The Magnetic Field Effects In P3HT Thin-film Devices

ABSTRACT:The MFEs shortly for The Magnetic Field effects are defined as the relative difference with and without an external magnetic field which can be observed in electroluminescence, electrical-injection current, photoluminescenc, and photocurrent in organic semiconducting materials. Since the effects show a high sensitivity under indoor temperature、low magnetic field and can be used as an experimental tool towards the research about the excited processes and charge transportation in semi-conductors, it draws the scientists’ interests around the world.In this work, we have measured the MFEs of the photocurrent in the organic solar cells. By altering the active layer thickness and introducing Donor/Acceptor interface, we discovered the positive and negative MFEs. The mechanisms underlying the organic MFEs are elucidated by investigating the role of exciton-dissociation and exciton-charge reaction in organic solar cells. The main works are listed as following:1%We fabricated the P3HT Thin-film Devices with the structure of ITO/PEDOT/P3HT/Al, tested the photocurrent change with and without magnetic field at0bias voltages. We found that with the active layer became thicker, the value of the MFEs became smaller and finally the sign of the effects changed from positive to negative. We assume that the excition-dissociation dominated by singlets and excition-charge dominated by triplets responsible for the generation of the photocurrent in the P3HT devices. The magnetic field change the singlets and triplets ratio lead to the photocurrent change, while the thickness of the P3HT layer decide the population of charger collection by electrodes.2、We fabricated the bulk heterojunction Thin-film Devices with the structure of ITO/PEDOT/P3HT:PCBM/Al, tested the photocurrent change with and without magnetic field at0bias voltages. We found that introducing the donor/acceptor interface could annihilate the MFEs. We also altered the thickness of the P3HT:PCBM devices as the same distribution of the P3HT devices, interestingly, the thickness dependent MFEs disappear in P3HT:PCBM devices which indicates the collection of singlets is responsible for the positive MFEs.