Control of exciton spin statistics through spin polarization in organic optoelectronic devices

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 the thermal energy. By using this method, we demonstrate that singlet exciton formation can be suppressed by up to 53% in organic light-emitting diodes, and the dark conductance of organic photovoltaic devices can be increased by up to 45% due to enhanced formation of triplet charge-transfer states, leading to less recombination to the ground state. Control of spin statistics by spin injection from ferromagnetic electrodes has been shown to achieve only weak effects in organic optoelectronic devices. Wang et al.use instead polarization of spins after injection, at high magnetic fields and low temperatures, achieving a 50% change in device characteristics.