic mirror with a high numerical aperture for tip illumination and signal
collection.The DIP molecular domain boundaries being one to four molecular layers (1.5–6nm) high are
resolved topographically by a shear-force scanning tip and optically by simultaneously recording the
6x1E5 times enhanced photoluminescence(PL).The excitation is 4x1E4 times enhanced and the
intrinsically weak PL-yield of the DIP-film is 15-fold enhanced by the tip.The Raman spectra indicate an
upright orientation of the DIP molecules.The enhanced PL contrast results from the local film
morphology via stronger coupling between the tip plasmon and the exciton-polariton in the DIP film.
Parabolic mirror-assisted tip-enhanced spectroscopic imaging for non-transparent materials
Zhang, D.*, Wang, X., Braun, K., Egelhaaf, H.-J., Fleischer, M., Hennemann, L., Hintz, H., Stanciu, C., Brabec, C. J., Kern, D. P., Meixner, A. J.*
Journal of Raman Spectroscopy 40 (2009) 1371
A versatile and efficient tip-enhanced spectroscopic imaging technique based on a parabolic mirror (PM) assisted near-field optical microscope is demonstrated. The replacement of the conventional objective lens with a parabolic mirror allows the non-restricted investigation of sample materials regarding their opacity. In addition, an improved signal collection efficiency and effective excitation of the longitudinal plasmonic oscillation in the tip apex are obtained. The capabilities of PM-assisted tip-enhanced Raman (TER) and photoluminescence (PL) imaging in distinguishing the individual domains made of different chemical components in poly (3-hexythiophene)/[6, 6]-penyl-C61 butyric acid methyl ester (P3HT/PCBM) solar cell blend film and in the investigation of the plasmonic properties of geometrically well-defined Au cones are demonstrated.
Confocal and near-field spectroscopic investigation of P3HT:PCBM organic blend film upon thermal annealing
Wang, X., Zhang, D.*, Braun, K., Egelhaaf, H.-J., Meixner, A. J.
Proc. SPIE 7395 (2009) 73950F
The poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM) organic films are widely employed as electronic donor and acceptor in the field of organic film solar cell because of their high photovoltaic conversion efficiency. A home-built parabolic mirror assisted confocal and apertureless near-field optical microscope was used to investigate the degradation behavior of the film and to distinguish the donor and acceptor domains both topographically and optically. Under ambient condition, the degradation rates are decreased in the sequence of pristine P3HT, blend P3HT:PCBM film and pristine PCBM. N2 protection dramatically slows down the film degradation rate. Using confocal spectroscopic mapping, we are able to distinguish the local distributions of P3HT and PCBM. Micrometer PCBM aggregates were observed due to the thermal annealing process. Our experimental methods show the possibility to investigate morphology and the photochemistry properties of the organic solar cell films with high spatial resolution.
