The surface photovoltage of an increasing series of polyarenes: Anthracene, tetracene, and pentacene

Abstract

The surface photovoltage signals and the associated relaxation times generated by a laser pulse at the surface depletion layers of anthracene (0.8 μV, 5.6 msec), tetracene (12. μV, 10.0 msec), and pentacene (17.5 μV, 20.0 msec) appear to vary with the increasing amount of electron delocalization. As expected, the photovoltage of these materials depends logarithmically on light intensity until a saturation value corresponding to the complete energy band flattening at the surface is achieved, and this energy band bending is larger for pentacene than it is for tetracene. The photovoltage signal is observed to decay exponentially following the laser pulse with a relaxation time that is independent both of the wavelength and intensity of the light. It is established that this is in agreement with theoretical predictions based on a simple model involving the recombination of the photoinjected charge. The photovoltage spectral dependence of all three polyarenes have maxima which correspond to maxima in the corresponding optical absorption spectra due to the allowed singlet–singlet transitions. In addition, the photovoltage spectrum of anthracene has maxima that correspond to the ’’forbidden’’ singlet–triplet transitions, which are comparable in size to the photovoltage arising from the allowed singlet–singlet transitions. This observation implies that the dissociation of excitons to form free carriers is independent of the distance of the exciton from the anthracene surface. The corresponding singlet–triplet transitions for tetracene and pentacene are outside the spectral region examined and thus were not observed.

Spectroscopic Imaging of Photopotentials and Photoinduced Potential Fluctuations in a Bulk Heterojunction Solar Cell Film

“…While surface photopotential spectroscopy has proved a powerful tool for studying the sign and dynamics of photoinduced carriers in inorganic semiconductors, , there is little precedent for acquiring surface photopotential spectra of organic semiconductors , and no precedent for acquiring variable wavelength contact potential images of organic semiconductor films. Much prior work has been done to understand photocurrent generation in PFB:F8BT films.…”

Benzene Adsorption on Rh(111): A New Perspective on Intermolecular Interactions and Molecular Ordering

“…Previous investigations were motivated by financial and environmental concerns in heterogeneous catalysis; for example, the concentration of aromatic species in diesel fractions had a negative impact on the fuel quality while also resulting in problematic emissions present in the exhaust gas [14][15][16][17] . Modern research is focused on the application of aromatic molecules in devices such as photovoltaic cells 18 , field-effect transistors 19 and organic light-emitting diodes (OLEDS) 20 . Establishing a better understanding of the π-metal interaction on various surfaces is crucial to the development and optimization of such devices.…”

“…As the smallest possible aromatic hydrocarbon molecule, the adsorption of benzene on transition-metal substrates has been extensively studied in surface science, serving as an appropriate model for the interaction of a π-conjugated system with metal surfaces. − This is a subject of broad interest, not only on a fundamental level but in applied research as well. Previous investigations were motivated by financial and environmental concerns in heterogeneous catalysis; for example, the concentration of aromatic species in diesel fractions had a negative impact on the fuel quality while also resulting in problematic emissions present in the exhaust gas. − Modern research is focused on the application of aromatic molecules in devices such as photovoltaic cells, field-effect transistors and organic light-emitting diodes . Establishing a better understanding of the π-metal interaction on various surfaces is crucial to the development and optimization of such devices.…”

Photochemical Charge Separation in Poly(3-hexylthiophene) (P3HT) Films Observed with Surface Photovoltage Spectroscopy

“…Also, as a contact-less technique, SPV does not require fully assembled devices, but rather films on a conductive substrate are sufficient. To date, there are only a few documented cases of the use of SPS on organic semiconductors. − For organic semiconductors the related Kelvin probe or electrostatic force microscopy techniques are generally preferred, − even though they generally do not provide information on the spectral dependence of the transitions …”