Studies On The Magnetic Field Effects Of The Organic Photo-electronic Devices

In this thesis,we mainly studied the magnetic field effect(MFE)on both the organic light-emitting diodes(OLED)and organic solar cells(OSC).It was demonstrated that an applied magnetic field can affect the electroluminescence(EL)of OLED and the photocurrent density of OSC.The first part of our experiment is about the research related with the MFE on OLED.The OLED devices with the structure of ITO/NPD/Alq₃/LiF/Al were fabricated and MFE on its EL were measured. We found that there was no effect on the photoluminescence from the Alq₃ layer within the IT magnetic field.In stead the EL exhibited obvious MFE,and the intensity of EL strongly depend on the applied bias voltage.At low bias,the MFEs first rapidly increased with the magnetic field and then saturated at about 500 Oe.However at high bias the EL decreased after this saturation.The larger the bias is,the stronger the decrease shown.A qualitative explanation was given as:the excited singlet excitons produced by the triplet-triplet pair's mutual annihilation and the interaction between triplet excitons and excess carriers of Alq₃ are the physical mechanisms leading to this phenomenon.The second part of our experiment is about the research related with the MFE on OSC.We fabricated the OSC devices with the structure of ITO/PEDOT:PSS/P3HT:PCBM/Ca/Al and measured their MFE on the photocurrent density(defined as J)around the open-circuit voltage(OCV).Without the applied magnetic field,the J-V curves of the devices changed with temperature.The OCV increased with the decreasing temperature but the short-circuit current decreased at the same time.This behavior could be attributed to the decrease of carrier mobility with the decreasing temperature and the recombination of electrons and holes from the excitons' dissociation.Besides,an applied magnetic field can also change the photocurrent density of OSC.The photocurrent density is originally small around the OSV.The applied magnetic field can enhanced the photocurrent in reverse direction,so as to lead the clear magnetoresistance(MR)effect around the OSV.When the bias is smaller than OSV,the MR calculated with our definition was negative;while it became into positive when the bias voltage is larger that OSV. This change didn't depend on the direction of the magnetic field.We attempted to give an explanation to the physical reason of these phenomena as:the magnetic field can enhance the transition from short life-time singlet excitons into long life-time triplet excitons,and the increasing of triplet excitons can enlarge the photocurrent in reverse direction,resulting in the MR effect around the OSV.