Organic Thin Films for Optoelectronic Applications

In the research towards significant improvements in the performance of organic optoelectronic devices and in getting a deeper understanding of their photophysical processes, one important task is to provide highly ordered thin films. Most recent and impressive evidence that this concept is valid is provided by the experiments of the Lucent group lead by B. Batlogg. Further development in this direction requires the use of highly ordered or even single-crystalline thin films. The goals of this part of the cluster project is to investigate the prospects of highly oriented thin films for practical applications in organic electronic and photoelectronic devices. Based on samples grown at first in the own evaporation systems and with progressing project using films electrically characterized in Prof. Batlogg`s group within Prof. Sariciftcis project, and later grown in Prof. Sitters group and characterized by the other partners as well, we will investigate the materials parameters by STM, photocurrent STM and in devices. Spatially resolved measurement of the morphology but also of electrical and photoelectrical properties will be performed using a specially equipped STM. The technique enables photo current measurements with a resolution of about 1 nm. These measurements will supplement the polarized UV-Vis absorption, photo- and electroluminescence measurements, polarized IR spectroscopy as well as photoindiced absorbtion (PIA) (as performed by our partners) to provide necessary feedback information to Prof. Sitters group about molecular packing and orientation with respect to the substrate. To test the device (LED and Solar Cell) performance, two basic structures shall be investigated: devices based on an insulating substrate (mica or mica-paper) covered with a highly oriented films. Here the devices need to be deposited along the substrate direction, if possible in and perpendicular to the needle growth direction in the case of para-sexiphenyl. For the phthalocyanine films these directions are perpendicular to the growth direction of crystallites. The classical geometry of devices based on sandwiches becomes only applicable if either a thin (preferably atomically flat) metal (e.g. gold) film can be deposited onto the mica before film growth without changing the orientation, or if conductive layered semiconductor substrates like MoSe2 can be used for oriented growth. Both approaches will be investigated in this project.