טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentDevir Wolfman Ayeleth
SubjectMagnetic Field Effects in Pi-Conjugated Organic
Opto-Electronic Devices
DepartmentDepartment of Physics
Supervisor Professor Emeritus Eitan Ehrenfreund
Full Thesis textFull thesis text - English Version


Abstract

Organic semiconductors based devices attract a lot of attention as a cheap, versatile alternative to the commonly used inorganic semiconductors based devices.

In the recent years, researchers have studied and modeled the effects that external magnetic field have on these organic based electronic devices, and organic light emitting diodes in particular. The effects varied from changes in their electrical properties to changes in their luminescence properties.

However, the magnetic effects measured in organic based photovoltaic cells did not fit the same physical model that describes the magnetic effects in organic light emitting diodes.

In this work we show that the measured effects in high fields, of up to 8.5 Tesla, are actually composed from three independent processes that occur simultaneously and independently within the devices under the presence of the magnetic field. We found that besides the known hyperfine interaction mechanism that enables effects at low magnetic fields of up to 0.05 Tesla, there are two more mechanisms in progress. These two mechanisms are effective when the opposite-charged carriers (polarons) have a slightly different gyromagnetic factors, which is essentially possible when organic material in the device is actually composed from two different organic materials. The two mechanisms defer one from the other by the spin-pair that enabled it: long-lived polarons in one, and short-lived charge-transfer-excitons in the other.