M.Sc Thesis

M.Sc StudentRavia Israel
SubjectEnergetic Disorder in Amorphous Materials - Diople Effect
and Recombination
DepartmentDepartment of Electrical and Computer Engineering
Supervisor PROF. Nir Tessler


Since the discovery of conductance in conjugated polymers, this area received a significant attention mainly due to the discovery of the high photoluminescence properties in these materials. Consequently, the research interest in this field was on opto-electronics such as Light Emitting Diodes (LED) and Solar Cells as well as Field Effect Transistors (FET).

While in conventional crystal semiconductors the electrons are described as Bloch functions, in amorphous materials the electron states are localized and the charge transport is done by hops of charge carriers between the sites.

The hopping rate between two sites is highly sensitive to the energies of the states and therefore the mobility of the charge carrier is influenced by the energetic disorder in the materials. In fact it is established that charge transport related properties are dependent on the material density of states (DOS) and it has recently been suggested that charge recombination (exciton formation) is also affected by it. In the first part of the thesis we look into the DOS shape and examine the effect of the materials being used in a form of thin film and that sometimes the transport is along one of the interfaces (as in FET). To examine these finite size effects we look into the model that associates the energetic disorder with the presence of electric dipoles in the organic films. In the second part of the thesis we test the hypothesis that the recombination (exciton formation) process is affected by the DOS. We present a new measurement technique that is based on a well-known Time of Flight measurement that enables to measure the Recombination rate for different charge carrier concentration and Electric Field.