Lecture by Dr. Jianpu Wang on Oct. 10th
Published：2012-10-10
Control of exciton spin statistics through spin polarization in organic optoelectronic devices
Dr. Jianpu Wang
(Cavendish Laboratory, J.J. Thomson Avenue, Cambridge CB3 0HE, United Kingdom)
Report lacation: Room No.138,（HengLong Physics building）
Report Time: 10:00, Oct. 10th
Abstract:
Spintronics based on organic semiconductor materials is attractive because of its rich fundamental physics and potential for device applications. Manipulating spins is obviously important for spintronics, and is usually achieved by using magnetic electrodes. Here we show a new approach where spin populations can be controlled primarily by energetics rather than kinetics. We find that exciton spin statistics can be substantially controlled by spin-polarizing carriers after injection using high magnetic fields and low temperatures, where the Zeeman energy is comparable with thethermal energy. Using this method, we demonstrate that singlet exciton formation can be suppressed by up to 53% in organic light-emitting diodes (OLEDs), and the dark conductance of organic photovoltaic (OPV) devices can be increased by up to 45% due to enhanced formation of triplet charge-transferstates, leading to less recombination to the ground state. The role of spin-dependent recombination in organic devices is still controversial, and our technique allows models for device operation to be tested by achieving direct control of spin populations in a manner that is energeticly controlled. These effects are unique to organicsemiconductors, since they are free from the Pauli paramagnetism effects, high doping densities, and strong spin-orbit coupling typically present in inorganic semiconductor devices.
About Dr. Jianpu Wang
Dr. Jianpu Wang has been a postdoctoral research associate in Cavendish Laboratory, University of Cambridge since 2009. His research interests are organic/solution processable semiconductor devices (including OLED, OPV, OFET and organic memory) and device physics. Currently he is studying the magnetic field effect on charge recombination/transport in organic optoelectronic systems, in order to reveal the role of spins in limiting the device efficiencies of OPVs and OLEDs. He did his PhD study in the same laboratory in year 2006-2009, when he investigated organic semiconductor/inorganic nanocrystal memory devices. Prior to his PhD, he worked as a research engineer in Samsung Electronics in South Korea in 2003-2006, for developing ink-jet printing technology and large size OLED displays.