Showing papers by "Eitan Ehrenfreund published in 2006"

Internal electric field in organic-semiconductor-based photovoltaic devices

Abstract: The authors performed transient photocurrent measurements under applied bias and electroabsorption spectroscopy on devices based on a pristine poly(phenylene vinylene) derivative as well as its mixture with 1% of a methanofullerene electron acceptor. Combining both techniques allows us to directly determine the internal electric field and to conclude on its implication on the photovoltaic performance of the devices. The electric field is identified as the driving force of the photocurrent, hence indicating the maximum obtainable photovoltage. Acceptor concentrations as low as 1% shift the energetic alignment of the top electrode to the reduction potential of the acceptor, reducing the internal electric field.

Magneto optics of single photons emitted from single InAs/GaAs self-assembled quantum dots in a planar microcavity

Abstract: We fully characterize the fine spectral structure of neutral and negatively charged single microcavity quantum dot excitons, using polarization-sensitive magneto-photoluminescence spectroscopy. We show that the microcavity allows the simultaneous detection of both the bright and dark excitons using Faraday configuration. Thus, we were able to fully determine the fine structure and the g -factors of the neutral and negatively charged single exciton states within the same single quantum dot. Our measurements are in excellent agreement with novel, many carrier model calculations, which take into account Coulomb and exchange interactions among all the confined e–h pair states.

The effect of intermediate layers on the internal electric field in organic semiconductor devices

Abstract: In this work we study the internal electric field (Vint) present in devices based on an intrinsically semiconducting polymer. Intermediate layers between the indium-tin-oxide and Al electrodes and the photoactive layer are able to influence and alter this electric field. The two commonly used intermediate layers, namely poly(3,4ethylenedioxythiophene) doped with poly(styrenesulfonate) (PEDOT:PSS) and LiF, are subject of this study. Their influence is studied with Electroabsorption (EA) spectroscopy as well as transient photocurrent measurements under applied bias. While PEDOT:PSS has no significant influence on Vint, introducing LiF increases Vint close to the bandgap of the studied semiconducting polymer. However, using PEDOT:PSS directly influences the spectral EA response. The interface between PEDOT:PSS and the conjugated polymer is studied by impedance spectroscopy. We interpret the results in terms of the presence of charges at the interface.